Advice on setting up Mk4 GTI for autocross

Now that we have our Challenge GTI (thread here) off jackstands and driving, we want to start getting it dialed in for the autocross. From what I've read, we'll want a lot of negative camber up front, and possibly some in the back. And it seems like we will want the rear end pretty stiff, either with the addition of a sway bar or stiffening the springs. Having never been an autocrosser, and having zero experience making a front wheel drive car handle, we're a bit lost on what the optimal set up will be.

Up front, we have adjustable camber plates, so we can go pretty aggressive if that makes sense. I have a line on a rear swaybar but am not sure I can fit it in budget. Another option would be to try to find a pair of shorter/stiffer springs than what we currently have (pictures of our set up below).

Something from the back catalog that might help:

Make your front-wheel-drive car faster | Advice from pro racer Robb Holland

Thanks David. I'll give that a read.

Anyone else have any experience autocrossing a FWD car?

I haven't re-read the article, but I'm certain this was addressed: Tire pressures are something you can play with. On my FWD cars I run pretty high pressure in the rear to help with rotation. 
Plant the front, rotate the rear...

Tire pressures are your suspension tuning after getting a good alignment.  I would typically end up running 5-10lbs more pressure in the rear, typically int the 50's.    I'd run as much castor as you can get, ~1.5-2deg neg camber up front, 1-1.5deg neg camber rear, 1/16 toe out in rear.

Go have fun and spend as much seat time as you can.  It's very worthwhile to get some of the course guru's to take a lap with you as passenger to see their lines.  They'll also have input on what they like and don't like on the setup.  It's embarrassing getting spanked by a rando stranger in your own car but will make you better.

Great information. Thanks! I wouldn't have thought to run such high tire pressures in the rear, so that is especially helpful.

For the central Florida folks, it looks like there is auto-x at Daytona on both 9/24 and 9/25. Am I reading the schedule correctly? If so, that would be a great test and tune for us.

Depending on if it is a really fast or really technical course the pressure is a big deal.  Effectively you want to toss the rear end and have it super loose to be able to straight line the course.

I have been autocrossing FWD for over 20 years, and I still know very little about car setup.  I do know that testing is the only way to find what works for your car. Run it, check temps and chalk marks, adjust pressures. Some cars wanted a lot more pressure out back, some wanted less than the fronts or the car would spin.  Because a setup worked on someone else's MK4 doesn't mean its right for you. 

pinchvalve (Forum Supporter) said:

I have been autocrossing FWD for over 20 years, and I still know very little about car setup.  I do know that testing is the only way to find what works for your car. Run it, check temps and chalk marks, adjust pressures. Some cars wanted a lot more pressure out back, some wanted less than the fronts or the car would spin.  Because a setup worked on someone else's MK4 doesn't mean its right for you. 

Duly noted! We'll try to hit as many events as we can in advance of the big day!

Note that running higher pressures in the rear is a workaround for having an understeer-biased suspension setup, this is reducing rear grip through overinflation to adjust the handling balance. Ideally you should have the tires on both ends optimized for maximum grip (typically you'll have pressures that are proportionate to the car's weight distribution when they're optimized) and use sway bar and spring stiffness to adjust the handling balance. So if rear overinflation helps, it means you need a stiffer rear sway bar or stiffer springs in the rear. The FWD cars that spin with higher pressures in the rear have better suspension setups.

dyintorace said:

For the central Florida folks, it looks like there is auto-x at Daytona on both 9/24 and 9/25. Am I reading the schedule correctly? If so, that would be a great test and tune for us.

That is correct, registration opens in eight days. We run on the kart track for the autocross, and there will also be a track sprint using the infield Road racing course on Saturday. I can't comment on any details on the track sprint, it will be the first one we've done there that I know of.

I seem to recall reading something on this forum about those cars actually wanting a bigger FRONT sway bar instead of a bigger rear one. Does that ring any bells to someone smarter than me?

thatsnowinnebago said:

I seem to recall reading something on this forum about those cars actually wanting a bigger FRONT sway bar instead of a bigger rear one. Does that ring any bells to someone smarter than me?

I remember that as well. I think because the camber curve on MK4 cars are pretty bad. Lowering the car or compressing the front suspension results in positive camber, so a bigger front bar keeps the outside front suspension from compressing too much, resulting in positive camber. I think Audi TT front knuckles are better. With the adjustable camber plates this might be a non-issue. 
 

For rallycross I really liked some toe out on the front. It made the car much more responsive during turn-in. That combined with lift off oversteer really helped to rotate the car aggressively at slower speeds. My MK4 had stock bars, front and back. 

Compensation for the camber curve is usually outsized camber, which should be easy with the plates. Depending on what you use it for no front bar, big rear bar, or big rear spring rates can come in handy. As said, some people really like a big front bar but it makes you push like crazy and then have to overcompensate with the rear bar/rate and the whole things gets out of hand. Oh, more camber until you start looking stancy.

I've heard less bar upfront, more bar and/or spring out back before. It evidently helps with getting the car to rotate.

This is how the car was set up when we bought it. Lots of front camber is available!

Paul_VR6 (Forum Supporter) said:

Compensation for the camber curve is usually outsized camber, which should be easy with the plates. Depending on what you use it for no front bar, big rear bar, or big rear spring rates can come in handy. As said, some people really like a big front bar but it makes you push like crazy and then have to overcompensate with the rear bar/rate and the whole things gets out of hand. Oh, more camber until you start looking stancy.

Maybe that article I'm half-remembering was talking about stock class or something that didn't allow camber plates. That would make sense with what you're saying. 

