Tyre Size Equivalents: Alternatives to Your Size and Australian Limits

An equivalent tyre size is a different size designation whose overall diameter stays close to the size your manufacturer specified, with a load index and speed rating that are at least as high. For a 225/60R17, that means sizes such as 215/65R17, 235/55R17 or 225/55R18 can work, while 225/65R17 sits outside the usual limit. Diameter is only the first check. Clearance, load, speed rating and your insurer’s view all matter too, and this guide walks through each one with worked numbers.

TL;DR

• An equivalent size keeps the overall diameter close to the original. For passenger cars, Australia’s Vehicle Standards Bulletin 14 allows no more than 15 mm larger or 26 mm smaller than a manufacturer-designated tyre.
• For a 225/60R17 (about 702 mm overall), the diameter window is roughly 676 mm to 717 mm. Sizes like 215/65R17, 235/55R17, 235/50R18 and 225/55R18 fall inside it.
• Load index and speed rating must be equal to or above the tyre placard values. A matching diameter never makes up for a lower rating.
• Check clearance on both axles, the rim width and your insurer before you buy. Changes outside the placard can affect warranty and insurance cover.
• Not sure? Use our tyre size calculator to compare two sizes, then confirm fitment before you order.

Table of Contents

• Read your current size first
• What counts as equivalent in Australia
• Equivalents for 225/60R17, worked through
• Rules of thumb for moving between profiles
• Beyond diameter: the checks that decide whether it fits
• What changes when you switch size
• When you need a certifier
• A practical way to choose
• Our perspective
• Compare, then book with a local fitter
• FAQ
• Sources

Read your current size first

Every equivalent starts from the size you already have, so read the sidewall properly. Take 225/60R17 99T. According to CHOICE’s guide to reading a tyre, the 225 is the width in millimetres, the 60 is the profile (sidewall height as a percentage of the width), the R means radial construction and the 17 is the rim diameter in inches. The final marking, 99T, is the load index and speed rating.

That gives you three numbers that change when you move to another size, and two that must not drop:

• Width (225 mm): affects grip, rim fit and clearance.
• Profile (60%): affects sidewall height, ride comfort and overall diameter.
• Rim diameter (17 inches): must match your wheel, or change with the wheel.
• Load index (99): must not be lower than the placard requires.
• Speed rating (T): must not be lower than the placard requires.

If you are not sure which size your car left the factory with, our guide to finding your car’s original tyre size shows where to look. The tyre placard, usually on a door jamb or in the glovebox, is the reference. For how rim and tyre measurements pair up, see wheel vs tyre size.

What counts as equivalent in Australia

Australia’s Vehicle Standards Bulletin 14 (VSB 14), Section LS, treats an equivalent tyre as one whose overall nominal diameter stays close to a size designated by the vehicle manufacturer. For passenger cars, the diameter must be no more than 15 mm larger or 26 mm smaller than the manufacturer-designated tyre. The same bulletin also requires the replacement to meet separate clearance, construction, load and speed rating requirements.

Three things follow from that:

1. Equivalence is about overall diameter, not about matching the three numbers on the sidewall.
2. The window is asymmetric. You have more room to go smaller than larger.
3. Diameter is a necessary check, not a sufficient one.

The formula is simple. Overall diameter in millimetres is twice the sidewall height plus the rim diameter converted from inches. Sidewall height is width times profile divided by 100. Our guide to calculating tyre size within the limits covers the method in more detail.

Equivalents for 225/60R17, worked through

Here is the 225/60R17 example, since it is one of the most searched sizes. Its overall diameter works out at about 702 mm (sidewall of 135 mm on each side, plus 431.8 mm for the 17 inch rim). Applying the VSB 14 window gives a range of roughly 676 mm to 717 mm.

These figures are our own calculations from the size markings. Your own vehicle’s placard decides what is actually approved.

A few observations from the table:

• 215/65R17 keeps the same 17 inch wheel and adds sidewall height. It suits drivers who want a slightly more comfortable ride on rough roads, but the narrower tread may not suit a heavier vehicle.
• 235/55R17 is the common wider, lower-profile swap on the same rim. Check the rim width and clearance, since 10 mm of extra width puts the tyre closer to the guards and suspension.
• 225/55R18 and 235/50R18 need an 18 inch wheel. The tyre is only part of the cost, because you are buying or changing wheels as well.
• 245/50R17 and 245/45R18 sit near the lower limit. Technically inside, they leave little margin and raise speedometer and clearance questions.
• 225/65R17 looks only one profile step away, but it breaks the +15 mm allowance.

