275/60R20 Tyre Size: Dimensions, Alternatives & Speedometer Effect
Measured from the ground to the top of the tread, a new 275/60R20 tyre stands 838.0 mm tall (33.0 inches). The sidewall — the rubber between the rim edge and the tread — is 165.0 mm high, the tyre covers 2632.7 mm of road per revolution, and it completes 611.3 revolutions in a mile. Those numbers come straight from the three figures in the size code: 275 mm width, 60% aspect ratio and a 20-inch rim. This guide explains the maths behind them, lists the sizes that match this one most closely, and works out what fitting a different size would do to your speedometer reading.
People usually land on this page for one of three reasons: checking a tyre already on the car, shopping for a replacement, or wondering whether a slightly different size will work. In all three cases the approach is the same — start with the exact measurements, then compare. A 275/60R20 is a wide size, a tall, flexible sidewall that absorbs bumps well and suits rougher roads, at the cost of slightly softer handling, and the tables below let you hold it up against the nearest alternatives on diameter, sidewall and revs per mile. The disclaimer box just below is part of that comparison: these are calculations, and the final fitment check belongs to your placard and a tyre professional.
This is a calculation, not a safety approval. Always check your vehicle's door-jamb placard, load index and speed rating, and confirm fitment with a tyre professional before fitting a different tyre size.
What does 275/60R20 mean?
Read the code left to right. 275 means the tyre is 275 mm wide across the tread. 60 is the aspect ratio, so the sidewall is 60% of the width — 275 x 0.60 = 165.0 mm of rubber between rim and tread. R20 means it mounts on a 20-inch rim (508.0 mm). The overall diameter is the rim plus two sidewalls: 508.0 mm + 165.0 mm + 165.0 mm = 838.0 mm. Once you can do that sum, you can decode any size code you meet, and you can see why two sizes with the same rim can still be very different heights.
275/60R20 dimensions
| Measurement | Value |
|---|---|
| Overall diameter | 838.0 mm (33.0 in) |
| Sidewall height | 165.0 mm |
| Circumference | 2632.7 mm |
| Revolutions per mile | 611.3 |
| Rim diameter | 20 in |
The diameter of 838.0 mm (33.0 in) is the headline number because everything else follows from it. The circumference, 2632.7 mm, is pi times the diameter, and it is the distance the car travels each time the wheel turns once. Divide a mile (63,360 inches) by the circumference in inches and you get 611.3 revolutions per mile — the figure the speedometer and odometer effectively count. A tyre with fewer revs per mile covers more ground per turn, so the car travels faster than the speedometer thinks if you fit a taller tyre without recalibrating. All of these are nominal new-tyre figures: real tyres vary slightly by brand, model, wear and inflation pressure, so treat the decimals as precise maths on a nominal size, not a measurement of your individual tyre.
Closest alternative sizes to 275/60R20
Diameter is the right way to compare candidate replacements, and the table ranks the nearest three. The best match is 285/60R20 at +1.4% (+12.0 mm). Sizes inside plus or minus 3% of the original diameter are the ones usually considered for a swap, because the speedometer error they introduce is small. Outside that band the error grows and so do the knock-on effects on gearing, odometer readings and, on some cars, the calibration of driver-assistance systems that assume a standard rolling circumference.
| Alternative size | Diameter | Sidewall | Diameter difference | Within ±3% guideline? |
|---|---|---|---|---|
| 285/60R20 | 850.0 mm (33.5 in) | 171.0 mm | +1.4% | Within the guideline |
| 285/55R20 | 821.5 mm (32.3 in) | 156.8 mm | -2.0% | Within the guideline |
| 275/55R20 | 810.5 mm (31.9 in) | 151.2 mm | -3.3% | Outside the guideline |
Speedometer effect of changing from 275/60R20
The speedometer effect is a straight ratio. Fitting 285/60R20 (850.0 mm) in place of 275/60R20 (838.0 mm) changes the diameter by +1.4%, so every indicated speed is multiplied by 1.014 to get the real speed. At 30 mph on the dial the true speed is 30.4 mph, at 50 mph it is 50.7 mph, and at 70 mph it is 71.0 mph. The table below shows the same working for all three alternatives, so you can see at a glance which swap keeps the error negligible and which one starts to matter.
