Tire Size & Vehicle Performance

Tires are a critical component of vehicle performance. Rim diameter, sidewall height, overall height, and tread pattern can greatly affect how a tire, and ultimately the vehicle itself, performs under a variety of terrain and conditions. At Northwoods Performance, we are driven to improve the trail capability of smaller SUVs, we will concentrate this discussion on increasing the tire size of smaller SUVs and the possible effects on mileage and performance.

Many small SUVs can increase tire size one inch without serious adverse effects to mileage and performance, or exhibiting issues with severe tire rubbing. The use of larger tires allows a greater tire selection of all season or off road tread patterns, adds a more aggressive look to the vehicle, and most importantly provide an increase in true vehicle ground clearance for off road and trail performance. And for many of us, ‘off road performance’ can mean enough ground clearance and an aggressive winter tire so we can clear the snow berms to get to the ski hill on a pow day!

Northwoods Performance has tested many tires and sizes. One of our RAV4 test mules originally had stock 225/65 R17 tires. Overall tire height was 28.5”. We installed 245/65 R17 tires with a total height of 29.5”. This provided an additional half inch of ground clearance above the 1-1/2” the Northwoods Performance lift kit had provided, for a total ground clearance increase of 2”. The aggressive all-terrain tread pattern provided dramatically improved off road and winter performance, while the stiffer sidewall of the tire reduced off road punctures and greatly improved on road performance for more spirited driving. Matched to our Northwoods Performance lift and engineered springs, the overall performance gain is dramatic.

With over 2000 miles of testing of the above setup on our RAV4 mule, we noted the overall gas mileage has decreased an average of .7 mpg. Performance losses in acceleration and increased braking have not been significantly noticeable. Of course individual driving style and type will change these averages and apparent changes to performance. An increase in tire size may be right for your driving style and adventures. Please see the table below to compare your stock tire sizes to possible upgrade sizes for some of the common small SUV tires.

Tire sizes as noted on the sidewall usually look something like 225/65 R17. Here's how to read that number:

  • 225 is the tire width in millimeters
  • 65 is the aspect ratio, such that the sidewall height is 65% of the width, or 146 mm in this case
  • R stands for radial, and the 17 is the tire diameter in inches (just to make things confusing)

Tire Size Tire Width Tire Height
225/65 R17 8.8" 28.5"
225/70 R17 8.8" 29.4"
225/75 R17 8.8" 30.29"
235/65 R17 9.2" 29.0"
235/70 R17 9.2" 30.0"
235/75 R17 9.2" 30.9"
245/55 R17 9.7" 27.6"
245/65 R17 9.7" 29.5"
245/70 R17 9.7" 30.5"
255/65 R17 10.0" 30.0"
265/65 R17 10.4" 30.5"
245/60 R18 9.7" 29.5"
255/55 R18 10.0" 29.0"
255/65 R18 10.0" 31.0"
265/60 R18 10.4" 30.5"
265/65 R18 10.4" 31.5"

Tire Diameter Calculator