Quote:
Originally posted by Zeke
Look. Bushings, bearings, steering bushings and u joints don't vibrate. They are all slaves to the big thing spinning with all the weight. Yes, you will notice more shimmys and shakes if you have other issues, but a car with perfect tires will hardly show up other worn out parts unless they are simply junk. Not so good shocks will work, a little bit of slop in the steering will feel fine and old wheel bearings that are not making any noise won't even come into the picture.
Add a bad set of tires and any or all of these things could appear and drive you crazy. Yes, again, you want good parts in yout car, but the tires are the only connection to the road and they tell the story.
I have posted this numerous times and have had many others chime in with very good thoughts. The first thing you do with a new tire is match it with the wheel; heavy spot on tire over light spot on wheel. The 2nd thing is to spin it up and put a runnout gauge on the tread. 1/16 runnout is 100lbs out-of-balance (depending on tire/rim size) at 60 MPH. The thing is, it gets worse as higher speeds whereas the weight stays the same. this is due to tire expansion and the OOR spot now being further from the rotation axis.
YOu must have absolutey round tires or you will have OOB tires at some speed, usually higher the rounder the tires are. Tires must be "run in" a bit before truing them with a tire truing machine. this si the same machine you hear about on Tire Rack when they shave your tread for racing (and making them round). You have never driven on good tires until you have drivnen on shaved and erfectly balanced tires. the steering wheel becomes like one in a small plane while in flight.
Well, on to balancing the perfectly round and run-in tire. It must be dynamically balanced on a computer to offsett weight descrepencies fom side to side ot the vertical centerline of the weight mass. This means you must accept weights on the outside bead as well as the inside or be able to calculate how to place them just inside the spokes as for outward as possible.
Finally, the tires must be trim balanced oin the car with a strobe. Once dialed in, they should not be oriented on the lugs differently and definately not rotated. The man who taught me all of this holds several patents in this feild and claims if the car is properly aligned and perfectly balanced, you don't need to rotate tires or even rebalance them as the wear down perfectly.
Using his method, I have gotten some incredible mileage out of tire on my Porsches not to mention a perfectly steady steering wheel I could write a note on at any speed as long as the road itself was smooth enough.
I got over 60,000 on some Potenzas on the '77 Targa and I have 30,000 on the Continentals that came on the Boxster ans they show no signs of needing replacement anytime this year and probably into next. You don't see numbers like that often, but I will concede my wife drives these cars more than I do. Still, some tires wear out due to improper installation no matter how gentle you are with them.
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Yes, but suspension systems are designed to decouple small vibrations, and can hence tolerate some tire variation without it showing up in the steering wheel. MB and Porsche don't trim balance on the car at the factory, and they don't shave tires either. But my wife's MB cruises beautifully at all speeds, and so does my SC.
A really decent balance can be achieved using a Hunter road force balancer. Most upscale dealerships have one. It places a 1000lb load on the tire during the balance, and computes weight placement to minimize effects of radial variation. It will also tell you if you have a sprung cord, a flat spot, or a bent wheel. If your suspension is marginal and you don't feel like replacing bushings, this is an easy alternative.