Originally Posted By: ARCOgraphite
I think there may be a disconnect here, but to the original question on revs per mile - take a tape measure and measure the drive wheel circumference directly. There are no other related factor other than possibly a minor tyre circumference growth factor at speed. That tyre must travel its circumference once every revolution, Period. NO GPS, NO speedo error. Kudos to colt45ws for getting to the heart of the issue rather than talking around its "circumference".
Arco,
Unfortunately, that isn't how tires work. It turns out that if you measure the circumference of a NEW tire, then multply that by 0.97, you get the rolling circumference. If you want the rolling diameter, you divide that by pi (3.14159).
I've back calculated this, and that particular diameter happens to be the diameter of the belt. I've theorized that the tire is acting like a tank track, with the belts acting like the links of the track - and that is how I envision that.
- And, no, you can't measure the rolling radius by measuring from the ground to the center of the axle. That is called the "Static Loaded Radius", and while that has a direct bearing on the ride height of the vehicle, it doesn't in any way correlate to the rolling diameter.
Short version: You can NOT directly measure the rolling circumference or the rolling diameter. The only way to get an actual measurement is to mark the sidewall of the tire near the tread, then mark where that contacts the ground, then roll the tire one revolution, and make another mark on the ground, then measure betwen the marks.
BTW, the way the company I work for does revs/mile is to calculate it based on the overall diameter. It's not exact, but it is close enough.
I think there may be a disconnect here, but to the original question on revs per mile - take a tape measure and measure the drive wheel circumference directly. There are no other related factor other than possibly a minor tyre circumference growth factor at speed. That tyre must travel its circumference once every revolution, Period. NO GPS, NO speedo error. Kudos to colt45ws for getting to the heart of the issue rather than talking around its "circumference".
Arco,
Unfortunately, that isn't how tires work. It turns out that if you measure the circumference of a NEW tire, then multply that by 0.97, you get the rolling circumference. If you want the rolling diameter, you divide that by pi (3.14159).
I've back calculated this, and that particular diameter happens to be the diameter of the belt. I've theorized that the tire is acting like a tank track, with the belts acting like the links of the track - and that is how I envision that.
- And, no, you can't measure the rolling radius by measuring from the ground to the center of the axle. That is called the "Static Loaded Radius", and while that has a direct bearing on the ride height of the vehicle, it doesn't in any way correlate to the rolling diameter.
Short version: You can NOT directly measure the rolling circumference or the rolling diameter. The only way to get an actual measurement is to mark the sidewall of the tire near the tread, then mark where that contacts the ground, then roll the tire one revolution, and make another mark on the ground, then measure betwen the marks.
BTW, the way the company I work for does revs/mile is to calculate it based on the overall diameter. It's not exact, but it is close enough.