[GMS]

In terms of performance (grip) and not the looks these would be my recommendations:

1. 17" and 18" combo over 18" and 19". Tire width? You want the widest and softest tires (lower the treadwear rating, the better) you can fit and still bring them to the operating temp. Tires that are wide and hard, will perform worse than soft narrow tires that are operating its ideal temp range. In 4C the front end is very light, so anything wider than 225 at the front, you will be having hard time to heat up. The rear end is quite heavy though and also has the drive, so you can easily run 265 tires and you'll still heat them up. In my case 215 front and 265 rear seems to be close to the ideal combo. Both tires heat up evenly and wear out pretty evenly as well. I believe that 215 / 275 combo might be even better, but 275 rears are hard to come by. For 215 you need at least 7" wheel width and 9" for 265. Ideally +0.5" up on the minimum wheel width to provide more stability to the tire side wall. Of course, you don't want low profile tires as they poorly absorb road imperfections, temperatures fluctuate a lot and generally drive worse than slightly higher sidewall tires. They look cool though.

2. The rims width should be adjusted to suit the tires and not the other way around. So once you know what tires you will be running, you can choose the optimal wheels width.

3. Alignment. There is no ideal alignment that would work best in all circumstances, but here are some guidelines. Caster is needed to provide straight line stability and dynamic camber gain upon cornering. On a 4C you want as much caster as you can get as the car is already very twitchy. Negative camber is needed to compensate for the body roll and softer your car is sprung and stickier the tires you run, the more negative camber you'll need. With toe you can make car's front or rear end more or less prone to steer. If you want more initial turn in, you'll toe out the front, and if you want more straight line stability and less responsive front end you'll add some toe in at front. However, toe in in the world of performance driving is not a common thing to see. 4C is already very nimble at front, so I would suggest to keep the front toe close to 0°, perhaps a slight toe out on a tight twisted tracks, but no excessive toe out is needed as with FWD or some other nose heavy cars is. On the rear you want a healthy amount of toe in to keep the rear end planted. 4C has very short wheelbase and very wide track, which means a generally nervous car with quick wheel load transfer, so any oversteer that might happen, will happen suddenly and quickly and you definitely don't want a zero toe or even toe out int that situation. Also with all the weight at the rear axle, you can easily reduce the potential understeer with slight throttle lift off and the rear end will start to turn in nicely. Do that with not enough toe in at the rear and you'll drive backwards sooner than you'll realize. This is very simplified, but you get the idea. It is impossible though to say what's the perfect alignment for 4C, without knowing all the details (tires, suspensions, weight, intentions of use, etc.). But let's say you have a mildly modded 4C (better, wider tires, remap, perhaps suspension) and like to occasionally push it, but otherwise you drive normal. In that case, I would recommend about +4°00' of caster, -2°00 deg of front camber, +0°02' of front toe, -2°15' of rear camber and +0°18' of rear toe (with uniballs or uprated control arms, otherwise +0°20'). This will provide a nicely balanced alignment that will be OK for street driving, yet decently perform on a track and won't chew the tires excessively. That's about the performance driving.

 

[4Channel]

If I could add one thing, it is an extremely common misconception that front toe-out improves turn-in. The effect of toe is to "preload" tires with slip angle, such that when lateral load transfer occurs, the slip angle "preload" of the loaded outer tire generates a large lateral force immediately when normally the tire would have to rotate relative to the direction of travel beforehand. So in the case of front toe-out, the load transfer to the outside tire, which is pointing outwards, actually stabilizes the car. You can test this in a racing simulator by setting an impractically large amount of front toe-out, and noting how sluggish the response is. Likewise a car with front toe-in will start to rotate as it keels over, even if you don't apply more steering input. If you think about the tires acting about the center of mass, it makes sense that a front toe setting would have the opposite effect of a rear toe setting. So front toe-in will destabilize the car, while rear toe-in will stabilize it. Although I do agree that generally large toe settings are disliked in racing setups and should be used sparingly to correct undesirable behaviour inherent in a car.

 

[OriginalForza]

If I could add one thing, it is an extremely common misconception that front toe-out improves turn-in. The effect of toe is to "preload" tires with slip angle, such that when lateral load transfer occurs, the slip angle "preload" of the loaded outer tire generates a large lateral force immediately when normally the tire would have to rotate relative to the direction of travel beforehand. So in the case of front toe-out, the load transfer to the outside tire, which is pointing outwards, actually stabilizes the car. You can test this in a racing simulator by setting an impractically large amount of front toe-out, and noting how sluggish the response is. Likewise a car with front toe-in will start to rotate as it keels over, even if you don't apply more steering input. If you think about the tires acting about the center of mass, it makes sense that a front toe setting would have the opposite effect of a rear toe setting. So front toe-in will destabilize the car, while rear toe-in will stabilize it. Although I do agree that generally large toe settings are disliked in racing setups and should be used sparingly to correct undesirable behaviour inherent in a car.

This is the long version of exactly why I say zero/no toe, especially for the 4c. Because of the shorter wheelbase, the turning dynamics need absolutely no help like 99% of overpowered luxury boats, which "tuners" are functionally fixed on repeating which is why these idea show up on a "squared" car like a 4c. The Lancia Stratos racing development has YEARS of data and research into our platform's dynamics, which has been repeatedly defaulted to by every engineer I asked anything about, and those notes basically eliminated toe out experiments versus squared toe and stronger/more rigid link points, as well as straight condemning toe in as total stability failures that costed confidence and time. What's crazy is the 4c development team wasn't even aware of the Stratos' notes, and basically retread unfortunately only the first few months of that proven experience OFF ROAD. For those unaware, the Stratos that are left don't hunt ruts and feel planted when changing vectors at high speeds, even when the road is dust so, there's a lot to copy from that. The 4c is a MUCH faster car than 8mins on the Nurburg, it just needs the right suspension which has been proven for over 30 years+, twice as long as the 4c platform has even existed. So basically, upgrade/change the sad factory suspension links and whatever the caster and camber, wheel size you prefer for what you're doing, keep the tires pointed straight forward, especially on loose/bad (basically real) roads.

