Compare two sizes › Tire sizes › 185/65R15
185/65R15: 621.5 mm (24.47 in) tall
A 185/65R15 tire is 185 mm wide with a 120.25 mm sidewall on a 15-inch rim. It turns 824.2 times per mile. Below: every dimension, a drawing to scale, and the 29 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 | 185.0 mm | 7.28 in |
| Sidewall height65 % of the width | 120.25 mm | 4.73 in |
| Rim diameterbead seat, as printed | 381.0 mm | 15 in |
| Overall diameterrim + two sidewalls | 621.5 mm | 24.47 in |
| Circumferenceπ × diameter | 1,952.5 mm | 76.87 in |
| Revolutions per mileunloaded, geometric | 824.2 | |
| Revolutions per kmunloaded, geometric | 512.2 | |
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 185/65R15 means
- 185
- Section width in millimetres (7.28 in), sidewall to sidewall. It is measured on the rim width the tire standard lists for that size; on a wider or narrower rim it changes by roughly 5 mm per half inch.
- 65
- Aspect ratio: the sidewall is 65 % as tall as the tire is wide — 185 × 65 ÷ 100 = 120.25 mm. It is a percentage, not a height.
- R
- Radial construction (not "radius"). Written ZR, it is a radial rated above 240 km/h.
- 15
- Rim diameter in inches (381.0 mm): the wheel this tire mounts on.
- after
- The load index and speed symbol follow the size (for example 185/65R15 91V or 94W XL). The same size is sold with several; type yours into the calculator below to decode it.
Drawn to scale
Closest swap
On the same rim, 175/70R15 is nearest in diameter: +0.7 %. Going up to a 16-inch rim, 165/65R16 is nearest: −0.1 %, so the speedometer reads +0.1 %; at an indicated 60 mph you would do 59.9 mph.
Sizes within ±3 % of 185/65R15
Every size in the grid (widths 165–205 mm in 10 mm steps, aspect ratios 25–80 in steps of 5) whose overall diameter is within ±3 % of 621.5 mm. ±3 % is a rule of thumb many tire fitters use, not a law. The “really doing” column assumes the speedometer was right on 185/65R15: 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 10
| Size | Diameter | vs 185/65R15 | Really doing |
|---|---|---|---|
| 175/70R15 | 626.0 mm24.65 in | +0.7 %+4.5 mm | 60.4 mph100.7 km/h |
| 205/60R15 | 627.0 mm24.69 in | +0.9 %+5.5 mm | 60.5 mph100.9 km/h |
| 195/60R15 | 615.0 mm24.21 in | −1.0 %−6.5 mm | 59.4 mph99.0 km/h |
| 165/75R15 | 628.5 mm24.74 in | +1.1 %+7.0 mm | 60.7 mph101.1 km/h |
| 165/70R15 | 612.0 mm24.09 in | −1.5 %−9.5 mm | 59.1 mph98.5 km/h |
| 175/65R15 | 608.5 mm23.96 in | −2.1 %−13.0 mm | 58.7 mph97.9 km/h |
| 195/65R15 | 634.5 mm24.98 in | +2.1 %+13.0 mm | 61.3 mph102.1 km/h |
| 205/55R15 | 606.5 mm23.88 in | −2.4 %−15.0 mm | 58.6 mph97.6 km/h |
| 185/60R15 | 603.0 mm23.74 in | −3.0 %−18.5 mm | 58.2 mph97.0 km/h |
| 185/70R15 | 640.0 mm25.20 in | +3.0 %+18.5 mm | 61.8 mph103.0 km/h |
One inch smaller: 14-inch rim 9
