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Bump Steering, How Dangerous Is It?

14K views 48 replies 14 participants last post by  Bradt56 
#1 ·
One of my cars has a custom designed front clip. It has needed alignment for sometime but it wasn't until last week I was told I had Bump Steer problems with the steering mechanism and this alignment shop told me not only could they not align the car, but it was very dangerous to drive until the bump steer was fixed. I informed my fab guy about this and he told me he could get a bump steer kit for it and correct the problem but that he felt the amount of bump steer it has, is not that big a danger to drive. I'm sure he can fix it, but I'm pissed it has this problem to begin with.
Bob
 
#3 · (Edited)
I don’t see how bump steer would prevent a static front end alignment. Anyway it’s useless for someone to say it has bump steer without measuring it and giving the value.

A lot of older cars have bump steer but a poorly designed front end could have a lot and be a real white knuckle drive. I would have your guy measure it and then fix it. If he doesn’t know how to measure it then he shouldn’t be designing and building front ends imho....

A friend of mine had some hillbilly mechanics install a rack and pinion in his 55 Chevy pickup. The amount of bump steer it had was epic. They had no idea what they were doing.

There are so many well engineered front suspension and steering options out there, no need for a custom setup imho....

Don
 
#4 ·
No one checks bump steer on an alignment rack unless the installed system just looks incorrect to a seasoned alignment specialist & raises red flags then the only thing that can be done is read the toe then jack the chassis a couple of inches then read the toe again to determine if there is a change. The springs & shocks need to be removed to check / set bump steer. The procedure is to set toe steer (Ackerman) first with the spindle pin @ ride height from your datum line then bump steer it.

Suggest getting an opinion from another shop.

My bump / toe steer set up with toe plates & dial indicators.

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#5 ·
Excellent replies !!

As written, Bump Steer can be dangerous, beyond a vague amount ! It has been written that all cars have some bump steer, but very minimal. So as shown a Bump Steer Gauge is required to be able ti Minimize Bump Steer, it's also very annoying.

The question is ,, WHY does your car have bump steer ?? And How much.

Generally moderate bump steer can be Felt when driven and running over a bump or hole in the road, esp in a corner.

Can you provide an explanation of the changes made in your front suspension, and photos.

I've also agree with the post that few alignment shops will or know how to measure or Deal with bump steer. It is best, as noted, to remove the springs and a bump steer gauge is required. A quick check can be made by pulling the front cross member down, but this is sloppy and unprofessional.

I'm guessing that the alignment shop visually saw some front suspension Modifications, or the like, and tried to politely Bail Out for the alignment thinking that your front suspension might be unsafe.

I have a close friend that had 2 inch spacer blocks added on the straight axle in his '56 Dodge Pickup Truck to raise the front end while the shop was replacing the front springs and bushings. This resulted in some moderate bump steer. The Fix was simple once he explained to me the work this shop had completed.

This is a pretty good shop and has an excellent alignment rack and Tech, but no understanding as to what they had done. The Steering rod from the Steering Box Pitman arm to the Steering Arm on The front Spindle was 2 inches higher at Pitman arm end. When you understand this geometry your on the way to understand Bump Steer and Ackerman.

Michael...
 
#6 ·
The question is ,, WHY does your car have bump steer ?? And How much.

I've also agree with the post that few alignment shops will or know how to measure or Deal with bump steer.
It's easy to build-in bump steer, by installing a rack from another vehicle without regard to the length of the rack.

Most alignment shops will test drive the vehicle and it may have been noticeable to the aligner. They will refuse to align it for their protection.
 
#7 ·
How bad bump steer is and what to do to correct it will cover a wide range.

Bump steer is when toe-in changes as the suspension moves up and down. Many don't even recognize that, calling other troubles "bump steer" when they are really something else.

The worst examples are straight axles where the steering linkage is done all wrong.

With IFS the usual cause of bump steer is when the inner pivot points of the tie rods and lower control arms do not line up. This is a typical problem with a rack & pinion conversion where the rack's connections to the tie rods are outboard of the pivot point for the lower control arm. This is difficult to fix as narrowing the rack too much limits its steering travel.

This is one reason that you often should avoid doing a rack conversion on many cars, instead if you want R&P you should do a complete frame clip using parts that are engineered to work together.

One common classic car that has bump steer from the factory is a 62-67 Chevy II/Nova. This is due to the placement of the inner tie rod on the center link to allow enough room for a cylinder type power steering assist. All 62-67 Nova cars had this problem, power steering or not. 55-57 Chevys with factory power steering have this problem too but it is not as acute. (Manual steering 55-57 Chevys don't have this problem.)

Some 60s cars have minor bump steer that can be corrected with a "bump steer kit" that moves the outer tie rod pivot point up or down.

Since bump steer is caused by suspension travel, one simple solution to it is to limit suspension travel during normal driving. An example of that is to install a heavy sway bar on a Chevy II, it will do wonders for bump steer. Not because it eliminates it, but rather you just don't get the extremes of it in normal driving.

