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OS20 Wheel Size - All you need to know!

John Bentley's Supercross SX450 OS20.

What Is OS20?

OS20 is NOT 22”. OS20 is 20”, but bigger. There are two wheel sizes in the 20” category – the 20” on Jr/mini bikes which uses the 451mm diameter wheel in narrow widths (for 20-1/8” & 20-3/8” tyres), and the conventional 20” which uses the smaller 406mm diameter wheel but in wider widths. OS20 is 451mm wheel diameter in similar widths as 406mm wheels.

OS20 tyres are not compatible with Jr/Mini sized rims, and OS20 rims are not compatible with Jr/Mini sized tyres.

Is OS20 Race Legal?

Independently verified, OS20 wheel and tyres are within UCI BMX sizing regulations for 20”.

What Do I Need For OS20?

OS20 specific frame, OS20 specific wheels and tyres (including OS20 rim strip and OS20 innertubes) are essential for OS20. Many current front forks made for 20” bikes will work with OS20.

Why OS20?

OS20 rolls faster and retains greater forward momentum. This is achieved by a few factors.

First, it is well understood that minimising the energy loss from the tyre casing's deflection is key to reducing rolling resistance. The tyre's sidewall compressing when weight is applied is one example of casing deflection. When compared with 20”, OS20, with its larger diameter and greater air volume, exhibit a smaller proportion of its casing deflecting as it rolls – so smaller casing deflection, less energy loss.

Second, the shape of the tyre's contact patch also affects rolling characteristics. The contact patch the shape of the tread as it meets the ground. OS20 tyre's larger air volume creates a different contact patch due to less casing deflection (see above). OS20 tyres exhibit a smaller footprint resulting in lower rolling resistance.

Another benefit of smaller casing deflection is being able to maintain more forward momentum. As larger diameter tyre casings deflect less when rolling, less energy is wasted in overcoming the casing deflection, thus more forward momentum is maintained. OS20 has potential for higher top-end speed and more efficiently maintains the speed.