315/40R18 vs 285/35R20 tire size comparison
Change either size and everything below updates.
Start from your car make, model, year
That size does not exist: the overall diameter must be larger than the rim. The results below still show the last valid pair.
Width in mm · aspect = sidewall height as a % of width · rim in inches
Flotation (LT) sizes, all in inches: overall diameter × section width, then rim
315/40R18: 27.92″ (709 mm) tall, 12.40″ (315 mm) wide, sidewall 4.96″ (126 mm) — 722 revolutions per mile.
Well within tolerance
−0.24% diameterThe overall diameter changes by less than 1.5%, so speedometer error is negligible and ride height barely moves.
- Needs 20″ wheels: this tire does not fit your 18″ rims.
- 30 mm narrower: check the tire is approved for your rim width.
Check what fits your car Factory tire sizes for every make, model and year.
Tires in 285/35R20
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| Measurement | 315/40R18 | 285/35R20 | Diff | % |
|---|---|---|---|---|
| Overall diameter | 27.92″709 mm | 27.85″708 mm | −0.07″ | −0.2% |
| Section width | 315.0 mm | 285.0 mm | −30.0 mm | −9.5% |
| Sidewall height | 126.0 mm | 99.8 mm | −26.3 mm | −20.8% |
| Rim diameter | 18″ | 20″ | +2″ | +11.1% |
| Circumference | 87.72″2228 mm | 87.51″2223 mm | −0.21″ | −0.2% |
| Revolutions per mileturns per distance; drives the odometer | 722449 /km | 724450 /km | +2 | +0.2% |
| Ride height change | — | — | −0.03″ −0.8 mm | |
Speedometer reading
Overlay
Plus sizing: 315/40R18 on smaller or bigger wheels
Sizes fitted to cars that keep the overall diameter within 3% of 315/40R18 on a rim one inch smaller or up to two inches bigger, closest first.
How to use the tire size calculator
Put your current tire size — width, aspect ratio and rim diameter — into the first form, then your desired size into the second. You’ll get the difference between the new and the old size, plus the speedometer reading difference and your actual speed on the new set. Both metric and flotation (LT inch) sizes are supported.
The calculator helps you decide whether a set of tires and wheels will fit your car. To compare tires by brand and model instead, use our tire comparison tool; to look up factory sizes, browse by car make.
Changing wheels too? The wheel offset calculator shows how far a new wheel width and offset move the tire toward the suspension and the fender.
Reading a tire size
- 225
- Section width in millimetres
- 45
- Aspect ratio — sidewall height as a % of width
- R
- Radial construction
- 17
- Rim diameter in inches