So Trifecta, one question is what kind of suspension does your car with alleged "bump steer" have? What does this "bump steer kit" do to fix it?
 
#8 · (Edited)
Yes, everyone here has given me great input, and yes the tie rods and lower control arms do not line up. The alignment shop owner told me he raised the front end and from what I understood the tires caved in at the bottom. A friend of mine that races old stockers told me they deal with bump steer and I believe he told me their cars are inspected regularly for bump steer. He looked at the steering set up and he repeated almost word for word what the shop owner told me.
The shop owner did not want to spend the time to fix it, but my racing buddy sez he can do it.
I told the guy that installed it and he told me he could align it. He didn't say anything about fixing the bump steer. So yes, he should be the one fixing it on his dime, but I might just pay someone a quarter and get it done right...funny thing is I've put on about 200 miles on the street and highway and I never noticed anything seriously wrong, other than a rumbling noise when I'm parked and I turn the wheels. Kinda like needing a purge.
I'll take some pics later. It does have an S Type suspension, what ever that means.

Bob
 
#9 ·
The alignment shop owner told me he raised the front end and from what I understood the tires caved in at the bottom. A friend of mine that races old stockers told me they deal with bump steer and I believe he told me their cars are inspected regularly for bump steer. He looked at the steering set up and he repeated almost word for word what the shop owner told me.
When the tires "cave in" at the bottom when the front end is raised, this is a camber situation not bump steer. The tires do not toe in or out when this occurs. And that would be very unusual for most front ends.

You don't "regularly inspect" for bump steer. It's either there or not. If you correct it, it doesn't come back.

I think between you, your alignment shop owner, and this racer, there is some misunderstanding and lack of knowledge.

Which of your cars is this? Also find out what a "Type S" suspension is and pass it on to us.
 
#10 ·
I remember from Bobs older thread on this build it is a modified S-10 front suspension. I also remember trying to steer him away from it. ans instead going with an engineered front clip from a known mfg like hiedts or tci.

I also agree what is described is not bump steer and is not a real issue unless the bottom of the tire is moving in more than a few degrees. A Chevelle has the opposite problem where the top of the tire moves in and out several degrees on full suspension travel.
 
#11 ·
When a story like yours is told it just brings to mind what else in the conversion is screwed up. As sited here if the guy screwed this up I definitely wouldn’t want his services any longer. A parts replacer is not what is called for here when dealing with geometry and setup of a reengineered steering/suspension.

Best to educate yourself on the issue and fix it yourself the right way. Even if it means starting over.
 
#13 ·
The top of the tire moving in as the suspension compresses is known as camber gain and is generally a good thing imho.

Don
 
#15 ·
I think he said it was moving in when the suspension dropped which would likely mean the top moves in when the suspension compresses.

Anyway a lot of folks touching the OP’s car are making claims that aren’t supported with any real data or apparent understanding...

Classic example why home brewed suspension and steering is generally a bad idea. Stick with properly engineered solutions.

Don
 
#19 ·
The photos show how a rack installation gone bad can create bump steer.

Also as rogueant posted, the steering arms should point outward if the steering is in front of the wheels. The spindles are swapped side to side from their intended locations. This is an additional problem because this geometry creates "backward Ackerman" steering. Ackerman steering is where when you are in a turn, the inside wheel turns farther than the outside wheel - which means the wheels don't fight each other while turning.

It's going to take more than a "bump steer kit" (whatever that is) to straighten out this mess. The rack is going to have to be re-mounted. No guarantees it will fit where it needs to be. Also something has to be done with the steering arms.

How dangerous is this? I'd say pretty significant.
 
#20 ·
S10 are front steer, the same as this install so I don't think the spindles are swapped side to side. the spindle steering arm is a one piece unit.
I do agree that the poor rack install could cause a dangerous amount of bump steer.
 
#21 ·
Thanks for that John. I'm including some pics I took this morning, and for the benefit of those that don't know what a "Bump Steer Kit" is I'm including the Speedway Motors number for the one I'm expecting today. (QA1 BAX102)
I drove this car for several hundred miles with just a rough shop alignment, and I never noticed an Oversteer or Understeer. That's not to say it wasn't there, I just never noticed it, or any deviation from a straight line.
Bob

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#22 ·
in looking at these pics I don't see any horrific issues, will it have bump steer YES will it be bad, probably not, what ever you do DO NOT USE THE BUMP STEER KIT POSTED ABOVE (QA1 BAX102). WHAT IT USES FOR TIE ROD ENDS ARE NOT ACCEPTABLE FOR STREET USEAGE. FIND ANOTHER ALIGNMENT SHOP.
 
#25 ·
Bennie, from what I understand, if while driving, the front end of the car leaves the ground such as by hitting a bump or large pothole, the tire should come down at the same angle and/or direction it was going in. The danger in bump steer as I understand it would be the change in direction of the tire causing the car to veer off in a different direction. I've driven this car for several hundred miles, and I've never felt this problem. That's not to say it isn't there, or that it couldn't use some adjustment but I've never felt a sense of danger. I've had the car at 80-90+ MPH and I did feel the front end getting a little light but that could have been due to air under the hood causing it to lift. Now that scares me if the hood latch should fail.

