So many misconceptions, so little time. *sigh*
The first law of automotive vibration says that
ALL vibrations on cars are caused by things that are spinning. DOH! (Ga-aw-lee, Sargent Carter, I never woulda guessed it!)
Roadforce balancer. Sounds really high tech, right? Well it's not. It's a tire balancer that has a roadforce measuring attachment on it, and programming for the computer to use it. The new machine from Hunter now has a drum for the tire to roll against at slow speed. The tech moves it up against the tire and locks it in place and turns on the machine which then measures the resistance of the slow roll it induces to detect any hard spots in the tire.
If there are any, the tire must be discarded! It will
never be alright and there is no way to balance out the hard spot. This is a relatively rare condition, especially with these high dollar tires.
Out-of-round tire/wheel assembly. Ususally this is felt at a certain speed, 55-65 mph on most passenger car tires, provided they're properly balanced. Before it, smooth as glass, after it, still nothing. But at that certain speed, a steady continuous vibration (with
one out-of-round tire). I've never had the occasion to see this in a low profile tire, but I suppose the speed for this type could be higher.
Vectoring is where the high spot of the tire is matched (aka, vectored) to the low spot of the rim. (If a tire or rim is out of specs, they must be replaced.) The new Hunter machine tells the tech where the high and low spots are, but he must dismount and remount the tire to match them up. More work. I always used to just find the low spot of the rim
before I put the tire on and used the blue dot indication for the high spot of the tire (a DOT requirement) to vector mount. If your tires are not vectored properly, a R/F balancer
will fix your problem, as well as check for a bad tire.
Harmonic vibration. This happens when something vibrates, perhaps not noticeably, at a frequency that causes some other component, like a steering wheel or column to vibrate noticeably, like a tuning fork. The steering wheel has a harmonic "sound", a specific frequency, that if slighly induced by a matching frequency, like from a tire or the engine, will cause it to "wake up" and vibrate. Adjusting the rack pre-load would change it's frequency as well, but it still would have to be something else (that's spinning) causing the "seed" vibration. That this vibration you have "comes and goes" tells me you have two things, each vibrating a little that converge at times adding up to a lot of vibration that comes and goes. This is called a
harmonic convergence.
In the final analysis it sounds to me like you're getting a run-around by a tire shop that either doesn't know what it's doing or is trying to blow you off rather than fix their mistake.
Before you got the tires, no vibrations, right? Then right after you get the tires, this condition you describe all of the sudden appears and somebody's saying what?- the rack is bad? I'm sorry, why do new tires expose a bad rack? Go back to where you bought the tires and demand satisfaction. I cut my mechanics teeth on front-end alignments and tires and I have
never seen alignments or steering components
cause vibrations of any kind. Vibrations are
always caused by round things that spin fast. Duh! Also, a tire balancer that is off it's calibration
won't balance the tire, if the guy using it is using it properly. He should put the weights on and spin it again to check it. If the machine is off, it'll tell him that tire needs
more weights, ad infinitum, and he'll know something's wrong with the machine. My guess is the tires aren't mounted right, given they've checked the balance and say it's right. Out-of-round wheel assemblies sounds likely.
Anyway the tires are the problem! And don't go to that dealership that says it doesn't warrantee for speeds in excess of the speed limit. A statement like that is just setting you up so they don't have to fix your problem. First off, you don't have to exceed the speed limit to properly install and balance tires designed to go 148 mph. If they vibrate at 80 or higher, they're not right at 65 either. You might not notice it on the car but the equipment they use to do the job ought to. Balancers go to 1/4 oz, some even measure tenths. It takes a lot more than that to shake the tire at 80. Mine goes 120 and is smooth as a baby's ass and I got mine installed at Firestone on a dinosaur of a tire balancer (not a roadforce machine) with the guy eye-balling the placement of the weights!
Secondly, if he says something like that to a Marauder owner, you don't want to do business with him in the first place. Ask him if the initials F.O. mean anything to him.