When history provides advice... LISTEN, people, or be fated to waste your time on lessons already learned.

 

[OriginalForza]

In terms of performance (grip) and not the looks these would be my recommendations:

1. 17" and 18" combo over 18" and 19". Tire width? You want the widest and softest tires (lower the treadwear rating, the better) you can fit and still bring them to the operating temp. Tires that are wide and hard, will perform worse than soft narrow tires that are operating its ideal temp range. In 4C the front end is very light, so anything wider than 225 at the front, you will be having hard time to heat up. The rear end is quite heavy though and also has the drive, so you can easily run 265 tires and you'll still heat them up. In my case 215 front and 265 rear seems to be close to the ideal combo. Both tires heat up evenly and wear out pretty evenly as well. I believe that 215 / 275 combo might be even better, but 275 rears are hard to come by. For 215 you need at least 7" wheel width and 9" for 265. Ideally +0.5" up on the minimum wheel width to provide more stability to the tire side wall. Of course, you don't want low profile tires as they poorly absorb road imperfections, temperatures fluctuate a lot and generally drive worse than slightly higher sidewall tires. They look cool though.

2. The rims width should be adjusted to suit the tires and not the other way around. So once you know what tires you will be running, you can choose the optimal wheels width.

3. Alignment. There is no ideal alignment that would work best in all circumstances, but here are some guidelines. Caster is needed to provide straight line stability and dynamic camber gain upon cornering. On a 4C you want as much caster as you can get as the car is already very twitchy. Negative camber is needed to compensate for the body roll and softer your car is sprung and stickier the tires you run, the more negative camber you'll need. With toe you can make car's front or rear end more or less prone to steer. If you want more initial turn in, you'll toe out the front, and if you want more straight line stability and less responsive front end you'll add some toe in at front. However, toe in in the world of performance driving is not a common thing to see. 4C is already very nimble at front, so I would suggest to keep the front toe close to 0°, perhaps a slight toe out on a tight twisted tracks, but no excessive toe out is needed as with FWD or some other nose heavy cars is. On the rear you want a healthy amount of toe in to keep the rear end planted. 4C has very short wheelbase and very wide track, which means a generally nervous car with quick wheel load transfer, so any oversteer that might happen, will happen suddenly and quickly and you definitely don't want a zero toe or even toe out int that situation. Also with all the weight at the rear axle, you can easily reduce the potential understeer with slight throttle lift off and the rear end will start to turn in nicely. Do that with not enough toe in at the rear and you'll drive backwards sooner than you'll realize. This is very simplified, but you get the idea. It is impossible though to say what's the perfect alignment for 4C, without knowing all the details (tires, suspensions, weight, intentions of use, etc.). But let's say you have a mildly modded 4C (better, wider tires, remap, perhaps suspension) and like to occasionally push it, but otherwise you drive normal. In that case, I would recommend about +4°00' of caster, -2°00 deg of front camber, +0°02' of front toe, -2°15' of rear camber and +0°18' of rear toe (with uniballs or uprated control arms, otherwise +0°20'). This will provide a nicely balanced alignment that will be OK for street driving, yet decently perform on a track and won't chew the tires excessively. That's about the performance driving.

The only reason zero toe would be such a negative when weighed against a toe in to help reign in the snap oversteer characteristics is because the driver isn't driving the platform they are driving, but trying to drive the FR lightweight typical/default to driver's expectations. In short, the driver will need to reprogram drive our short, wide platform... Look at the 911's destroying Nurburg times: the "ideals" here are all counter intuitive, but when the drivers reprogram to drive a 911 GT2 RS, you see clearly how the overall physics benefits in putting enough power down longer and with enough confidence to pass all the rest.

I do understand you are trying to provide your experience in helping the average driver with information here, but also important to elucidate that there is also another way which requires not "more engineering" but more driver education and experience. Why compromise stability with toe in when it is only to cover the symptoms of the wrong driving disease? Cure the syndrome and the compromise is no longer needed.

 

[GMS]

If I could add one thing, it is an extremely common misconception that front toe-out improves turn-in.

I'm sorry, I cannot agree with you on this one, because...

Both toe-in or toe-out generate slip angles also when driving straight on both tires of course, I agree. But, when cornering, the outside tire requires a larger turning radius than the inside tire. In other words, the inside tire has to turn more sharply than the outside tire to get the maximum combined cornering force. With a car that has toe-in, the inside tire is constantly turned in, and it is fighting the outside tire and detracting from the total front cornering power. This reduces the ability of the front end of the vehicle to turn into the corner. However, by having the front wheels set with a small amount of toe-out, the instant you turn the wheel, the action of the inside tire turning more sharply than the outside tire already exists and the car turns into the corner "like it is on rails". Once the car sets in the corner, which means that the weight transfer has already happened, the front toe has no more effect on the handling because inner tire is now pretty much unloaded compared to the outer. So, front toe only affects initial steering feel.

