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Street Touring Hatchback (STH) discussion/setup

GTIfan99

Autocross Champion
Location
FL
I’m dumb and forgot I had aftermarket suspension for a minute. Need to do some research and see what size EQT uses. I know spring rate is 8k front 5k rear.
How does 8k/5k not understeer terribly?
 

Will_

Autocross Champion
Location
SF Bay Area
Car(s)
2017 GTI S DSG
How does 8k/5k not understeer terribly?
25mm RSB and 2.5F/2.0R camber helps out. My car is definitely setup to lean towards under steer (which I don’t mind for track driving tbh, makes it a bit safer to drive hard) but I can induce liftoff oversteer pretty easily when needed.
 

xXDavidCXx

Drag Racing Champion
Car(s)
2017 GTI SE DSG

xXDavidCXx

Drag Racing Champion
Car(s)
2017 GTI SE DSG
How does 8k/5k not understeer terribly?
8k (456 in/lb) and 5K (285 in/lb) is very mild, and I would argue, too little rear spring.

What assumptions about why this spring combo leads you to believe it would understeer?

I've found that understeer is first more a function of lack of camber and lack of tire pressure, or both. And secondly, lack of body roll control, which is why I think a stiffer FSB is more important than a stiffer RSB.

You can get the rear to rotate with just tire pressure (40 psi +) and/or rear toe-out.

I really think GTI owners should get off the "get a rear bar first thing" band-wagon. The issue is with the front of the car, not the rear.
 

xXDavidCXx

Drag Racing Champion
Car(s)
2017 GTI SE DSG
That's...stiff...

I guess it makes sense for a ST car, and probably a reason I don't want to have a ST car...lol
It wouldn't be that bad except for two things.

1. The crappy streets made of concrete with expansion joints every 5 feet.
2. Not enough rebound from the Ohlins R&T shocks

I can't fix #1, but I have PSI working a custom setup & quote so I can use the higher spring rates.

I may end up way back down on spring rates while I wait though.
 

GTIfan99

Autocross Champion
Location
FL

GTIfan99

Autocross Champion
Location
FL
Why? It's barely different from what you suggested yourself.

I think you misunderstood, I think you're right that 375/600 would be the right choice and would allow me to keep the car steerable and get some rotation without a crazy alignment that eats tires.
 
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xXDavidCXx

Drag Racing Champion
Car(s)
2017 GTI SE DSG
I think you misunderstood, I think you're right that 375/600 would be the right choice and would allow me to keep the car steerable and get some rotation without a crazy alignment that eats tires.
OIC, but for autocross, you would still want the rear toe out, surface grip depending.

Remember, the spring split is mostly for bump control and ride comfort, and needs to be matched with enough rebound to settle the car over bumps.

I've found rotation is either self-induced with lots of forward weight transfer and then steering input, or rear-toe out. Sometimes you don't want to dump all the weight forward in order to turn or get the rear to rotate, that's when rear toe out helps.

Also, it's easy to set rear toe yourself, so you could just mark the spot for a normal alignment, and then at the track or whenever, adjust for full toe-out. For me, that was about 0.14 deg per side which translates to about 1/4 in total toe out.
 
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GTIfan99

Autocross Champion
Location
FL
Corrected post. Damn, I'm tired and English is sounding like a second language at this point.

Anyway, if I do the redshifts, I'll do 375/600. Thanks for the suggestion.

Have a good night, all, I'm off to sleep.
 

JackRabbitSLIM

Go Kart Champion
Location
OHIO
Car(s)
MK7 GTI
I really think GTI owners should get off the "get a rear bar first thing" band-wagon. The issue is with the front of the car, not the rear.
Agree with David. I know we're talking about keeping things street-able, but I want to add to this.

It's a really common thing for fwd people to apply the same thinking and setup as a Miata (50/50 weight, perfect suspension). The rules and trends only work when you are starting from an equilibrium point (does not mean equal roll stiffness). Unfortunately most suspension tuning material is based on cars that are well balanced and rwd.

