Bump Steer

[clownshoemotorsports]

To go along with my thread about the Motorsport Steering rack, I thought I'd ask about bump steer solutions. My current E21 race car is low, very low. It works great with the exception of some bump steer. I would like to find a solution that would lower the tie rod end mount point. Commonly this is done with a spacer, different tie rod ends, or a combination of both. Anyone already have or know of a proven solution for the E21?

Thanks,
-bj

[TopCat]

from our pm exchange - you know what you are about here!!

but for benefit of our readers I set out a helpful explanation of bump steer causes and cures here:

http://www.longacreracing.com/articles/art.asp?ARTID=13

the main problems as I see it (and bear in mind that we havent race prepared a BMW) is that the front end is limited by difficult to adjust macpherson struts, - the engine is canted over, and the steering geometry is well made but not race cutting edge!
have noted that our TCB Racing tweeks are used by others !!!

Might add that the other piece of typically well made BMW kit we have reused out of location is an E30 Convertible rear heater/ demister unit fitted in lieu of the normal front windscreen heating system- means that in the rain I can at least see out whilst trying to keep the monster on the black stuff!

[clownshoemotorsports]

Might add that the other piece of typically well made BMW kit we have reused out of location is an E30 Convertible rear heater/ demister unit fitted in lieu of the normal front windscreen heating system- means that in the rain I can at least see out whilst trying to keep the monster on the black stuff!

Awesome suggestion! I've parted out two E30 convertibles--of course I didn't save that component, because this idea never occurred to me. Thanks for the great idea!

-bj

[clownshoemotorsports]

Just a quick update. I've been researching this, and I can't find a bumpsteer correction kit anywhere. I've been talking to Andy at AKG Motorsports here in the States and he can make them. Let me know if anyone is interested. Alternatively, I am considering having using a Escort MKII quick ratio racing rack, having custom brackets made to make it a bolt on, and bumpsteer correcting tie rods made, too.

[nas80]

cool. id hazard a guess that escort bumpsteer kit would work esp. if its rose jointed.

what i was going to ask you if you could post a pic of your ride height. what sort of angle are your suspension arms sittig at?

[TopCat]

Might add that the other piece of typically well made BMW kit we have reused out of location is an E30 Convertible rear heater/ demister unit fitted in lieu of the normal front windscreen heating system- means that in the rain I can at least see out whilst trying to keep the monster on the black stuff!

Awesome suggestion! I've parted out two E30 convertibles--of course I didn't save that component, because this idea never occurred to me. Thanks for the great idea!

-bj

Was going to add that by doing this freed up valuable firewall space from removal of all heater matrix etc which we filled with an Acusump with a 20psi automatic solenoid

[clownshoemotorsports]

what i was going to ask you if you could post a pic of your ride height. what sort of angle are your suspension arms sittig at?

I don't have any static pictures and the car isn't stored at my home, so I can't take any measurements. I do know that the car is low. Low enough that bumps on the straightaways will induce bumpsteer. The control arms are very much at an upwards angle. On an E30 or E36, I'd say that's a problem, but on a E21 the control arm design has much less of a dynamic toe curve than an E30, so it shouldn't be much of problem. In fact I picked up time when I lowered the car. There are a lot of odd things with the car. For example I'm running -4 degrees of camber in the rear and -4.5 in the front. This is more than I run on any of my other race cars. Tire wear is excellent. Temps across the tires are even.

Please note that in the picture above, that the flares make the car look a little lower and that the suspension is a little loaded up. That being said, the car seems lower than it looks in this photo when you see it in person.

-bj

[nas80]

my suspension arms are level with the ground. I dont tend to get bump steer - the car tracks very straight on the bumpy country lanes. i run -1.5 at at the front and -2 at the back. I have found this makes the car really chuckable and controllable on the limit and isnt too bad with tyre wear. (i have m50 24v)

you run so much camber it made me actually smile... how do your front brakes work lol you must lock up lots!?

[clownshoemotorsports]

my suspension arms are level with the ground. I dont tend to get bump steer - the car tracks very straight on the bumpy country lanes. i run -1.5 at at the front and -2 at the back. I have found this makes the car really chuckable and controllable on the limit and isnt too bad with tyre wear. (i have m50 24v)

you run so much camber it made me actually smile... how do your front brakes work lol you must lock up lots!?

I was I was surprised as you that the car worked with that much camber. Ideally, I wanted -3.5 in front and -2.75 to -3 in the rear. The car is amazingly good under braking. Until I lowered the car more and corner balanced it, it had a tendency to over rotate under braking. As it sits, I can brake late and deep into the corner. The place where I feel the camber is hurting me the most is on corner exit--I get lots of rear wheel spin. The car just doesn't have enough mechanical grip. My new E21 will have a lot more tire than the 225/45-15's I'm running on my current E21.

I had the car up where the arms where level before I dropped the ride height more. The car is much more settled with the exception of over low frequency high amplitude bumps. I'm sure a bumpsteer kit will solve my problems, though.

BTW, I'm running this much camber because of the rear of the car. I could run much less in front, but in the rear, even with slotted adjustments in the subframe, I couldn't get any less than -4.

-bj

[Jason_323i]

I modified the cross member to drop the pick up points and used rose joints for the ends of the tied rods, and just reamed out the struts to take a bolt.