The toe-out will improve initial turn-in. Toe-out at front makes the car noticeably more responsive at the front. As mentioned, it doesn't reduce the understeer in mid corner or corner exit, but it does make the front end turn more "lively", less initial understeer we can say. Quick swerving left and right will most noticeably show this effect. Toe-in will make the car's front end feel more sluggish on direction changes and same goes for the rear. If you set up a car with front toe out and rear toe out it will be extremely easy to rotate, but pretty much impossible to drive fast as the front end will be very responsive and the rear end will tend to rotate as well. Such setup would be useful on an AutoX event with slow and tight track, but not even remotely useful on any fast track or street. Also, as mentioned with rear toe close to zero, the 4C's rear end will be far too nervous to drive with confidence. About +0°17' per wheel at the rear (with uniballs) is minimum I would suggest, to have at least some margin for driver error, otherwise the 4C's rear end will bite on you. Most probably when you'll come a bit too hot into the corner, abruptly lift the throttle and turn in. With rear toe below the recommendation, get ready for a spin! But it will turn in well, we have to admit that.

Of course, a great effect on how the handling feels, also depends a lot of the suspension, mostly ARB's. A car with stiff ARB rear and soft ARB front, will turn in much quciker than the other way around...it's about the weight transfer and how it affects the tire load.

 

[4Channel]

But, when cornering, the outside tire requires a larger turning radius than the inside tire. In other words, the inside tire has to turn more sharply than the outside tire to get the maximum combined cornering force.

It is definitely true that the inside tire must travel a smaller radius path, and this is why passenger cars have close to 100% or "perfect" Ackermann geometry. However, at the high speeds and high cornering forces we care about, the picture becomes a lot less clear. Additionally, this is not of importance in an unsteady-state scenario, such as initial turn-in.

With a car that has toe-in, the inside tire is constantly turned in, and it is fighting the outside tire and detracting from the total front cornering power. This reduces the ability of the front end of the vehicle to turn into the corner.

However, you later say this:

However, by having the front wheels set with a small amount of toe-out, the instant you turn the wheel, the action of the inside tire turning more sharply than the outside tire already exists and the car turns into the corner "like it is on rails".

The issue is there's no indication of what makes each statement qualitatively unique. What's stopping me from saying, for example, in a toe-out car, the outside wheel is fighting the inside tire and detracting from the cornering power? While in a toe-in car the action of the outside tire already exists? Additionally, because this is an unsteady-state scenario, "total cornering power" is not relevant.

Okay, so let's establish that the greater the load on a tire, the more lateral force it will generate for a given slip angle.

Therefore, due to the load transfer to the outside of the car, even if both inside and outside tires have a slip angle of X˚, the outside tires will still generate more lateral force. Now imagine the case of a car with 0.2˚ of front toe-out (a large amount). Let's say the steering has parallel geometry, and the driver instantaneously rotates the wheels until the outside wheel is steered straight ahead, while the inside wheel is steered 0.4˚ in the direction of travel. Due to the load transfer, the loaded wheel is now the outside wheel, which has 0˚ of slip angle. This means that the outside wheel is generating 0 lateral force. The unloaded inside wheel is responsible for generating all the cornering force. However, because it's unloaded, it generates less lateral force at 0.4˚ than the loaded outside wheel would generate at the same slip angle. Even though this is a very small overall steer angle, and the driver only remains at this small steer angle for a small fraction of a second, this is what is responsible for the slight sluggish feeling of toe-out. The opposite situation occurs in a car with front toe-in.

It's true that the effect of static toe in mid-corner is negligible, however there is a reason why you may want a large amount of toe-in mid-corner that I won't get into.

 

[John4C]

It's true that the effect of static toe in mid-corner is negligible, however there is a reason why you may want a large amount of toe-in mid-corner that I won't get into.

Or do… you know, time permitting. This is terrific stuff. 🤓

 

[4Channel]

Or do… you know, time permitting. This is terrific stuff. 🤓

Okay, okay...it'll have to wait 'till tonight though 😅

 

[GMS]

However, you later say this:

By "turned in" I meant it's pointing inside towards the center of the car, not outwards as it does in case of toe-out.

What's stopping me from saying...

Additionally, because this is an unsteady-state scenario, "total cornering power" is not relevant.

Nothing stops you from saying that. You are actually right, but as soon as you give it some steering angle, both tires (in case of toe-out) will now want to turn in. The inner even more so. In case of toe-in, both tires will turn in too, but inner less so. This trend will continue through entire steering wheel turning process so in case of toe-in you will constantly have the inner tire wanting to turn less than you'll be asking the car to. From this point I see somewhat more logical to say that in case of toe-in the inner tire is fighting the outer, because the goal there is to make a turn and the inner tire is trying to fight against this action.

By total cornering power I meant the work done by both front tires. If both tires are pointing into the turn, they are both contributing to creating the cornering force in same direction. That would be the toe-out. With toe-in, the outer tire is doing its work by steering the car into the corner, while the inner wheel wants to go more straight and that's isn't contributing to creating the cornering force in same direction.

Perhaps the simplest statement I can make would be: With toe-out the car will always want to turn in one or other direction and will prefer anything but straight line. With toe in, it will rather go straight than turn.

...the driver only remains at this small steer angle for a small fraction of a second...

Exactly. That tiny fraction of a second in this particular steering wheel angle, is the only time that toe-out setup situation is worse for turn in than the toe-in setup, but as you said, it's just a fraction of the steering process, so we could say it's negligible compared to the benefits, of having toe-out if you are looking for a good turn-in. On other hand, having wheels set to toe-in, you'll be fighting the inner wheel all the time except that tiny second of a fraction you mentioned, so we can assume, it's not helping with the turn in ability.

