Steering wheel shimmy going over bumps.

At first I thought it was from the result of the bent wheel being a little out of balance from being repaired. Replaced shocks, mounts, and got new wheels and tires. Car only has 86k miles. The steering wheel now has a minor shimmy when going over bumps, but not every time and it smooths out almost immediately. It feels similar to a when a wheel is out of balance and the steering wheel shimmies, but it only happens when hitting a bump. There�s no evident play anywhere in the steering. I get the car on a lift and there is no vertical or lateral play in the wheels. All the components look fine. No knocking/clunking. Car drives shimmy free at speed too until some irregular pavement comes along, which may or may not get it to shimmy, but it probably will. What do I check next? What are the odds that the wheels are out of balance? Would that even cause the symptom if it only happens over a bump?

My first thought is that you have some bump steer going on. Try and identify if your front toe arms are perpendicular to the ground or if the go up at a slight angle from the wheel to the body.

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That�s the thing� I didn�t get this issue until I got new wheels and tires�these new wheels are a bit heavier than the last wheels I had if that makes any difference�

Wider front tires could cause wandering and/or bump steer. Heavier wheels and tires could also cause more bounce which would in turn induce bump steer.

Tie rods don�t look like they�re out of the ordinary or need a bump stop kit. I ordered one anyways and have an appointment on Tuesday to get things looked at.

Wheel dimensions F&R incl offset and weight as well as tyre dimensions, brand, Model designation, DOT and pressures would help.

I hope it is not rude of me to jump in here but i am hoping my issue and the OP post align with some ideas that you guys can suggest. If i go over bumps it feels like the car jumps around a bit on the front end. My indy looked at my tires and said ahhh those tires are notorious for making the car feel odd, he explained at is a yawing effect of the car.. my car has the aero kit along with the factory GT3 type rims from new, and Previous Owner PO had Feal 441 coilovers installed, the ride height is a little lower than factory. The Tires are Michelin Pilot Sport A/S 225/40 ZR18 3+ The DOT code ends in 3118 which i take to be the 31st week of 2018... When i last checked the tires for pressure i set them to comfort settings. I am not sure how to set up the coilovers or if they are the issue..am considering a "good" alignment next. any guidance would be welcome.

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From a mechanical standpoint...always go back to the last thing you did. Meaning the new wheels and tires. Perhaps you have your old wheels and tires and you could mount them and compare the differences.

Did you lower your car? Are you running 19s now?

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Wheels and tires are OE GT3 fitment. Front: 235/40-18 // Rear: 295/30-18 Tire pressures are at 35psi and are Conti Extreme Sport2s with September 2022 date codes No longer have old wheels, so I can�t compare anymore, but the older wheels were ~6lbs lighter per wheel. I feel like this was something that just recently happening and is slowly getting worse; hard to say other than it definitely not being around on the old wheelset. Still 18s, suspension height didn�t change from before and after current wheels. Here are the alignment spec on old wheels with new tires in September, and then new wheels/tires/alignment in November. I know toe will cause bump steer as well�but the toe doesn�t look bad enough to cause shimmy? Not even sure the angles are extreme enough where a bump steer kit will even help?

Thanks for the details. 35PSI is what the sticker says for the 225/45R18 front tyres on my 996.1c2. Yours is a 996.2c2 40 Jahre, right? 35 psi should be ok for a 235/40 too but the rear pressure at 35 PSI is significantly lower than the 43.5 PSI on my sticker for 285/35R18. 43.5 is good for speeds greater than 100mph but 35psi seems low for the rear tyres even for speeds up to 100mph. Would have thought 38-40 PSI. Rear camber seems a bit high, perhaps the conti doesn't suit that. Especially with lower pressure than recommended you can get quite a camber induced cornering force on truck grooves leading to a rear end feeling wiggly. Something to address even though you mention crossing bumps with the front wheels leading to a steering wheel shimmy. What seems odd to me is that the LF shows a negative value for camber but in the picture the top of the tyre is tilted outward. That is generally considered to be positive camber. As you haven't mentioned pulling to the left I take it the diagram is just wrong but since front camber is the biggest change between both alignments and more negative camber reduces contact patch size straight ahead, this could be the culprit. Front overall toe spec is 0.17 so .12 is a little towards the lower acceptable value but better than before wrt shimmy. In short and in order of effort -Lower front tyre pressure by 3PSI -Increase rear tyre pressure to 38-40 PSi -change front camber back to what it was. -Change rear camber to what it was. Looking at the angle of the front control arm it seems your car is very low. If so, that is the biggest contributor even if you haven't changed height going to the gt3 wheels (Mk1 or Mk2 gt3?). The heavier wheels exacerbated the tendency to shimmy.

