Bump and Steer Sapcers

Targa Dude · Targa Dude's Garage

My 911 was lowered to Euro specs and weight Balanced,
Should I install Bump and steer spacers?
Do they really work or just another gimick and If I decide to install them will I have to perform a realignment?

Thanks all,

Jorge (Targa Dude)

nhromyak · nhromyak's Garage

If you install them, toe will have to be reset.

I have them installed on mine. I am below "euro-height".

After a four wheel alignement, I have very little bump steer.

I am not CERTAIN on their usefulness.
They do seem to be popular though...

marcesq · marcesq's Garage

If the car is set lower than 25" in the rear and 25.5" in front, the general wisdom says spacers are required.

My car is set to the above specs and I have not noticed a need for the spacers.

FWIW

Eric Coffey · 02-07-2002, 02:35 PM

The short answer: No, you don't need them. I am not running rack spacers, and with my car set at 24.75 front, and 24.5" rear height (and that's with 16" wheels/tires), I don't have bump-steer issues. However, if you are running anything less than that, or you are experiencing "bad geometry" symptoms (adverse kick-back, etc.), it might be something to think about.

antares · antares's Garage

I have 17's on my SC. It is lowered and I had bump steer bad until I replaced a lousy front right tire that was coming about inside. Dont notice it too bad now. Smart racing has a kit for around $ 230.00 and yet Performance has a washer spacer kit for around $ 80.00 so what is the difference. Anybody?
Antares

RoninLB · 02-07-2002, 02:52 PM

I am under the understanding that the tie rod should be parallel to the ground after adjusting ride height. Not positive since I may have read it 30 years ago. If true it would be an objective way for the weekend wrench to know if a rack spacer it needed. It is how I adjusted my rack.

911pcars · 02-07-2002, 02:54 PM

Bump steer is not steering effort feedback or any abnormal "bump" you might feel due to lowering the car.

Bump steer refers to toe in/out changes as the suspension moves up and down. Ideally, if a car is "bump steer corrected", there is little or no toe change during suspension movement. This results in a more stable vehicle during cornering and braking maneuvers. Bump steer toe change can be exaggerated by lowering the front vehicle height. The steering rack spacers are an attempt to return the steering rack and tie rod ends to a more normal relationship.

True bump steer measurements are made with a dial indicator setup on the wheel plane. Bump steer correction is by changing the tie rod install height at the outer tie rods, bending the steering arm or adjusting the height of the steering rack. Refer to any race setup book. Fred Puhn's "How To Make Your Car Handle" is one example.

Sherwood Lee
http://members.rennlist.org/911pcars

Kemo · 02-07-2002, 03:30 PM

Antares,

I dont think you should pay more than 15 bucks for a bump steer spacer kit. Mine included a couple of spacers (real thick washers) and longer bolts.

Doug Zielke · 02-07-2002, 05:49 PM

Thanks for that information, Sherwood. I never really understood the term before your explanation.

antares · antares's Garage

Okay guys, if spacers are the answer then the variables would be just exactly how much deflection is present. But would'nt one have to consider both the tire and wheel height and just how much the car was lowered? Now it seems to me without a dial indicator or a way to adjust the space between the rack and the mount thereby measuring that the rack is adjusted back into plane and taking all these variables into consideration, then just how would one know exactly how thick of a washer to use? Now is this the right line of thought?

Antares

RoninLB · 02-07-2002, 09:27 PM

Ant...you ask an educated question. A little research will reveal if my "tie rod parallel to ground" theory is valid. If I have to I could put some time into it. The little fuel burner between my ears is/some times running full throttle trying to stay up with the excitement that is happening on this BB

911pcars · 02-07-2002, 10:29 PM

Antares,
You're correct. Those washers are only an approximation to reduce bump steer/restore the factory relationship. Everyone's ride height is different, thus rack height adjustment is different/limited as well. If one really wants to measure/correct it, here's the short story:

Remove the springs from the front struts so the suspension is free to move up and down throughout its travel. Bolt a flat plate onto the face of the wheel hub. Position a dial indicator onto the flat plate. With the indicator preloaded and zeroed, move the suspension up and down relative to the body/chassis and record the indicator needle movement in either positive (toe out) or negative (toe in) direction.

To adjust bumpsteer, either:
a. Bend the steering arm and/or
b. Adjust the height of the tie rod attachment on the steering arm and/or
c. Adjust the height of the steering rack relative to the body/chassis

....until the needle deflection is close to zero (indicating zero toe change)

If you have a race car or very serious, you will want to do this to maximize the handling characteristics. If you have a street car, better off using the $14 steering rack spacer kit or equivalent.

