How to read tyre sidewall sizes: 120/70-17, 4.00-8, 26x2.10 and more
120/70-17, 4.00-8, 26x2.10 — the numbers on the sidewall tell you exactly which size to order. We explain each format with examples for motorcycles, bicycles, ATVs and equipment.
Not sure how to read tyre sizes? The sidewall shows 120/70-17, 4.00-8 or 26x2.10 — these codes tell you exactly which size to order. In this guide we explain formats for motorcycles, bicycles, ATVs and equipment, with real examples from Roataway.ro stock.
Tyre sizes (26x2.10, 120/70-17, 4.00-8) are moulded on the sidewall, next to the brand — not on the tread.
Where to find tyre sizes on the sidewall
The size is marked on the sidewall — the side of the tyre — together with brand, model and load/speed indices. If the old tyre is too worn to read, check the owner’s manual or a sticker on the frame or swingarm. Golden rule: rim diameter does not change — a 17-inch tyre fits only a 17-inch rim.
What 120/70-17 means on motorcycle tyres
This is the most common format on motorcycles and scooters. Each number has a clear role:
- 120 — tyre width in millimetres;
- 70 — aspect ratio: sidewall height is 70% of width (here, 84 mm);
- 17 — rim diameter in inches.
If the letter R appears between aspect ratio and diameter (e.g. 120/70R17), the tyre is radial; a plain hyphen (120/70-17) means bias ply. Common examples: 90/90-10 and 120/70-12 on scooters, 110/80-19 front and 140/80-17 rear on off-road motorcycles.
What 4.00-8 and 3.50-10 mean
The inch format is still widely used on classic scooters, mopeds, wheelbarrows, tillers and small trailers:
- 4.00 — tyre width in inches (approx. 102 mm);
- 8 — rim diameter in inches.
With this format, sidewall height is usually equal to width (100% aspect). Popular sizes: 4.00-8 tyres on wheelbarrows and tillers, 3.50-10 on Vespa-style scooters, 2.75-17 on mopeds. Find these in equipment tyres and motorcycle & scooter tyres.
What 26x2.10, 27.5x2.25 and 29x2.40 mean on bicycles
On bicycle tyres, both numbers are in inches:
- 26 — approximate outer wheel diameter in inches;
- 2.10 — tyre width in inches.
The sidewall often also shows the ETRTO code, e.g. 54-559: 54 mm width on a rim with 559 mm inner diameter. ETRTO is the most accurate compatibility check, because “26 inch” can mean different rims. Common matches: 26" = 559 mm, 27.5" (650B) = 584 mm, 28"/29" (700C) = 622 mm.
ATV tyre sizes: 25x8-12 and 23x11-10
ATVs use their own three-number format, all in inches:
- 25 — overall tyre diameter;
- 8 — tyre width;
- 12 — rim diameter.
Note: on ATVs, front and rear tyres are almost always different sizes — e.g. 25x8-12 front and 25x10-12 rear. Check both axles before ordering in Off-Road and All-Road.
Load and speed index: what 66M means
After the size you usually see a number + letter, e.g. 66M:
- 66 — load index: maximum weight the tyre can carry (66 = 300 kg);
- M — speed index: maximum permitted speed (M = 130 km/h).
The new tyre must have indices at least equal to those recommended for your vehicle — higher is allowed, lower is not.
Know your size? Find your tyre
Search your size on Roataway.ro — original Vee Rubber and Vee Tire Co tyres, real stock and fast delivery across Romania.
FAQ
How do you read the size marked on a tyre?
On the sidewall you will find a code such as 120/70-17, 4.00-8 or 26x2.10. The first number is width, the next (if present) is sidewall height, and the last is rim diameter. On bicycles, 26x2.10 means wheel diameter × width, both in inches.
What does 120/70-17 mean on a motorcycle tyre?
120 is width in millimetres, 70 is the aspect ratio (sidewall height = 70% of width, here 84 mm), and 17 is rim diameter in inches. The letter R (120/70R17) means radial construction; a hyphen (120/70-17) means bias ply.
What does 4.00-8 mean on a tyre?
4.00 is tyre width in inches, and 8 is rim diameter, also in inches. This classic format is used on wheelbarrows, tillers, small scooters and equipment — a 4.00-8 tyre fits only an 8-inch rim.
What does 26x2.10 mean on bicycle tyres?
26 is the approximate outer wheel diameter in inches, and 2.10 is tyre width, also in inches. The sidewall often also shows an ETRTO code, e.g. 54-559, giving rim width and inner diameter in millimetres — the most accurate way to check compatibility.
Can I fit a 130/70-17 instead of 120/70-17?
Only if the rim and fork or swingarm clearance allow the extra width. Rim diameter (17) must stay the same. For width changes, check the manufacturer’s recommendations or ask us before ordering.