Rim brake on disc-specific rim?

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UpFromOne
Posts: 1181
Joined: Wed Apr 08, 2009 5:23 am
Location: Olympic Nat'l Park, WA

by UpFromOne

So what do you think would happen if one were to use a rim brake (cantilever) on a disc-only rim?
Assuming the edges are parallel to the spokes, and have enough surface to contact the brake pads.

Jmdesignz2
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by Jmdesignz2

you'd brake badly then they'd break badly

by Weenie


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UpFromOne
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Joined: Wed Apr 08, 2009 5:23 am
Location: Olympic Nat'l Park, WA

by UpFromOne

indeed. anyone here ever actually try it?

mattr
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Location: The Grim North.

by mattr

Yes.
It depends very much on the rim. Some early "disc only" rims were just the same as the dual purpose ones, but with the brake track machining deleted. These will work ok (not as good as a rim with a machined brake track obviously) and should last as long as a normal rim brake rim.

Newer disc only rims are designed around not needing a wear surface, so they can use different alloys, different surface finishes and thinner walls/different profile.
So unless you know, in detail, how the rim has been designed and manufactured, you'll be running a significant risk of having a failed rim, either after a few weeks (wear) or a few days (if the wall is too thin to take braking loads).

What rim were you thinking of?

TheRookie
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Location: Midlands, United Kingdom

by TheRookie

I agree with Matt, it depends very much on the rim in question.

I once rented a bike with a Disc specific rim and V-brakes, it was a cheap (thick) rim, braking was poor until the anodizing wore away (helped by chucking a handfull of sandy dust in the pads everytime I stopped), after that it was fine.

The irony is that early disc specific rims were heavier than the machined rim brake rims despite the fact that they didn't need the extra thickness to allow for wear, not so much 'disc specific' as 'cheap'!
Impoverished weight weenie wanna-be!
Budget 26" HT build viewtopic.php?f=10&t=110956

UpFromOne
Posts: 1181
Joined: Wed Apr 08, 2009 5:23 am
Location: Olympic Nat'l Park, WA

by UpFromOne

Thinking of trying Velocity Blunt (28mm) or Blunt SS (30mm) or Kinlins on a cantilever fork. No hucking, no jumps, no DH, just light xc & gravel.

TheKaiser
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Joined: Thu Sep 05, 2013 3:29 pm

by TheKaiser

UpFromOne wrote:Thinking of trying Velocity Blunt (28mm) or Blunt SS (30mm) or Kinlins on a cantilever fork. No hucking, no jumps, no DH, just light xc & gravel.


Blunts are on the light end of the spectrum for aluminum rims of those dimensions. Not as light as some of the American Classics, or the WTB KOM rims, if memory serves, but that suggests that those wall thicknesses are on the minimal side, and you would have minimal margin for wear. I have seen rim brake wheels fail before simply from the sidewalls getting so thin that the tire pressure splits them, and that would be my primary concern with your idea...basically that you might wear through them quite quickly.

I doubt the alloys are going to be that different from rim to disc, so if you can get accurate sidewall wall thickness measurements to compare disc vs. rim then that would give you better info to make an educated decision. I am not sure how accurate those cross sectional drawings are, so it would probably be worth verifying with some caliper measurements before going for it.

UpFromOne
Posts: 1181
Joined: Wed Apr 08, 2009 5:23 am
Location: Olympic Nat'l Park, WA

by UpFromOne

Thanks Kaiser! I agree the alloys are probably the same, the only difference being a dedicated rim brake track, thus making the sidewall thicker.

Issue came up when researching very light rims, almost all of which are labelled disc-specific.

TheRookie
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by TheRookie

For a reason!
Impoverished weight weenie wanna-be!
Budget 26" HT build viewtopic.php?f=10&t=110956

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

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