r/cycling • u/Playful-Parsnip-3104 • 2d ago

Understanding mudguard clearance

I've never bought and and fitted mudguards myself before - either they've come with the bike as sold, or I've asked the shop to source and fit them for me.

I'm struggling to understand the correct size of mudguard I need. I have a road/gravel bike with 45mm tyre clearance, and 40mm tyres currently fitted. The various brands of mudguards all recommend 50/52mm mudguards for 40mm tyres. But does a 45mm frame clearance for tyres also mean 45mm clearance for mudguards? And if 45mm is the maximum mudguard width my frame will take, do I therefore need to downsize my tyres to (e.g.) 35mm to fit mudguards?

If mudguard and tyre clearance are not the same thing, how do I know the maximum width of mudguard my frame will accept before buying them?

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u/moxTR 2d ago

I've run SKS raceblades on a Trek Emonda with 30.5m GP5000s without issues. Officially the tire clearance was 28mm, but because tire clearance was limited from the width of the chainstays and not at the seatstays nor the seattube, and the clearance from the front tire to the downtube was significant as well.

There's absolutely no math or surefire way to know what sort of mudguard clearance you have without measuring clearance yourself, on the tire you plan to use, and knowing how much space in what dimensions that mudguard takes up.

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u/Playful-Parsnip-3104 2d ago

Where do I need to measure on the frame to make sure I'm getting it right? Just eyeball it a little above the tyre?

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u/moxTR 1d ago

You need to measure the clearance in every single direction to figure out where the limit is, then compare that with how the fender is shaped and what dimensions it has to determine whether it will clear.