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Suspension modeling

Phur

Autocross Champion
Location
IN
Car(s)
2013 VW GTI Autobahn
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Oversteermybagel

Go Kart Champion
Location
Boston
Car(s)
mk7 2017 GTi Sport
I don't think it exists for the Mk7
https://whitelineperformance.com/products/kca472-roll-centre-bump-steer-correction-kit

Above is the only adjustable ball joint product that I know of with mk7 listed fit. People have fitted mk6 adjustable ball joints to the cars, but there are clearance concern. Its my understanding that the ball joint has clearance issues with aftermarket control arms and BBK. Frankly, this does not look like a quality product and it looks prone to slippage if you are generating grip. I would love to be proven wrong though
 

Raguvian

Autocross Champion
Location
Bay Area, CA
Car(s)
2019 GSW 4MO 6MT
https://whitelineperformance.com/products/kca472-roll-centre-bump-steer-correction-kit

Above is the only adjustable ball joint product that I know of with mk7 listed fit. People have fitted mk6 adjustable ball joints to the cars, but there are clearance concern. Its my understanding that the ball joint has clearance issues with aftermarket control arms and BBK. Frankly, this does not look like a quality product and it looks prone to slippage if you are generating grip. I would love to be proven wrong though

Why do you feel it's not a quality product? I thought Whiteline is one of the better companies?

Also curious what people think of this:

https://whitelineperformance.com/bl...oll-centre-and-how-does-ride-height-affect-it

As you lower your coilover equipped car, with MacPherson suspension the lower control arm will eventually start to point upwards at the outboard end, referencing ground level. What this does in reality is drop the roll center below ground. The impact this has dynamically though, is far greater than a static drawing would show.

With the roll center below ground height more weight is transferred via the springs (likewise raising the roll center reduces weight transfer through the springs and increases weight transfer through sprung mass). This makes body roll more pronounced and in turn increases the leverage against the lower roll center, making the instantaneous center move well outside the vehicle causing even more weight transfer and roll. Eventually the car will “fall over” onto the outside front wheel. The tires limits of grip will now have been breached, no more weight transfer can occur. To the driver this is a very frustrating feeling, quite often on a front wheel drive car the rear inside wheel will now be airborne, and the car just understeers relentlessly.
 

bfury5

Autocross Champion
Location
CT
Basically every single off the shelf kit goes with a much stiffer front than rear. I can't speak to companies like Ohlins but most of the other ones are much stiffer front, and then the band aid solution is to put a big ass RSB to get the rear to rotate more.
Stiffer front than rear springs with all else left alone will result in this chassis being sightly pushy on the edge. Understeer is usually referred to as "safer" than oversteer, which is why most spring kits off-the-shelf are like this.
 

Oversteermybagel

Go Kart Champion
Location
Boston
Car(s)
mk7 2017 GTi Sport
Why do you feel it's not a quality product? I thought Whiteline is one of the better companies?

Also curious what people think of this:

https://whitelineperformance.com/bl...oll-centre-and-how-does-ride-height-affect-it

Sure. I worry that you will not be able to get those bolts tight enough to avoid slipping your alignment at high traction loads. I do not know this for sure though, but you don't see hardware like this in purpose built McStrut race cars. For comparison consider the adjustable ball joints on the front LCA in the mk7 GTi TCR/LMS cars


You can see its adjusted via threaded rod to prevent slippage.

As far as roll center. A high roll center will resist roll. This is good. It is not the only effect though. When you raise the roll center you increase the vertical component of the force vector found by drawing lines the tire contact patch and the roll center and the ground. As a result you end up increasing force in the vertical direction which results in suspension jacking which acts to raise the CoG. Changing the roll center location also affects the camber curve of the strut.

Ideally you want the roll center to be at the CoG and you want both those things to be as close to the ground as possible. But with dynamics moving everything around and a variety of other compromises that must be made this is not really possible.

Exactly where the roll center ends up is not as important as it being close to CoG wherever that is
 
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tpellegr

Go Kart Champion
Location
Boston, MA
Car(s)
2016 GTI S 6MT
From what I can find, it looks like the Ohlins R+T are also setup with stiffer front than rear (399/285). @xXDavidCXx what was the rationale for adding such stiff rear springs vs stiffer rear bar (or do you have both), class limitations?
 

Oversteermybagel

Go Kart Champion
Location
Boston
Car(s)
mk7 2017 GTi Sport
From what I can find, it looks like the Ohlins R+T are also setup with stiffer front than rear (399/285). @xXDavidCXx what was the rationale for adding such stiff rear springs vs stiffer rear bar (or do you have both), class limitations?

Ohlins actually switched to 399/399 for the newest (MT21) R+T kits. I emailed Ohlins to ask what the difference between VWS MP20, MP21, and MT21 are and ill post here if they get back to me.
 

Raguvian

Autocross Champion
Location
Bay Area, CA
Car(s)
2019 GSW 4MO 6MT
From what I can find, it looks like the Ohlins R+T are also setup with stiffer front than rear (399/285). @xXDavidCXx what was the rationale for adding such stiff rear springs vs stiffer rear bar (or do you have both), class limitations?

From my understanding going with a much stiffer front rate will cause extra understeer, so people go with a big bar in the rear to get the oversteer back. To me that seems like you're just decreasing the overall grip of the chassis, rather than going with softer front springs (more front end grip) and stiffer rear springs (to help with rotation).
 

Raguvian

Autocross Champion
Location
Bay Area, CA
Car(s)
2019 GSW 4MO 6MT
Sure. I worry that you will not be able to get those bolts tight enough to avoid slipping your alignment at high traction loads. I do not know this for sure though, but you don't see hardware like this in purpose built McStrut race cars. For comparison consider the adjustable ball joints on the front LCA in the mk7 GTi TCR/LMS cars


You can see its adjusted via threaded rod to prevent slippage.

As far as roll center. A high roll center will resist roll. This is good. It is not the only effect though. When you raise the roll center you increase the vertical component of the force vector found by drawing lines the tire contact patch and the roll center and the ground. As a result you end up increasing force in the vertical direction which results in suspension jacking which acts to raise the CoG. Changing the roll center location also affects the camber curve of the strut.

Ideally you want the roll center to be at the CoG and you want both those things to be as close to the ground as possible. But with dynamics moving everything around and a variety of other compromises that must be made this is not really possible.

Exactly where the roll center ends up is not as important as it being close to CoG wherever that is

Thanks for the post! I would assume that for a mainly street driven car, the Whiteline kit would still be fine? For $135 I am tempted to try them anyways.
 

Oversteermybagel

Go Kart Champion
Location
Boston
Car(s)
mk7 2017 GTi Sport
Thanks for the post! I would assume that for a mainly street driven car, the Whiteline kit would still be fine? For $135 I am tempted to try them anyways.

I don't think there is a safety concern, I just don't want to be the one developing this part for the 200tw market. It might just work it might not--its hard to tell. If you buy it mark the adjustment with a paint pen and report back here after a bit of flogging please!
 

Raguvian

Autocross Champion
Location
Bay Area, CA
Car(s)
2019 GSW 4MO 6MT
I don't think there is a safety concern, I just don't want to be the one developing this part for the 200tw market. It might just work it might not--its hard to tell. If you buy it mark the adjustment with a paint pen and report back here after a bit of flogging please!

It probably won't be any time soon as I'm still trying to figure out the proper spring rates for my wagon (thinking 6k front, 8k rear).
 
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