| Replacement size | Diameter change | Actual speed at 30 mph indicated | Actual speed at 50 mph indicated | Actual speed at 70 mph indicated |
|---|---|---|---|---|
| 285/60R20 | +1.4% | 30.4 mph | 50.7 mph | 71.0 mph |
| 285/55R20 | -2.0% | 29.4 mph | 49.0 mph | 68.6 mph |
| 275/55R20 | -3.3% | 29.0 mph | 48.4 mph | 67.7 mph |
Wider, narrower or taller than 275/60R20: what actually changes
What actually changes if you move away from 275/60R20? Width first: a wider tyre puts more rubber on the road, which usually helps dry grip and can hurt fuel use a little through extra rolling resistance. Height second: because the sidewall is 60% of the width, widening without lowering the aspect ratio raises the diameter, lengthens the gearing and lifts the car slightly. A shorter sidewall sharpens steering response but transmits more of the road surface into the cabin. The practical rule is to hold the diameter as steady as you can — that is what the alternative table above is for — and to check that a wider tyre still clears the suspension and arches at full lock before committing.
How to check 275/60R20 fits your vehicle
Do the checks in this order. Read the placard and note the specified size, load index and speed rating for your exact vehicle. Compare the candidate size against the placard diameter using the plus-or-minus 3% guideline. Confirm the load index and speed rating are at least what the placard asks for. Confirm the rim width suits a 275 mm tyre. Then confirm physical clearance at full steering lock and under load, and confirm the pressure-monitoring system still works. A tyre professional can run through all of that quickly, and that confirmation is the step this page cannot replace. The 275/60R20 measures 838.0 mm across, so that is the diameter the placard figure has to be compared with.
Mistakes to avoid with 275/60R20
The most common mistake is reading the size off the tyre already fitted and assuming it is the correct size — a previous owner may have changed it. The second is going wider without adjusting the aspect ratio, which quietly makes the tyre taller and throws the speedometer off. The third is ignoring the load index and speed rating, which matter as much as the dimensions. The fourth is fitting different sizes on the same axle, which the car was not designed for. And the fifth is forgetting that the spare, the pressure-monitoring system and the speedometer all assume the standard size — change the size and all three need a thought. For a 275/60R20, that means checking the 275 mm width, the 60% aspect ratio and the 20-inch rim against the placard before you buy.
Related 275/60R20 sizes and tools
- 275/40R20 tyre size
- 275/45R20 tyre size
- Use the Tyre Size Calculator to compare 275/60R20 against any other size.
- Use the Plus Sizing Calculator to find a wider size that keeps the diameter close to 275/60R20.
Frequently asked questions
What is the overall diameter of a 275/60R20 tyre?
The overall diameter of a new 275/60R20 tyre is 838.0 mm, which is 33.0 inches. That is the rim diameter (508.0 mm) plus twice the sidewall height (165.0 mm). It is a nominal figure, so an individual tyre can vary slightly by brand, model, wear and inflation pressure.
How tall is the sidewall on a 275/60R20 tyre?
The sidewall is 165.0 mm tall, because the aspect ratio is 60% of the 275 mm width (275 x 60/100 = 165.0 mm). A tall-sidewall sidewall like this one means a tall, flexible sidewall that absorbs bumps well and suits rougher roads, at the cost of slightly softer handling. The sidewall height is the main thing that decides how much cushioning the tyre gives over bumps.
How many revolutions per mile does a 275/60R20 tyre do?
A 275/60R20 tyre completes 611.3 revolutions per mile, based on its 2632.7 mm circumference. That figure matters because the speedometer and odometer count revolutions: fit a tyre with a different circumference and the readings drift by the same percentage as the diameter change.
What is the closest alternative size to 275/60R20?
The closest size in the chart is 285/60R20, which differs in diameter by +1.4% (+12.0 mm). The commonly used guideline is to stay within plus or minus 3% of the original diameter, and the alternative table on this page shows which sizes meet that. Diameter is only one check, though — load index, speed rating and physical clearance still need confirming.
Will changing from 275/60R20 affect my speedometer?
Yes. The speedometer assumes the original circumference, so a diameter change shifts every reading by the same percentage. Fitting 285/60R20 instead of 275/60R20 changes the diameter by +1.4%, so an indicated 70 mph would really be 71.0 mph. Keep the diameter within plus or minus 3% to keep that error small, and check the placard before fitting anything different.