10R22.5 vs 305/70R22.5
A 10R22.5 tyre is 254 mm wide with a 88% profile, fits a 22.5-inch rim, and has an overall diameter of about 1020 mm (40.2 inches).
A 305/70R22.5 is 305 mm wide with a 70% profile on a 22.5-inch rim, and about 999 mm (39.3 inches) across.
Load not checked — neither size states a load index.
How to read a tyre sidewall
10R22.5, as it is moulded into the rubber. Touch any part of it.
10 Nominal width
A size class, not a measurement. It reads as 10 inches — 254 mm — but the tyre is 254 mm across, which the two happen to agree on rather than convert to. There is no sum that gets from one to the other, which is why this size has to be looked up in UN R54 rather than measured off the designation.
Also moulded on the wall
- 10
- A nominal size class, not a measurement — and this is the number that catches people out. It reads as 10 inches, which would be 254 mm, and the tyre is 254 mm across — which those two happen to agree on, and that is luck rather than arithmetic. It is not a conversion, rounded or otherwise. Across the regulation's table the gap runs from 10 mm narrower to 40 mm wider, and one nominal figure can stand for several different tyres — a designation starting 9 covers 4 widths, from 230 to 258 mm. So the width cannot be worked out from the size; it has to be looked up, which is exactly why the regulation publishes a table and why this calculator will not quote a designation it does not hold.
- 22.5
- The rim, and here the inches are genuine: 22.5 inches is 572 mm, which is what UN R54 states to the millimetre. TRA, standardising the same rim, specifies 571.5 mm — the exact conversion. Half a millimetre between two standards bodies, and worth knowing that the round number is one body's rounding rather than the last word. That is the contrast worth remembering — in 10R22.5 one number is a measurement and the other is a label, and nothing on the sidewall tells you which is which.
| Spec | 10R22.5 | 305/70R22.5 | Difference |
|---|---|---|---|
| Section width | 254.0 mm | 305.0 mm | +51.0 mm |
| Profile | 88% | 70% | -18% |
| Sidewall | 224.0 mm | 213.5 mm | -10.5 mm |
| Rim | 22.5" | 22.5" | +0" |
| Overall diameter | 1020.0 mm | 998.5 mm | -21.5 mm |
| Circumference | 3204.4 mm | 3136.9 mm | -67.5 mm |
| Revs / km | 312 | 319 | +7 |
| Revs / mile | 502 | 513 | +11 |
| Speedo error | reads 100, doing 98 | ||
| Ground clearance Δ | -10.8 mm | ||
- Diameter: 1020 mm (40.2 in)
- Sidewall: 224 mm (8.8 in)
- Circumference: 3204 mm (126.2 in)
- Revolutions: 312 per km
What you can buy in this size
53 products registered as truck tyres on the EU register. These are counts of what exists, not a recommendation.
- Fuel
- C is the best you can get in this size, on 15 of them. Registered across C (15), D (38).
- Wet grip
- A is the best you can get in this size, on one product. Registered across A (1), B (14), C (37), D (1).
- Noise
- A is the best you can get in this size, on 18 of them. Registered across A (18), B (35).
- Measured
- 67–75 dB between the quietest and the loudest.
- Winter
- 16 of 53 carry 3PMSF severe-snow certification.
From the EU product register, so it covers tyres placed on the European market. A size sold in South Africa, the Americas or Asia may come in grades that are not counted here. How to read the label these grades come from.
Tyre size FAQ
How do I read a tyre size like 265/65R17?
265 is the section width in millimetres, 65 is the aspect ratio (sidewall height as a percentage of the width), R means radial construction, and 17 is the rim diameter in inches. So 265/65R17 fits a 17-inch rim, is 265 mm wide and has a sidewall about 172 mm tall.
How do I know if a different tyre size will fit?
As a rule of thumb the overall diameter should stay within about 3% of the original, and the rim diameter must match. TyreCalculator shows the diameter difference as a percentage and flags it green (within 3%), amber (3–5%) or red (over 5%, or a different rim size).
What is the 3% rule for tyre sizes?
Keeping the overall diameter within about ±3% of the original keeps your speedometer, odometer, gearing and ABS/traction systems close to their factory calibration. Beyond that those readings and behaviours drift, which is why the verdict turns amber and then red.
Will a bigger tyre affect my speedometer?
Yes. A larger overall diameter covers more distance per revolution, so your speedometer reads slower than you are actually travelling. TyreCalculator shows this directly — for example "reads 100, doing 107" — based on the diameter difference between the two sizes.
Can I fit a wider tyre on the same rim?
Often, within limits. Each rim width suits a range of tyre widths, and a wider tyre can foul suspension or bodywork. TyreCalculator shows the section-width difference so you can judge the change, but always check the physical clearance on your own vehicle. Clearance is not the only limit: the Tire and Rim Association notes that the load and cold inflation pressure put on a rim and wheel must not exceed the rim and wheel manufacturer's recommendations even where the tyre is approved for more. Some rims and wheels are stamped with a maximum load and pressure; where they are not, the wheel maker is the one to ask. A load index tells you what the tyre can carry, not what the wheel under it can.
What kinds of tyre can I look up?
Car, van and light-truck sizes (265/65R17, LT265/70R17, 215/70R16C), flotation sizes (33x12.50R15), metric motorcycle sizes (120/70ZR17), truck metric (315/80R22.5), agricultural, earthmover and industrial metric (480/70R38, 380/85R34, 750/65R25), and bicycle sizes in ISO/ETRTO or French form (37-622, 700x35C). Inch-denominated sizes such as 11R22.5, 12.4-28 and 4.00-18 are recognised and explained but not measured: their overall diameters come from ETRTO and TRA lookup tables rather than from the size itself, and an estimate would be out by more than the 3% a fitment decision turns on.
How do I read a bicycle tyre size?
The ISO/ETRTO size is two numbers, such as 37-622: 37 is the tyre width in millimetres and 622 is the bead seat diameter of the rim, also in millimetres. The rim must have that same bead seat — the inch name on the wheel will not tell you, because a "26 inch" wheel can be 559, 571 or 590 mm. The French designation (700x35C) is the same wheel written differently: 700C is always a 622 mm bead seat.
What is the EU tyre label and how do I read it?
It is the sheet that comes with every new car, van and truck tyre sold in Europe, compulsory since May 2021 under Regulation (EU) 2020/740. It grades three things: fuel efficiency (rolling resistance) from A to E, wet grip (braking distance on a wet surface) from A to E, and external rolling noise as a measured value in decibels plus a class from A to C. Two pictograms may also appear — the three-peak mountain snowflake for severe snow, and the ice grip mark, which only a car tyre can carry. None of it is moulded into the sidewall: the label is on the tyre in the shop, in the seller’s listing, and in the EU’s public register behind the QR code. Grades only compare between tyres of the same class, so a truck tyre’s B is not a car tyre’s B.
What do overall diameter and rolling circumference mean?
Overall diameter is the full height of the inflated tyre; rolling circumference is the distance it travels in one revolution (π × diameter). Together they set your effective gearing and the revolutions-per-kilometre figure TyreCalculator calculates.