In short. A tyre does not have one correct rim width: it has a range of permitted rims, and the range depends on both its width and its aspect ratio. A 225/45 fits rims from 7 to 8½ inches, a 225/40 from 7½ to 9, a 225/55 from 6 to 8; inside each range sits the measuring rim on which the tyre's published size is measured (7½ inches for the 225/45). These ranges come from the standards of the European tyre and rim body (ETRTO) and its American counterpart, the Tire and Rim Association (TRA); we extracted them from Continental's technical tables and checked them against Michelin's US data, which matched on 207 sizes out of 209. The data sheet of the exact tyre you buy has the last word.
The chart: permitted rims and measuring rim
Each cell gives the permitted rim widths in inches, then the measuring rim in brackets. Example: a 245/45 fits rims of 7½ to 9 inches and is measured on an 8-inch rim. Series 35 and 40, 50 and 55, 60 and 65 share a column because Continental's tables give them identical ranges at every width where both exist.
| Tyre width | 30 series | 35 and 40 | 45 | 50 and 55 | 60 and 65 | 70 |
|---|---|---|---|---|---|---|
| 175 | — | — | — | 5–6 (5½) | 5–6 (5) | 4½–6 (5) |
| 185 | — | — | — | 5–6½ (6) | 5–6½ (5½) | 4½–6 (5½) |
| 195 | — | 6½–7½ (7) | 6–7½ (6½) | 5½–7 (6) | 5½–7 (6) | 5–6½ (5½ or 6) |
| 205 | — | 7–8 (7½) | 6½–7½ (7) | 5½–7½ (6½) | 5½–7½ (6) | 5–7 (6) |
| 215 | — | 7–8½ (7½) | 7–8 (7) | 6–7½ (7) | 6–7½ (6½) | 5½–7 (6½) |
| 225 | — | 7½–9 (8) | 7–8½ (7½) | 6–8 (7) | 6–8 (6½) | 6–7½ (6½) |
| 235 | 8½ only | 8–9½ (8½) | 7½–9 (8) | 6½–8½ (7½) | 6½–8½ (7) | 6–8 (7) |
| 245 | 8–9 (8½) | 8–9½ (8½) | 7½–9 (8) | 7–8½ (7½) | 7–8½ (7) | 6½–8 (7) |
| 255 | 8½–9½ (9) | 8½–10 (9) | 8–9½ (8½) | 7–9 (8) | 7–9 (7½) | 6½–8½ (7½) |
| 265 | 9–10 (9½) | 9–10½ (9½) | 8½–10 (9) | 7½–9½ (8½) | 7½–9½ (8) | 7–9 (8) |
| 275 | 9–10 (9½) | 9–11 (9½) | 8½–10½ (9) | 7½–9½ (8½) | 7½–9½ (8) | 7–9 (8) |
| 285 | 9½–10½ (10) | 9½–11 (10) | 9–10½ (9½) | 8–10 (9) | 8–10 (8½) | — |
| 295 | 10–11 (10½) | 10–11½ (10½) | 9½–11 (10) | 8–10 (9½) | — | — |
| 305 | 10½–11½ (11) | 10–12 (11) | 9½–11½ (10) | 8½–11 (9½) | — | — |
| 315 | 10½–11½ (11) | 10½–12½ (11) | — | — | — | — |
A dash means the size is not in Continental's tables, not that it is forbidden. Only the 195/70 changes measuring rim with diameter (5½ in R14, 6 in R15 and R16).
How we built it. Continental's Technical Databook says its data "are based on ETRTO, ISO, WdK and DIN standards". We extracted its 361 car and 4x4 sizes (pages 26 to 61), reading the measuring rim from the bold type. We then read the size data of seven Michelin US product pages, last updated by Michelin on 10 October 2026. Of 209 sizes in both at the same diameter, 207 give the same minimum, maximum and measuring rim. For the other two (265/35 ZR20, 255/40 ZR21), Michelin lists two versions of the size, one of which stops half an inch lower: read the sheet of the exact tyre.
What we could not read. The ETRTO Standards Manual 2026 and the TRA's 2026 Year Book are sold, not published, and we did not buy them. Our ranges are what two tyre makers publish from those standards.
By tyre width: the questions people ask
What rim width for a 205 tyre?
A 205/55 R16 fits 5½ to 7½ inches and is measured on 6½; a 205/45 R17 fits 6½ to 7½ (measured on 7); a 205/40 R17 fits 7 to 8 (measured on 7½). A 7-inch rim sits inside all three ranges.
