Sorting Out Steering Kickback
 

Hello Pelican!

I am looking for some ideas on what is causing some pretty serious steering kickback while cornering at speed in my '86 Carrera.

I have been sorting the car out since purchase back in the fall of '17. I have refreshed a lot of the suspension while keeping the following parts installed by the PO- Rebel Racing Triangulated Strut Brace, 22/29 elephant bars (soon to be swapped for 21/27's), Turbo tie rods, spherical/teflon front bushings (early elephant possibly? RSR? they are black and unmarked) and Tarett sway bars front and rear (not sure size). I have installed Bilstein RSR struts (19mm raised spindles) and shocks custom valved by Steve Weiner, Rebel Racing Bump/Steer kit, new OEM ball joints, new sport rubber upper shock mounts and Rebel Racing rear spring plate bushings with new spring plates.

Car is on 15" Fuchs (7's and 8's), R888 tires.

Alignment specs here-

http://forums.pelicanparts.com/uploa...1586659607.jpg

I know the numbers are funky... My shop cannot get more than -.7° of camber on the left side, they are saying its because the RSR Struts are de-cambered(?).

I have a great baseline to know how my car is supposed to drive- my dad's much cleaner, much less bastardized similarly setup '86 Carrera. I have gone back and read every thread I can find on bump/steer, kickback and scrub radius but most of the discussions involve widebody cars and nothing I have read seems to apply to my setup.

Any ideas? My steering wheel goes nuts when I hit bumps during spirited driving and I am desperate to sort it out.

Thanks!

I had a similar problem in an 86 Carrera. Part of the steering rack had pushed out the side of its case. It was some kind of bushing that the rack goes through. This caused the tie rod to move around causing the steering to kick around.

My first thought,

In summary, excessive bump steer.

Check that the control arms pitch down slightly: higher on the inside.

Same with the tie rods.

Re-reading your post, it sounds like you describe two symptoms:

serious steering kickback while cornering at speed (corning, no bumps??)

steering wheel goes nuts when I hit bumps during spirited driving (straight, with bumps??)

Can you clarify for us?

Ride height and wheel offset?
 

What is the ride height, torsion bar center to wheel center? With the bump steer spacers, I am guessing you could have the front ride height 17mm lower than stock spec and not have any bump steer problems, (hope someone with experience can verify). With these spacers And the dropped spindles, you might be ok at -36mm.

A second possibility is wheel offset greater than stock, or front spacers, either of which could increase the scrub radius, making the steering heavier.
On a similar note, if the aftermarket shock tube/spindle/hub depth, have greater lateral offset, this could affect the scrub radius.

Is everything tight up front, rack, tie rod ends, ball joints, wheel bearings, steering shaft joints?

Curious,
chris

Any wheel spacers? As mentioned, what is your ride height.

When the spindles were raised, were the steering arms bent to compensate? If not you will need the bumpsteer kit that replaces the tierod ball joint. https://www.rsrproducts.com/product-page/basic-bump-steer-tie-rod-end-kit
No way to restore correct steering with raised spindles with rack spacers AFAIK.

Also, maybe not the main issue, but you need to figure out why you have 1,4 degrees neg camber on your right front strut. That much difference between the two fronts will cause problems.

I just had the rack out to replace the steering coupler. I was pretty sure I checked for this then but I wanted to double-check so I pulled the boots this morning and I think they look ok.


http://forums.pelicanparts.com/uploa...1586714845.jpg

http://forums.pelicanparts.com/uploa...1586714845.jpg

Here is a couple pictures of the control arm and bump/steer pitch (with the wheel jacked up to simulate being on the ground). I don't think anything looks really out of whack.

http://forums.pelicanparts.com/uploa...1586730723.jpg

http://forums.pelicanparts.com/uploa...1586714997.jpg

The kickback occurs when hitting bumps in the road during cornering. It is fine when going straight and hitting bumps

I am not sure about ride height. It was pretty low before but I raised it up today.

http://forums.pelicanparts.com/uploa...1586716761.jpg

I didn't have a chance to really drive the car after raising her up but on my ride home from my shop I did not notice any improvement or difference.

I'm not sure about offsets but these wheels are off my dad's '86 and there was no issue with them on his car. I do know my hubs are pushed out a bit compared to my dad's and other's '86 Carerra's. I found this out when I bought a set of Minilites from a guy with an '86. They fit his car and my dad's car fine but were pushed out about 3/8's of an inch on my car for some reason. No spacers. Everything is tight up front.

RSR Bump/Steer Kit installed! No wheel spacers.

Thanks everybody for your responses and thoughts

How much were the spindles raised?

Hard to tell from the angle of the pic, but it looks to me like you don’t have a big enough bump steer kit. They sell a racing one that is adjustable, and can be dropped further to get the toe curve better. They sell double sheer braces that I’d recommend using with the longer drop links.

