Driveline Vibrations

So I just got my car back from a very reputable Indy Porsche shop that knocked out an alignment for me, now I�m noticing an increase in vibration throughout the chassis above ~50 mph. At 50mph, there is a slight vibration in the steering wheel but then, as I accelerate, the magnitude of the vibration through the chassis increases in a linear fashion. I don�t remember it being this bad prior to the alignment. Every single part of the front and rear suspension is new, engine mounts are new OE mounts, trans mount is relatively new, and the car drives fantastic below 50mph. This Winter I had the wheels checked for deviations, one was straightened, then powder coated and balanced by a Porsche recommend shop. The tires look good but are getting old - and this is where I suspect I�m having the issue. The rears have a 2020 DOT code on them and are noticeably louder when driving over expansion joints and what not. There is no noticeable play in the wheel bearings, though I haven�t measure the runout on them. Before I go buy new tires, any suggestions?

Get your tire balance checked. Vibrations at and over 50 are very typical symptoms for tire balance issues. It may be a coincidence that it happened after an alignment and could be something as simple as a wheel weight falling off. If you don't feel any play in the front end when you jack it up, they probably didn't leave anything loose after the alignment.

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Yeah might be worth a second opinion. Doesn�t appear to be any wheel weights missing but who knows.

Wheels out of round, tires out of round or tire/wheel balance off woukd be my guess.

I have sometimes noticed vibration issues at hight speed ... caused from surface imperfections of the road. Even on recently finished roads. Your mileage may vary.

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Any good way to check the tires? Would the wheels balance with out of round tires? Can you just spin it on a machine and measure sidewall deviation or something? Or I guess you could get it to ride height while still on the car and measure for run out? The shop that just refurbed my wheels has a great reputation. They straightened one wheel, said everything balanced out fine. Maybe I�ll take it for a second opinion.

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I never balanced a tire personally on a balancing machine but am told by my indy that they can figure out what is wrong with their balancing machine.

I would suggest going to a tire shop with road force balancing. especially when looking for higher speed vibration.

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Yeah, absolutely. Isn�t that pretty much the standard now though?

Seems odd that it only occurred after an alignment. I'd contact the shop and tell them what happened. If they're reputable as you say they should work with you to troubleshoot.

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^^^this If everything is new and it is now worse after the alignment take it back to the shop. Yes, a belt can slip. Don't go to a second shop unless this one has already told you to go pound sand. Does the vibration settle down at higher speeds? Or does it just continue to get worse until it's undrveable?

I have a similar experience on mine. New tires were the fix. now granted my tires were pretty old; and the car hadn�t been driven in about two years before I put it back on the road.

Flats spots on tire if sitting for awhile, old tires, over inflated tires that track every nook and cranny in the road all can cause vibration. Add in a new suspension, engine and transmounts and you may have more vibration. Further add in reconditioned wheel that may be out of round and an improper tire balance and you have even more vibration. Its one of the above or a combo.

Its also pretty easy to go to a tire shop, get everything perfectly balanced and then go to a car wash and have a weight get blown off the wheel from the water stream or by hand when washing the wheels if you arent paying attention. Been there and done that many times early on in 996 ownership. You then learn to make sure whatever balancing place you go too, has the aluminum tape to put over the weight as a just in case. On the track I have had plenty of times on very hot sticky days that the tires slightly rotate on the wheel under heavy braking and they get out out of balance by the end if the day. Same with very hot tires that pick up clack on the side of the track which sticks to the tores and throws off the balance until it either comes off during the session or you take it off after the session when the rubber is still hot. The point is that it doesnt take much to get out of balance.

Took it back to the shop that did the alignment today. It was pulling to the right just a bit, so I had them fix that, and then had them re-check the balance on the wheels. Turns out one of the wheels was a bit off. Driving the car back, now the vibration is between 50-60 mph. Car drives like a dream below 50, start feeling it in the chassis and steering wheel at 50, most of it seems to go away by 60, and the wheel doesn�t shake above 60 but there may be a small vibration in the chassis still.

Do you have wheel spacers? If so, remove them to test.

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No.

If you can borrow a set of front wheels, try it to rule out a rim, tire, or balancing problem. It doesn't cost anything. If your tires have a DOT code older than 2021, it won't be a waste of time to change them.

Confirm on different roads at that speed range too. Sounds dumb, but I have a local highway with a bit of a shake for a few miles and it looks the same (pretty smooth tbh) as the rest. The steering feel in these cars really is a cut above� definitely better than the arsehole in the steamroller that laid down that asphalt.

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Ya, time for a new shop imho. As with all new alignment equipment the specs and current settings are all posted and printed out if wanted. So an error large enough to cause a pull to one side would no doubt be way out of specs and in the 'red zone' on alignment machine. Something like that should not be missed by a decent alignment tech, not to mention the out of balance or belt separation vibration you are suffering from. Both your problems should be solved by a competent alignment shop familiar with the 996.... Its common on older Porsche cars to have tire belt separation problems. These cars commonly sit in the garage for days/weeks/months and get flat spotted tires. Newer quality tires can take flat spotting to some degree. Problem comes from tires getting flat spotted time after time, again and again, then add in some low inflation drives, eventually the flat spot will not smooth out with driving. The tire belts have now started to separate internally and no amount of balancing or driving will fix this. The tire is damaged and more susceptible to blow out now. Time to change out tires... Try to avoid flat spotting new tires by keeping car partially lifted keeping full weight off tires while in storage/not being driven regularly. Or there are some tire pads designed to avoid flat spots you can put under tires..