The Alloy Wheel Fitment, Tyre Stretch, Rolling Radius & Speedo Error Calculator

Insert your existing alloy wheel and tyre specs, and the desired size. The outcome is shown on the diagram.

Your existing setup

Existing Tyre
Existing Wheel

Your new setup

New Tyre
New Wheel
Your Results

Existing

New

Diameter
642.9mm
645.2mm
Circumference
2019.7mm
2027mm
Poke
38.9mm
78.7mm
Inset
138.9mm
162.7mm
Speedo error
0%
-0.36%
Reading at 30mph
30mph
29.89mph
Reading at 60mph
60mph
59.79mph
Ride height gain
0mm
1.15mm
Arch gap loss
0mm
1.15mm
Wheel Fitment Guide

Compared to your existing wheel, this new wheel will have an inner rim which is 23.8mm closer to the suspension strut. The outer rim will poke out 39.8mm more than before.

The strut shown in the diagram is for show only. Don't worry if the wheel looks like it fouls!

Bear in mind most tyre manufacturers vary slighty from the specs, and that it could be dangerous to run tyres on wheels they aren't designed to fit.

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18x9-5 ET42 (+-5mm) wheels
WORK Wheels
SSR Wheels
JR Wheels
Rotiform Wheels
Rota Wheels
Concaver
Motegi
Fuel Wheels
Bola Wheels
3SDM
7Twenty
2Forge Wheels
1Form
Niche
Autostar
Dare

Will They Fit - The No.1 Online Alloy Wheel & Tyre Fitment Calculator

Use our comprehensive online wheel size calculator to visualise different alloy wheels and tyre combinations. Calculate your offset, compare tyre stretch, rolling radius and more. Compare your new and existing setup and our tool will show you key measurements for accurate wheel and tyre fitment.

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