Sherwood Lee
http://members.rennlist.org/911pcars

Kemo · 02-08-2002, 09:33 AM

came across this interesting article, with pictures (for us who like pictures) explaining "Bump Steer"

http://www.hcrpca.org/newsletter/decjan02/page15.html

RoninLB · 02-08-2002, 02:18 PM

Kemo...thanks for finding that info. Relaxes me to see the "tie rods parallel to ground" theory confirmed. So a level ground and 3 ft $10 level is good enough for a weekend wrench to do a great/maybe not perfect job of setting bump steer.

Kemo · 02-08-2002, 02:23 PM

im guessing the closer to "level" the better. I beleive you will have to get your wheels aligned afterwards...camber, toe, or something technical...

RoninLB · 02-08-2002, 02:46 PM

Kemo...no guessing. The article said "parallel" 2 X. The toe-in, toe-out is adjusted with tie rod extend/shorten. If car was lowered and bump steer adjusted then a full alignment is in order. If only the bump steer is corrected then a cheap toe alignment is all that is needed, assuming every thing was OK before, IMO. Or you can do a string-method toe adjustment and confirm your results with temperature probe on inner, center, and outer section of tire. That's another story. Although the string method is easy/simple. I do it. I like being simple minded.

antares · antares's Garage

Gee Whizz...and here I was going to use my 6-inch torpedo level I found stuck in my ol tool belt that is magnitized on one side for sure stick'em-up power baby.
Yeah
Anatares

rob911 · rob911's Garage

At last. Now I am beginning to understand what bump steer is all about.
Two thought I still have, can anyone confirm. I am not so technical, espicailly with suspension so bear with me.

1. using the standard torsion bar setup there is only one pivot point. This means that (when you hit the "bump") the suspension travel will describe an arc. Imagine standing with your shoulder against a wall, arm out stretched, when your arm moves up and down the wall the tips of your fingers draw and arc.
Surely this means that there will *always* be an slight element of bump steer.

2. looking at my (non-turbo) tie rods, it seems that unless the inner pivot is exactly parallel to the ground *during* the turn, any bump you meet will kick the steering rack quite noticeably.
The suspension cannot travel until the pivot is horizontal surely?

Maybe I really should get out a bit more, but the car is laid up

dickster · 03-12-2002, 06:45 AM

i'm looking at this as well.

from what i've read i do know that "bump steer" is not felt as steering input from bumps as many think. the bump changes the geometary(spelling?) of the steering arms, changing the "toe", and it affects the handling of the car. quote "can make it feel darty".

many people report that they do not need to raise the rack or anything, their car steers fine, with unparallel rods. this proves the point.

its just the difference between a good steering car, and an excellent steering car (B anderson i think).

my car is very low, and the tie rods are nowhere near parallel. i don't know whether to go for the washers or the expensive kit.

the expensive kit covers a wide range of measurements, and is made for the job (move the steering rack - just doesn't seem like the way it should be done. surely the rack was meant to be where it is??), but it is expensive

i'd be really interested to hear from people using the "proper" expensive stuff.

Tyson Schmidt · 03-12-2002, 07:27 AM

Bump steer is caused by non-parallelism of the suspension and steering. As it relates to our cars, this means the tie-rod length must be exactly the same as the length of the lower control arm so they travel in the same arc, staying parallel throughout suspension travel.

Actually, with a McPherson Strut design, even if they are the same length they won't stay parallel due to the camber change of the Strut design. You'd have to have equal-lenth upper and lower control arms to achieve zero bump-steer.

So, on virtually any car, all you can do is try to minimize bump steer as much as possible. Keeping the tie-rod angularity as close to factory spec is all we can do.........Enter; bump steer kits.

Here's a good tip though, as well. It is very important to make sure the "adjusted" length of the tie-rods is equal from left to right. Since the tie-rods length is adjusted to set the toe, it is possible to have the left one longer than the right one. To avoid this, adjust toe so that the amount of threads showing is equal on both sides once the toe is set correctly, then remove and re-center the steering wheel if it is off.
I've seen mechanics use only the tie-rod adjustment to center the steering wheel, resulting in nearly no threads showing on one side, and only a few threads holding on on the other!!!!!!! Scary!!!!

A quick way to check that your steering rack is perfectly centered in the housing, is to count the number of turns from lock to lock, the mark the center. With the wheels pointed straight ahead, this mark should be at the 12:00 position. Or you could just peek at the threads showing on both tie-rods and measure, if you have the turbo versions. It's harder to judge the non-Turbo style this way, due to the adjuster design.