P.S.:

I made this post with intention to respond to the @OriginalForza's question about the alignment. I believe my explanation was fairly correct with no major flaws. We've provided numerous setups for different cars, including 4C's and we did bring some trophies from racing events home as well, so I guess there is not much wrong with my approach, but I'm always willing to learn and educate. I believe I have decent racing pedigree but I must say, that I've never seen a track car with toe-in at front to be honest. At least not the one on the podium. I always like to get the ideas of how and why by looking into the F1 cars, and I we've never seen front toe-in setup there either. Among various alignment setups I've had, particularly on a 4C, I've also tried to dial in some toe-in at front on my own 4C to gain some straightline stability and it did help, noticeably, but the car felt a bit too slow on the turn in for my taste (sluggish), so I dialed in some toe-out again. For me and for every serious track user I would say that toe-out at front is the only way. However, I must say, that for street users we do recommend slight toe-in at front to increase straight line stability even though slight initial turn-in is sacrificed. But on a car like 4C with very light front end, even with toe-in the turn-in is very good. In the end, if the setup you have is working for you, then that's it, no need to chagne it or follow other's advice. There are people running square setup tires on 4C and seem to enjoy it, so toe-in or toe-out at front won't change the world either, but it does feel different if you can feel it.

Here is my setup recommendation:

And the rare F1 setup chart:

 

[4Channel]

I made this post with intention to respond to the @OriginalForza's question about the alignment. I believe my explanation was fairly correct with no major flaws.

Sorry, I'm not trying to pick on you at all...I mostly wanted to write this for myself to show to people as needed since I see this mistake so often and just ended up choosing your post. In fact, the only time I've seen it NOT made was talking to a vehicle dynamicist. It's a tiny nitpick anyway, and static toe isn't even that important.

By "turned in" I meant it's pointing inside towards the center of the car, not outwards as it does in case of toe-out.

Geometrically, it doesn't matter. The net steer angle will be the same. It only matters because of the load transfer.

You are actually right, but as soon as you give it some steering angle, both tires (in case of toe-out) will now want to turn in.

If both tires are pointing into the turn, they are both contributing to creating the cornering force in same direction.

The loaded outside tire in fact doesn't necessarily turn in until you reach a large enough steering angle to overcome the toe-out, as explained in the example with the 0.2˚ toe-out car.

In case of toe-in, both tires will turn in too, but inner less so.

The inner tire does not even necessarily steer into the turn at first, but because it is unloaded, it is not a big deal relative to the outer tire.

Exactly. That tiny fraction of a second in this particular steering wheel angle, is the only time that toe-out setup situation is worse for turn in than the toe-in setup, but as you said, it's just a fraction of the steering process, so we could say it's negligible compared to the benefits, of having toe-out if you are looking for a good turn-in.

I only chose 0 degrees for the outside tire in my example for illustrative purposes, it would also be possible for the loaded outside tire to be pointing in the wrong direction, or to only have a very small slip angle in the correct direction. Sorry, I didn't mean to imply that the effect only applies at a particular instant.


Also, one thing I neglected to mention is that in the time the driver of a neutral-toe car could steer the loaded outside tire 5˚, the driver of the 0.2˚ toe-out car would have only steered the outside tire 4.8˚, increasing the delay between driver input and acquisition of the slip angle and decreasing the driver perception of turn-in. This effect is mostly inconsequential though.

I must say, that I've never seen a track car with toe-in at front to be honest. At least not the one on the podium. I always like to get the ideas of how and why by looking into the F1 cars, and I we've never seen front toe-in setup there either.

Neither have I, and I think it is because there is pretty much no reason for a car with front toe-in, for mostly the same reason there is no point in rear toe-out. Why make your car more unstable? Generally, toe settings are a band-aid, and if you have a mid-corner push or something you'd be better off chasing the real source of a problem rather than trying to coax the car to yaw on turn-in. In the case of F1 cars, they mostly (or perhaps all teams do) run static toe-out just because of the twitchy nature of the cars. So it only makes sense if the car is twitchy as a facet of the design and you just need to tone the instability down a bit. As far as amateur level setups go I suspect the placebo effect does quite a bit of legwork.


Okay, to continue on this point:

It's true that the effect of static toe in mid-corner is negligible, however there is a reason why you may want a large amount of toe-in mid-corner that I won't get into.

If we take a look at the lateral force vs slip angle graph again:

Notice how when a large load is applied to the tire (as in the 1800lb plot), peak lateral force is achieved at a high slip angle. At lesser loads, peak force occurs at a lesser slip angle. This is one facet of what is known as "tire load sensitivity"

Let's consider another hypothetical situation. For the sake of the plot above, we'll say that the car is a 5400lb porker, but is low to the ground such that only 2/3 of the weight transfers to the outside during cornering. Assume 50/50 F/R weight distribution. Therefore in a corner each inside wheel experiences 900lbs of load while each outside wheel experiences 1800lbs of load. Looking at the plot again:

Lastly, let's assume a very high speed turn such that the difference in path radii between the inside and outside tires is negligible. The driver is probably going to drive the car to a point such that the loaded outside tires are at a ~6.5 degree slip angle, since they generate much more force than the inside tires. However, in a car with parallel steering, what this means is that you've actually gone 0.8˚ past the peak force slip angle of the unloaded inside front tire. So what if the car was holding both front tires at their optimal slip angle? It would look something like toe-in, but it would be impractical to have 0.4˚ of static toe-in.

Quick detour in case you aren't familiar with Ackermann steering geometry. Fundamentally: At low speeds, when slip angles are almost zero, it is best if the inside front tire rotates more than the outside front tire for a given steer angle to prevent scrubbing. Most passenger cars have near-perfect Ackermann geometry to minimize tire wear and improve low-speed maneuverability.

