Why is my car wandering all over the lane

[jwakil]

My 930 just started wandering all over the road when I'm driving in a straight line. It's a little scary as I constantly have to hold the steering wheel and feel like if I had to make an emergency lane change at high speeds it would go out of control as it oscillates. Going around a curve is actually not that bad, and sharp turns at low speed seem as good as before. It definitely feels like the FRONT wheels are what's causing the wandering. This started after I did two things at once:
1. For a couple of weeks I had the rear end jacked up about 8 inches to do some engine work, so the car was resting on the front wheels.
2. I got two new REAR tires when I finished the engine work. The tires that were on before were 245/45-16s, the new ones I bought were 245/50-16s, since you can't find 245/45s any more! I do have the 8 inch wide Fuchs, so I understand that the 245s are oversized, but I didn't think the slightly taller 245/50s would make that much difference. In fact, I've had 17" wheels with slightly taller (but lower profile tires) on before and they didn't have this issue.

I'm trying to figure what could be causing the wandering at highway speeds. Is it the tires or did my alignment go out of wack or something. I also hear rattling coming from what sounds like the right front wheel well when I go over bumps. Its much louder now than before. Not sure if that is related.

Looking for any insights from the experts before I start my hunt.

[Josh D]

Check your tire pressures first. If when you had the rear tires installed you have not checked the tire pressure, I can almost guarantee the installer has them overinflated. Start with the tire pressure recommendation on the door jamb and adjust from there.

Obviously check the fronts too for pressure and tread. Make sure you turn the wheel so you can see the entire tread and not just the outer tread. If you car has some camber dialed in, the inside tread is going to be worn more than the outer.

[964TargaC2]

check ball joints, tie rod ends and shock mounts. that rattling means something..

My Volvo was doing the same thing and I would have sworn the right side ball joint was the culprit..turned out to be the left side ball joint

[jwakil]

Originally Posted by Josh D

Check your tire pressures first. If when you had the rear tires installed you have not checked the tire pressure, I can almost guarantee the installer has them overinflated. Start with the tire pressure recommendation on the door jamb and adjust from there.

Obviously check the fronts too for pressure and tread. Make sure you turn the wheel so you can see the entire tread and not just the outer tread. If you car has some camber dialed in, the inside tread is going to be worn more than the outer.

I have played with tire pressure to no success. Started from lower than spec to slightly higher than spec. Front tire tread looks fine.

[redranger]

Caliper(s) sticking?

[T77911S]

make sure the rear has settled back donw to its origianl height. bounce on the rear, better if you can do it while it is rolling.
grab the tops of each wheel and shake it in and out.

go get an alignment done. i just did an $80 alignment at the local tire shop. he idd a great job. just look for someone with the latest machine and make sure he has done a 911/930.
tell him what is going on.

[cgarr]

If it's good in a turn could be toed out that how we setup the race car makes it a little twitchy. And any height change will change toe.

[Dantilla]

Originally Posted by cgarr

If it's good in a turn could be toed out that how we setup the race car makes it a little twitchy. And any height change will change toe.

+1.

My autocross car is twitchy out on public roads. Worth it when the competition is so tight!

[RSTarga]

Wheel bearings, shocks , rod ends.
Same manufacturer and model of front and rear tires?
Age of front tires?
Aspect ratio of fronts versus rears.

[kenhep]

Check that the tire rotation is also correct. I do know of a 930 that had the tires on backward and a e30 that hit the ditch because the tire rotation was wrong.

[Eric Hahl]

Good article on Tirerack explains what might be happening to you.

[ClickClickBoom]

Originally Posted by jwakil

I also hear rattling coming from what sounds like the right front wheel well when I go over bumps.

This....

[Trackrash]

I had the same problem with my 911 after getting new rear tires. Car was scary to drive on freeways with grooves.

After doing everything I could think of over the period of a year, I finally got four new tires. Problem solved.

[jwakil]

Originally Posted by Eric Hahl

Good article on Tirerack explains what might be happening to you.

Good article, unfortunately it basically says anything could be the cause But it does suggest that wider tread tires (which the new ones are) exacerbate the problem, and that lowering the pressure might help. I will try that since I don't think I tried going down below 38psi on the rear, as intuition told me higher pressure should help.

[Stonestreet]

I have been told that the car will have major tracking issues if you don't have the right tires. If the problem only started right after you put the new tires on, that's where I'd be looking as the car has most likely settled back down on the suspension.

It's not so much about having shorter or taller tires as it is about having the front and rear be compatible.

Marc

[jason2guy]

get two new front tires to match the rear. thats the problem

[copbait73]

Don't know the history other than '81 gray market. You really should stop reading replies and inspect that noise on the right side. You could have serious rust and or accident damage. I would be pushing, pulling and prying to see if there is excessive movement where it shouldn't be.

[msterling]

Your rear tires are the SAME width as before. They are just a little bit taller. That would tweak the alignment a little bit. I think rear toe-in can be effected by that. Are the new rears the same Brand and model as the fronts? If not then you should expect problems. Also, new tires commonly feel a little (or even a lot) squirrely for a couple hundred miles. A few doughnuts will take care of break-in.

The rattling in the front was there before so it probably is not the culprit BUT don't ignore something like that. Jack up the front wheels and see if there is play by yanking on the wheels. Could be tie rods, steering rack, bushings, shocks etc. A busted front suspension can kill you dead.

[jwakil]

Originally Posted by msterling

Your rear tires are the SAME width as before. They are just a little bit taller. That would tweak the alignment a little bit. I think rear toe-in can be effected by that. Are the new rears the same Brand and model as the fronts? If not then you should expect problems. Also, new tires commonly feel a little (or even a lot) squirrely for a couple hundred miles. A few doughnuts will take care of break-in.

The rattling in the front was there before so it probably is not the culprit BUT don't ignore something like that. Jack up the front wheels and see if there is play by yanking on the wheels. Could be tie rods, steering rack, bushings, shocks etc. A busted front suspension can kill you dead.

The new rears are NOT the same brand as fronts now. I was hoping to avoid getting new front tires as they still have good amounts of tread. The new (different brand) rears are the same width, but the tread is totally different, much wider grooves. That article talked about how the wider tread can increase the wandering. Will definitely check the front noise as well. Its annoying and needs to be taken care of regardless. I probably have a combination of non-compatible rear tires and something loose in the front.

I'm pretty sure the rear suspension has settled by now. I've driven it probably ~100 miles.

[john walker's workshop]

put your leg against the side of the bumper and push the car side to side. watch the bottom of the tire while you're doing it. lots of movement means weak sidewalls and can certainly be your problem. good tires hardly move at all. front rattle can be a loose strut insert retaining nut.