Front Suspension Question

[DEWFPO]

Subject vehicle : 1998 S90, 73,700 miles.

Both front tires have both (inside and outside) edges feathered. Swapped fronts for rears and criss-crossed, now the rear tires (now on front) are showing the same signs. This happened with the previous tires as well and I am getting a "drump, drump," sound whilst rolling at low speeds. Tires were recently re-balanced before the rotation to eliminate balance issues.

I am 100% certain it's the suspension. I rotate tires every 5,000 miles. The car handles well and feels fine at speed although not as smooth as it could be. No noticeable play or rhythmic vibrations.

Air pressure in tires is 32 psi and there is no play that I can find by shaking the lifted tires 3-9 or 12-6.

Thinking it might be lower control arm bushings.

Your opinions are appreciated.

Thanks, DEWFPO

[jda2000]

Under inflation can cause the problem you're seeing, with the edges wearing out faster than the center.

Raise the tire pressure to 36 psi and the wearing of the tire will be more even.

[Tom]

Is the feathering kind of a saw-tooth wear pattern? It's common for too much toe-in to cause that on the outside tire edges, and too much toe-out to cause that on the inside tire edges. Maybe one end is toed in and the other is toed out.

I've had toe-in problems after bringing my 850 in for a professional alignment ... all my rims are a little bent and I suspect that the guy doing the alignment didn't compensate for that properly when he set up the machine. After driving it for 6 months, I saw that it was chewing up the outside tire edges so I measured with a tape measure and found it had half an inch toe-in, front and rear. A tape measure is not the most sophisticated way to do alignment, but if you put a mark on each tread, measure on one side of the tire, roll the car and measure on the other, you can get the toe measurement to within 1/16 of an inch or so. And it's forgiving to bent rims. I've readjusted the front and rear toe angles on the basis of these measurements, and after driving another 6 months it's clear that the tire wear has stopped. No more professional alignments for me.

Tom

[Drew]

Is the feathering kind of a saw-tooth wear pattern?  It's common for too much toe-in to cause that on the outside tire edges, and too much toe-out to cause that on the inside tire edges.  Maybe one end is toed in and the other is toed out.

I've had toe-in problems after bringing my 850 in for a professional alignment ... all my rims are a little bent and I suspect that the guy doing the alignment didn't compensate for that properly when he set up the machine.  After driving it for 6 months, I saw that it was chewing up the outside tire edges so I measured with a tape measure and found it had half an inch toe-in, front and rear.  A tape measure is not the most sophisticated way to do alignment, but if you put a mark on each tread, measure on one side of the tire, roll the car and measure on the other, you can get the toe measurement to within 1/16 of an inch or so.  And it's forgiving to bent rims.  I've readjusted the front and rear toe angles on the basis of these measurements, and after driving another 6 months it's clear that the tire wear has stopped.  No more professional alignments for me.

Tom

←

I learned this trick years ago with my Jeeps. If you do a google search on "shade tree alignment" you'll find a ton of info.

When I changed my power steering rack on the Volvo with all new inner and outer tierods I did my own alignment. The goal is to be within 1/8th of an inch of toe. I used 2 lengths of 3 foot angle iron held horizontally on the wheel with bungies. Use 2 tape measures, one going across the front of the wheels and 1 going behind the wheels.

I have put close to 30k miles on the Volvo since then and have no abnormal tire wear, and It looks like I've got about another 15k left on the tires, and the car handles great. I haven't had a "professional" alignment either for YEARS!

The most difficult thing about alignments around here is to find someone who will take the time to do it right......Most don't take the time.

Good Luck

DougA

[Kashif]

I think it's an alignment issue too. You can go to Sears and they can check the alignment for free, and they charge 59.99 to fix it (Well thats what they do here in Santa Clara).

[DEWFPO]

Yes it is a sawtooth pattern and it is showing on both the inside and outside of both front tires. The wear pattern is not indicative of low tire pressue (outsides are not wearing more than the insides). This car was designed to run these Michelins between 28 psi (comfort) and 36 (mpg) and I am currently running them at 32 PSI.

Thanks, DEWFPO

[850cabman]

I've never had an alignment but just accepted wear on the outer edge of both front tyres. I now run them at 40psi and swap them front to back when they get low on the edges and this seems to make them last a little longer (I get about 20-22K miles from each tyre).

Most front-wheel drive cars I've had have worn tyres in a similar way, especially with power steering.

However the inside edges seem to look fine on mine - I thought wear on both edges was supposed to indicate under-inflation but 32psi should be enough.

[Bay13]

I'd suspect toe is off, unless you have smacked something on both sides to throw off camber, and I don't think that would have happen. The lower control arm bushings do need replacing in time, you can see the cracks in them upon inspection.

[DEWFPO]

Thanks All.

DEWFPO