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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...



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.
Running front -1.8 deg neg camber, zero toe and standard inflation pressure of 26 psi checked every morning of the Tour. Tyres? The much maligned but playful P-Zeros. 馃榿 Rears were evenly worn. Your recommended toe-in and -2deg of camber each side.
 

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Discussion Starter · #22 ·
With zero toe I wouldn't expect inner edge wearing out, so might be worth checking the toe again and trying a tad higher pressure, regardless of recommended specs. Somewhere from 1.9 to 2.0 for a test.

-1掳48' is solid camber for street driving and occasional blasting, but could be on a low side for spirited canyon driving, depending of the spring rates and ARB's.
 

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Discussion Starter · #24 ·
We did have disagreement regarding the effects of toe-in / toe-out at front, but I believe we agree on the rest, so I'm confident to say, that you won't miss a good baseline by following the recommendation below. For aggressive street and decent track setup, you should be looking into the middle column. Start with these specs and then fine tune once you'll get some miles on it and get some tire wear based on which you can then orientate on what you need to optimize.

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At the risk of appearing to have ADHD: did @GMS and @4Channel agree on a set up for: a) aggressive street; and b) track day? Did I miss the plane landing?

@Alfanut, what does -1.8 degrees look like? Can post a pic.
A photo of each side of my 4C.
Photos courtesy of Alf Alpha while we were at Eastern Creek six weeks ago.
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Great stuff, this topic, appreciate all your input!

We did have disagreement regarding the effects of toe-in / toe-out at front, but I believe we agree on the rest, so I'm confident to say, that you won't miss a good baseline by following the recommendation below. For aggressive street and decent track setup, you should be looking into the middle column. Start with these specs and then fine tune once you'll get some miles on it and get some tire wear based on which you can then orientate on what you need to optimize.

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@GMS could you clarify the toe-settings - the advise in your picture w setup advise mentions total toe +0掳38' whilst in one of your other posts in this topic you mention "always kept the rear toe-in between +0掳15' and + 0掳17' per wheel ever since, as this has proven to be the sweetspot" which means +30' to +34' total.

On the first post the advise is "and +0掳18' of rear toe (with uniballs or uprated control arms, otherwise +0掳20')" which totals to +36' to +40' latter for non-uniballs

That's quite a difference.
For (spirited) street and canyoning driving, what values best to be used for non-uniballs and what with uniball?

Appreciated!
 

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Discussion Starter · #30 ·
could you clarify the toe-settings - the advise in your picture w setup advise mentions total toe +0掳38' whilst in one of your other posts in this topic you mention "always kept the rear toe-in between +0掳15' and + 0掳17' per wheel ever since, as this has proven to be the sweetspot" which means +30' to +34' total.
+0掳38' of total toe is for street setting on uniballs. High amount of rear toe-in makes the rear end feel more "on rails" and less likely to oversteer on braking or throttle lift or aggressive acceleration. A safe setup suitable for any novice user with lots of driver error margin avaialble. On the very limit, the transitions from neutral to oversteer will be more snappy then lesser toed-in setup, so not the prefferd setup for serious track users.

Personally, I always kept between +0掳30' to +0掳34' of total toe in. I prefer a car with a bit more rear steer under throttle and braking modulation and more fluent transitions into oversteer.

On the first post the advise is "and +0掳18' of rear toe (with uniballs or uprated control arms, otherwise +0掳20')" which totals to +36' to +40' latter for non-uniballs. That's quite a difference.
OP was asking for recommended alignment setup for fast street, occasional track use. That's where suggested +0掳36' of total toe-in comes from. For non-uniballed setup, a slightly higher toe-in is required to compensate for flexing in the rear rubber bushings. In reality with rubber bushings, toe is all over the place most probably, so don't bother too much dialing in the perfect setup as it will dynamically change during cornering.

For (spirited) street and canyoning driving, what values best to be used for non-uniballs and what with uniball? Appreciated!
I would suggest upgrading to the uniballs or full rear control arms and then following the recommended guidlines posted here: The Dark Art of Suspension Geometry. Or, if you plan to stay on rubber bushings, then set total rear toe-in to +0掳40'.
 

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Hey @GMS , question: would you be interested in developing spherical joint multi links out of the most ideal material for any cost? Especially, maybe weld on upper mounts (maybe some bolt on units from the bottom mounts and some point on the subframe?) with a multilink upper/McPherson "delete" conversion for the rear? This way, the ideal alignment can be locked-in for every situation with absolute freedom, maybe even getting that little bit more caster/longer wheelbase for more stability going straight.

This would also resolve the clearance issues on the rear that your arms ran into, and provide the strongest links without maintenance or greasing?

Also, this may lead into a sort of "staged kit" to optimize the 4c with weight reduction, cooling increase, brake fluid improving, Oil Catch can, etc, etc that would maybe be the most popular aftermarket item for all 4c owners as it basically, unanimously corrects the whole platform with all this tune and test you've been doing all these years, successfully I might add. Slap a fair price tag after getting a "commitment list" (add me!), and maybe even change the entire public impression on the 4c forever, increased demand and values, etc cycles and karma, etc... Then let owners retune for a faster track setup or more comfortable road setup or even have the option to go rally and hillclimb as the rear now allows for all sorts of wheel travel options.

