Wheel and Tire Tech 101 - Cuttin’ Corners

Inflation Pressures

Getting the most out of your tires.

To achieve maximum performance from your tires and the handling of your vehicle, it’s important that you have the tires properly inflated. Over-inflated tires have smaller “footprints” and produce less traction, but on the flipside, under-inflated tires have decreased durability and life.

Although both cases have their negative side effects, it’s important to remember that a minimal variance of 6 psi will significantly impair performance. In order for the tire to have optimum ground contact and to transfer power effectively, a vehicle’s tires must be properly inflated and aligned.

Furthermore, correct inflation pressures prove optimum comfort, performance, and longevity. To add to the importance of proper inflation, one must consider that a proper psi settings also stabilizes the vehicle’s structural rigidity. From the tire’s structure, traction, and responsiveness all of the way to handling, it’s very important to understand.

• Abnormal tire wear—center wear of tread
• Jumpy ride discomfort
• Vehicle stability decrease

• 6 psi under will weaken the tire’s internal structure and eventually lead to tire failure.
• Lower psi also create more tire deflection.
• Tread life can be diminished as much as 25 percent.
• Under-inflation will also cause irregularities in tire wear and provide extreme shoulder wear.
• Separation and cord break can happen due to heat buildup.
• Poor cornering
• Hydroplaning
• Standing wave phenomenon


• Because air expands as the temperature rises, inflation pressure increases after running.
• It’s best to check inflation pressure when the tire is cold.
• Special care is required for tire inspection of front-wheel-drive vehicles because the front wheels bear a heavier load.
• If a hot tire shows less than the recommended cold inflation pressure, then the tire is under-inflated. Inflate it to the recommended cold inflation pressure plus an additional 10 percent. As soon as the tire cools downs, recheck and set the pressure to the recommended level.

Tire Rotation

A change in position can make a big difference.

Using tires for a long period of time in the same positions will typically create more wear, especially on the front. The front tires wear quicker than the rear because they generate more use since they steer, brake and take the most of the load during cornering. For longer tire life, it’s necessary to perform tire position rotations periodically as recommended by the tire manufacturer, but tire rotations are usually recommended every 5,000 to 7,000 miles. Please note that tire rotation is not possible with certain applications such as staggered fitments.

• Prevention of uneven
tread wear.
• Extension of tire service life.
• Averaging of tire fatigue.

Tire Replacement

Triangular-shaped marks on the sidewall show the tread groove position of the tread wear indicators (TWI). The TWI represent 1.6 mm of remaining tread depth, at which time the tire should be replaced.

Arrow-shaped marks on the sidewall show the tread groove position of the “platform wear indicators.” This shows 50-percent of the wear of original tread depth, at which time it should no longer be used as a winter tire, but can be used as a normal tire.

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 tires 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.

6. Deflection
The measured difference between the tire’s free radius and the loaded radius when mounted on a rim which 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.

Raised Letters

10. Nominal Rim Diameter
This is measured as a linear distance between the bead seats which are taken at the widest point.

11. 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.

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