Tyre Size Comparison
Put two tyre sizes side by side and see exactly what changes: overall diameter, speedometer error, ride height, width and sidewall. Drawn to true scale, with a plain-English verdict. No signup.
New to tyre sizes? How to read yours
Find it printed on the tyre sidewall, or on the sticker inside the driver’s door jamb. Type it in any style: 225/45R17, 225 45 17 or 2254517 all work.
Size finder: keep your speedo accurate on a different wheel size
Pick the wheel size you want. We show the tyre at each width that stays closest to your current overall diameter. Tap one to compare it.
Figures are nominal (a new tyre on its measuring rim). Real tyres vary by brand, wear, pressure and load, usually by about 1%.
- Load index and speed rating must meet or beat the car’s original. Check the door-jamb sticker.
- Make sure the tyre suits your wheel width. Use the Tyre Stretch Calculator to check.
- If your car is already off factory size, compare against the factory size too. Changes add up, and the 3% guideline is measured from stock.
- Check how far the wheel will sit out with the ET / Offset calculator, then test for rubbing at full steering lock and over bumps.
- Confirm the size actually exists in the brand and model you want. The finder works from geometry, not a catalogue.
Quick answers
What is the 3% rule?
A common guideline says a replacement tyre’s overall diameter should stay within about 3% of the factory size. Beyond that, the speedometer, odometer and wheel-speed sensors used by ABS and traction control start to disagree with reality.
Trucks and SUVs often tolerate more, especially with a lift, and a tuner or scan tool can recalibrate the speedometer if you go outside it.
Will a wider tyre change my speedometer?
Only if its overall diameter changes. But watch the profile number: the same profile on a wider tyre is also taller, because sidewall height is a percentage of width. A 245/45R17 is about 2.8% taller than a 225/45R17.
How do I stay the same diameter when I go up a wheel size?
Go up one inch in wheel diameter and drop the profile by roughly 5 points, for example 225/45R17 to 235/40R18. The size finder above does the maths for any wheel size and width.
Why does the car sit higher with a bigger tyre?
The axle sits one tyre radius above the ground, so ride height changes by half the diameter difference. The same amount is lost from the gap between the top of the tyre and the fender, because the suspension has not moved.
How accurate is this?
The maths is exact for nominal sizes. Real tyres differ slightly by brand, wear, inflation pressure and load, and the actual width changes with wheel width (roughly 5 mm for every half inch of rim width). Treat the results as a very good guide, then confirm with a test fit.
Tyre size comparisons are calculated from nominal dimensions and are for guidance only. Always confirm fitment, load index, speed rating and clearance with a qualified tyre fitter before buying.