A 33-inch tyre is one that stands about 838 mm tall overall (33 × 25.4 mm), and a 35-inch tyre about 889 mm. In metric sizes, that puts sizes such as 285/75R16, 285/70R17 and 295/70R17 in the “33” class, and 315/75R16 or 315/70R17 in the “35” class. HILO lists 33-class sizes in the X-TERRAIN XT1, X-TERRAIN MT1 and WILDGRIP RT1 off-road patterns (plus two highway-terrain SPORT XV1 sizes), and 35-class sizes in MT1 and RT1.
When a customer walks in asking for “33s”, that number is only the starting point. This guide shows how to turn a metric size into inches, which HILO sizes fall into each class, and what to check before you quote.
How to work out a tyre’s diameter in inches
A metric size such as 285/75R16 gives you three numbers: the section width in millimetres (285), the aspect ratio, which is the sidewall height as a percentage of the width (75), and the rim diameter in inches (16). Our guide to reading the numbers on your tyre sidewall explains each part.
The overall diameter is the rim plus two sidewalls:
- Sidewall height = width × aspect ratio ÷ 100. For 285/75R16: 285 × 0.75 = 213.75 mm.
- Rim diameter in millimetres = rim inches × 25.4. For a 16-inch rim: 406.4 mm.
- Overall diameter = rim + 2 × sidewall. 2 × 213.75 = 427.5 mm, and 406.4 + 427.5 = 833.9 mm.
- Divide by 25.4 to get inches: 833.9 ÷ 25.4 = 32.8 inches.
That is a calculated, nominal figure. HILO’s specification table lists LT285/75R16 at 834 mm, so the maths and the published figure agree here. Use the published overall diameter for the exact tyre whenever the manufacturer gives one.
Flotation sizes such as 33X12.50R15LT state the diameter in inches up front: 33 inches tall, 12.50 inches wide, for a 15-inch rim. Treat that first number as a nominal label. HILO lists both its 33X12.50 sizes at 826 mm (32.5 inches) and both 35X12.50 sizes at 877 mm (34.5 inches).
Metric sizes in the 33-inch and 35-inch classes
The table below uses the calculation above. The last column shows where the size appears in the HILO range. Sizes marked “not listed” are included only so you can recognise them when a customer quotes them.
| Size | Calculated diameter | In inches | HILO listing |
|---|---|---|---|
| 285/55R20 | 821.5 mm | 32.3 | WILDGRIP RT1 (LT) |
| 245/85R16 | 822.9 mm | 32.4 | X-TERRAIN XT1 (LT) |
| 285/65R18 | 827.7 mm | 32.6 | Not listed |
| 265/70R18 | 828.2 mm | 32.6 | SPORT XV1 (H/T, passenger construction) |
| 285/70R17 | 830.8 mm | 32.7 | XT1, MT1, RT1 (LT) |
| 305/70R16 | 833.4 mm | 32.8 | X-TERRAIN MT1 (LT) |
| 285/75R16 | 833.9 mm | 32.8 | XT1, MT1, RT1 (LT) |
| 275/60R20 | 838.0 mm | 33.0 | SPORT XV1 (H/T, passenger construction) |
| 275/70R18 | 842.2 mm | 33.2 | Not listed |
| 295/70R17 | 844.8 mm | 33.3 | WILDGRIP RT1 (LT) |
| 285/60R20 | 850.0 mm | 33.5 | Not listed |
| 315/70R17 | 872.8 mm | 34.4 | Not listed |
| 315/75R16 | 878.9 mm | 34.6 | X-TERRAIN MT1 (LT) |
| 305/70R18 | 884.2 mm | 34.8 | Not listed |
Two things stand out. First, the 33-class sizes in this table range from 32.3 to 33.5 inches, so two tyres sold as “33s” can differ in height by about 28 mm. Second, the same nominal diameter can come in quite different widths: 245/85R16 and 285/55R20 are almost the same height, but one is 245 mm wide on a 16-inch rim and the other 285 mm wide on a 20-inch rim.
The HILO sizes, with their full specifications
These are the HILO entries whose published overall diameter falls between 822 mm and 878 mm. Several sizes come in more than one load and ply option, so the full description matters.
