Bay tool
Tire upsize calculator
Enter the tire on the truck today and the size you are considering. The comparison uses section width in millimeters, aspect ratio, and wheel diameter in inches. The default pair is 265/70R17 against 285/70R17.
What the numbers mean
Sidewall height is the section width multiplied by the aspect ratio. Overall diameter adds that sidewall twice, top and bottom, to the wheel diameter converted from inches to millimeters. Circumference is that diameter times pi, and revolutions per mile follow from there. If the new tire is taller, each revolution covers more ground, so an indicated 60 mph is actually faster than 60. The percent line is the change in diameter divided by the original diameter.
A change larger than 3 percent is marked because that is a common screening threshold for speedometer error and clearance risk. It is a rule of thumb, explained in the plus-sizing guide. It does not know your fenders, your offset, or your brake calipers. Read the size markings with the tire size guide before you type them, and check wheel fitment if the wheel is changing along with the tire.
These figures are estimates for metric sizes only. They are not a fitment approval. Confirm load index, speed rating, wheel width, offset, and physical clearance before you buy or mount anything.
Questions
Why does a wider tire on the same wheel show a warning?
If the aspect ratio stays high, extra width adds sidewall height and the tire grows. Width alone is not a same-height change. Drop the aspect, or move to a larger wheel with a shorter sidewall, if you are trying to plus-size rather than lift the truck.
Can I enter a flotation size such as 33x12.50R17?
Not directly. Those numbers are already inches of diameter and width. This calculator expects metric width, aspect, and rim. Convert only if you know the metric equivalent, and treat the result as approximate.
Does the tool account for load range or tread depth?
No. It is geometry only. A new tire with deep tread is slightly taller than the same size worn down, and an LT tire can be built on a different measuring rim. Use the result to compare sizes, then read the actual tire you plan to mount.