Just an idea, but I won't lie, this would be the PERFECT aftermarket solution for me, as I will be looking for bombproof daily driven suspension that will play best with my personal track times, maximizing enjoyment and predictability over what a real/serious racer will know to bespoke for themselves anyways. I would be surprised if anyone serious enough to pay you a fair compensation to make all your work so far come to a point of "maximization" (if you will) would feel any different. Just a "one shopping cart item" kit that come with a detailed install pdf and alignment specs for each popular tire and setup you've already tested. Done.

Yes?
 

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Discussion Starter · #32 · (Edited)
Thank you for thinking of GMS as a key to do it. I already received a similar question some time ago and my short answer is "no" and let me explain it why.

MacPherson is not bad at all. It has some drawbacks, but nothing major really. Perhaps unsprung weight and potential flexing would be the main drawbacks, while the camber and toe changes are not significant and can be adjusted and tuned to one's favor. MacPherson is actually a very good, simple and compact design. All Porsche Cayman series run MacPherson front and rear, while 911 series ran MacPherson at front until this latest 992 series. Clearly that wasn't a bottleneck in terms of performance, neither it is in 4C. There are cars like Megane RS that are decently capable and run torsion beam at the rear, which is prehistoric and not nearly as good solution as MacPherson, yet these cars have no issues setting decent lap times on a track. Why? Because on the track where surface is quite smooth, it doesn't matter all that much whether you run torsion beam or super-duper multi link 3D+ suspension layout. We need to know that 4C or any other serious sport cars don't have particular long suspension travel, let's say 5cm up and 5cm down, so there is very little change in camber and toe during movement, so it's not really causing any performance related issues. Quite opposite, you do want to gain some negative camber and toe-in when car squats or rolls into the corner and MacPherson can give you that. It can also slightly widen the track upon squatting or body rolling when setup right, so it's quite good really. Also pretty much all the cars (except early 4C's which don't have ARB's at the rear), run ARB's, which in a way, bind together independent movement of left and right suspension, and that reduces the benefits of independent left / right suspension a bit. If you have multi-link layout and ARB's connected to it, you're getting close the torsion beam properties in a way, if I say this very simplified.

Suspension layout will dictate the surface soaking abilities and handling properties on a car, the layout should be suited according to the needs. For Baja, good and quick absorption of large potholes and bumps is crucial, so there you have long double wishbones without ARB's, capable of huge suspension travel and relatively low unspung weight if we don't mind the tires and wheels. On the other hand, a capable offroader like Wrangler runs solid axles to maximize the wheel articulation / flexing, as this is more important over unsprung weight and independent movement of left and right suspension in this case. It doesn't provide the best handling experience on the road or fast gravel, but surely climbs as hell on a rough terrain. On a comfortable, modern road car, the double wishbone layout with no dynamic toe and camber changes and no ARB's for fully independent operation would be optimal. This way when a particular wheel would hit a pot hole, it could deal with it in most pleasent way for a passenger and driver. A pickup truck would be probably best suited with leaf rear coils to crank up its maximum potential pay load. On a track car, as mentioned, a few cm's of travel don't really matter enough to select A-arms over MacPherson as the benefits are negligible.

So if we return to the 4C, there is no need for double A-arms in the rear I firmly believe. It's not gonna drop the lap times because the current MacPherson layout, when setup right (control arm angle, bump steer, roll center, camber, toe), is just as versatile, let alone justify the costs and engineering involvement. OEM 4C's rear MacPherson layout is setup very well. There is no bump steer, roll center is OK, dynamic camber change and toe change are OK as long as you don't lower the car too much. The only issue, but quite serious is the long leverage of rear control arms in combination with rather soft rubber bushings, which causes lots of unwanted movement in the bushings which then causes dynamic toe changes which is the main cause of handling issues. It's just impossible to drive a car on the limit, fast, if it is unpredictable and floaty, and it will be floaty and unpredictable if there are constant toe changes happening when you drive. It's very similar feel to driving a car with lots of play in the bushes. Feels disconnected and imprecise. Not something you want to drive fast. But this is an issue of the rubber bushings, not the MacPherson layout. Switching to uniballs cures this issue and the 4C does become a very versatile weapon on the track, even with the MacPherson in the rear. No worries, MacPherson rear layout is not gonna cost you time on a track over double wishbone setup.

Now if one was to still go after a double wishbone conversion at the rear for some reason, there is no such thing as a plug and play solution. Lots of engineering, CADing, CNCing, fabrication, cutting and welding. You would need 4 control arms, 2x toe rods, 2x kingpins and all new mounting points, uniballs / bearings, etc. Second it is no joke to make kinematics right to avoid any weird handling characteristics. And when you get all this done you would still need coils and dampers and that's another challenge then to tackle, getting all the correct spec'd parts.

Personally, I find this project unreasonable in pretty much all the aspects, because as mentioned, the rear MacPherson on the 4C is done right, except for the bushings, but that's a minor thing to sort out with major impact on the handling characteristics. If you want to go faster on the track, there are other much more cost effective upgrades over rear double wishbone conversion, I believe.
 

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Somebody a short while ago was asking what -1.8 and -2.0 deg of camber looks like on a 4C. The photos below are of my rear Pirelli road tyres that have done over 15,000km of touring and back-road driving. Suspension alignment set to Rudi鈥檚 mid-specs. Fairly even wear, a bonus from less toe-in.
Tire Wheel Automotive tire Light Synthetic rubber


Tire Wheel Automotive tire Light Synthetic rubber
 
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