Compare two sizes › Tire sizes › 31x10.50R15
31x10.50R15: 787.4 mm (31.00 in) tall
A 31x10.50R15 tire is 31 in (787.4 mm) tall and 10.50 in (266.7 mm) wide on a 15-inch rim, which leaves a 203.20 mm sidewall. Flotation codes print the height instead of an aspect ratio; worked backwards, the sidewall is 76.2 % of the width. It turns 650.6 times per mile. Below: every dimension, a drawing to scale, and the 21 metric sizes within ±3 % of its diameter on 14, 15 and 16 in rims, with what the speedometer would read on each.
Every dimension
| Measure | mm | inches |
|---|---|---|
| Section widthsidewall to sidewall, as printed | 266.7 mm | 10.50 in |
| Sidewall height(overall − rim) ÷ 2 | 203.20 mm | 8.00 in |
| Rim diameterbead seat, as printed | 381.0 mm | 15 in |
| Overall diameterrim + two sidewalls | 787.4 mm | 31.00 in |
| Circumferenceπ × diameter | 2,473.7 mm | 97.39 in |
| Revolutions per mileunloaded, geometric | 650.6 | |
| Revolutions per kmunloaded, geometric | 404.3 | |
Nominal figures for a new, unloaded tire. Under a car's weight it squashes and turns roughly 2–3 % more often per mile; the maker's datasheet figure is measured and wins.
What 31x10.50R15 means
- 31
- Overall diameter in inches (787.4 mm): the height of the new tire, mounted and inflated. A metric code never prints this; here it is the first number.
- 10.50
- Section width in inches (266.7 mm), sidewall to sidewall, measured on the rim width the tire standard lists for that size.
- R
- Radial construction (not "radius").
- 15
- Rim diameter in inches (381.0 mm): the wheel this tire mounts on. The sidewall is what is left: (31 − 15) ÷ 2 = 8.0 in.
- after
- Flotation sizes are light-truck tires, usually written with LT (31x10.50R15LT) and followed by a load index and speed symbol, often with a load range letter such as C, D or E. Type yours into the calculator below to decode it.
Drawn to scale
Closest swap
On the same rim, 255/80R15 is nearest in diameter: +0.2 %. Going up to a 16-inch rim, 255/75R16 is nearest: +0.2 %, so the speedometer reads −0.2 %; at an indicated 60 mph you would do 60.1 mph.
Metric sizes within ±3 % of 31x10.50R15
A flotation size has no exact metric twin, so here are the metric sizes that come closest. The grid is laid out around 265 mm, the metric width nearest 31x10.50R15's 266.7 mm section. Every size in the grid (widths 245–285 mm in 10 mm steps, aspect ratios 25–80 in steps of 5) whose overall diameter is within ±3 % of 787.4 mm. ±3 % is a rule of thumb many tire fitters use, not a law. The “really doing” column assumes the speedometer was right on 31x10.50R15: it is your true speed when the speedometer shows 60 mph (and, below it, 100 km/h). Not every size here is made by every maker, and a size being close in diameter says nothing about clearance, load rating or what the car maker approves. Tap a size to load it into the calculator.
