Tire size comparison calculator
Enter your current size and the size you are considering to see the difference in diameter, width and sidewall, and your true speed when the speedometer shows 60 mph. For example, going from 225/65R17 to 235/65R17 makes the tire 1.79% taller, so the speedometer shows 60 mph at 61.1 mph.
| 225/65R17 | 235/65R17 | Difference | |
|---|---|---|---|
| Overall diameter | 28.52 in | 29.03 in | +0.51 in (+1.79%) |
| Section width | 225 mm | 235 mm | +10 mm |
| Sidewall height | 5.76 in | 6.01 in | +0.26 in |
| Wheel diameter | 17 in | 17 in | same wheel |
| Revolutions per mile | 707 | 695 | -12 |
Speedometer with the new tires
The speedometer is set for the current size. With the new size, each box shows what the speedometer reads and your true speed underneath.
Ride height changes by about 0.26 in (taller). Check the load index and speed rating of the new tire meet the ones on your door placard.
What the 3% guideline means
Your speedometer, odometer, ABS and stability control are set up for the original tire diameter. A size within about 3% of it keeps those readings close, which is why tire shops use 3% as a rule of thumb. It is a guideline, not a law or a standard, and it says nothing about whether the tire clears your suspension and bodywork. The new tire also needs a load index and speed rating at least as high as the ones on your door placard.
Not sure what your size means? Decode a tire size → or check the load index chart and speed rating chart.
Keep the new tires at the right pressure
The pressure to run is on the placard in the driver's door jamb, not the maximum printed on the tire. Check it cold, once a month.
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Frequently asked
How much bigger can I go on tire size?
Tire shops commonly use 3% of the original overall diameter as a guideline. Past that, the speedometer and odometer read noticeably off and the tire may rub. The load index and speed rating should stay at least as high as the original.
Do bigger tires change the speedometer?
Yes. A taller tire covers more ground per turn, so the car goes faster than the speedometer shows. With a tire 3% taller, the speedometer shows 60 mph at about 61.8 mph.
Is 235/65R17 the same as 225/65R17?
No. 235/65R17 is 10 mm wider and about 0.51 inches taller (1.79% in diameter). It fits the same 17-inch wheel and is within the common 3% guideline, but check clearance and the load rating.
How is overall tire diameter calculated?
Sidewall height is the width times the aspect ratio. Overall diameter is the wheel diameter plus two sidewalls. For 225/65R17: 225 x 0.65 = 146 mm sidewall, so 17 in + 2 x 5.76 in = 28.5 in.