Tire Calculator

Vehicle Specific Tire Charts

Basic Rules for Changing Tire Width:
  • Wider is better on a surface that doesn’t move (Dry Roads)
  • Narrower is better on loose surfaces over roads (Snow or Water)

Weight dispersion:

The entire weight of your vehicle rests on your tires.  When you spread this weight out over more surface area, it reduces the amount of downward force on any given amount of your driving area (every square inch (or cm) has less weight acting on it.    Conversely, if you have narrower tires, you have more weight for the area, forcing down on the ground.

This is where narrower tires help on snowy roads.  The idea is to dig down to a usable surface, and that is where gravity comes in.   This works against you when there isn’t a usable surface underneath (like sand dunes) where you’re just going to dig yourself a hole.

Friction:

On a surface that doesn’t move, surface area changes do not affect how much force reaches the road.  When you have more surface area, more friction is present, and thus, more traction reaching the road.

What do larger rims do for a car?

The sidewall of a tire flexes left and right as you turn the wheel.  Increasing the amount of wheel diameter that is metal instead of rubber improves(reduces) response time.  This is why sport cars have less rubber sidewall exposed than normal passenger vehicles. 

More rubber on the sidewall gives smoother response (not as jerky) when turning the wheel, and also provides more room for the wheel to conform to terrain on uneven surfaces (woods trails, offroading).

How does changing the height of a tire affect handling?

One of the factors in changing diameter is that the sidewall will be affected (as above).  It also can increase/decrease ground clearance.  This is typically done in addition to raising or lowering a vehicle, as suspension has more effect on ride height than changing tire size.  

What problems can I face with changing tire height?

Larger tires will reduce the amount of leverage and torque that actually makes it to the road. 

The largest concern of changing tire diameter is how it will affect circumference and rotations per mile/km, which affects how accurate your speedometer and Odometer readings are. You could also do this to correct a faulty speedometer, but isn’t typically done.

The most common problems that people face with “too big” or “too small” tires are the vehicle bottoming out (scraping the road) or tires rubbing inside of the wheel wells.