Tires and Wheels! Let the Fun Begin!

There is a lot of fun science that goes into wheels and tires, both for the street and racing. But today, we are just going to focus on one element: tire stretch.

Tire stretch is the ratio between wheel width and tire width. For example, if you put a 205mm wide tire on a 6.5" OEM wheel, it will look a lot like an old-school NASCAR wheel, with the tire bulging out past the rim.

If you put that same 205mm tire on an 8" wide wheel, it will be stretched such that the sidewalls are angled in towards the center of the wheel.

 

 

So why does this matter?

When the car goes into a corner, the part of the tire in contact with the road does not want to move. The car, however, has inertia and resists changing direction. As a result, the car (and by extension, the wheel) will shift until the sidewall of the tire stops this motion.

Take a look at the pictures below of a car with a wider tire on a narrow wheel. The tire has "shifted" on the rim to the point that the rim has actually become the farthest point out. It has shifted about 1.5 to 2 inches until the sidewall got tight enough to stop it.

 

 

Here is that same wheel, unloaded.

 

 

Now compare that to this car, which has a narrower tire fitted to a wider wheel. The tire is already "stretched" and thus can't move once introduced to the corner. The amount the sidewall is stretched is the same when going straight as it is in the corner. (Compare the front and back wheels, which are seeing different loads.)

 

 

What does all this mean? In short, more stretch equals more control and immediacy to the drive, while less stretch allows more tire flex and compliance.

If you're building a cruiser designed for comfortable, casual driving, a tire with less stretch will give more comfort and compliance to the road, leading to a smoother, softer ride.

If you're looking for a sporty feel, free of any "floaty" handling characteristics, then going with a pre-loaded stretched setup will be what you want. This reduces the time between a steering input and a response from the car.

How wide you can go, what tire you need, and what wheel/tire combo is the best is highly dependent on your car setup, race class, ride height, and driving style. If you need help making a decision, give us a call! We'd love to brainstorm with you on what would be ideal for your ride!

We are an official TireRack distributor and can get any tire you need. We can also mount, balance, and install your tires at our shop.