Same 15-inch rim 8
| Size | Diameter | vs 31x10.50R15 | Really doing |
|---|---|---|---|
| 255/80R15 | 789.0 mm31.06 in | +0.2 %+1.6 mm | 60.1 mph100.2 km/h |
| 275/75R15 | 793.5 mm31.24 in | +0.8 %+6.1 mm | 60.5 mph100.8 km/h |
| 285/70R15 | 780.0 mm30.71 in | −0.9 %−7.4 mm | 59.4 mph99.1 km/h |
| 265/75R15 | 778.5 mm30.65 in | −1.1 %−8.9 mm | 59.3 mph98.9 km/h |
| 245/80R15 | 773.0 mm30.43 in | −1.8 %−14.4 mm | 58.9 mph98.2 km/h |
| 265/80R15 | 805.0 mm31.69 in | +2.2 %+17.6 mm | 61.3 mph102.2 km/h |
| 285/75R15 | 808.5 mm31.83 in | +2.7 %+21.1 mm | 61.6 mph102.7 km/h |
| 275/70R15 | 766.0 mm30.16 in | −2.7 %−21.4 mm | 58.4 mph97.3 km/h |
One inch smaller: 14-inch rim 4
Plus one: 16-inch rim 9
| Size | Diameter | vs 31x10.50R15 | Really doing |
|---|---|---|---|
| 255/75R16 | 788.9 mm31.06 in | +0.2 %+1.5 mm | 60.1 mph100.2 km/h |
| 275/70R16 | 791.4 mm31.16 in | +0.5 %+4.0 mm | 60.3 mph100.5 km/h |
| 265/70R16 | 777.4 mm30.61 in | −1.3 %−10.0 mm | 59.2 mph98.7 km/h |
| 285/65R16 | 776.9 mm30.59 in | −1.3 %−10.5 mm | 59.2 mph98.7 km/h |
| 245/80R16 | 798.4 mm31.43 in | +1.4 %+11.0 mm | 60.8 mph101.4 km/h |
| 245/75R16 | 773.9 mm30.47 in | −1.7 %−13.5 mm | 59.0 mph98.3 km/h |
| 265/75R16 | 803.9 mm31.65 in | +2.1 %+16.5 mm | 61.3 mph102.1 km/h |
| 285/70R16 | 805.4 mm31.71 in | +2.3 %+18.0 mm | 61.4 mph102.3 km/h |
| 275/65R16 | 763.9 mm30.07 in | −3.0 %−23.5 mm | 58.2 mph97.0 km/h |
Compare 31x10.50R15 with any size
Working it out…
Speedometer error
The speedometer counts wheel turns and assumes the current tire.
| Speedometer shows | You are really doing | Difference |
|---|
Both to scale
What the codes say
Load index and speed rating tables (ISO 4000-1 / ETRTO)
Side by side
| Measure | Current | New | Difference |
|---|
The sums for 31x10.50R15
diameter = 31 × 25.4 = 787.4 mm sidewall = (787.4 − 15 × 25.4) ÷ 2 = 203.20 mm width = 10.50 × 25.4 = 266.7 mm circumference = π × 787.4 = 2,473.7 mm revs per mile = 1,609,344 ÷ 2,473.7 = 650.6 revs per km = 1,000,000 ÷ 2,473.7 = 404.3
Speedometer error is the ratio of the two diameters: true speed = shown speed × new diameter ÷ 31x10.50R15 diameter. Fitting 255/75R16 (788.9 mm) in place of 31x10.50R15, an indicated 100 km/h is really 100.2 km/h, and the odometer is off by the same proportion.
Why this size has a page
We found no public list of the most-sold flotation sizes that we are allowed to reuse either, so the four flotation pages follow a stated rule: overall heights of 31, 33 and 35 in, one section width per height (10.50 in for 31, 12.50 in for 33, 12.50 in for 35), on 15- and 17-inch rims, keeping each combination whose sidewall, (height − rim) ÷ 2, is 8 to 9 in. That drops 31x10.50R17 (7 in sidewall) and 35x12.50R15 (10 in sidewall). 31x10.50R15 has a 8.0 in sidewall. All size pages and their rules.
What this page cannot tell you
- Whether a size is right for your car. Clearance to struts, arches and brake calipers, wheel width and offset, steering lock and suspension travel decide that, and none of them is in the size code. Start from the sizes the car maker lists (door-jamb placard, handbook, registration papers), then check the physical clearance.
- Load capacity. An alternative size must carry at least the load index and speed rating the car maker specifies; a narrower or lower-profile tire often has a lower load index in the same construction, so check the XL / reinforced version.
- Exact real-world size. Makers build to a tolerance of a few percent, and a new tire with 8 mm of tread is about 13 mm taller than one worn to 1.6 mm.
- LT or passenger construction. The same size is made as a passenger (P-metric or Euro-metric) tire and as a light-truck (LT) tire. The dimensions on this page are the same for both, but the load an LT tire carries is quoted at a higher inflation pressure, and swapping one construction for the other changes the pressure you need; the tire maker's load and inflation table decides it, not the size.
- Your speedometer's own error. Under UN ECE Regulation 39 a speedometer must never read below true speed and may read up to 10 % + 4 km/h high, so most cars already over-read a little. A taller tire eats into that margin.
Other sizes
- 33x12.50R15 838 mm
- 33x12.50R17 838 mm
- 35x12.50R17 889 mm