Motorcycle tyres come in different sizes (although they’re mostly all the same shape!).
One of the common questions we’re asked when it comes to tyre sizes is whether you can change the size of the tyre on your motorcycle.
Most of the time, people want to do this for aesthetic reasons (mainly fitting a wider rear tyre). However, some customers want to play around with tyre sizes on their track bike or if they’re struggling to find the exact tyres for their motorcycle (usually when trying to convert from imperial to metric sizes).
Calculating Circumference
When you change the width of your tyre, let’s say from a 180/60 to a 190/55, you’re not only fitting a wider tyre but the aspect ratio is different too (55% as tall as it is wide, compared to 60% as tall as it wide).
Therefore, the width (W) AND aspect ratio make a difference to the tyre’s height and profile. This also affects the tyre’s rolling circumference.
When it comes to track bikes, most people playing with tyre sizes are also trying to increase the contact patch of the tyre at lean. If you take two tyres with the same width, the one with the larger aspect ratio will be taller and this tyre will also have a larger contact patch when on its edge.
Keep in mind that the rolling circumference (C) of a tyre on its edge (E) is different to the rolling circumference of the centre of the tyre (D), when the tyre is upright. If you have been paying attention when you’re on track, you might have noticed your engine revs rising as you lean the bike over. Your speed won’t have changed that much, but the rolling circumference will have decreased; therefore, the engine revs rise to compensate.
Motorcycle Tyre Circumference Chart – Road & Track
| Tyre | Height (H) (mm) | Diameter (D) (mm) | Circumference (C) (mm) |
|---|---|---|---|
| 120/70-17 | 84 | 600 | 1883 |
| 125/70-17 | 87.5 | 607 | 1905 |
| 160/60-17 | 96 | 624 | 1959 |
| 180/55-17 | 99 | 630 | 1977 |
| 180/60-17 | 108 | 648 | 2034 |
| 190/50-17 | 95 | 622 | 1952 |
| 190/55-17 | 104.5 | 641 | 2012 |
| 190/60-17 | 114 | 660 | 2071 |
| 200/55-17 | 110 | 652 | 2046 |
| 200/60-17 | 120 | 672 | 2109 |
| 200/65-17 | 130 | 692 | 2172 |
| 200/70-17 | 140 | 712 | 2235 |
The graphic below compares common sizes and the effect of different widths and aspect ratios on a tyre’s height and rolling circumference.
This infographic is a useful way of visualising what happens when you change the width and aspect ratio of your motorcycle tyres.
You can see all of our Sports motorcycle tyres here and all of our Track motorcycle tyres here.
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