Disc brakes on 'Rim only brake' wheels

[tonypreece]

This sounds pretty obvious doesn't it ? ...
I've just collected my bike from the store following a warranty repair, they've replaced the front wheel for me, but with a different rim as they couldn't get hold of the original. The bike has disc brakes, but the new rim, Alexrims CX28 comes with a warning saying 'for rim brakes only'.

Before I take it back and kick off at the store, can anyone tell me how safe/dangerous it would be with this setup and how much of a fuss I should make, if any?

[foxyrider]

What quite do you think the isssue is?

There is no good reason for not using 'rim brake' rims with discs, the thing not to do is the opposite, that is run rim brakes on 'disc' rims.

Unless of course Alex have specifically weakened their rim the sticker seems to be a rather stupid addition.

[Cyril Haearn]

We don't know what we don't know, maybe there is a reason

[gxaustin]

Can we assume the wheel is not radially spoked?

[andrew_s]

Putting Alex CX28 into google gave 6 shops selling wheels with CX28 rims on the first page, and all of them are offering disc hubs.

I might go back to the shop and ask why Alex put the sticker on, to see if they could come up with an answer, but only if it was convenient.
The only things that make a wheel unsuitable for use with disc brakes are radial spokes and not having a disc hub.
I can only guess that Alex want you to pay more for a disc-specific rim (which may be a bit lighter)

[PT1029]

I recall ages ago 1 rim coming out saying the center section (ie spoke holes bit) was thicker to with stand the extra stresses of disc brakes on the spokes, so there could well be something in the validity of the sticker.
Alex Rims - http://www.alexrims.com/products/cx28/ (their site seems a bit slow...) - don't say don't use disc brakes on their website, but the picture does have (part of) the sticker visible that says for rim brakes.
Disc brakes don't feature in the FAQs either.

So no definative answer for you, from me at least.

I too saw the top of the Googling offering the rime with disc hubs.

[andrew_s]

Surely any stresses on the spoke seats from disc brakes twisting the hub within the wheel would also occur from pedalling forces when used in a back wheel?
I can't see anyone putting a "front wheels only" sticker on their rims.

[[XAP]Bob]

Surely any stresses on the spoke seats from disc brakes twisting the hub within the wheel would also occur from pedalling forces when used in a back wheel?
I can't see anyone putting a "front wheels only" sticker on their rims.

Bakes are much, much stronger than legs.

A brake will take you from 20+mph to 0 in a few metres - no way on earth you’ll manage the same in reverse by pedalling...

[thirdcrank]

... Bakes are much, much stronger than legs.

A brake will take you from 20+mph to 0 in a few metres - no way on earth you’ll manage the same in reverse by pedalling...

(Thinks.) We did have a thread on here not so long ago where some argued that fixed wheel was a very efficient way of performing an emergency stop. ......

[Brucey]

FWIW rear wheels with disc brakes still crack rims, but they tend to crack on the drive side, even when the hub is relatively torsionally flexible, and braking loads are not well transferred to the DS spokes.

I suspect that the real reason for this sticker is lazy label making; you have a sticker saying 'disc brake only' on disc rims, so why not the same thing with one word changed in the rim brake rims...?

cheers

[[XAP]Bob]

FWIW rear wheels with disc brakes still crack rims, but they tend to crack on the drive side, even when the hub is relatively torsionally flexible, and braking loads are not well transferred to the DS spokes.

I suspect that the real reason for this sticker is lazy label making; you have a sticker saying 'disc brake only' on disc rims, so why not the same thing with one word changed in the rim brake rims...?

cheers

Yes - the real reason is almost certainly marketing.

The normal mechanism for rim cracking is fatigue though I guess - and despite the lower loads that the chain drive produces compared with the loads of a disc brake they cycle twice per pedal revolution, so the cycles add up pretty fast.
The braking stresses will be higher, but will only be rarely loaded.

IF the limit was pure strength on a deliberately weakened/lightened central section of the rim then disc brakes are more likely to cause failure than pedalling forces. That's unlikely to be the real risk though.

[freeflow]

It probably means that they have brake tracks for rim brakes. Illogical labelling though.

[unnamed]

Sort of related label