What rim width for a 225 tyre?
A 225/45 R17 fits 7 to 8½ inches (measured on 7½); a 225/40 R18 or 225/35 fits 7½ to 9 (measured on 8); a 225/55 or 225/50 fits 6 to 8 (measured on 7). On a 6½-inch rim, only the 225s of 50 series and taller are inside their range.
What rim width for a 245 tyre?
A 245/45 fits 7½ to 9 inches (measured on 8); a 245/40 or 245/35 fits 8 to 9½ (measured on 8½); a 245/30 fits 8 to 9 (measured on 8½); a 245/50 or 245/55 fits 7 to 8½ (measured on 7½); a 245/70 fits 6½ to 8 (measured on 7). An 8-inch rim is inside every one of these ranges.
What rim width for a 255 tyre?
A 255/35 or 255/40 fits 8½ to 10 inches (measured on 9); a 255/45 fits 8 to 9½ (measured on 8½); a 255/50 or 255/55 fits 7 to 9 (measured on 8). An 8½-inch rim is inside all of these.
What rim width for a 265, 275 or 285 tyre?
A 265/35 fits 9 to 10½ inches, a 275/35 9 to 11, a 285/35 9½ to 11, each measured on 9½, 9½ and 10. In the 45 series the ranges are 8½ to 10, 8½ to 10½ and 9 to 10½. Above 255, the range moves up by about half an inch for every 10 to 20 mm of tyre.
The reverse chart: which tyre widths fit my rim?
If you already have the wheels, read the chart the other way. For each rim width, the table lists the tyre widths whose permitted range includes it, among the sizes in Continental's tables. This is our calculation from the same 361 sizes.
| Rim | 35 and 40 series | 45 series | 50 and 55 series | 60 and 65 series |
|---|---|---|---|---|
| 6½ in | 195 | 195–205 | 185–235 | 185–235 |
| 7 in | 195–215 | 195–225 | 195–255 | 195–255 |
| 7½ in | 195–225 | 195–245 | 205–275 | 205–275 |
| 8 in | 205–245 | 215–255 | 225–295 | 225–285 |
| 8½ in | 215–255 | 225–275 | 235–305 | 235–285 |
| 9 in | 225–275 | 235–285 | 255–305 | 255–285 |
| 9½ in | 235–285 | 255–305 | 265–305 | 265–285 |
| 10 in | 255–305 | 265–305 | 285–305 | 285 |
| 10½ in | 265–315 | 275–305 | 305 | — |
The upper ends partly reflect which sizes exist: there is no 295/60 in the tables, for example.
Reading a rim: 8J x 18, flange width, measuring rim
A rim is marked by width in inches, then the letter of the flange profile, then the diameter: 8J x 18 is 8 inches wide between the flanges, with a J flange, for an 18-inch tyre. Continental defines rim width as the "flange distance" and gives it in millimetres for J rims:
| Rim | 6J | 6½J | 7J | 7½J | 8J | 8½J | 9J | 9½J | 10J | 10½J | 11J |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Width between flanges | 152.5 mm | 165 mm | 178 mm | 190.5 mm | 203 mm | 216 mm | 228.5 mm | 241.5 mm | 254 mm | 266.5 mm | 279.5 mm |
The flanges themselves add to the wheel's overall width; our guide to rims, wheels and tyres names each part.
UN Regulation 30, the car tyre regulation applied in Europe, the UK and other signatory countries, defines the measuring rim as the rim on which a tyre must be fitted for its size to be measured. In the United States, FMVSS 139 tells the test lab to "mount the tire on the measuring rim specified by the tire manufacturer or in one of the publications listed in S4.1.1" (S6.1.1.1.1). Michelin's US pages put it plainly: the measuring rim width is the rim width "used to determine the tire's published dimensions", and the rim width range is "the range of rim widths" Michelin lists for use with that tyre.
What half an inch of rim changes
The tyre follows the rim. UN Regulation 30 corrects section width for the rim with a coefficient K of 0.4: 0.4 mm of tyre for each millimetre of rim. Half an inch is 12.7 mm, so our arithmetic gives 12.7 × 0.4 = 5.08 mm. Continental says the tyre width changes "by approx. + 5 mm" per half inch, and Michelin's US pages say about 0.2 in (5 mm). Continental's own tables agree: of the 1,128 half-inch steps we counted, 1,101 add 5 mm (97.6 %), 25 add 6 mm and 2 add 4 mm.
