Push, Push, Push
 

My son & I did our first autocross of the season this past weekend with mixed results. We made several changes to the ti over the winter which moved us out of HStreet and moved us into STX. Here are a list of the changes:

3.45 Limited Slip
Koni Yellows, all the way round (Fully Adjustable)
H&R Race Springs (2 of the 4 springs that came off the car were broken)
X-Brace
Bimmerworld Camber Shims ( camber is currently at -3.8 degrees)

Previous mods:
Ventus rs-3
Polyurethane front sway bar bushings

The handling of the car is greatly improved. We figure we have gained about 2 seconds over an average 45 second course.
The problems, When really pushing hard, the nasty understeer pops up and the front end washes away. We were running pretty soft on the front struts (about 3/4 turn from softest setting) and a bit stiffer on the rear shocks (1 3/4 turns) Front tire pressures 38psi and rears 41 psi.
We both like the handling & characteristics of the new setup but the car seems to continue to feel and look like it rolls a lot in the corners, and we still need to figure out a way to dial out the rest of the understeer and get the car to rotate more in the corners. I know some of the problem is my driving (I suck) but my son (teen ti) is better and he is having the same problems.

I am thinking we need to stiffen up the rear more and we can still put in a stiffer bar and possibly a shock tower brace. What about wheel spacers to widen the track and some toe out? (we are now without any toe out)

If anyone has any ideas, we would greatly appreciate it.

Here is a link to my sons best run yesterday:

https://www.youtube.com/watch?v=A7UMPP39sI4

Bigger front sway bar. I run a 33mm hollow front bar on my car. You're probably rolling over your tires and losing contact patch with the stock front sway bar. It couldn't hurt to stiffen up the front a little at the same time too.

Needs more rear spring. Ditch the H&R rears and put a coilover spring back there, 500lb is probably a good start. ~5.5 - 6" tall should be good and you can use spring pads to adjust ride height.

I'm running 450f/600r, 28mm front bar full stiff and no rear bar. As much neg camber as vorshlag plates allow.

The car is neutral to slight oversteer on track. I had 700lb rears but they were causing more oversteer than I preferred.

Honestly, I had very similar problems and I found (with the help of a few others) that with the H&R race springs -we're just concentrating on the fronts for now- the ride height was so low that I was riding on the bumpstops in the front. So if you were to corner hard and brake, you'd be bottoming out the front strut, so you'd get the initial turn-in like you'd expect, but you'd bottom out the suspension before the apex (usually) and would proceed to plow right past where you wanted to go.

The common temporary fixes I've heard of are additional springs pads up front to raise your front static ride height, get back some of that travel- however, in the end, the common issue is that the springs are too low, too soft for the usable travel you have in the front end. If you could go to a stiffer front spring, that would help, and maybe get the front end back up to a happier point in the travel. Or, you could figure out if there's taller front strut mounts or even shorten strut bodies, allowing you to drop further before bottoming out the strut, but then it's up to you to figure out what's the next thing to interfere (like other suspension components, the car body, etc.)

Thanks so much for the responses. Would a cross brace in the front and/or rear help? I will continue to stiffen the rear shocks a quarter turn at a time. Does anyone know if there are any easier ways to stiffen the springs without changing them? I know in the past, Nascar cars here at the Glen used to stick in spring rubbers (hard rings of a rubber compound to fit between the spring coils) to increase the rate of the springs. Is that an option here? Could it be done? SHOULD it be done? If so where could you find something like that. I agree that the front shocks may be bottoming out because the front of the car is really leaning to the point that we were consistently lifting the inside tire under heavy cornering. Make no mistake, the car is vastly improved over stock, but I am not liking the way it is still rolling in the corners. And of course, no matter what happens, we always seem to want more! Thanks again!

Front sway bar will do more to control body roll than a xbrace or shock tower bar.

Getting more front strut travel is good advice too.

I'd just cut your losses and sell the h&r race stuff and get a ground control coilover conversion. Thats probably the most effective way to use your current struts/shocks and get usable spring rates and ride height adjustment.

I would not feel comfortable with those spring pads in an h&r spring. The coils are already very close to each other when at static compression, if you remove a coil from that stack it puts more force on the rest which may cause coil bind. You'd then end up with snap oversteer during hard corners.

We're also picking up the front inside wheel fairly often an three wheeling it around some of the tighter corners which certainly isnt helping either

lifting the front tire on a BMW is very normal especially with stiffer suspension. Most people ditch the rear sway bars and find they don't do much if anything when you get into coil over setups. Big front bar is a must I also use a 33mm hollow bar (Hotchkis) on my H Street Ti. cheapest I found was Jegs.com. they are adjustable but I run mine full stiff.

OK, Here is a picture of the car under MODERATE cornering during our last autocross. On the harder corners we were lifting the inside tire. The second picture is of the rear shock-spring. Koni Yellow, H&R race. same up front. Question. If I replace the springs with the Ground Control coilover conversion and the largest front sway bar I can find, is that going to help with that body roll?

Start with the large front bar Turner motorsports sales a solid 30mm front bar or Hotchkis has a 33mm hollow not sure which one is the best but the Hotchkis is less weight. If you go to coil over suspension most people are 600 or 650 on rear and 400/450/500 on front I think you will coil bind the rears if you go any softer then 600. And to your question, yes it will stop the body roll but that oversized hole in your roof is probably making it worse then normal. That's one reason why people building solo and road race cars prefer the no sunroof option.

Haha! Joe, I love that you had the Cali top wide open! :cool:

Yeah! That was my son (teen ti) with the roof open. I never run with it open but he loves it! That being said, I know the big hole in the roof causes some chassis flex problems, but didn't think it would contribute much to the body roll issue. It is what it is! That is our only option for autocrossing so that is what we have to go with. I was also thinking of stress bars front & back to deal with body flex (and the huge hole in the roof). Will start looking for the biggest front bar I can find.

Ya, for the flex reasons, I run Mason bars front and rear, along with a X-brace on my Cali. I'll see how much flex I end up with later this month.


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I really wonder how close a 318ti could get to a 325i/328i in STX with full prep.

Proper DA coilovers w/ 500F/600R spring rates
Fat front sway bar (Turner or Hotchkis)
LSD
245 RE71R's on 17x8.5/9 rims
Lightweight custom exhaust
Tune
All the weight reduction allowed in the class.

If I had the budget I'd try. I've got the right 318ti for it as it is a '96 slicktop (non-sunroof) without any OBD2 emissions stuff such as secondary air systems. No cruise, or no traction control either as it was a very base M-sport model.

Not sure how well it would do. Not a lot of power and too much weight, even pushing the rules to the max. I just like the car, its fun, It is reasonably competitive on the local level. I like being with my son & working on the car with him, figuring out changes to make and on track strategies, etc. I still have to use the car as a daily driver at times so I can't go too wild on it. Just trying to improve ourselves each time out.