Would tire pressure make it shimmy though? I'll up the pressure and see how that affects things. I used 35 psi cause that's what all the GT3 guys here run their tires at...so I just followed suit. Yeah, the diagram is just for illustrative purposes, not really showing what's actually happening. The car tracks perfectly straight, not does it pull one way or the other, even when hitting the bump. I forgot to mention or make clear, the very last alignment was done on the old wheels. I didn't get the alignment WITH the GT3 wheels. When the new wheels came in, I simply jacked up the car and swapped them over. I have an alignment appointment on Tuesday, 2/14. What are the odds I'll need the bumpstop kit to be installed? The tie rods don't look to be at an agle required for it. Infact 3 of my buddies cars are lower than me on coilovers and they don't have a bumpstop kit or the wheel shimmy over bumps....which makes me wonder wtf is going on. Wouldn't an out of balance wheel make my steering wheel shimmy all the time or at a certain speed? The car is lowered with X74 springs and Bilstein B8 struts/shocks. I do have Tarret toelinks in the back, just curious if the wider/GT3 wheels need the car to be realigned because they're a little wider. Previous wheels were 8" up front and 10" in the rear, OEM tire size.

When I changed mine from 17" to 18" GT3 wheels, I ended up with a vibration at 65mph. It would go away by 70mph. This is typically wheel balance, so I had it checked. It was fine. So I rotated the 2 front tires and the problem went away. 5k miles later, it is still fine. My current thinking is that the wheel bearings with 100k miles on them are just worn enough to allow an 'in-balance' tire to move enough at speed to shimmy. The plan is to change the bearings with the next wheel(or brake) change. I'm also at X74 height. I run 30psi front and 40psi rear. I also don't have any special hardware to put things into alignment. Maybe the play in the tie rod ends and rack are just enough, and the wider tires add just enough additional force to make things waggle about for a moment. Good luck with the diagnostic.

�My indy looked at my tires and said ahhh those tires are notorious for making the car feel odd, he explained at is a yawing effect of the car..� ^^^That has to be one of the silliest things I�ve ever heard�😆 I�d find a new �Indy��

Nate, welcome back on the forum. What are you running for coilovers and what settings? I'm running Bilsteins PSS9s. Stiffest setting on rear. One notch above mid stiff on front. Tarret sway bars are tightest in rear and loosest in front. I feel everything in my steering wheel but track straight over bumps.

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No coilovers. X74 springs on Bilstein B8s.

Nate, sounds like you need an indy that can drive your car and figure it out.

No bump steer kit required as you don't suffer bump steer. Lower tyre pressure at front increases foot print slightly (making it longer) thereby increasing pneumatic trail length of the tyre. This increaes damping of wheel shimmy. You still haven't mentioned wheel size or what gen GT3 they are from but I take it they're gem 2 with 8,5 wide fronts? Are they et52 whereas previous 8" wide were et50? Perhaps the wear pattern on 8" is just that little different so that on 8.5" combined with the new alignment you get the shimmy. Did you drive the old wheels and current alignment long enough that you would have noticed the shimmy too, had it been there? Greater ET on current wheels should lessen tendency for shimmy, that's why I point to the change in wheel width whilst keeping the same (worn-in) tyres. Were left tyres kept and the left and right on the right? If you like me to contribute more to help.you get to the bottom of this I kindly ask you to provide the answer to all questions in my posts.

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I did mention wheel and tire size in 3 separate replies above. They are .2 spec wheels, so yeah 8.5in. I drove the old wheels on the new alignment for about 2 weeks, roughly 500 miles, had no noticeable shimmy. New wheels got new tires, so nothing was reused.

Maybe its just a suspension link or shock top mount going bad. Im guessing a lot of the parts in there r almost 20 yrs/old.

Nate, my memmory may be off but didn't you run over a meridian which damaged the wheels on one side?

