Rear-end seem to hops under heavy braking?

[jkilla71]

I am thinking there must be a way to correct the way my rear-end jumps around under heavy braking while changing lanes.
I also notice it while going around a corner under strong acceleration when there is a high crown on the road too.
It is almost like the suspension is too stiff and a wheel is almost coming off the ground. However it is most noticeable when braking and when I shift the weight back and forth.
I am running Bilstein PSS and I have the tire pressure at 30 lbs front and rear. I have the BAV camber kit in the rear and strut-brace in the front, x-brace underneath and eyeball CABs. Control arms are new up front and so are the tie-rods. I have not replaced the sub-frame bushings
The car is a 1995 sport. I am thinking tire pressure might be the culprit but the car seems dialed in cornering on flat roads no matter what the speed.

I don't track the car so it is not a pressing issue but I would like it to feel perfect.

Any suggestions?

[316i compact]

Thicker sway bar rear, or stiffer shocks-springs at the rear. But you have very good suspension (PSS) so only sway bar. Also check your subframe bushings, they could be the cause.

[jkilla71]

Originally Posted by 316i compact

Thicker sway bar rear, or stiffer shocks-springs at the rear. But you have very good suspension (PSS) so only sway bar. Also check your subframe bushings, they could be the cause.

Thanks -

I will see if I can find a 16mm rear sway bar and go from there.

[momorugger]

as you stated, I think that tire pressure is the culprit. I run 35 psi after having similar issues at just 30 psi.

[jkilla71]

Originally Posted by momorugger

as you stated, I think that tire pressure is the culprit. I run 35 psi after having similar issues at just 30 psi.

Are you running 35 for both front and rear??

I use to run at 35 in the front/rear but I started to notice the centers of the tires in the rear were wearing quicker than the inside and outside. Also the car felt much better at high speed with only 30psi but my perception about the cars handling at high speeds could have been due to my inexperience as I never drove a car competitively.

[momorugger]

yea, 35 all around. so far tire wear is extremely even. I bring them up to 40 psi for track days, but run 35 on the street

[jkilla71]

Thanks -

I'll give changing to 35 PSI a try but the 16mm & 18 mm rear sway bars I have found are both under $200 so I am going to give those a try too.

[mohaughn]

If you are going to put a thicker sway bar on the back you should also reinforce the mounting tab on the trailing arm. If you don't you run the risk of actually ripping the tab off of the trailing arm. The reinforcement kit is pretty cheap, you just have to get somebody to prep and weld it on for you.

[jkilla71]

Originally Posted by mohaughn

If you are going to put a thicker sway bar on the back you should also reinforce the mounting tab on the trailing arm. If you don't you run the risk of actually ripping the tab off of the trailing arm. The reinforcement kit is pretty cheap, you just have to get somebody to prep and weld it on for you.

Thanks for looking out.

I am moving back to Pa in May so I will get my old man to weld them in and buy the sway bar at the same time.

I take it there is a big handling difference with the larger sway bar?

[mohaughn]

Depends on the setup of the car. Larger rear sway bar will help eliminate any rear body roll that you have. But it may also cause the inside wheel to lift when cornering hard or cause the rear of the car to be twitchy. If you are experiencing understeer adding a larger rear sway bar can eliminate that problem. But I would try to get rid of any suspension issues with tire pressure first, then replacing the rear subframe bushings, and finally upgrading the rear bar. When I put in my new subframe bushings my car felt a lot less twitchy and the steering/tracking of the car greatly improved as well.

If the rear subframe and all of the associated suspension parts are moving around on worn out bushings the rear of a Ti will do some very weird things. Very large wheels can also cause unusual suspension characteristics.

What kind of adjustability to you have on your coilovers and how do you have them set? Having them set to full hard could cause some weird issues as well.

[318iS]

Originally Posted by mohaughn

What kind of adjustability to you have on your coilovers and how do you have them set? Having them set to full hard could cause some weird issues as well.

PSS are only height adjustable

[jkilla71]

Originally Posted by mohaughn

Depends on the setup of the car. Larger rear sway bar will help eliminate any rear body roll that you have. But it may also cause the inside wheel to lift when cornering hard or cause the rear of the car to be twitchy. If you are experiencing understeer adding a larger rear sway bar can eliminate that problem. But I would try to get rid of any suspension issues with tire pressure first, then replacing the rear subframe bushings, and finally upgrading the rear bar. When I put in my new subframe bushings my car felt a lot less twitchy and the steering/tracking of the car greatly improved as well.

If the rear subframe and all of the associated suspension parts are moving around on worn out bushings the rear of a Ti will do some very weird things. Very large wheels can also cause unusual suspension characteristics.

What kind of adjustability to you have on your coilovers and how do you have them set? Having them set to full hard could cause some weird issues as well.

The PSS system in the rear uses the same basic setup as stock; lower springs but the coil-overs are only on the front. I thought of getting the PSS-9 but I didn't like the idea of all the weight on the rear shock mounts. After having the BAV camber kit installed in the rear; I could kick myself for not changing the sub frame bushings at the same time. (Live and learn)

I am going to take advantage of your advice and change the sub frame bushings first if a change in tire pressure doesn't produce results.

Perhaps if I get rid of the Kuhmo all-seasons next time I need tires and go with a softer summertime tire I might see some better performance too.


Thank you for all the input, I really appreciate it.

[jkilla71]

I added an additional 5 PSI to my front and rear tires and there is a noticeable improvement. However I still plan to drop the funds to replace the sub frame bushings because I am not completely satisfied and if the some new urethane sub frame bushings don’t completely solve it, a larger rear sway bar is next.

Most folks would think the car handles extremely well and I promised in another thread that I will have the car painted by the end of 2007. The paint will be done this year but the handling of the vehicle is the #1 priority to me even though I don’t track the car. Maybe I’ll take some lessons someday and give it a try. I have driven over a half million miles in my lifetime but never had any instruction on how to drive competitively

[momorugger]

you should definitely check out a driving school. Even if you don't plan on tracking your car, the benefits carry over onto the street.

[mohaughn]

There are two tracks in the Miami area. They have probably 1 or 2 DEs in that area every month. All in all if you can borrow a helmet from somebody a DE weekend will run somewhere around 500 bucks when you factor in having the car inspected, entry fees, oil change, and the wear on brakes and tires.

It's funny how much my road driving has changed since I did my first DE. I used to be a 11 and 6 two handed driver. I'm almost always 3 and 9 now.. I'd also say my overall car control is much better as I have a lot better understanding of what a car feels like when you really start to push it. I'm no where near the level of most of the people that I run with most of the time, but I've made major improvements. It seems like 5 or 6 hours of good instruction can really teach you a lot.