Shaky steering

[Team996]

A week ago I was driving down to San Diego from the Valley when I blew a rear tire 230 miles away from my destination. AAA towed me the rest of the way for free to Big O Tires in Carlsbad, where I had fortunately already ordered 2 rear Fuzion replacements rom TireRack. Fairly seamless, and I'm lucky I noticed the severity of the tread wear in time to buy the tires in the nick of time.

One thing that remains a nagging annoyance to my P-driving enjoyment is this untolerable shakiness in general, but is especially pronounced between 68 and 75 mph. It's much better around 90 mph, but doesn't solve my problem. When I took it into Hoehn, my service writer told me the shakiness was a result of improper balancing and not alignment issues. So he advised me o replace the front tires before getting them rebalanced.

My questions are:

A. Has anyone experienced this ridiculous shakiness?

B. What is the difference between balance and alignment?

C. Does the service writer's diagnosis sound correct?

D. Does it really make more sense to balance once I replace the front tires?

Thanks, Porschefans.

[White987S]

Rebalance the tires and make sure you have 4 matching (brand & type) tires.

[vette67]

I agree with White987S but Ill go even further. The 996 is the most tire-sensitive car Ive ever driven. Its really amazing how things like the difference in a couple of pounds of air pressure between your tires will affect your ride. Or how about this: I had a real slow, annoying leak in my back driver side tire ever since I bought the car. I had it to the stealer twice and to a local tire shop and nobody could seem to fix it. (doh!) Finally I just put a can of fix-a-flat in it. Leak stopped but I swear I can feel a difference in the ride. A vibration at speed. Sucks.

As far as alignment vs. balance, that easy. Take a close look at your front tires. An alignment problem will show up as uneven treadwear... either on the inside or the outside edges of your tire... but only on one edge or the other. If you have too little air in the tire you will see more wear on BOTH outside edges of your tire. Too much air pressure and the middle of your treads will be worn lower than your edges. Alignment usually (and probably some racers will correct me on this if Im wrong) doesnt create vibration in your ride. On a newer car like the 996, tire balance is usually the problem, or uneven tire pressure or both. BTW, dont pay extra for "high-speed balancing".. its usually a waste of money. On older cars you need to inspect your suspension to make sure you havent worn out a spacer or damaged a tie-rod end, etc. Suspension problems usually show up as alignment issues and less often are vibration issues, but it can happen.

If you want the sweetest ride possible, go ahead and get 4 new tires instead of 2. You will also get a quieter ride with all new, top-quality tires. You will get them balanced at the same time of course. If you noticed the uneven tire wear on your existing front tires like I mentioned, get your car aligned at a top speed shop or at the stealer. The local tire shops (at least in Atlanta) arent capable of doing a front-end alignment on a 996.

Edited February 17, 2008 by vette67

[2Fast996]

If all diagnostics are within spec you may consider a "force balance" (I believe is what it it called) or perhaps load balance. Not real expensive however, not all shops can perform this test and the tires must be warm before testing. I once had a 7 series BMW with a shake in the steering that would not respond to any corrective measures. The aforementioned balance demonstrated a bad belt in the tire. New front tires promptly fixed the problem.