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philehidiot

Joined:

Feb 09

Posts: 4772

philehidiot says:

The idiot and his rim size

Eh up,


I have a bike with stupid tyre sizes - 100/90 -19 and 130/80 - 17. I'm looking at the possibility of sticking different tyre sizes on the same rims. I've done this before but what I need to know is how far can you go with each measurement (width and aspect ratio) when putting different sizes on and at what point are you taking the piss?

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  • Posted 3 years ago (25 August 2012 16:28)

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jaffa90

Joined:

Mar 09

Posts: 9029

jaffa90 says:

sizes

Stick to the recommended sizes in the owners manual,this will make your insurance company unhappy. 

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eatcs01

Joined:

Aug 02

Posts: 3287

eatcs01 says:

tyres

You can go up by 10 on the width, but you need to down by 10 on the profile, ie. 100/90x19 would be 110/80x19
It is only recommended that you go up/down by 10...

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philehidiot

Joined:

Feb 09

Posts: 4772

philehidiot says:

cheers

both of you. Doubt it'd help if I have to go down on the aspect ratio. 


Last time I did this I checked with my insurance company at the time and they were okay with it but ebike do seem to be stricter on things so they might well disapprove - good point.

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eatcs01

Joined:

Aug 02

Posts: 3287

eatcs01 says:

tyres sizes

If you DON'T go down on the aspect ratio then the tyre will have a much flatter shape, and certainly won't handle as well.

If you go UP on the width, THEN YOU MUST GO DOWN ON THE RATIO TO MATCH.
Or just stick to the OE sizes.

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Dabbsy

Joined:

Aug 02

Posts: 500

Dabbsy says:

tyre sizes

As one figure is a linear measurement and the other is a ratio they can’t be transposed. If you look at Bridgestone’s BT45s which are widely sold, the 130/80 x 17 is 638mm wide and fits rims between 2.5 inches to 3.5 inches with 3 inches the optimum. A 140/70 x 17 is 627mm wide and fits rims between 3.5 to 4.5 with 4 inches the optimum. Stick to the manufacturer’s recommendations.

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