| Size | Diameter | vs 185/65R15 | Really doing |
|---|---|---|---|
| 205/65R14 | 622.1 mm24.49 in | +0.1 %+0.6 mm | 60.1 mph100.1 km/h |
| 165/80R14 | 619.6 mm24.39 in | −0.3 %−1.9 mm | 59.8 mph99.7 km/h |
| 175/75R14 | 618.1 mm24.33 in | −0.5 %−3.4 mm | 59.7 mph99.5 km/h |
| 185/70R14 | 614.6 mm24.20 in | −1.1 %−6.9 mm | 59.3 mph98.9 km/h |
| 195/70R14 | 628.6 mm24.75 in | +1.1 %+7.1 mm | 60.7 mph101.1 km/h |
| 185/75R14 | 633.1 mm24.93 in | +1.9 %+11.6 mm | 61.1 mph101.9 km/h |
| 195/65R14 | 609.1 mm23.98 in | −2.0 %−12.4 mm | 58.8 mph98.0 km/h |
| 175/80R14 | 635.6 mm25.02 in | +2.3 %+14.1 mm | 61.4 mph102.3 km/h |
| 165/75R14 | 603.1 mm23.74 in | −3.0 %−18.4 mm | 58.2 mph97.0 km/h |
Plus one: 16-inch rim 10
| Size | Diameter | vs 185/65R15 | Really doing |
|---|---|---|---|
| 165/65R16 | 620.9 mm24.44 in | −0.1 %−0.6 mm | 59.9 mph99.9 km/h |
| 195/55R16 | 620.9 mm24.44 in | −0.1 %−0.6 mm | 59.9 mph99.9 km/h |
| 175/60R16 | 616.4 mm24.27 in | −0.8 %−5.1 mm | 59.5 mph99.2 km/h |
| 185/60R16 | 628.4 mm24.74 in | +1.1 %+6.9 mm | 60.7 mph101.1 km/h |
| 205/50R16 | 611.4 mm24.07 in | −1.6 %−10.1 mm | 59.0 mph98.4 km/h |
| 205/55R16 | 631.9 mm24.88 in | +1.7 %+10.4 mm | 61.0 mph101.7 km/h |
| 185/55R16 | 609.9 mm24.01 in | −1.9 %−11.6 mm | 58.9 mph98.1 km/h |
| 175/65R16 | 633.9 mm24.96 in | +2.0 %+12.4 mm | 61.2 mph102.0 km/h |
| 165/70R16 | 637.4 mm25.09 in | +2.6 %+15.9 mm | 61.5 mph102.6 km/h |
| 165/60R16 | 604.4 mm23.80 in | −2.8 %−17.1 mm | 58.3 mph97.2 km/h |
Compare 185/65R15 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 185/65R15
sidewall = 185 × 65 ÷ 100 = 120.25 mm diameter = 15 × 25.4 + 2 × 120.25 = 621.5 mm circumference = π × 621.5 = 1,952.5 mm revs per mile = 1,609,344 ÷ 1,952.5 = 824.2 revs per km = 1,000,000 ÷ 1,952.5 = 512.2
Speedometer error is the ratio of the two diameters: true speed = shown speed × new diameter ÷ 185/65R15 diameter. Fitting 165/65R16 (620.9 mm) in place of 185/65R15, an indicated 100 km/h is really 99.9 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 tire sizes that we are allowed to reuse, so the 5 sizes on this ladder follow the same plus-sizing rule as the other ladders. 185/65R15 is the anchor for small-car sizes: a 65-series sidewall on a 15-inch rim, 30.9 mm shorter overall than the 205/60R16 compact-car anchor. For each rim from 14 to 18 inches, pick the size with the closest overall diameter to 185/65R15 among widths 165 + 10 × (rim − 15) to 205 + 10 × (rim − 15) mm in 10 mm steps and aspect ratios 35–75 in steps of 5. 185/65R15 is on that ladder, 0.0 mm from 185/65R15's 621.5 mm diameter. From the 14-inch step (175/75R14) to the 18-inch step (235/35R18) the sidewall drops from 131.3 to 82.3 mm while the diameter stays within 3.8 mm. 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.