But what we want is for the outside wheel to rotate more quickly as the driver steers. This way we don't have to have static toe-in but still get the benefits of toe-in in the corner. This is called anti-Ackermann geometry, and it's basically limited, once again, to F1 cars and similar because the poor low speed behavior just isn't worth the minuscule benefit in passenger cars.

An example of anti-Ackermann on an F1 car in a photo taken just before disaster:

One more thing: if one were to implement anti-Ackermann on their racecar, it could only be optimized for a single speed, and would become more suboptimal the further away one gets from that speed. The purpose of the Mercedes F1 DAS (dual axis steering) system was that the driver could set the appropriate amount of toe-in before entering the corner, while keeping neutral-toe on the straights. It was important enough to make the Mercedes car significantly faster in the 2020 season, apparently.

Take this with a large grain of salt: I think one of the secrets to the obnoxiously low 'ring times of Porsche cars (other than buttering up Michelin) is that their active rear-wheel-steering system is designed to take advantage of this, but in the rear.

Thank you for listening to my Ted Talk.

 

[GMS]

Thank you for your thorough explanation. I would like to discuss this more as it seems I have much to re-learn, but I must admit it kind of hurts to have someone tell you you've been doing it wrong all the time, living in a lie if I may say so. What hurts even more is the idea that my feelings about the handling are off. So if I may have a few more questions?

If I understand, you are a firm believer that front toe-in makes the car unstable and front toe-out makes the car more stable?

I always feel that toe-out noticeably changes front end initial turn in making it much happier to turn, but gets a bit twitchy in a straight line? My feelings are off?

If you change default OEM front toe-out setting on a 4C to toe-in, the car is much less prone to tramling. Are my feelings off again?

So what you would say, why factory cars all come with toe-in? To make car more unstable at front? And race cars come with toe-out to make the car more stable?

 

[Zala]

Thank you for your thorough explanation. I would like to discuss this more as it seems I have much to re-learn, but I must admit it kind of hurts to have someone tell you you've been doing it wrong all the time, living in a lie if I may say so. What hurts even more is the idea that my feelings about the handling are off. So if I may have a few more questions?

If I understand, you are a firm believer that front toe-in makes the car unstable and front toe-out makes the car more stable?

I always feel that toe-out noticeably changes front end initial turn in making it much happier to turn, but gets a bit twitchy in a straight line? My feelings are off?

If you change default OEM front toe-out setting on a 4C to toe-in, the car is much less prone to tramling. Are my feelings off again?

So what you would say, why factory cars all come with toe-in? To make car more unstable at front? And race cars come with toe-out to make the car more stable?

I'm just following along and enjoying both applied and academic accounts (both of which have value to pull out). I'm personally this driver right here as stated in your original post and actually landed on this relative alignment target with hands-on test-and-driving by my 4C mechanic and my personal preferences for street driving (I prefer neutral toe up front):

"But let's say you have a mildly modded 4C (better, wider tires, remap, perhaps suspension) and like to occasionally push it, but otherwise you drive normal. In that case, I would recommend about +4°00' of caster, -2°00 deg of front camber, +0°02' of front toe, -2°15' of rear camber and +0°18' of rear toe (with uniballs or uprated control arms, otherwise +0°20'). This will provide a nicely balanced alignment that will be OK for street driving, yet decently perform on a track and won't chew the tires excessively. That's about the performance driving."

Reading along I feel like there's two distinct definitions of "stability" being applied here and maybe that's worth clarifying (unless I'm misinterpreting the disconnect)? I use "stability" typically to convey to your average drive-my-4C-to-Cars&Coffee driver to define a straight line non-twitchy driving experience and minimal expectation of aggressive response to inputs. I also understand there's an element of predictability in the middle of long hard turn (I feel it on my local back road drives and interestingly among all my toys (Lotus Elise, various NC Miatas), I "feel" the 4C is the least stable of the bunch in this setting despite very similar alignment targets on all the cars. I feel the 4C micro-twitch on me my slightly mid turn as my most uneducated way to describe it given similar speed and approach. Now I have different tire setups on all the cars (all 300 TW), of course the Lotus is a superhero because of how light it is, and my NCs feel more stable at 10-15 mph less speed than my mid engine cars mid cars, but despite all that, what I feel in the 4C is distinct I feel and I'm not trying to pick a favorite because I love my cars all the same and enjoy them for their differences.

I too see very little value in toe in up front and prefer always neutral toe up front for street driving to give me enough, but not too much responsiveness to imperfect roads and mild toe in for the rear so that the car doesn't decide to steer from the back (referring to the infamous Lotus Elige toe link failures).

Anyway, that's all I have to say. Happy to see the discussion continue for our collective benefit. An admin should pull out these posts into a more easily identifiable discussion on alignment theory and experience.

 

[4Channel]

There's actually one thing I completely forgot about, which is that static camber actually generates a small lateral force in a straight line. If you imagine a wheel with negative camber, and then imagine a point in the wheel centerline rolling along the outside diameter, you'll notice that as the point reaches the ground it gets pressed into the contact patch and can no longer move laterally such that the tire deforms inwards relative to the plane of the wheel, generating a lateral force. The picture below is a top-down view that demonstrates:

The effect of this lateral force is the same as toe: during load transfer, the camber force on the outside tire will be emphasized. So negative camber increases turn-in in a similar manner as toe-out. So in fact, I think this is one of the main reasons racecars might use toe-out, to counter the static camber force when running a large amount negative camber.

