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Tyre size and EV range calculator

Thinking of bigger wheels or wider tyres? See how far the change could cut your range, what it does to your speedo, and whether it stays within Australia's limits.

Last updated November 2026

Current tyre

Width

Printed on the tyre sidewall, e.g. 235/45 R18.
235 = width in mm, 45 = sidewall height as % of width, 18 = wheel (rim) diameter in inches.

mmProfile%Wheelin

Rolling resistance class

From the EU tyre label, shown by most tyre shops and maker websites.
A is the most efficient. EV-specific tyres are usually A or B.
Not sure? Leave C.

New tyre

WidthmmProfile%Wheelin

Rolling resistance classExtra weight per wheel

Extra weight per wheel

Bigger wheels and wider tyres are usually heavier.
1–3 kg more per corner is common going up an inch.
Use 0 if the same.

Your car

Body type

Sets typical drag and frontal area.
Sedans are the most slippery; utes and large SUVs the least.

Weight with driver

Kerb weight from the maker's specs, plus people and luggage.

kgRange now

Range now

Your real range at this speed on the current tyres.
Or the official figure from the Green Vehicle Guide.

Results

	235/45 R18	245/35 R20
Overall diameter	669 mm	680 mm (+11 mm)
Sidewall height	106 mm	86 mm
Speedo shows 100 km/h	100 km/h	101.6 km/h real
Estimated range at 100 km/h	450 km	427 km (−5.2%)

You'd lose about 23 km of range at 100 km/h. At this speed, tyre rolling resistance uses about 31% of the energy, so moving from class B to C matters more than the extra width.

✓ Diameter change +11 mm: within the national limit for cars (+15 mm / −26 mm from a factory size).
✓ Width +4%: within the 30% limit over the widest factory tyre.
⚠ Speedo will read low: you'd be doing 101.6 km/h when it shows 100. That can mean speeding fines.

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Estimate only, at a steady speed on flat road. Wheel design and aero covers also change drag, which this doesn't model. Compare the first size with the size on your tyre placard; check fit and legality with a tyre shop or your state's registration authority.

How it works

Diameter = wheel size in mm + two sidewalls (width × profile %).
Speedo: a bigger diameter covers more ground per turn, so the speedo reads low.
Range compares the road-load force at a steady speed: air drag, rolling resistance and the car's weight. Wider front tyres add a little frontal area; a lower rolling resistance class and lighter wheels help.

What usually costs the most range

Rolling resistance: grippy performance tyres flex more and turn more energy into heat.
Wheel design: open sporty spokes stir up more air than flat aero covers.
Weight: bigger wheels and wider tyres are usually heavier.
Width: matters less than most people expect.

Read the full explainer: do bigger wheels reduce EV range?

Official sources

VSB 14 National Code of Practice — Section LS: Tyres, Rims, Suspension and Steering — Tyre size limits for modified cars: overall diameter, width, track and speedo accuracy.
Transport Tasmania — Speedometer accuracy — What the Australian Design Rules require of a speedo.
EU tyre label — Regulation (EU) 2020/740 — Where the rolling resistance classes A to E come from.
Green Vehicle Guide (Australian Government) — Official energy use and range for every new model.

General information only. States can add their own rules, and the tyre placard and your insurer still apply. Check with a tyre shop or your state's registration authority before changing sizes.