WHEEL & TIRE DYNAMICS
Understanding the relationship between rims and rubber
To better appreciate the dynamic relationship between a wheel and a tire you have to first understand the mechanical characteristics of their unison. Let’s face it, there’s no other single component more important than your rims and tires since this is what everything else rests on. So to get a better education on this versatile subject we spoke with Mark Chung of Yokohama Tires. At the heart of the conversation was a detailed breakdown of wheel and tire dynamics. We’ve also created a detailed outline of the measurements that you should better understand as both a consumer and enthusiast of aftermarket wheels.
1. OVERALL WIDTH
This defines the overall width of a tire, which is measured from the inner to the outer sidewall. If your tire has a lip bead (or protective rib or raised lettering) then this is included in the measurement.
2. SECTION WIDTH
This is the measurement of the tire’s width from sidewall to sidewall (not including the protective ribs). It’s important that this measurement be taken when the tires are properly mounted and inflated with no load on the tires.
3. FREE RADIUS
This is the distance from the wheel’s axle center to the outer tread surface of the unloaded and properly inflated tire.
4. RIM WIDTH
This is the linear distance between the outer and inner rim flanges on which the tire bead rests.
5. STATIC LOAD RADIUS
This measurement is measured with load on the tire and is taken from the axle centerline to the treat contact area or patch.
The measured difference between the tire’s free radius and the loaded radius when mounted on a rim that is inflated to test pressure and under a prescribed or predetermined load.
7. TREAD WIDTH
The distance from the outer edge to the inner edge of the tread.
8. TREAD RADIUS
The design curvature or contour of the tread profile.
9. SECTION HEIGHT
This is measured off of the vertical distance between the tire’s bead seat and outer tread surface when properly mounted and inflated with no load on tire.
10. RAISED LETTERS 11. NOMINAL RIM DIAMETER
This is measured as a linear distance between the bead seats, which are taken at the widest point.
12. OVERALL DIAMETER
You probably don’t need help understanding this but it’s the distance from the tread surfaces at its widest point. The tire should be aired to the prescribed air pressure and under no load.