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Discussion Starter · #61 · (Edited)
@GMS - What is the optimal lowered height for the new front A-Arms?
With OEM control arms, for optimal geometry I would suggest that the car's static height is no lower than 110mm of ground clearance at the front (picture 1, 2) and 120mm at the rear (picture 3, 4). With such set static height, even during suspension travel the geometry stays OK (track width, roll center, camber gain), unless completely bottoming out and you keep at least some minimum chassis rake that prevents the car from catching "boat gliding" effect by lifting front and squatting rear end and catching the air underneath. The softer the car, the bigger the problem of geometry and rake.

I have a bit more positive rake on my car with 100mm of ground clearance at front and 125mm at the rear due to increased rear downforce we are planning to run. With GMS front control arms the front end static height should be set with at least 95mm of ground clearance, while the rear end shall be at least 10mm higher to keep positive rake and should be increased accordingly on cars with increased rear downforce.

From geometry perspective, the rear static height should be set at minimum of 100mm of ground clearance which is quite low, but with such a low ride height at the rear you would need a front ride height set at 90mm to maintain at least minimum positive rake. But as mentioned above, with OEM front control arms you are out of its optimal geometry range already with any front ride height under 110mm.

The side skirt to ground clearance should be just an orientation as the panel gaps, tolerances, tire size and grounds are not valid measuring reference. On my car there is about 4-6mm of difference left/right if measuring from the side skirt to the ground. I strongly suggest to set the car by measuring the threads on the coilovers and using side skirt to ground clearance just for a first reference when you start to adjust the ride height. Don't forget to load the car (fuel, driver) as stock 4C with base suspension tends to sit quite a bit.

I'm off to alignment and corner balance rig on Friday, so I'll report more on that later...


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The side skirt to ground clearance should be just an orientation as the panel gaps, tolerances, tire size and grounds are not valid measuring reference. On my car there is about 4-6mm of difference left/right if measuring from the side skirt to the ground. I strongly suggest to set the car by measuring the threads on the coilovers and using side skirt to ground clearance just for a first reference when you start to adjust the ride height. Don't forget to load the car (fuel, driver) as stock 4C with base suspension tends to sit quite a bit.
Just a suggestion for further down the line, maybe specify difference in height between two fixed reference points at inner and outer part of arm? Something like this:
115837

Would not that be a better starting point, since tire diameter, pressure and spring rates varies?

Might be a bit more tricky to measure, but I'd personally prefer that to take away any guesswork.

Anyway, it seems like your arms are the way forward for me, when I've decided for coil over and got them installed and approved. When that is, no one know due to the current pandemic. However, you know that you'll get rid of a set one day.
 

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@GMS - I'll second @AAaF recommendation that we might want to find a better measurement point. There seems to be two "primary" height measurement points that this forum has used for lowered cars. The skirt height as you have shown, and the top of the wheel arches. Both of these are body panels measurements and we know that the body panels have a tendency to be much more variable due to initial fitment variability and potential body damage that has "moved" these reference points for track cars.

@GMS - I assume that is the FZ201S, the soft version with 40 tread wear?
 
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Discussion Starter · #67 · (Edited)
Dear all,

I'm very excited to officially announce the long awaited GMS performance front control arms.

Before proceeding, let's make a "short" review for those who haven't been following this thread from the beginning.

We have designed GMS performance front control arms from ground up, with one goal in mind - ultimate performance. A set of 25CrMo4, TIG welded, non parallel, unequal length, double wishbones, GMS roll correction kit and legendary GMS uniballs for razor sharp handling, unfiltered feedback and optimal geometry on lowered cars. This upgrade consists of 4x 25CrMo4 TIG welded double wishbones (2x lower + 2x upper), 8x GMS front control arm uniballs, 2x GMS roll center correction kit ball joints and 2x GMS upper front control arm ball joints).

Isn't stock good enough?

4C has spot on most of the geometry specs for standard (non sport) suspension height (120mm ground clearance). Positive caster is a bit low making the car prone to tramlining and the rubber bushings make the front end a bit numb, but other than that it's very good. Bump steer is good, control arm angles are good, kingpin inclination angle is good, scrub radius is good, roll center is good. OEM setup provides a very good setup for standard suspension height (non sport, non lowered cars) and standard low grip tires. It provides neutral geometry during suspension stroke up and down which provides stable and neutral setup with minimal tire wear. Not much to improve here in terms of casual driving. Outstanding work from engineers, so leave it be or...get me going lower and faster? If yes, is your answer, then we have more for you further down...

If you are in to performance driving, we have a good news. It's all about the grip and optimal geometry is the key. There is always a room for improvement and GMS performance front control arms are here to fill that gap. We have improved 6 very important handling characteristics.

First - Roll center. Lowering the car without correcting the roll center, severely effects the body roll and most of 4C's are lower than stock height, run stiffer springs, thick swaybars and yet they are plagued by significant amount of body roll, taking away the precious grip. The solution is here. Revised geometry of GMS performance front control arms utilize special GMS ball joints which provides corrected roll center on lowered cars and decreases body roll during cornering.

Second - Dynamic negative camber gain. On stock control arms, if during cornering your 4C's body rolls for +3° and your run -2° of static negative camber, without any dynamic camber change, you are effectively, running +1° of positive camber that moment, which means that the car now runs only on the outer edge of tire, reducing the grip. As a solution, GMS performance front control arms are designed with inbuilt dynamic negative camber gain which means, that when the car's body rolls, also negative camber is gained, so if your body rolls for +3°, while you run -2° of negative camber and we add additional -1° of dynamic negative camber, you are at effectively at 0°, now running on entire tire patch, extracting the optimal grip out of your tires.

