posted January 05, 2003 10:18 PM
Dapper (may I use your first name?),
We are all familiar with balancing a tire. This is a mass distribution problem and an improperly balanced tire could result in a vibration. But there is another source of tire vibrations related to the stiffnes of the tire.
If you look at a tire on the ground, you will notice that a portion of the circumference of the tire is flat (the part in contact with the ground). If you take a measurement of the axle's height above the ground as you slowly roll the tire around its circumference, you will find the height varies very slightly. (We are talking thousands of an inch). This is due to a variation in the stiffness of the tire. Some people think this is an indication of "roundness" or runout and try to measure this on an unloaded tire. But it is related to loaded runout, which is only loosely connected to unloaded runout. We call this Uniformity or Force Variation.
There are machines available to measure this. The best machines are multi-million dollar, research lab machines, which are useful to the tire manufacturers (and they all have them) and some vehicle manufacturers.
The next level down are production level machines which are used by tire manufacturers to measure uniformity as part of the production inspection process. This machines are on the order of 3/4 million dollars each and tire manufacturers will have many in every factory. It is not uncommon for some lines of tires to be 100% measured.
The lowest level is relatively new and I know of only one machine: Hunter GSP9700. It's still expensive (about $10,000) but that makes it within reach of the average tire store. You can read about this machine at:
A word of caution when you visit this site: These folks are trying to sell machines so they overstate its capabilities and understate its shortcomings.
The causes of force variation are complex and from outward appearances, you can not tell a high force tire from a low force tire.
EXCEPT: In the case of tires with substantial wear (as discussed in the topic you referenced), you might be able to detect a high force tire by looking at the worn tread pattern. If it has isolated areas of high wear, this tire probably has high forces. I should point out, that 1) even tires with even wear can have high forces, and 2) even tires with funny wear patterns might not have detectable vibrations.
Hope this helps.