Insert your existing wheel and tyre specs, and the desired size, and 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
662.6mm
647.1mm
Circumference
2081.6mm
2032.9mm
Poke
65.6mm
78mm
Inset
137.6mm
138mm
Speedo error
0%
2.4%
Reading at 30mph
30mph
30.72mph
Reading at 60mph
60mph
61.44mph
Ride height gain
0mm
-7.75mm
Arch gap loss
0mm
-7.75mm
Wheel Fitment Guide

Compared to your existing wheel, this new wheel will have an inner rim which is 0.3mm closer to the suspension strut. The outer rim will poke out 12.4mm 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.