For a 225/45 R17, Continental's maximum width in service goes from 229 mm on a 7-inch rim to 234 mm on 7½, 239 mm on 8 and 244 mm on 8½. These are maximums including sidewall markings, not the nominal 225. Our reading: at the same offset, a rim half an inch wider also moves each flange out by 6.35 mm, which matters under the arch and near the suspension. Our guide to wheels or tyres rubbing works through that, and the wheel offset calculator compares two wheels to the millimetre.
Why percentage rules get it wrong
A rule of thumb circulates: the rim should be 70 % of the tyre width for 50 series and taller, 85 % for 45 series and lower. We calculated, for all 361 sizes, the measuring rim in millimetres divided by the nominal tyre width:
| Series | Measuring rim ÷ tyre width | The rule of thumb |
|---|---|---|
| 25 to 40 | 0.88 to 0.94 | 0.85 |
| 45 | 0.83 to 0.87 | 0.85 |
| 50 and 55 | 0.77 to 0.83 | 0.70 |
| 60 and 65 | 0.73 to 0.79 | 0.70 |
| 70 | 0.72 to 0.79 | 0.70 |
| 75 and 80 | 0.66 to 0.74 | 0.70 |
The rule is close in the 45 series and too low almost everywhere else. For a 205/55: 205 × 0.70 = 143.5 mm, or 5.65 inches, when the measuring rim is 6½ inches (165 mm). For a 255/35: 255 × 0.85 = 216.75 mm, about 8½ inches, when the measuring rim is 9. The ratio falls as the sidewall gets taller, which no single percentage captures.
LT and P-metric tyres
Light-truck tyres can have narrower ranges than the passenger tyre of the same size. Across 21 LT-metric entries on Michelin's US pages that have a passenger equivalent in Continental's tables, the measuring rim was the same every time, but 11 had a narrower range: an LT265/70 R17 stops at 8½ inches, where the passenger 265/70 goes to 9. Read the LT sheet if your truck runs LT tyres.
P-metric sizes, common on older US cars, are a TRA designation. The ETRTO's recommendations (edition of 8 September 2025) say a P195/70 R 13 and a 195/70 R 13 "are almost identical in size" and may be mixed on a vehicle but not on the same axle, if load and speed capabilities match and both are listed for the vehicle. Continental's tables list 11 P-metric sizes; for the eight that also exist there without the P, the permitted range and the measuring rim are the same.
What the rules say, country by country
United States. Two federal standards tie rim and tyre together. FMVSS 139, S4.1: "Each manufacturer of tires must ensure that a listing of the rims that may be used with each tire that it produces is provided to the public." The listing can be the maker's own, filed with NHTSA, or the publications of the TRA, the ETRTO, the Japanese makers' association, the Tyre and Rim Association of Australia and others (S4.1.1); S5.1 adds that "each tire shall fit each rim specified for its size designation". FMVSS 110, S4.4.1, requires each rim on a new vehicle to "be constructed to the dimensions of a rim that is listed by the manufacturer of the tires as suitable for use with those tires". These bind tyre and vehicle makers; wheels changed later fall under state inspection rules, which we did not survey.
Canada. Section 110 of the Motor Vehicle Safety Regulations (text current to 21 September 2026) requires vehicles of 4,536 kg or less and "every tire rim manufactured for use on those vehicles" to conform to Technical Standards Document No. 110. We did not read that document; it is Transport Canada's counterpart to FMVSS 110. Provinces run their own inspections.
United Kingdom. No rule lists rim widths. The MOT manual, updated on 14 October 2026, fails as major "a wheel and its fixings not compatible" (5.2.2 (d)), "a tyre fouling a part of the vehicle" (5.2.3 (f)) and "a tyre incorrectly seated on the wheel rim" (5.2.3 (k)). Regulation 27 (1) (a) of the Construction and Use Regulations 1986 forbids using a tyre that "is unsuitable having regard to the use to which the motor vehicle or trailer is being put". Our reading: a tyre outside its permitted rim range is hard to defend under that wording. Tell your insurer about any change of wheels.