Now, the thing is that camber properties vary a lot by tire. Road tires will probably be designed to maintain a lot of their grip even when 5˚ off camber, while race cars will be a lot more sensitive to changes and also generate a lot more force/degree of camber. I also once heard a rule of thumb somewhere that recommends 0.1˚ of front toe-out for every 1˚ of negative camber, which seems like a lot. That might be for racecars though. It seems like the Arrows setup posted earlier follows that rule.

I actually wonder if there is a proper term that describes these combined effects such as "transfer steer" or something (which would be distinct from roll steer, which has to do with suspension articulation).

Thank you for your thorough explanation. I would like to discuss this more as it seems I have much to re-learn, but I must admit it kind of hurts to have someone tell you you've been doing it wrong all the time, living in a lie if I may say so. What hurts even more is the idea that my feelings about the handling are off. So if I may have a few more questions?

Honestly, I think that short of proper race teams with access to comprehensive data from the tire manufacturer, a lot of this stuff is not as exact a science as we'd like. I know you move through different tire brands a lot (or did at one time) so it could easily be the case that different tires have different properties regarding camber or cornering stiffness that end up changing the working of the setting a lot.

If I understand, you are a firm believer that front toe-in makes the car unstable and front toe-out makes the car more stable?

I always feel that toe-out noticeably changes front end initial turn in making it much happier to turn, but gets a bit twitchy in a straight line? My feelings are off?

It could also have something to do with tires or the camber properties of the tires, although if you're changing absolutely nothing about the setup but toe and then experiencing this, that would be weird. But your setups don't call for an extreme amount of toe anyway. When I've played around with toe in simulators it seems to take quite a bit of toe until you can say 100% for sure that what you're feeling is really the effect of toe.

So what you would say, why factory cars all come with toe-in? To make car more unstable at front? And race cars come with toe-out to make the car more stable?

Do passenger cars come with front toe-in? I would assume they come with close to neutral for minimum wear, or maybe toe-out like the stock 4C to make the steering less reactive. In the case of racecars, I would say it's a combination of making the steering less reactive in a twitchy car and countering the camber force.

If you change default OEM front toe-out setting on a 4C to toe-in, the car is much less prone to tramlining. Are my feelings off again?

I haven't experienced tramlining as much as some here have, so I can't say much, but I've noticed that when I have, it's usually because one of the wheels ran over some kind of extended section of the pavement at a weird camber. The thing is, if tramlining was working by a mechanism through which the road applies a lateral force to the tire, which provides a torque into the steering, we would actually expect the steering torque to be opposite in the direction of the tramline (that's why steering wheel torque is opposite of the direction of travel). But that doesn't seem right just thinking about it. It would make sense that the road surface is applying a torque directly to the tire which then applies a lateral force. So at this point I think toe isn't that relevant to the discussion and you'd have to talk to someone who actually designs tires. Or, it could be possible that toe-in actually does reduce tramlining since, because the steering torque is applied opposite to the lateral force, the induced steering effort naturally corrects the toe-steer effect. Okay, sorry if that doesn't make sense because I'm not sure it does and I'll have to think about it some more.

Reading along I feel like there's two distinct definitions of "stability" being applied here and maybe that's worth clarifying (unless I'm misinterpreting the disconnect)? I use "stability" typically to convey to your average drive-my-4C-to-Cars&Coffee driver to define a straight line non-twitchy driving experience and minimal expectation of aggressive response to inputs. I also understand there's an element of predictability in the middle of long hard turn (I feel it on my local back road drives and interestingly among all my toys (Lotus Elise, various NC Miatas), I "feel" the 4C is the least stable of the bunch in this setting despite very similar alignment targets on all the cars. I feel the 4C micro-twitch on me my slightly mid turn as my most uneducated way to describe it given similar speed and approach. Now I have different tire setups on all the cars (all 300 TW), of course the Lotus is a superhero because of how light it is, and my NCs feel more stable at 10-15 mph less speed than my mid engine cars mid cars, but despite all that, what I feel in the 4C is distinct I feel and I'm not trying to pick a favorite because I love my cars all the same and enjoy them for their differences.

Ah yeah, I am definitely using stability in a very colloquial manner to describe the behavior of the car during initial steering. There in fact is a textbook definition of stability, and it is a mid-corner phenomenon, although I guarantee it's not what most people think it is.

 

[GMS]

...I feel the 4C micro-twitch on me my slightly mid turn as my most uneducated way to describe it given similar speed and approach.

On stock control arms or with uniballs?

Do passenger cars come with front toe-in? I would assume they come with close to neutral for minimum wear, or maybe toe-out like the stock 4C to make the steering less reactive. In the case of racecars, I would say it's a combination of making the steering less reactive in a twitchy car and countering the camber force.

Yes, in OEM format, it's front toe-in all the cases I know and seen, also the FWD cars. Sometimes, close to neutral, but never toe-out.

...It would make sense that the road surface is applying a torque directly to the tire which then applies a lateral force. So at this point I think toe isn't that relevant to the discussion and you'd have to talk to someone who actually designs tires. Or, it could be possible that toe-in actually does reduce tramlining since, because the steering torque is applied opposite to the lateral force, the induced steering effort naturally corrects the toe-steer effect. Okay, sorry if that doesn't make sense because I'm not sure it does and I'll have to think about it some more.

4C has positive scrub radius at front and adding low ET wheels at front, further promotes the "instability" by amplifying the road imperfections to transfer through the wheels into the steering wheel. With having no hydraulic assisted steering rack, these effects are much more noticeable than they would be if 4C had one. 4C's front end is very sensitive to any changes (caster, camber, toe, wheels ET). I agree that negative camber will effect straight line "stability" more than toe-in will be able to solve, but on bone stock 4C with very low front negative camber, the front toe-in does settle the front end noticeably. Please give it a try, I'm sure you'll be able to feel it for yourself.