Third - Steering feedback. Front end in stock format feels quite numb. By replacing the rubber bushings with GMS uniballs we have eliminated any flex at the front end, making the car provide you all the required, unfiltered feedback to tell you exactly how close to the limit are you. On the other hand, your steering input will be much more precise, so the car will go directly where you point it to.

Fourth - Steering precision. Front end on 4C feels light, is prone to tramlining and hard to drive precisely. By replacing the rubber bushings with GMS uniballs we have eliminated any flex at the front end, making the car much more precise to your inputs. Point it the way you want to go and it will go.

Fifth - Weight distribution. By running front end a bit lower than the rear end, a weight distribution is shifted slightly more to the front, which is a very welcoming benefit on a rear heavy 4C.

Sixth - Positive rake angle. By running front end a bit lower than the rear end, creates a positive rake angle, making entire underbody of the car acting like a huge diffuser, providing the much needed downforce at high speed cornering.

Still not convinced? :cool:

PREORDER - EXPECTED DELIVERY TIME 30-60 DAYS UPON PLACING AN ORDER.

We are fabricating a batch of 10 sets for the first round. We have already allocated preorders for the most anticipating customers and we have a few more sets now available for this first release, expected in June 2021. There is also free shipping as usual with a new GMS product release. Use promo code: "PREORDERFA".

Preorder your set here: ALFA ROMEO - 4C - Performance front control arms | GMS
 

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Question...
Let’s say I want to track regularly AND use the car for daily driving. With my KW coilovers and the GMS performance front arms, between track days, would handling at factory ride height on roads be acceptable or would the GMS arms mean factory ride height no longer works?
 

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What's your "factory ride" height in numbers?
All Euro 4C don’t have the same factory ride height? Why not? Anyway, it goes over speed bumps at like 15 - 20 mph no problem so it’s pretty high I’d say. It could go a bit lower and still cruise over bumps. 1/2” max.
I would like the improved handling of the performance arms for my 1.5” lower track day setup but would the GMS arms diminish handling when car is only lowered half inch in road tune?

I will try to give you numbers that I consider standard ride height in a bit.
 

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Discussion Starter · #72 ·
I would like the improved handling of the performance arms for my 1.5” lower track day setup but would the GMS arms diminish handling when car is only lowered half inch in road tune?
You'll be running 1.5" drop for trackdays and 0.5" drop for a road? How do you plan to switch between these two setups? Unless you have "on the fly" height adjustable coilover system, you'll probably abandon this idea pretty soon, because adjusting ride height is not so quick and changing the height by so much will already affect the alignment. I would ditch this idea and rather settle for a ride height that would be fast on a track, yet drivable on the street. A bit lower than "standard" ride height, but not too low. More info below...

1.5" / 38mm drop is too much, even from a "standard" factory height (non sport = 117,50mm - 38,00mm = 79,50mm). With GMS performance front control arms, as mentioned, I would recommend minimal 100mm of ride height at front and about 115mm at the rear (for winged 4C, the rear could be additional +10mm higher as the rear wing will press the rear end down a bit a high speeds). With this setup the car will be drivable on the street (carefully over bumps), yet fast on a track, body roll will be minimized, you will have some positive rake angle to promote downforce, slightly more forward weight distribution and the most important - will keep the geometry optimal during entire suspension travel. That would be my recommended setup for trackers that drive their cars on the roads as well.
 

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Just a suggestion for further down the line, maybe specify difference in height between two fixed reference points at inner and outer part of arm? Something like this:
View attachment 115837
Would not that be a better starting point, since tire diameter, pressure and spring rates varies?

Might be a bit more tricky to measure, but I'd personally prefer that to take away any guesswork.

Anyway, it seems like your arms are the way forward for me, when I've decided for coil over and got them installed and approved. When that is, no one know due to the current pandemic. However, you know that you'll get rid of a set one day.
@GMS did you look at this?
 

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Discussion Starter · #74 · (Edited)
I did. Measuring two points at lower control arms is unnecessary complicated and the inner point (towards the wheel) is dependent on wheel ET, width, spacers, etc. Simply measuring the front lower control arm angle is good enough. Measure the angle (inclinometer or phone) of your lower front control arm and if it is horizontal or tilted upwards, you're too low. From here on you can play with height adjustment. I'll stick with ground-skirt clearance. Here is how I set up my car:

  1. Adjust the coilovers to the same height (measuring the threads on the coilovers left/right)
  2. Measure the front arm angle. if tilted downward OK, if tilted upward, raise the front end.
  3. Adjust the front end height (go as low as you can - for track), while still maintaining front lower control arm tilted downward. In my case with GMS performance control arms that is about 95mm front (skirt to ground clearance) and 125mm rear (skirt to ground clearance) to get the rake angle. The actual skirt to ground clearance left and right side vary and so do the wheel arch gaps, but for me having the coilovers set to the same height is what I am for. For OEM control arms is about 10mm - 20mm higher.
  4. Alignment
  5. Corner balance
  6. Fine alignment
 

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Mine were about 98mm at the front on Tuesday but settled after 50 miles of hard driving home. I went to drive it the next day and I had arch contact.
Im going to adjust it up a bit to stop contact for the drive to the garage and get it re-adjusted with the guidelines posted above! Thanks
 

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Discussion Starter · #78 · (Edited)
The G-forces with the new GMS performance front control arms are there. Over 2g peak G and about 1.5g stable on semislick tires on a hot day with 30° ambient temps. Grip is phenomenal, the tram lining is non existing and the steering wheel weight feels perfect - slightly heavier at high speeds and during cornering. It's what I was looking for. The feeling was good and the measured data has proven it. We look forward to deliver this upgrade to first customers.

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