This car with the 5.3 Ls engine and the 4l60e transmission, Sanderson headers and cold air intake has great acceleration and a good cruising speed. I love the way it handles, but I will make double sure my front suspension and steering will not shorten my life expectancy. I appreciate everyone's inputs. It's the only way I'm gonna learn.

Bob
 
#27 ·
Technically, bump steer is when the toe-in changes as the suspension moves. The concern is not really when a tire hits a bump or a pothole, because even the best suspension designs can have problems with that. Rather, it's a concern when cornering as the outside wheel is in compression and the inside wheel is in extension. Add in the wheels self steering as this happens and you have a problem with the front end not going where it's pointed.

Trifecta, you also mentioned oversteer and understeer. Bump steer could cause understeer but there are many other causes. Remember it this way, if you are driving on a circle track and you lose control with understeer, the front wheel/fender hits the wall because the front tires have lost traction. If you lose control with oversteer, the rear wheel/fender hits the wall because the rear tires have lost traction.
 
#28 · (Edited)
Bump Steer Kit Installed

I was advised not to install the Bump Steer Kit on my Olds. This advice came after I had already ordered the Bump Steer Kit, so I had the option of installing the kit, returning the parts or just shelve the parts for now.
I looked into the installation of the kit, and I decided to take a chance on it. I had it done this weekend and I'm waiting for a toe in adjustment before I drive it out. It looks a lot better, and I believe the alignment shop will be much happier with the result.
If for some reason, it continues to be a problem, I will have the kit removed and redesign the whole damn front end. I don't think I'll need to. :):p3:

OOPS!!! I was just informed the rack and pinion is too long and wont allow adjustment for toe in. Looking for a solution now.
Bob


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#29 ·
#30 · (Edited)
You don't need a new rack.

The new adjustment sleeves should have deep threads inside of them cut some material from each end of each sleeve to shorten them to get the correct toe in adjustment.

In a perfect world the rack (length) ball socket centers should intersect the imaginary vector lines between the upper & lower control arm inner pivots.

Rack installed height & for / aft placement will also contribute to a toe in / out change during bump & turning.

Suggestion: Set the toe in then turn the steering wheel 1 full turn & check the toe in again. If toe in reading moves 1/8" toward toe in or out on turn your good. Toe out on turn is desirable however I doubt rocking off ramps @
100mph is the goal. There is enough tire sidewall compliance & thread squirm to compensate for small toe changes on turn without much effect on handing on a street driven vehicle. If excessive toe change toward toe in on turn slow down when the streets are wet or change / reposition the rack & mounting or steering arm angles for more Ackerman.

Bump steer is also "droop" steer, when the chassis rises the suspension droops. You can get an indication of how much "bump" steer you have by taking a toe in reading then jacking up the chassis 2" & taking another toe reading. Bump steer is adjusted by moving the tie rod ends up / down or moving the center link or rack up / down or moving the steering arms up / down. If anal about it all remove the springs & check toe change through full suspension travel. Clock the steering wheel & check toe change on turn. IIRC I posted a pic in this thread setting bump & toe steer using toe plates & dial indicators.

Bottom line: If you have some bump or toe steer on your streeter its not a big deal tire sidewall compliance & thread squirm compensate for much of it.
If you determine that you have more bump or toe steer than you like slow down when the streets are wet until you fix it.

End.
 
#31 ·
Toe change with steering input is mostly controlled by "Ackerman". That's the placement of the steering arms/outer tie rod ends with respect to the lower ball joint. With the steering linkage behind the spindles, the steering arm angles in when viewed from above, and it angles outward when the steering linkage is in front of the spindles. Toe-out when the steering is turned means that in a turn, the inner wheel turns more than the outer. This means the wheels don't fight each other.

This is why you don't convert a trifive to front steer using the stock steering arms switched from one side to the other.

Bump/droop steer complicates the Ackerman effect.
 
#32 ·
The big problem here is those rod ends are not up to the task for a street car and will develop slop and potentially fail in a reasonably short time compared to a real tie rod end. been there done that. Very very poor choice here!
 
#36 ·
Tony, the Bump Steer Kit is in and we had to do exactly what you did, but we did it on both left and right tie rods. The fix is in and the toe in has been set, and it is now aligned. I know Tehachapi John was totally against it and I appreciate and respect his opinion, but since I already had the kit, I decided to try it. I've driven the car and steering seems fine even if a little light at higher speeds. I wish it had a ratio adjustment such as some new cars. I will do a periodic check on this car, but since it is not a daily driver I won't be putting a lot of miles on it until I feel comfortable. Driving to car shows and cruises for now.

Bob
 
#35 ·
Ok my two cents. Bump steer is caused by the tie rods not moving up and down in the same ark as the lower control arm. Therefor when the lower control arm moves up or down it pulls the tie rod in. The bump steer kit you installed looks li will correct this but as mentioned I don't think that's street worthy. Concider lowering the rack to make the tie rods the same plane as the lower control arm with the control arm level
 
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