A tyre in the right diameter band is still not automatically right for your car. A 225/60R17 car with a 99 load index needs the replacement at 99 or above. A 215/65R17 comes in several load indexes, and a lower one is not an equivalent.

Rules of thumb for moving between profiles

You do not always need a calculator to get a shortlist. As a rough guide, widening the tyre by 10 mm while dropping one profile step (for example 5 points, such as 60 to 55) keeps the diameter near the same. Going up one rim size usually means dropping profile by about 10 points or so and widening slightly. For example, 225/60R17 to 225/55R18 is a nearly identical diameter.

CHOICE notes that on most cars you can move to rims one or two inches bigger, which requires different widths and aspect ratios. The limits above still apply to the final diameter.

The older rule of keeping within about 3% of the original diameter is a common rule of thumb, but VSB 14 is the Australian reference for passenger cars, so use the millimetre limits for your own check.

Beyond diameter: the checks that decide whether it fits

This is where most alternative-size mistakes happen. A size can pass the diameter test and still fail on the road.

Load index

Under VSB 14, passenger cars made after 1972 must have a tyre placard, and the fitted tyres must have a load rating not less than the lowest load rating listed on the placard or an equivalent variant of that model. A narrower tyre often carries a lower load index in the same profile, so read the number, not just the size. We explain how to read the figure in our guide to tyre load index.

Speed rating

For light vehicles under 4.5 tonnes that must comply with ADR 24, the same VSB 14 section sets minimum speed ratings. Passenger tyres must have at least an S rating when the placard requires higher, tyres on off-road vehicles at least N, and all other vehicles at least 120 km/h. A lower rating is only allowed in special circumstances, with confirmation from the registration authority. Tasmania’s transport department also says vehicles that do not meet the load and speed rating requirements are not to be passed fit for registration. Our article on never fitting a lower speed rating goes further.

Clearance

Acceptable load capacity or overall diameter does not guarantee adequate clearance. Bridgestone’s tyre replacement manual says body and chassis clearance must be checked on the front and rear axles. Carsales adds that tyres must not contact bodywork, steering, braking or suspension components, and that on 4WDs the wheel track must not be more than 50 mm wider than original. Check at full steering lock and with the suspension compressed, since that is when a wider tyre rubs.

Rim width

Each tyre width has an approved range of rim widths. A 235 on a rim made for a 205 will not seat or wear properly. Check the rim width stamped inside the wheel before you shortlist a wider size.

Warranty and insurance

NSW’s guidance says it is advisable to check with your manufacturer and insurer before changing tyres outside the placard limits, as it might invalidate the warranty or void insurance cover. Michelin Australia also notes that some manufacturers list optional approved fitments on the placard or in the owner’s manual, which is the safest place to look for an alternative first.

What changes when you switch size

Once you have a short list, think about how the car will feel.

Speedometer. Your speedometer reads off wheel rotation, so a different diameter shifts the reading. Using our diameter figures: a 215/65R17 is about 1.4% larger, so when the speedo shows 100 km/h you are actually doing around 101 km/h. A 235/55R17 is about 1.6% smaller, so the same display means about 98 km/h. A 245/50R17, at about 3.6% smaller, would mean roughly 96 km/h. Going to a taller tyre makes the car travel faster than the display shows, which matters for fines. The smaller the diameter change, the smaller the error.

Clearance. Taller sidewalls reach higher into the wheel arch. Wider tyres reach further out and in. Both can rub on a lock or over a bump.

Ride and handling. Lower profiles give sharper steering response and a firmer ride, since there is less sidewall to flex. Taller sidewalls cushion bumps better and protect the rim on rough roads. Neither is better in general. It depends on what you drive on.

Cost. Larger rim sizes often cost more per tyre, and bigger wheels cost more again. Compare the full set of four before you commit.

When you need a certifier

Small diameter changes within the VSB 14 window are one thing. Bigger changes are another. NSW guidance says a compliance certificate from a licensed certifier may be required for significant modifications, for example replacement tyres that change the overall diameter by more than 7%. The same guidance says the placard identifies the manufacturer’s recommended tyre and wheel combinations, and it advises consulting a licensed certifier when a change is significant or you are unsure. It also recommends a warning label near the driver if the replacement speed rating is lower than the placard shows.

