Jupiterfish

Just got my car back from an Indy shop in town for a motor out service. No front end work. Now I notice a pretty bad steering wheel shake between 45-55 mph then it goes away and is smooth after 55. No shake at all. New rear tires installed with roadforce balance before service. Installing new fronts this week. Car does not wander to either side.

Does a motor out require an alignment after? All lugs are good and tight. Front tires are down to wear bars on inside but didn't have steering wheel shake prior to service.

Hoping during the test drive somebody didn't hit a Michigan pothole. Ugh.

Just noticed the date code on the tires are 14-08. 9 yrs old tires. Oops.

OverBoosted28

Motor out, usually will need an alignment.

pp000830

Re-read the original posting. Let's assume some rear suspension arms were detached and the rear setting are way off after reassembly. How would this cause a shimmy in the front end?

nile13

If the car sat on the floor for some time while motor had been fiddled with, the old front tires got "square". As in, they are not round any longer And since they are old, they don't "pop up" as fast as they could have.

The vibration you are describing is a tire balance issue. Specifically, front tire balance issue if you feel it in the steering wheel. If you are replacing front tires, your shake will go away.

Churchill

Steering wheel vibration around the 50mph mark is often a case of worn front a-arm bushings. Chris Walrod and Elephant Racing make replacements. Easy to diagnose, just do a search on the forum. One of the most common 993 probs.

stubble88

Front tire pressure.

nile13

Just how does the tire pressure contribute to a resonant vibration??

Jeff Crowley

Either Bent wheel or "flat spotted " old tires or both.

NYC993

Those are symptoms of worn out LCA bushings. Have you done those?

It could be due to worn out tires, but you shoud have this before, and it should get worse with high speed, which is not the case.

i have no idea why peoplw say flat spotted tires...first how do you flat spot, second you would have vibration all the way through increasing speed.

NYC993

cars sit for months at a time all the time, do you think the tires would get foat spotted (not much weight on them either) over course of couple months? And if they did, wouldn't you have vibration at all speeds (well except for low speeds) and not just at 45-55mph?

nile13

Two setparate things:

1. Tires do get flat spotted from several months of seating. Easily and consistently. The more supple (new, high perdormance, i.e. made of actual rubber, not bricks) the tire, the more easily it would get flat potted and the more easily it could recover. My car seats on Hoosiers all season, sometimes 3-4 weeks between events. The first few hundred feet of driving after is great fun.

2. There's this thing, called "resonant frequency". The tires cause vibration. As a matter of fact, any tire on any car on any road known to man cause vibration. Whether you feel those vibrations depends on their amplitude. The amplitude depends on a couple of thing. Essentially, it depends on how deformed things are and how close to resonant frequency the vibration is. Below and above the resonant frequency the vibration might or might not be felt. At and around the frequency... hold on to your breeches. This is fairly basic physics, BTW, you can easily look it up in simple pictures.

LexVan

I say old front tires, and temp flat spotting from sitting. A couple extra PSI could help. Make sure your new front tires match the brand and model of the newer rears. You won't see optimum front grip for about 400 miles, until the mold release is scrubbed off. FYI.

NYC993

1. you are comparing Hoosiers to corded street tires. I had car sit for 4 month without any vibrations afterwards. What about all these 993s sitting over winters.

2. Ok possible, which I guess explains why worn LCA cause vibration only in 50-60mph range. But in my experience when there is unevenness on the tire (rubber buildup, unbalanced etc) the faster it spins the more it vibrates.

nile13

1. Hoosiers, specifically A7 that I'm running on, are radial tires. With chords. The fact that you did not experience something does not mean it doesn't exist. Moreover, the fact that you, personally, did not feel it, also doesn't mean that it's not the case.

2. You are welcome to argue this point with authors of any high school physics textbook. All I can do is point to the correct information, which was done above. The faster it spins the more it vibrates. Up to a point, when it vibrates less.

NYC993

my physics textbooks didn't have Porsche wheels with Hoosiers on them. So can't argue here.

Just sharing my experience from putting 40k miles in 4 years in all kinds of condition (except for snow). I've had all kinds of vibrations and noises with different tires in different conditions. Also have another 6 friends with 993s that we work on. None of them had any flat spot after cars sitting for months on street tires. Oh and which size Hoosier on which car are you basing your conclusion? So just because something exists in one case, doesn't make it a universal truth. Cheers.