New chapter:

I've been thinking more about this topic and got a few more thoughts together...

There is a limit on how much toe-in or toe-out should be used. At some stage, I was trying to make the 4C's rear end more stable by further dialing in rear toe-in. I went all the way to the +0°23' per wheel and the consequence was following. The car just didn't want to slide and felt pointy / darty. Regardless of how ideal I took the corner I never managed to get a nice neutral drive, something between understeer and oversteer where both front and rear wheels are sliding just a minimal bit. The rear end had the grip and once you were over the maximum grip threshold, it just transferred abruptly into oversteer, not in a pleasant manner but in form of snap oversteer. By the book adding more rear toe-in should help stabilize the rear end and prevent oversteering, but it didn't. Well, it did to point, the rear end did feel it had a good grip, but as mentioned, the line between the grip and oversteer became very narrow, resulting in snappy oversteering conditions once the rear tires went over it's peak grip. It was a setup that was impossible to drive on the limit with confidence. Two other things I've noticed is that trail braking technique was not very effective as the rear end just didn't rotate much. The benefit of this setup was, that on a tight tracks, the rear wheel spin was very rare and car tend to accelerate out of those tight corners nicely, without loosing the traction.

Next setup, I dialed rear toe settings to more neutral +0°18' and the car felt much different. On tight corner exits, the inner rear wheels did spin often so definitely I couldn't accelerate out of those tight corners as aggressively as before. However, everything else felt better. The car felt much more neutral (easier to achieve the ideal 4 wheel slide with both front end and rear end sliding just a bit at the very limit of ideal slip angle / adhesion). The trail braking and throttle modulation (slight lift off for improved turn in) became much more effective. I did notice slightly more frequent inner wheelspin on exits of tight corners though. That was the only downside. Later I did a few other tweaks to the alignment from here on, but always kept the rear toe-in between +0°15' and + 0°17' per wheel ever since, as this has proven to be the sweetspot. Anything lower than +0°15' and the rear end becomes to prone to slide around, most noticeably on throttle lift off, trail braking and exiting out of tight corners. The 4C just gets more and more driftable with such setup and that's definitely not the fastest way around the circuit. Anything over +0°20' and the car gets pointy / darty and hard to drive on the limit due to snappy oversteer characteristics.

I believe the reason that 4C has uncommonly high level of rear toe-in already in OEM format, is that the rear control arms - more precisely rubber bushings flex a lot and the rear toe is all over the place once you start to push the car and lean on the tires, so they had to add lots of rear toe-in, to prevent potential toe outing during the drive. The general rule is, that the more rigid the steering components are, less dynamic alignment changes will happen and less toe-in is needed. You can see that example if you compare regular 991 GT3 and CUP GT3 or GT3R. The later two run noticeably less toe-in at the rear than regular 991 GT3 does. The regular 991 GT3 is on rubber bushings and later two are all on spherical joints. Also goes for other comparable cars. 488 and 488 GT3, differ in a same way as well. Now the race cars definitely don't take away rear toe-in because they would like to make the car more unstable, but there is no need for so much toe-in if there is not much flexing in chassis, steering and suspension that would be the cause for lots of dynamic alignment changes. So yes, I believe there is a sweet spot on how much toe should be used for particular car and setup.

That's about the rear end.

Regarding the front end, here are my experiences.

OEM 4C tramlined quite bad on my local roads. Most noticeably on long straight roads with some imperfections, the car's front end would constantly pull either left or right, literally would go anywhere but straight. Increased caster (from about 2° to 4°) solved this a lot, but it was setting front toe from a default factory, quite aggressive toe-out (-0°07') to mild toe-in at +0°04 that really settled the car.

When we install camber plates on a customer's car, I drive the car then to different location for an alignment. When you install the camber plates, the position of front control arms changes noticeably. The upper control arms are pulled backwards and lower control arms move forward. Because of this, the position of steering rack tie rods moves and consequentially also front toe changes a lot. It jumps to around +0°30' per wheel. Now when I drive such misaligned car, it's terrifying. It's hard to describe, but the front end feels way off. Initially understeers already at very low speeds and then all the suddenly, it grips and pulls into the corner. Like you would have something underneath the front wheels that would be filtering your steering input. Like you would be driving over the marbles and the car wouldn't steer as nearly the same as you would expect it too, given the input you were giving it through the steering wheel and then, once you get the marbles from underneath of the wheels, the grip is all of the suddenly there. Sorry, I can't describe this better, but it's just weird. I never pushed car in such state as it already feels unpleasant just driving it to the alignment rack. Well that would be a too much of toe-in I guess.

I did quite some alignments in my motorsport career but let's focus on 4C. For me, the front toe if you want lively and pointy front end, it should be set to toe-out of no more than -0°04' per wheel. I feel this is more than enough of front toe-out to get the front end pointy and darty. But, it makes the car follow road imperfections and irregularities quite noticeably. If you want less lively front end, drive the 4C with one hand on the steering wheel and not worrying about unintentionally switching the lane or getting pulled off the road, a mild front toe-in is a must. I would say +0°04' per wheel is the upper limit before the front end starts too feel weird.