Rules differ by state and territory in detail. NSW vehicles must also meet the dimensional standards in the Tyre and Rim Association of Australia’s annual manual, and tyres must meet the construction standards in ADR 23. If you live in another state, check with your state’s road authority for the current requirements.

For 4WDs and light trucks, sizes work differently, with flotation sizes such as 265/70R17 or 315/75R16. Our guide to 4x4 tyre sizes covers how to read and check those.

A practical way to choose

1. Find the placard size and ratings. Note the size, load index and speed rating.
2. Look for approved alternatives first. The owner’s manual or placard may list them.
3. Calculate the diameter of your shortlist. Keep within 15 mm larger and 26 mm smaller of the original, and closer to the original if you can.
4. Match or exceed the load index and speed rating.
5. Check rim width and clearance at full lock and with suspension compressed.
6. Call your insurer if the size is outside the placard.
7. Have the fitter confirm it before the tyres go on. Our checklist for verifying tyre fitment before you buy walks through this.
8. Get the alignment checked. A change in tyre width or profile can alter how the car tracks, so a wheel alignment after a tyre change is worth considering.

Our perspective

Most of the questions we see about equivalent sizes start from the wrong end. People ask what else fits, when the better question is what their car’s placard already allows. In our experience, the safest and cheapest option is usually the original size, and an alternative earns its place only when there is a clear reason: a size that is hard to source, a rim upgrade you actually want, or a tyre type you can only get in another size.

We built the tyre size calculator and the search by model or size into Treadivo because the numbers are easy to get wrong by hand, and a mistake costs a set of tyres or, worse, a safety margin. Our view is simple. Treat diameter as the first filter, load index and speed rating as hard floors, and clearance as something you confirm on the car, not on a screen. If a size sits right at the edge of the window, choose the one closer to the original.

— Areesh

Compare, then book with a local fitter

If you have a size in mind, you can run it through the Treadivo tyre size calculator and then browse passenger, SUV and 4x4 tyres by model or size. You choose a local fitter, see the pricing before you pay, and check out in about three minutes, with same-day fitting confirmation. We also cover fitting in Perth and Melbourne.

If the size you want is outside your placard, talk to your fitter and insurer before you order.

FAQ

What are the equivalent sizes for 225/60R17?

Sizes such as 215/65R17, 235/60R17, 225/55R18, 235/55R17 and 235/50R18 all land within the 15 mm larger and 26 mm smaller window around the original’s roughly 702 mm diameter. A 225/65R17 is too tall. Always match or exceed the placard load index and speed rating, and check clearance on your own car.

Can I fit a different tyre size to my car in Australia?

Yes, within limits. The diameter must stay close to a manufacturer-designated size, the load and speed ratings must meet the placard, and the tyre must clear the bodywork and suspension. Bigger changes may need a licensed certifier, and your insurer should be told about anything outside the placard.

Will a different tyre size change my speedometer reading?

Yes, if the overall diameter changes. A tyre about 1.4% taller makes the car actually travel about 1.4% faster than the display shows, and a smaller tyre does the reverse. Keeping the new diameter very close to the original keeps the error small.

Is a wider tyre always better?

No. A wider tyre can add grip in some conditions, but it needs a suitable rim width, more clearance and may change steering feel and fuel use. Go no wider than your rim and your wheel arches allow.

Where do I find my car’s approved tyre sizes?

Check the tyre placard, usually on a door jamb or in the glovebox, and the owner’s manual. If neither helps, our guide to finding your tyre size shows how to use your registration and ADR details.

Sources

• How to read a tyre, CHOICE
• Section LS, Suspension and Steering, VSB 14, Australian Government
• Guidelines for alternative wheels and tyres, Transport for NSW
• Guidelines for alternative wheels and tyres, NSW (VSI 09)
• Can you change your tyre’s size? Michelin Australia
• Tyre Replacement Manual, Bridgestone
• Tyre and wheel size: how big and low can you go? Carsales
• Tasmanian Department of State Growth, vehicle tyre requirements

Recommended

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• Wheel vs Tyre Size: How Rim and Tyre Measurements Match
• Plus Sizing Tyres: 4 Australian Fitment Checks Before You Buy