Australia. In New South Wales, guideline VSI.09 (revision 5, 28 February 2019) says wheels and tyres must conform to the dimensional standards in the Tyre and Rim Association of Australia's Standards Manual, and "you must not fit wheels with rim widths less than the minimum width fitted by the vehicle manufacturer for the particular model". It also limits the increase in wheel track to 25 mm on passenger cars (50 mm on off-road four-wheel drives), and, for changes that need approval, refers to VSI.06 and VSB 14, citing as an example tyres that change the overall diameter by more than 7 %. The national code for modifications (VSB 14) and the other states' sites did not load for us on the day we wrote this; ask your state transport authority.
Outside the range: what is known
The tyre makers publish a range and nothing beyond it, and no source we read puts a figure on what happens on a rim that is too narrow or too wide. The ETRTO's recommendations send anyone outside the manual to the tyre and rim makers: for combinations not in the Standards Manual, on existing vehicles, "consult the E.T.R.T.O. Engineering Design Information and the tyre and rim manufacturers concerned." Our reading: outside the range, no standard and no tyre maker backs the combination. Have it checked by a tyre fitter before you drive on it. Michelin adds that only tyre professionals should mount tyres.
Before you choose a rim width
- Start from your car's listed sizes, in the handbook or on the door-pillar placard. Our guide to reading a tyre size explains every figure.
- Read the range for the exact tyre on its maker's data sheet; the chart above tells you what to expect.
- Place the wheel under the arch. Width and offset together decide where the flanges go: see what wheel offset (ET) means. Onyx Forged does not recommend a size or an offset: the car maker and the tyre maker set the permitted dimensions.
- If the tyre size changes, compare overall diameters with the tyre size calculator, and read how to choose aftermarket wheels for load rating and fitment.
Frequently asked questions
Can I put a 225 tyre on an 8-inch rim?
Yes for most series: 8 inches is inside the range of the 225/35 and 225/40 (7½ to 9), the 225/45 (7 to 8½) and the 225/50 to 225/65 (6 to 8). Check the sheet of the exact tyre.
What does 7.5J x 17 mean?
A rim 7½ inches wide between the flanges (190.5 mm, according to Continental), with a J flange profile, for a 17-inch tyre. The offset, marked ET, is a separate figure.
Is there an official rim width chart?
Yes: the ETRTO Standards Manual in Europe and the TRA Year Book in North America, both sold rather than published. Tyre makers publish their ranges per size, and FMVSS 139 requires them to make the rim listing public.
Why do two data sheets give different ranges for the same size?
It is rare: of 209 sizes, we found two differences between Continental and Michelin, both where Michelin lists two versions of the size. A maker can narrow the range for one product, and LT tyres often have narrower ranges than passenger tyres of the same size.
Will a tyre outside its rim range fail the MOT?
The MOT manual has no rim width table. It fails a tyre fouling the car, a tyre not seated on the rim and a wheel incompatible with its fixings, and the Construction and Use Regulations forbid an unsuitable tyre.
Does a stretched tyre fit?
A tyre on a rim wider than its listed maximum is outside every range we read; neither the ETRTO nor the tyre makers back it. Ask a tyre fitter before driving on it.
Made-to-order wheels: the width starts from the tyre
Onyx Forged is a French brand of made-to-order forged wheels, designed to JWL/VIA standards. Each wheel's width is set from the tyre you will fit and your car's documented dimensions, which we confirm with you in writing before production: see how to customise a set.
Sources
- Continental, Technical Databook Car · 4x4 · Van 2015-2016, pages 3, 9, 26 to 61, 96, 97 and 100.
- Michelin (USA), product pages with size data: Pilot Sport 4 S, CrossClimate 2, Defender2, Defender LTX M/S2, Defender LTX M/S, LTX A/T2 and Premier LTX.
- ETRTO, Recommendations, edition of 8 September 2025, passenger car tyres; Standards Manual 2024, passenger car tyres index (public extract).
- The Tire and Rim Association, publications (2026 Year Book).
- UN Regulation 30, as published in the Official Journal of the EU, 30 July 2008, measuring rim and coefficient K.
- eCFR, 49 CFR 571.139 (FMVSS 139) and 49 CFR 571.110 (FMVSS 110).
- Justice Laws Website, Motor Vehicle Safety Regulations, section 110, current to 21 September 2026.
- GOV.UK, MOT inspection manual, section 5, updated 14 October 2026; Road Vehicles (Construction and Use) Regulations 1986, regulation 27.
- Transport for NSW, VSI.09, guidelines for alternative wheels and tyres, revision 5, 28 February 2019 (copy hosted by a club; we could not load the original).
All pages were read on 16 October 2026.
The Onyx Forged design office.