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Tyre sizes imperial to metric

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SteveW:
My 650 needs tyres. Currently 3.5 x 19 and 4.5 x 17 imperial.

I realize 3.5 is going to be approx 90 mm width and 4.5 is going to be 110 /120 mm.

When looking on the web for replacements they have the second number which is guess is the profile as a percentage of the width (the same is a car tyre)

My question is what profile percentage would be closest to the original imperial tyres, most of the ones seem to have listed 70,80 and 90.

Hope this makes sense.

McCabe-Thiele (Ted):

--- Quote from: SteveW on September 15, 2021, 07:53:46 PM ---My 650 needs tyres. Currently 3.5 x 19 and 4.5 x 17 imperial.

I realize 3.5 is going to be approx 90 mm width and 4.5 is going to be 110 /120 mm.

When looking on the web for replacements they have the second number which is guess is the profile as a percentage of the width (the same is a car tyre)

My question is what profile percentage would be closest to the original imperial tyres, most of the ones seem to have listed 70,80 and 90.

Hope this makes sense.

--- End quote ---

It's my view that most old tyre sizes are 100% profile (think veteran cars) - you can of course fit a lower aspect ratio you then end up with an inaccurate speedometer due to the lower rolling radius and effectively lower final drive. Aspect ration is Height/Width as a percentage.

As a bonus you could convince yourself the bike is suddenly more economical.lol

Bryanj:
There is a "standard" aspect ratio for the imperial tyres but cant remember what it is

McCabe-Thiele (Ted):

--- Quote from: Bryanj on September 15, 2021, 10:18:42 PM ---There is a "standard" aspect ratio for the imperial tyres but cant remember what it is

--- End quote ---

I believe it's 90% so it's not marked unless it's below that but some show the 90 profile on scooters etc - on modern vehicles not counting baloon tyres for off roaders I think they generally start marking the aspect ratio from 80 and below

sye:
https://www.avontyres.com/en-gb/tyre-care/technical/tyre-size-information/

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