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Hopefully not a shock top mount, that was replaced with the shock a few hundred miles ago. There was a massive pothole. Everything on that side of the car that was damaged was replaced (spring just because, strut, and mounts)�nothing else was damaged. Car was put on a frame straightener just to check it was still straight and everything was straight. what�s peculiar is that the left side of that latest alignment is .3 degrees different than the other. I wouldn�t think that�s cause a shimmy though�

What about the undamaged parts in that side that may be worn out or all the stuff in the other side. It just doesnt make sence the issue is in the tires as the issue arises when u hit a bump, thus suspension? The front end is like headlights....to just replace one side is just delaying the inevitable replacemt of the other side. I know it was replaced due to damage but now u have 2 vastly different ages of parts in the front end.

Had an �83� GTI long time ago that would shimmy when driving over railroad tracks. Ended up being a broken tooth on the rack and pinion.

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Difference in age is around 6 months and roughly 6k miles, so not much different at all. That�s what�s mind boggling�only other thing I can think of is a bad shock right out the box, which isn�t rare, uncommon af, but it happens.

Found out the problem: A brand new Bilstein B8, blown in less than 2 months. That was the shock that was replaced. WTF.

I had a new Bilstein go bad on the M5. The car was in the air for its biannual CAT installation and the next day, I noticed something leaking from the left rear. The shocks had approximately 2500 miles on them. It was weird because there was still gas pressure even with the fluid leaking out. Bilstein's west coast facility is only ten miles away and a friend of a friend works there. He was able to get me two replacements at no charge which I think is their standard policy. Have you contacted Bilstein or who you purchased them from?

I've had my PSS9s for 15 years and not one leak and they are still going strong. When i replace them in the next year or two, i am going with another set of Bilsteins.

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That's EXACTLY what was going on with mine. It was still gas charged but was puking out fluid. Here's the kicker though, when I asked them (Bilstein and FCP separately) I asked if a faulty/improper dust boot could havecaused the issue. The ones I purchased were OEM Porsche that FCP instructed I get when I purchased my suspension. Both Bilstein and FCP told me "the blue bilstein dust boots you see are for coilovers and offroad shocks, hence why they're 10"+ long. The Porsche ones, undamaged, suffice as once the car is on the ground, the dust boot is sufficiently compressed and protexcting the strut. A failure like yours is the result of defect, not a dust boot." The dust boot: It doesn't feel like the right answer, but it obviously is if the other shocks are fine? Also, the B8s don't use external bumpstops as they're built in internally, so I'm sort of inclined to maybe just use that dust boot and just cut away the top of a bumpstop so it "seals" the pushrod? I dunno....I think I'm going to try and find Bilstein dustboots that fit and in the future use them instead.....anybody know off hand what part number they are? FCP doesn't even offer Bilstein dustboots, just Porsche/copies. Yeah, they're replacing it no questions...especially considering they have hardly any mileage on them. That's the best thing about Bilstein and/or FCP is that they actually stand behind what they sell.

Glad that got figured out.

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Yeah, it's been a huge PITA...it's funny how the very last thing it should have been, was actually the problem. They were actually joking about it in the shop "If those were like some other aftermarket thing or Koni's, I would have been like 'see, that's what you get buying cheap stuff.' but I never would have guessed Bilsteins." lol. Not sure I would have lumped Koni in there, but I assume since they're a race shop, they probably see quite a bit come through...hopefully I get the car back today and back on the road ready for Amelia/Werx Reunion in 2 weeks.

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Damn it! Missing another event.

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I'm surprised about their Koni comment too. I've never had an issue with them and always thought they were held in higher regard than Bilstein. At some point Bilstein switched from a threaded steel gland nut on the top to a plastic press fit cap. I'm curious if yours has the same type cap and if that cost cutting measure is part of the reason for the leaks. BTW, mine went out back in 2016 and it still feels like it has a full charge of gas 7 years later (I have no idea why I saved it this long ).

guys thanks for support, im definitely going to have rims looked at once again, maybe put car on lift and inspected, maybe even try a set a wheels (once I find a volunteer), if no luck, ill have another professional look at it, I cant see why im not able to run spacers. Also was debating with a friend of my about it, told me had same issue with his car and H&R spacers in past. Guys think its possible bad spacers is a thing? I find it hard to believe, since ive always ran h&R spacers in previous cars and never had an issue. IM almost certain the issue is there and spacers augment it . Guess i could also try using oem bolts for wheels not the H&R ones just to see if its a bolt problem. since another member had that issue. thanks for tips and support, any members here from Long Island NY.