245/40R18 vs 255/40R19
255/40R19 is +5.1% away from 245/40R18 on rolling diameter, well outside the 3% substitution rule. Expect rubbing at full lock or under compression unless the arches have been modified, plus 16.7 mm of extra radius to house. Speedometer and odometer error at this magnitude is large enough to matter for warranty mileage and for anything measured from wheel speed. Treat this as a modification, not a substitution.
- Diameter change
- +5.11%
- +33.4 mm
- Ride height
- +16.7 mm
- half the diameter change
- Tread width
- +10 mm
- 255 mm section
- Speedo at 60
- 63.1
- true mph when the dial reads 60
Side by side
| Measure | 245/40R18 | 255/40R19 | Change |
|---|---|---|---|
| Overall diameter | 25.72″ | 27.03″ | +5.11% |
| Section width | 245 mm | 255 mm | +10 mm |
| Sidewall height | 98.0 mm | 102.0 mm | +4.0 mm |
| Rim diameter | 18″ | 19″ | +1″ |
| Revolutions / mile | 784 | 746 | −38 |
Questions about this swap
›Can I fit 255/40R19 instead of 245/40R18?
Only with care. The diameter differs by +5.1%, outside the 3% rule, so clearance and speedometer accuracy both need checking first.
›How much will my speedometer be out with 255/40R19 instead of 245/40R18?
By about 5.1%. At an indicated 60 mph you would actually be doing 63.1 mph, so the dial under-reads your true speed.
›Does fitting 255/40R19 change ride height from 245/40R18?
Yes, by roughly 16.7 mm. Rolling radius is half the diameter change, so the axle sits that much higher and you need the same amount of extra room above the tyre.
›Will my odometer read differently on 255/40R19 rather than 245/40R18?
It will read 5.1% low. Over 10,000 recorded miles that is about 511 miles of difference against the true distance travelled.
Want to try other sizes? Open the calculator.