In reply to dyintorace :

Hell, that's perfect!  Leave it alone!    Just cruise the cones at 5mph.

(I jest)

https://motoiq.com/how-to-make-crappy-cars-handle-well/ will give you a very basic insight to the gemotery failings within the average hot hatch. 

Two ways FWD handling can be approached: 

What I call the Hondatech setup (no/limited front bar, too little front spring, poor geometry, TONS of rear spring and chasing the back of the car around all the time) in the right hands this can be fast but it for some reason has become the defacto way to make FWD cars turn and well quite frankly it's wrong. 

All the material to fix the geometry of a Dodge Omni cost $168 brand new from Summit Racing. If you cant/dont want to go that far keep it tall in an attempt to keep the roll center from plunging into ground level, stiffen up the rear beam with a swaybar, put as much rubber as you can up front with a 205 wide rear tire. 

Byrneon27 said:

https://motoiq.com/how-to-make-crappy-cars-handle-well/ will give you a very basic insight to the gemotery failings within the average hot hatch. 

Two ways FWD handling can be approached: 

What I call the Hondatech setup (no/limited front bar, too little front spring, poor geometry, TONS of rear spring and chasing the back of the car around all the time) in the right hands this can be fast but it for some reason has become the defacto way to make FWD cars turn and well quite frankly it's wrong. 

All the material to fix the geometry of a Dodge Omni cost $168 brand new from Summit Racing. If you cant/dont want to go that far keep it tall in an attempt to keep the roll center from plunging into ground level, stiffen up the rear beam with a swaybar, put as much rubber as you can up front with a 205 wide rear tire. 

So the Hondatech setup is the wrong way - got it. I'm interested in understanding what the right way is. Will the MotoIQ link give me that? We have budget room to get some/all of a correct set up (I'm guessing a bit) but I'm not sure what 'correct' is. 

You have budget, other than good struts probably. You can only take some of the Honda setup guidelines as you're talking a strut front on the VW which will have different limitations, and different fixes for them vs the Honda.

High/soft/camber front and stiff AF rear tends to be the quickest setup that I am aware of on the VW. Helps with drag launches too which may be better for the challenge too.

A hatchback/beam axle trick I learned from somewhere is to lower the rear as much as possible.  The roll center height is fixed, lowering the rear reduces the amount of torque that end of the car has on body roll.  Since this is not a C3 Corvette, the front and rear of the car are attached to each other, so the front has less body roll, and also unweights the inside front tire less, two things that are usually one or the other.

On the Golf I had, I did the plated rear beam and after I broke that off, I put Neuspeed "race" lowering springs in the rear only.  The plated beam mostly just changed the knee point between 4 wheel and 3 wheel cornering.  Lowering the rear reduced body roll significantly, to the point that the front had noticeably greater ability to put power down out of corners.  The absolute best thing I did to the car.  Looked stupid, drove brilliant.

Pete. (l33t FS) said:

A hatchback/beam axle trick I learned from somewhere is to lower the rear as much as possible.  The roll center height is fixed, lowering the rear reduces the amount of torque that end of the car has on body roll.  Since this is not a C3 Corvette, the front and rear of the car are attached to each other, so the front has less body roll, and also unweights the inside front tire less, two things that are usually one or the other.

 

On the Golf I had, I did the plated rear beam and after I broke that off, I put Neuspeed "race" lowering springs in the rear only.  The plated beam mostly just changed the knee point between 4 wheel and 3 wheel cornering.  Lowering the rear reduced body roll significantly, to the point that the front had noticeably greater ability to put power down out of corners.  The absolute best thing I did to the car.  Looked stupid, drove brilliant.

LOL. Are you saying I have to Carolina Squat the car?!? 

I do not know VWs but I'll give my thoughts/what I do/why I do for Chrysler and Honda FWD stuff, these same tricks made a pretty bad fast B15 Sentra at one time too.  I'll focus on twist beams because I think that's what is under the back of a Mk4 

Generic but important points: 

The rules force you to have four tires... Make them all do stuff ie avoid the peg-leg as much as possible yes this is difficult with a twist beam but its made worse with too much spring and a bouncy disposition. 

Focus on the front all the magic all the speed is in the front. Front grip is king. Front grip inspires confidence. Equal grip turns confidence into a fast time. 

Drop the front roll center as much as possible without going too agro with measurements try to keep the front control arms parallel to the ground, extended ball joints and flipped tie rods. Basically do your best to make the tie rod arc and control arm arc equal. Put all the spring and tire you can get ahold of up front and you're golden. Lower is better but only until you change geometry. How tall the car has to be to not devastate geometry on turn in is dependent entirely on the front spring rate. More or less find the tallest stiffest lowering springs you can buy and work around them. 

Positively locate the rear beam more than one way of  doing this, spread or split mounts (not square to the axle tube beam) can be located with stiff bushings. Square mounts (the rear axle assembly looks like an H) need hard bushings and a panhard rod or similar. Get a big sway bar in the axle or box it leaving an opening of about 10% of the beam length open in the center. Dial in some camber with shims and you're done. Work on getting a 205 tire to an even across tread temperature and fine tune handling with tire pressure. 

Correcting geometry and relying on roll stiffness rather than spring rate helps us to gain front grip and keep the car planted overall without the need for super spendy whizzbang shocks or other parts needed to help control giant spring rates. 

On this car, camber plates, stock or no front swaybar and the biggest rear swaybar you can get.  Kerma TDI still sells the Shine Racing rear swaybar for these, that's what I'd get.  Don't lower the car too much, use linear rate springs instead of progressive ones if you can find them.