33-inch class
| Pattern | Size | Load index / speed | Ply | Std. rim | Listed diameter |
|---|---|---|---|---|---|
| X-TERRAIN XT1 (A/T) | LT245/85R16 | 121/118Q | 10PR | 7J | 822 mm |
| X-TERRAIN XT1 | LT285/70R17 | 121/118Q | 10PR | 8½J | 832 mm |
| X-TERRAIN XT1 | LT285/75R16 | 121/118Q | 10PR | 8J | 834 mm |
| WILDGRIP RT1 (R/T) | LT285/55R20 | 122/119Q or 117/114Q | 10PR or 8PR | 9J | 822 mm |
| WILDGRIP RT1 | 33X12.50R17LT | 120Q | 10PR | 10J | 826 mm |
| WILDGRIP RT1 | LT285/70R17 | 126/123Q or 116/113Q | 10PR or 6PR | 8½J | 832 mm |
| WILDGRIP RT1 | LT285/75R16 | 126/123Q or 116/113Q | 10PR or 6PR | 8J | 834 mm |
| WILDGRIP RT1 | LT295/70R17 | 123/120Q or 118/115Q | 8PR or 6PR | 8½J | 846 mm |
| X-TERRAIN MT1 (M/T) | 33X12.50R15LT | 108Q | 6PR | 10J | 826 mm |
| X-TERRAIN MT1 | LT285/70R17 | 121/118Q | 10PR | 8½J | 832 mm |
| X-TERRAIN MT1 | LT285/75R16 | 126/123Q or 116/113Q | 10PR or 6PR | 8J | 834 mm |
| X-TERRAIN MT1 | LT305/70R16 | 124/121Q or 118/115Q | 10PR or 8PR | 9J | 834 mm |
| SPORT XV1 (H/T) | 265/70R18 | 116H | – | 8J | 829 mm |
| SPORT XV1 | 275/60R20 | 115H | – | 8J | 838 mm |
35-inch class
| Pattern | Size | Load index / speed | Ply | Std. rim | Listed diameter |
|---|---|---|---|---|---|
| X-TERRAIN MT1 | 35X12.50R15LT | 113Q | 6PR | 10J | 877 mm |
| X-TERRAIN MT1 | LT315/75R16 | 127/124Q or 121/118Q | 10PR or 8PR | 8½J | 878 mm |
| WILDGRIP RT1 | 35X12.50R17LT | 125Q or 119Q | 10PR or 8PR | 10J | 877 mm |
HILO does not list any size between 846 mm and 877 mm, so there is no HILO “34”. The SPORT XV1 sizes are highway-terrain tyres in passenger construction; they suit a customer who wants the height for a large SUV or ute that mostly stays on sealed roads, not someone after an off-road tread. To check any other size across all twelve HILO patterns, use the HILO tyre size finder.
What to check when a customer asks for “33s”
A larger rolling diameter can affect speedometer accuracy, gearing, braking and driver-assistance systems. Work through these points before you quote, and write the answers on the job card.
1. The placard size and load index
Start with the vehicle’s tyre placard. Transport for NSW notes that vehicles built since 1973 carry one, usually in the glovebox, engine bay or on a door pillar, and that it sets out the manufacturer’s wheel and tyre combinations, load capacity, speed rating and inflation pressure. Its guideline for alternative wheels and tyres (VSI 09) says replacement tyres must have a load rating equal to or higher than the original tyres.
Check the exact entry, not just the size. In the table above, LT285/75R16 in WILDGRIP RT1 is listed as 126/123Q 10PR (1,700 kg single) and as 116/113Q 6PR (1,250 kg single). Same size, very different load capacity.
2. The speed symbol
Every off-road size in the tables above carries a Q speed symbol, which the European Commission’s tyre-parameter guide gives as 160 km/h. If the placard specifies a higher speed rating, check the state rules before fitting. The NSW guideline, for example, allows a lower speed rating than the placard only where the specified rating is above 180 km/h, and never below the vehicle’s top speed. It also recommends a warning label in that case.