Spindles raised 19mm. That is the adjustable racing kit. It has some room to go and I could buy more spacers to drop it even more but it is close to parallel with the control arm now. It's hard to get the camera in there to show how its really sitting.

My car has this problem as well. its lowered and small rack spacers. So is it ideal to have the tie rod exactly paralell with the control arm or rack slightly above or below?

My understanding is that the tie rod is supposed to be almost parallel with the ground, but angled slightly down towards the outside of the car. With that being said I'm here for advice and I could be wrong!

Your alignment guys should have set your cambers even, if you can only get -.7 on the left you should set the right to the same. I don't like the mismatch of cambers on the rear either, or toe in at the front.

Perhaps. I used to think that as well. That is until I installed raised spindles. Getting the bump steer correct is more involved than eyeballing the tie rod angle.

Is there a guide you used to sort it out correctly? Thanks

There are guides, but here is basically what you have to do.

Measure and record your front toe at normal ride height.

Lower the front of the car one inch, us weights don't adjust the suspension, measure the toe.

Raise the front of the car 1 inch above the normal ride height, measure the toe.

Adjust the washers or spacers on the bump steer kit so the toe changes minimally from normal. You will be OK if it changes the same direction going up from normal to down from normal.

A royal PIA, but worth the effort. I used strings.

In your case, it doesn't sound to me like a bump steer problem you are having. If your bump steer is off you will have a darty and unstable feeling when gently turning at speed, like on the freeway.

Thanks Gordon! I would agree- the car feels pretty much fine on the highway. She can be a bit darty in a straight line, but I blame that on the tires.

The kickback happens during tighter, bumpy back road cornering. It also happens on the track during cornering. I have to really think about those symptoms as I have not been on track with the car since the fall and it doesn't look like I will be getting back anytime soon.

You have multi interrelated issues
* you must address the front camber disparity
* the steering tie rod ideally wants to be horizontal when the car is on the ground, the reason is that wheel travel pulls the arm when in droop and pushes the arm in bounce, you want to minimize the magnitude of the push/pull which will be when the arm starts off horizontally when at static ground position, a contributing factor is to try to keep wheel travel to a minimum
*any bump steer issue is magnifored by any increase in scrub radius w/ stock hubs and 7ET23.3 a 911 starts w/ a lot of feedback caused by the s/r of 52.4mm, push the same wheel out another 3/8" and that increases to 61.925mm, so any feedback from the wheels is amplified by ~18%
*any time an aggressive bump steer kit is added you need to measure the bump steer to see if it helps or hurts, either can happen. To measure bump steer you need a flat, rigid plate bolted to the hub, a strut w/o a spring or internals and a dial indicator, attach the plate to the hub, move the wheel through it's arc while measuring the toe and recording it correlated to travel from the neutral condition seen when the tire is on the ground and full weight is on it. You can still do it w/ the spring and shock internals in situ but it's going to be harder. The stack of steering arm o/s's that you keep should be chosen after measuring the effects of as many of them as you have the patience for. W/ an extra dial indicator you can also measure camber and draw a camber curve for you setup.

Here are the curves for a stock 3.2 Carrera at stock ride height
http://forums.pelicanparts.com/uploa...1586796744.jpg

This is true if the a-arm pivot (torsion bar center) and the ball joint are also level when compared to the ground. Actually the tierod needs to be parallel to the horizontal plane between the torsion bar center and the ball joint center.

This is what you want, in compression the steering is moved opposite to the motion in droop, they average out as much as possible.
http://forums.pelicanparts.com/uploa...1586802935.gif

not this, which is what I believe you just described, here the steering arm movement is always the same way, it just gets worse the more compression
http://forums.pelicanparts.com/uploa...1586802935.gif

Bumpb steer comes from the diffeening arcs of the oute end of the tie rod and the outer end of the A arm

here are 2 examples of relatively clean bump steer

this one is aspirational as in practice it's virtually impossible to do
http://forums.pelicanparts.com/uploa...1586803622.jpg


This one is closer to a 911, the plane you describe is far from the case. It's also far from the 911 case in that though the steering movement is all in one direction it at least decreases w/ bump travel. The arcs are determined by the relative geometry between the ends of the 2 relevant arms
http://forums.pelicanparts.com/uploa...1586803622.jpg

Again whatever bump forces are present are magnified when the wheel centerline is moved further outboard and a stock 911 starts w/ a large bump force component to the steering wheel

Yes, Bill. But you will notice I said in the plane of the ball joint and torsion bar. NOT the a-arm.

Like this.
http://forums.pelicanparts.com/uploa...1586804847.jpg

http://forums.pelicanparts.com/uploa...1586807311.jpg

Yes, still parallel in your bottom picture. That is the point, of course that is in a perfect world.

Your bottom pic in your post above shows what happens when the tierod is not parallel to the lower control arm axis.

Regardless, the only way to check and minimize bumpsteer is by measuring the toe change.

FWIW, I spent months adjusting my tierod to be perfectly level to the ground on my 911 after I raised my spindles. It handled like a pig until I got out the strings and started actually measuring my toe change and adjusted my bumpsteer setup accordingly.