All cars are setup from the factory to understeer, especially fwd. FWD cars always have a higher rear roll center, so the roll axis is nose down. Guess what, the front tires are easy to overload. If you are already overloading the front, more rear bar makes it happen sooner. The front must be propped up to have a good handling fwd car, especially when it's heavy.

Some perspective:
Common STX setup is for a twin is 400F/400R, 22mm front bar/softer than OE rear bar, strut front/multilink rear. Yes motion ratios are different, but let's assume front roll stiffness is similar enough for comparison.
Corner weight for each front on my BRZ is nominally 725lbf, total weight of ~2600lbf
What would you expect the result of adding 300 pounds to each front corner and not changing the roll rates would be? Reasonable to assume more understeer? Reasonable to assume you'd need more front roll stiffness to keep the balance?
 

RacingManiac

Drag Race Newbie
Location
MI
I think there is merit to the idea but in the confine of GS with limited knobs, saving front stiffness doesn't seem to help at least from easy to test things. We tested rear bars, from less stiff to a lot stiffer A-B-A on T&T course with 2 drivers and we find both time and preference was on the stiffer bar. At the end of my time with the car we've definitely got to the point we can take some rotation out of the car to make it faster. Combination between alignment, fat rear bar, damper tuning and tire pressure can get there.

If I have a STH build though I'd definitely get more front stiffness back in the car but I don't think I would be too afraid of still bias rear roll stiffness if I can...
 

xXDavidCXx

Drag Racing Champion
Car(s)
2017 GTI SE DSG
I think there is merit to the idea but in the confine of GS with limited knobs, saving front stiffness doesn't seem to help at least from easy to test things. We tested rear bars, from less stiff to a lot stiffer A-B-A on T&T course with 2 drivers and we find both time and preference was on the stiffer bar. At the end of my time with the car we've definitely got to the point we can take some rotation out of the car to make it faster. Combination between alignment, fat rear bar, damper tuning and tire pressure can get there.

If I have a STH build though I'd definitely get more front stiffness back in the car but I don't think I would be too afraid of still bias rear roll stiffness if I can...
I can theoize why you got the test results you did, but did you ever test toe-out on a stock rear bar?

I've got plenty of data that shows how bad the front loses camber, which is why I think that should be the focus. Create front grip, don't reduce rear grip, untill you have to.

Case in point, I ran STH light in 2018 with stiff front and rear bars on stock springs (stock alignment though) and did great locally and okay at Nats.

Either way, STH alows for many suspension options and I like exploring the fringe ideas that have merrit.
 

Mini7

Autocross Newbie
Location
Charlotte, NC
Car(s)
2017 GTi Sport PP
I’ve been chasing front end grip from day one on track.
Put on better tires and added a 034 RSB. Less understeer but still easy to lose front end grip. Lack of front end feel and responsiveness at turn in.

Fast forward fall last year. Re-valved my Ohlins for 8k/12k springs and dialed in -3.4 front camber and some front toe out. The front end was much more responsive.

I have been following this thread closely. Auto-X and Track/HPDE are to very different disciplines. Auto-X set-ups being more extreme, but overall because it is the same car it is directionally correct.

I have been against stiffer swaybars. Preferring to use spring rate to support the car and to control roll. The stiffer the bar, the less independent your suspension becomes. I’m starting to come round and thinking that a stiffer front sway may be in my future and potentially going back to a stock rear sway.

I’ve under-estimated the impact of camber loss in roll, to front end grip. Dialing in -3.4 of static camber has helped. Most probably need a little more. Need to get my tire pyrometer out and re-check tire temps. I’m also thinking that I need to adjust my driving style and reduce my usage of apex curbs which pitches the car further over.

I’m not bound by your Auto-X rules, so have had much more flexibility on suspension mods. The Verkline front LCA will give all sorts of adjustments. Given that I can dial in all sorts of front camber. I most probably will need to cap that at -3.8 for the track.

David, based on 450lb/672lb and an 034 RSB set on the softer of the two settings, what size front swaybar would you recommend?

I’m curious about going back to my stock RSB for my next event at VIR. It’s an easy swop on rhino ramps.

Also, I have more headroom to go to stiffer springs without needing a re-valve.
 
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