Now if I touch the front toe-in and toe-out dilemma for a bit more. Based on my experience, I'm still a firm believer that front toe-out will improve turn-in response and hurt the straight line "stability" which perhaps, more appropriate description would be, the car will be prone to follow the road imperfections and having hard time to maintain straight line direction. The reason I see for that is, that even though when you go perfectly straight and both wheels are pointing outwards (toe-out), as soon as you make even slightest steering wheel input, you will immediately dial in lots of steering angle to the wheels and overcome the outer wheel initial toe out. Perhaps it's this transition from the outer wheel toe-out to toe-in that makes the car feel like it's pleased to turn, you know, making the car feel pointy with a good turn-in, I don't know, I lack the knowledge to explain it scientifically correctly. I also think that because the both wheels are pointing out, one left, other right, the car's tendency will be to go either left or right, which is the cause of the poor straight line "stability". If we were to draw the line from both wheel's direction, in case of toe-out, the line's would be projected further apart at the front of the car and that is theoretically the direction where the car would want to go. In case of toe-in if, the line's would be intersected somewhere at the front of the car and that is theoretically the direction where the car would want to go, it's straight ahead, before it intersects and then starts to point outwards - left and right again, but that's very far ahead at the toe-in angle of about +0°04' per wheel. I don't have the scientific knowledge to explain why, perhaps you would be more successful at this, but I'll just go and accept my feelings and experience gathered throughout the career. I know, not the most scientific approach, but I'm more of a "try it and see it for yourself" type of guy. I was never was too good at school and did many mistakes in my life, but always had passion for motorsports and if something, I always felt my cars were competitive, especially in terms of handling once I sorted them out. I appreciate you tolerating my sometimes hot headed approach.

P.S.: Would any of admins be so kind to open new topic in technical section named - "alignment and suspension handling dynamics" in subforum tires, wheels and suspension, and move the posts from #23 onward there and delete these here.

 

[4Canada]

This discussion snipped from a conversation on wheel widening and offests.
It’s too good to lose!

 

[Alfanut]

This discussion snipped from a conversation on wheel widening and offests.
It’s too good to lose!

It’s a beauty! Thanks 4Canada and Rudi for the input.

 

[Sir5n]

It’s a beauty! Thanks 4Canada and Rudi for the input.

Work Order. R001890 VIN:

Licanse:

ALEX
Mileage
Date
5303
7/26/18 10:14 AM
Front: Left
Before
Specified Range
0 6°
0.9° 0.6°
2.3*
1.7° 2.7°
-2.7mm
-1.4mm -0.6mm
ZARBHAB4B-IN22855€
Actual
-2.2°
& Omm
Cross Camber
Cross Caster
Cross SAI
Total Toe
Cross Turn Diff.
Actual
0.0
0.1°
0.3°
Rear: Left
Before
Specified Range
-2 1°
•2.0 -1.5°
5.6mm
3.4mm
5. 144860
Cross Camber
Totel os
Thrust Angle
Actual
0.0•
5 UMm
0.00°
Alfa Romeo 2014-1B 4C
Cambe
Caster
Toe
SAI
Included Angle
Turning Angle DIff.
Front
Before
0.2°
0.1°
0.5°
1.2mm
Specified Range
0.3° 0.3°
2.9mm -1.2mm
Camber
Toe
Actual
2.2°
4 0mm
Rear
Before
0.1°
6.9mm
0.10°
Specified Range
6.9mm 10.2mm

This worked for me. Apologies I had difficulty pasting the original document for some reason.

 

[Zala]

On stock control arms or with uniballs?

Definitely fully stock control arms and only street camber/caster blocks... If I've interpreted your product thread correctly, I anticipate the new control arms on order will clean this up a good bit.

 

[Alfanut]

Definitely fully stock control arms and only street camber/caster blocks... If I've interpreted your product thread correctly, I anticipate the new control arms on order will clean this up a good bit.

I’ve received my front arms and am awaiting a slot at the workshop for fitment. Rudi’s words explain why on our last Alpine tour I wore out both edges (inside and outside) of a front pair of tyres on my slightly lowered 4C. The rears were evenly worn. My thoughts are that attacking enthusiastically 1000 bends in 90km (on one stretch) will help to do that but the results of the camber change when cornering were obvious. The centre of the tread was reasonably good.

 

[GMS]

Definitely fully stock control arms and only street camber/caster blocks... If I've interpreted your product thread correctly, I anticipate the new control arms on order will clean this up a good bit.

I'm confident to say - absolutely. It shall be a noticeable improvement. I look forward to hear your thoughts after you get it sorted out...

I’ve received my front arms and am awaiting a slot at the workshop for fitment. Rudi’s words explain why on our last Alpine tour I wore out both edges (inside and outside) of a front pair of tyres on my slightly lowered 4C. The rears were evenly worn. My thoughts are that attacking enthusiastically 1000 bends in 90km (on one stretch) will help to do that but the results of the camber change when cornering were obvious. The centre of the tread was reasonably good.

Camber doesn't change much even with rubber bushings. It's the toe that does and makes the car feel imprecise, on the rear especially due to long leverages of the control arms and not very rigid MacPherson struts. On the front, reason for both edges worn out could be different or multiple combined, but these three should be the first to look at - Underinflation and / or too much toe out with not enough front camber. Using IR temperature meter will tell you a lot about how appropriate your setup is for your kind of use before you even wear the tires. Or if you don't have one, the least you can do, is to touch the tires with hand (inner edge, middle, outer edge) and you'll definitely get the idea whether you're overworking inner or outer edge of tires. If you get inner edge hot while driving straight, you have too much on toe-out for your need. If you get outer edge (sidewall) worn out after a spirited canyon or track drive, you lack the negative camber. If you get more outer edge tire wear, but usually not the sidewall, even if you're just cruising, you're running excessive toe-in. If you get inner edge hot while cornering aggressively and yet you get visible marks of outer edge getting worn out too, you lack the negative camber and probably still run a bit too much toe-out. If you're driving straight and inner and outer edge are warm, you're underinflated.