Manfred

I have a lot shaking in my car which starts around 78mph, goes away from about 85-95mph and then starts again. Pretty annoying actually since I would probably spend a lot more time just shy of 80mph but I'm forced to go faster. Anyway, I suspect this is a tire balance issue (although from checking previous posts I gather I may have a flat spot since the PO only put 3000K in 3years on the car).

My question is this: Do I need to check with my shop to see if they have any special equipment or will any tire balance do?


Toyo Proxes T1R 255-40ZR17 in rear
225-45ZR17 in front

CanAmJohn

Easiest first check is get the tyres checked for balance at a tyre fitters. If that doesn't fix it then start pondering.

Manfred

Thanks John.

CanAmJohn

Pleasure. When the wheel is on the balancer, get them to show you the wheel spinning, you can then see if the rims are straight or there is an oval to the tyre shape at the same time. It will save testing for it again should the balance not fix the issue.

RKD in OKC

I've had tires/wheels balanced with not problems then done something as simple as adding crested valve stem caps that caused similar vibration problems. Rebalancing fixed it.

Manfred

Wow--sensitive--sounds like rebalancing is the first place to start.
Thanks, Dan.

JPTL

Find a shop with a road force balancer. That will isolate a bad wheel, an out of round tire, a flatspotted tire or a 'mismounted' tire, or simply an imbalance.

ckabee1

+1 on the Road Force Balance.

Last year, I had a horrible shimmy from 55 mph that progressively got worse the faster I went - very uncomfortable. Any way, I spent a lot of time and money replacing tires, an alignment, upper/lower ball joints, and tierod ends. The shimmy persisted.

Out of frustration, I went to Discount Tire and had them do a road force balance. $80 later it was smooth sailing up to 140.

Manfred

Tires are currently getting "road forced" for $65.
Thanks everyone, I'll keep you posted on the results.
Dan

Tampa 928s

+2 on the Road Force Balance

Just went through that, 3 year old tires no miles and balanced OK. Placed a borrowed set on the front and ran smooth. When road forced they showed 37 and 34 and should be under 20 as a rating for sidewall hardness and deflection. New tires were rated at 5 and 4 night and day, you maybe looking at new tires I had no choice.

Tails

Dont forget in the balancing process that you can get lateral out of balance also, that is if you look at the plane through the centre disc of you wheel and tyre and if the balance weight are put on either side of this plane then you can get lateral out of balance which can cause the wheel and tyre to shimmy.

Tails 1990 928S4 Auto

tailpipe

Please ask and find out how your tire shop balanced your wheels usually with aluminum rims tire shops try to do a static balance so that there are no tire weights on the "visual" surface of the rim. They do this so it looks good, this is not the best way to balance a high speed wheel this may work fine on a truck or a tractor NOT on a porsche. The best way to balance wheels is right on the car, very few tire shops can do this it takes a special machine it will balance everything turning, brakes and axles included it will also show any bent parts. The next best way is with a dynamic balance this has to be done on a good quality wheel balancer, to be done right though you may have to live with tire weights on both sides of your rim either the clip on type ot the glue on type,I prefer the gue on type. By the sounds of your symptoms this is all you will require.
I'm a little strange one of may favourite things to do is changing tires , I worked for the Goodyear tire company store here in London for a few years many years ago, for me seeing tire weights on the outside of a wheel tells me they did the job right. I see way to many that don't have wieghts on them and many people putting up with bad vibrations that they shouldn't have.

Good luck tell us how it goes


paul with 4 79 928s

Manfred

Thanks everyone. I got the tires road force balanced and they all came back at over 40. Guess that explains my vibrations! The right-side rims are both out-of-round as well. Looks like new tires are in my future--for now I'm just going to live with the shaking. I'll probably be starting a new thread in a few months titled, "Recommendations for new tires?"

Dan

RKD in OKC

Tires AND RIMS!

Michael Robinson

You know... I was just about to post on this issue too.

My 86' 928s has been sitting since August 2004 (I just got it out of storrage Dec. 30). And after getting it road worthy and putting it through an alignment, I took it out for a good exercise and noticed that just shy of 60mph all the way to 75 I was getting a wicked shimmy. I had the wheels balanced and they were off balance considerably. I had my shop strip all weights and start clean. I more than likely believe that I have some flat spots on my tires too, b/c after rebalancing the issue still remains.

Michael Robinson
1986 928s
5 SPD / 175K+
Blk / BLK