Thanks Bill!

Does anyone have experience with RSR struts? Is it true they come de-cambered? My shop seems to think so. I have not been able to get in touch with Steve W. (he sold them to me) but I know him, how he operates and he knew what was in/what was going in my car. I can't imagine he would sell me a set of struts that wouldn't work with my car.

I will re-measure the hub distance and start playing with the bump/steer when I have a chance.

Thanks!

The more I think and look at this the more I am thinking it is a scrub angle issue. Look how far away from the center of the wheel the bottom of the strut is.

http://forums.pelicanparts.com/uploa...1587667783.jpg

I can't jack the car up right now but I am thinking the car must have turbo hubs or something on it to push the wheel out that far.

scrub radius is defined here, though here it is called pivot radius
http://forums.pelicanparts.com/uploa...1587672045.gif

a stock 911 w/ 7ET23.3 Fuchs has a s/r of 52.4mm per the factory the back space of that wheel is 121.1mm, so if you can measure the b/s of your wheel you can then determine s/r.

b/s is defined here
http://forums.pelicanparts.com/uploa...1587672285.gif

Wouldn't that only be true assuming I have stock hubs? I know the wheel is pushed out further than stock, and these are Fuchs off my Dad's '86 Carrera that had no issues. I think the ticket is to measure these hubs and compare them to my Dad's and go from there.

You are right about that

I'm still confused by the hubs
AFAIK there are only 4 different hubs that have ever been used on any 911
early cars used 37 or 40mm hubs, for ~'69 thru 89 they used 47mm hubs, in 1980 930 got 68mm hubs but they can't be used on a n/b because they push the wheel way too far out for regular 911 front fenders, before 1980 930 used 911 hubs

I need to do some measuring. I do know for a fact that the hubs stick out further on my car than on a normal Carrera. I don't know why, but I cant imagine it's anything but something wonky with the hubs (as opposed to a different suspension/chassis component).

I was hoping to find a hub issue, no such luck. I measured width from rotor to hub face (where wheel mounts), rotor width and back of rotor to chassis. Everything checks out compared to my Dad's car. I even measured the A-Arms to make sure mine hadn't been modified at some point.

Bill I keep referring to the following post.

I feel that by measuring and confirming I have stock hubs (PN 911.341.605.4R) I have eliminated the possibility of a scrub angle issue.

I agree that the camber disparity needs to be addressed but I don't see how it would contribute to the kickback issue.

I feel similarly about bump/steer. As far as I know, my car does not display the symptoms of a bump/steer issue.

Am I wrong?

Thanks

Looks like you are running a pretty common, stock setup wrt hubs and wheels. 911 front suspension has scrub radius built into it by virtue of having strut suspension. You shouldn't have it any worse than other 911 drivers.

Given your setup, it doesn't necessarily look like bumpsteer should be a prominent issue either. Bumpsteer was my first thought in reading your first post. Trackrash's and Bill's comments are the generally accepted guidance, and you have the tie rod spacers which should help address bumpsteer. I'll only caution that bumpsteer, when you have it, can feel pretty unsettling and make the car feel unpredictable even when driving straight but especially when going over bumps. The car will dart around even with no steering wheel input. And the only way to really eliminate it is to measure it while exercising the suspension, and adjust the outer tie rod spacers accordingly.

Sorry if I missed it, but can you describe the kickback in more detail? E.g. over bumps, when you're turning, etc. Is there slop in your steering by chance?

Looking at that pic of your lower control arm and wheel, it definitely looks like you scrub radius is higher than stock.

If your wheels are 7” with ET 23, and your hubs are stock 47mm, then I would put money on your struts being decambered about 1 or 2 degrees.

Thanks Stownsen. The car in a straight line generally feels ok. Not perfect, some darting but I attribute that to the alignment and tires (R888R's). Bumps in a straight line do not cause feedback but during cornering the wheel "kicks" into the corner when the inner tire hits a bump. (for example, coming through a right turn, right front tire hits a bump and the wheel will kick right and then return to previous level of driver input). Coming through the same turn, if the outside (left/loaded) tire hits a bump there is little to no feedback.

What is odd is that I don't think this "kickback" has a significant effect on the trajectory of the car. The car doesn't seem to really change much direction as a result. (or maybe it is just hard to tell) I do, however, think that it definitely unsettles the car and I also hate the way it feels.

Thanks Tyson. I definitely think something is going on. I was really hoping to find I had some wonky hubs that were messing up my scrub angle. What throws me off about your hypothisis is that I have -1.4° of camber on the passenger side (Which is expected on a stock car). I don't have much of an explanation for the -.7° on the driver side other than the fact that the car had an impact there but the car was checked on a celette after and straightened out.

Measuring, comparing and finding very similar measurements on my dad's car still doesn't explain why the wheels I had fit on his car and stuck out on mine.

ttt