Rims for use with drum brakes

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Mr Tom
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Rims for use with drum brakes

Postby Mr Tom » 8 Dec 2018, 7:49pm

I'm looking for a replacement rim to build into a wheel with Sturmey Archer Steelite drum brakes. The rims I've found online which are the correct size all say 'For rim brakes only'. I can't see why it would be an issue using them with other kinds of brakes, but as it seems something they all list in their specifications I thought it was worth asking - is there something I'm missing? It seems like a stupid question to ask, sorry!

Brucey
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Re: Rims for use with drum brakes

Postby Brucey » 8 Dec 2018, 9:42pm

pretty much any rims will work with SA hub brakes. Do check yours but IIRC nearly all steelite hubs were 36 drilled. They will definitely benefit from being built with spoke washers; with some spokes two washers per spoke are best.

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LittleGreyCat
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Re: Rims for use with drum brakes

Postby LittleGreyCat » 8 Dec 2018, 10:05pm

Is there a difference in rims required for disc brakes?
Just wondering if it makes a difference if the centre the of the wheel is trying to stop the rim or vice versa.
Rear wheel the drive is from the centre anyway, but it might make a difference to the front.
Edit: thinking of the size and number of spokes.

Brucey
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Re: Rims for use with drum brakes

Postby Brucey » 9 Dec 2018, 8:38am

there are higher spoke loadings at the rim when a disc or drum brake is used. In practice with SA hub brakes they have 36 spokes, large flanges and the increased loading is no big deal. With derailleur geared disc brake wheels there are more greatly increased spoke loads because

a) the wheels are more dished and
b) manufacturers typically use fewer spokes (28 or 32 isn't unusual) and
c) the hub flanges are often quite small diameter.

These things add up and the result is that some spoke tensions might increase to about double what you might find in a hub-brake wheel when disc brakes are used hard. This loads the rim aggressively. Nonetheless in such wheels the most common rim breakage still occurs on the drive side rear spokes, presumably because that extra stress is there all the time, not just when you are using the brakes.

Most rim brake rims are strong enough not to crack at the drive side rear and therefore don't give problems if used in disc brake wheels either. It seems that those who specify disc brake rims on mainstream bikes will often choose a relatively lightweight and flimsy rim (possibly trying to make up for the weight of the disc brakes); failures at the rim (mostly at the drive side rear) are not at all uncommon.

cheers
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Mr Tom
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Re: Rims for use with drum brakes

Postby Mr Tom » 9 Dec 2018, 10:33am

Ah OK, thanks! I was wondering if stopping the rim from the hub was the reason. I'll look into the washers. There may be some on the old rim I can re-use.

Brucey
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Re: Rims for use with drum brakes

Postby Brucey » 9 Dec 2018, 11:55am

the washers you need to use are small ones that go between the spoke heads and the hub flange

Image

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Mr Tom
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Re: Rims for use with drum brakes

Postby Mr Tom » 11 Dec 2018, 11:28am

OK thanks! Have ordered some