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Suspension modeling

JackRabbitSLIM

Go Kart Champion
Location
OHIO
Car(s)
MK7 GTI
What is your XDS setting David? Do you have VAQ?
 
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xXDavidCXx

Drag Racing Champion
Car(s)
2017 GTI SE DSG
I think I figured a relatively easy way to measure the CG.

I have to replace the front springs, assuming I have the Ohlins installed, with a strong pipe of the same length as the compressed spring to keep the car at the desired ride height.

Then I can lift the rear the recommended 10-20 inches and note the change in corner weights.

I wasn't sure how to lock out the front suspension, but this should work.
 
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GTIfan99

Autocross Champion
Location
FL
Following.

I’ve run mine in SCCA GS trim several times now, with the usual big rear bar, a 25mm Eibach for me. I’ve wondered out loud elsewhere if a front bar would be better, for keeping the front of the car flatter. It’s kind of a painful experiment to perform though with having to drop the subframe just to try it. GS only allows changing one bar.

If I ever do run the car seriously again, I’ll probably give it a shot. This years plan was to codrive an SSC FR-S, so that’s mostly what I’ve one.

Zeroing out rear toe really helped with understeer, as well as a big RSB, when my car was in GS trim. My co-driver was consistently in top 3 pax in a region with 6 or 7 currect and former national champions, and I was consistently top 10.
 

anotero

Autocross Champion
Location
Hither and thither
Car(s)
Mk7 GTI
Somebody put together a Simulink model with transfer functions. :)
 

scrllock

Go Kart Newbie
Location
MI
Has anyone been able to use something like this to determine the point at which further lowering puts the control arm on the wrong side of the camber curve? Would be interested to know exactly how much of a drop is too much, given the apparent poor design of the whiteline kit. I've seen people speculate an inch, but a lot of the coils I've seen are a minimum 30mm drop...
 

xXDavidCXx

Drag Racing Champion
Car(s)
2017 GTI SE DSG
Has anyone been able to use something like this to determine the point at which further lowering puts the control arm on the wrong side of the camber curve? Would be interested to know exactly how much of a drop is too much, given the apparent poor design of the whiteline kit. I've seen people speculate an inch, but a lot of the coils I've seen are a minimum 30mm drop...
I can do that
 

xXDavidCXx

Drag Racing Champion
Car(s)
2017 GTI SE DSG
While I won't argue with the math here (because it's clearly thorough), it feels opposite to the experiences we've been having so far. Given your experience upping rear springrate David, it would seem counter to your experience to almost double the front springrate and not expect it to push, while only upping the rear ~30%.

Again, it's hard to argue with the math though. If it takes that much front springrate to prevent roll / ending up in the undesirable part of the camber curve then it might work.

I know your calculations assume you have -2.1deg static camber, which will really drive up the need for stiffer springs / bars to reduce roll and prevent the car from going +camber. How do the spring values change when running -3 or -3.5deg? I'd be curious to see those, I anticipate they'd be a bit lower.
The larger change in front spring rate is due to the fact that ride frequency is heavily influenced by corner weights.

I think I've had the most issue on turn-in after a heavy brake application, the front of the car is max compressed, and now while in the worst camber-range, asking the car to transition from braking, which it does well, to turning without enough camber and starts to understeer into corner entry.

I may try 550/750 which is 1.66/1.85hz, keeping the .2 higher rear that I've been targeting.
 

jmblur

Drag Racing Champion
Location
Massachusetts
Car(s)
2017 Golf R
David, any chance you could run a quick sim with Ground Control's minimum spring rates of 425/550? Ideally with R weights but that's just me being selfish :)

Curious where that would put me for a dual-use car... Might end up being not too bad.

As much as I prefer soft spring/stiff bar type setups, I definitely feel like I have too much dive under heavy braking and it takes too long to settle from transition.
 

w124_karl

Ready to race!
Location
NC
Zeroing out rear toe really helped with understeer, as well as a big RSB, when my car was in GS trim. My co-driver was consistently in top 3 pax in a region with 6 or 7 currect and former national champions, and I was consistently top 10.

I’ve zeroed the toe front and rear and taken out all the rear camber until the rear matched the front, which on mine is a paltry 0.5 deg negative. 50-55psi in the rear tires. Last time I ran it, at zMax in Charlotte, I tried a run with ESC all the way off via VCDS. That helped it some more, but disabling ECS is on pretty shaky ground rules wise. Pretty good event for me - 19th of 144 in PAX at a fairly big region.

I suspect that a big front bar with a stock rear would be less fun to autocross, but maybe it might be faster. Just from keeping the front tires off the sidewalls. It would be a painful experiment to go through all that hassle to find out that the big front bar sucks, though. :ROFLMAO:

This year’s plan was to run in SSC with some friends, but...2020. Unclear what the plan is for next year.
 
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jmblur

Drag Racing Champion
Location
Massachusetts
Car(s)
2017 Golf R
Can someone with an R measure the stock ride height from the middle of the forward lower arm bolt?

As accurately as I can measure, 6" dead to bolt center with 225/45r17s. (not a lot of room under there to get a more accurate measurement!) Pretty sure that's within an 1/8in. If you need more accurate I can give it another go, might be able to do a little better with some fussing.
 
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xXDavidCXx

Drag Racing Champion
Car(s)
2017 GTI SE DSG
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xXDavidCXx

Drag Racing Champion
Car(s)
2017 GTI SE DSG
Here is the correct chart showing body roll vs estimated camber.

Notice how soon the outside tire goes positive.

1609383276511.png
 
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