3. Wheels and rim width
Check that the customer’s wheels suit the tyre. HILO’s tables list a standard rim width for each size: 8J for LT285/75R16, 8½J for LT285/70R17 and LT295/70R17, and 10J for the 33X12.50 and 35X12.50 flotation sizes. If the customer is also changing wheels, the NSW guideline sets limits on rim width, wheel track and offset.
4. Clearance
Under the NSW guideline, the wheel and tyre must sit within the bodywork or mudguards, flares included, with the wheels pointing straight ahead. They must also not touch the body or suspension anywhere in the vehicle’s travel, including at full steering lock with the suspension fully compressed. Confirm this on the vehicle, not from a forum post about the same model.
5. Speedometer and certification
A taller tyre changes how far the vehicle travels per wheel turn, so the NSW guideline requires speedometer accuracy to be maintained and adjusted where necessary. Larger changes need a compliance certificate from a licensed certifier. As one example, the NSW guideline points to tyres that increase or decrease diameter by more than 7% of the original.
To see what that looks like in practice, take 265/70R17, which HILO lists at 804 mm. Moving to LT285/70R17 (832 mm) adds 3.5%. LT295/70R17 (846 mm) adds 5.2%. A 35X12.50R17LT (877 mm) adds 9.1%. Those percentages are arithmetic only. The NSW guideline also requires certification when the axle or suspension is modified, and each state and territory publishes its own requirements, so send the customer to their state transport authority or a licensed certifier for the final word.
6. Pressure set-up for the new tyre
The placard pressure applies to the tyres the vehicle manufacturer specified. If the new tyres differ in size or construction, ask for the load and pressure data for the tyre actually fitted. Maximum pressures alone show how different these tyres are: HILO lists a maximum pressure of 250 kPa (35 psi) for both MT1 15-inch flotation sizes, against 350 to 550 kPa for its LT metric MT1 sizes. Do not simply copy the placard figure across to a different tyre.
A quick script for the counter
When someone asks for 33s, three questions save a lot of back and forth:
- “What size is on the vehicle now, and what does the placard say?”
- “Is the vehicle lifted, or are you planning to lift it?”
- “Mostly highway, gravel touring, or mud and rock?” That answer points to SPORT XV1, X-TERRAIN XT1, WILDGRIP RT1 or X-TERRAIN MT1. Our guides on R/T vs A/T and when to choose MT1 cover that choice.
Ordering for your shop
When you send a trade enquiry, include the full description: pattern, size, load index, speed symbol and ply rating, plus quantity and delivery postcode. A listing in the HILO range is not a stock guarantee, so confirm availability for the exact entry. Use the HILO trade enquiry form, or the trade enquiry CSV template for several lines at once.
Frequently asked questions
What size is a 33-inch tyre in metric?
Any metric size whose overall diameter works out close to 838 mm. Examples include 285/75R16 (833.9 mm), 285/70R17 (830.8 mm) and 295/70R17 (844.8 mm). Work it out as rim inches × 25.4 plus twice the width × aspect ratio, then divide by 25.4.
What size is a 35-inch tyre in metric?
Close to 889 mm overall. 315/75R16 works out at 878.9 mm (34.6 inches) and 315/70R17 at 872.8 mm (34.4 inches). HILO lists LT315/75R16 in X-TERRAIN MT1, and 35X12.50 flotation sizes in MT1 (15-inch) and WILDGRIP RT1 (17-inch).
Does HILO make 33-inch mud tyres?
Yes. X-TERRAIN MT1, HILO’s mud-terrain pattern, lists 33X12.50R15LT, LT285/70R17, LT285/75R16 and LT305/70R16, all between 826 mm and 834 mm overall. Check the full load and ply entry on the MT1 specification table.
Is a 285/75R16 exactly a 33-inch tyre?
Not quite. It calculates to 833.9 mm, or 32.8 inches, and HILO lists it at 834 mm. It is in the 33-inch class but slightly under a true 33.
Can I fit 33s without any modification?
That depends on the vehicle, the original tyre size and your state’s rules. Load rating, speed rating, clearance at full lock and speedometer accuracy all need checking. Confirm with your state transport authority or a licensed certifier before fitting.
