Q – I have a vintage Turbo and the tires are shaking. I think I need a tire balance but I do not want the weights to show if that is possible. What do you suggest? Mark
A – There are a number of factors that affect a smooth feel from your tires and wheel. First, are the wheels true side to side and are they round? Second, do the tires pass the same test? While a bent tire or wheel can be perfectly balanced, the car will still shake.
Assuming that the every thing you can see looks good, then you can proceed to measure the balance. The two types of balance that affect shake are static and dynamic. Think of static as “up and down” imbalance. Up until the sixties, when tires were very narrow, this was correctable by using a bubble balancer, no electronics, no problem, just put an equal amount of weight on both sides of the wheel and you are set. Things have really changed (and now you know when I started working on cars.)
When the famous “Wide Oval” tires became popular a new consideration had to be made that involves “dynamic” imbalance. That is where side to side imbalance will also cause a shake or wobble. This is where hiding the weights can get tricky. With wide tires and wheels, if you simply find the point of static imbalance and put the weight essentially behind the spokes in the middle, you can still get shake.
On tires that need a lot of weight on opposite sides, inside and outside, hiding the weights may not work out to well. In that instance, the tire can be dismounted and rotated on the wheel and sometimes this helps. If you are as picky as me, it is worth the effort. If the tire needs weight in roughly the same spot inside and outside, you have a better chance of hiding the weight. In that instance, the machine can be “fooled” by programming in a narrower wheel and it generally tells you to put a heavier weight behind the spoke.
If you cannot hide the weight (and new Porsches do not have hidden weights) there are European chrome plated “Hershey bar” weights that look (and are) expensive. I have not been able to get the original weights from Porsche so these are a nice option.
How much weight does it take to feel a shake? Glad you asked (oh yeah, you didn’t ask). A tire imbalance of 15 grams can be felt at higher speeds. An imbalance of 20 grams can be felt at freeway speeds and an imbalance of 35 or 40 grams will annoy you almost all the time. Clearly the goal is 5 grams or less. –MC