Hub dimensions and changing wheels

ravey1981

This might be a daft question or it might be valid..I don't know...

I'm going to get some new wheels at some point and then use my old ones for on road duties with some slick tyres fitted. My current wheels have a Novatec hub, not sure of the exact model.

My question is... are all disc hubs spaced the same? That is, does the disc and the cassette end up in the exact same position regardless of what hub is used. Or are they slightly different and I will end up having to adjust my brakes and gears every time I swap between wheels?

ugo.santalucia

Pretty much all disc hubs are 135 mm rear... there is a very small number of 130 mm rear, but they are meant to go on some disc road bikes. If you have a cyclocross bike it will be 135 mm, which is the standard.
If your hubs are Novatec, you can read the hub model number on them, typically, not always though

ravey1981

Sorry, maybe I should have described what I meant better. I know the axle spacing is 135 but does that mean that the bolt holes where the disc mounts to the hub are spaced from the left dropout the same on all hubs or do they differ? For example, if I got some of the kinesis wheels would the disc end up in the same place exactly as with my current Novatec hubs?

Ouija

Never met two sets of hubs that sit the disc rotor in exactly the same position. They are always a mm closer in or further out, requiring a bit of adjusting of the pads.

ugo.santalucia

As above, but it's less than one millimetre difference typically. You'll have to adjust the pads, that's a given

ravey1981

Cheers, not what I was hoping to hear but probably what I was expecting.... I wonder if the new breed of hydro discs with "auto" pad adjustment for wear will be able to take up the difference...

ugo.santalucia

ravey1981 wrote:

Cheers, not what I was hoping to hear but probably what I was expecting.... I wonder if the new breed of hydro discs with "auto" pad adjustment for wear will be able to take up the difference...

Probably need to adjust the calliper and have the disc centred.

Ouija

ugo.santalucia wrote:

ravey1981 wrote:

Cheers, not what I was hoping to hear but probably what I was expecting.... I wonder if the new breed of hydro discs with "auto" pad adjustment for wear will be able to take up the difference...

Probably need to adjust the calliper and have the disc centred.

That's probably the only disadvantage of Hydros over mechanicals. With BB7's, after switching wheels, i only really have to turn the adjustment wheels on the pads one or two clicks to get everything back to normal. Takes five seconds. No need to unclamp the whole caliper since it's already faced with the rotors. With BB5's and some other types of mechanicals with only one adjustment wheel (typically on the static pad) it can be a bit more of a pain faffing around with the barrel adjusters on the brake levers or unclamping the cable from the caliper to pull it tighter or loosen it.

With Hydros the rotor HAS to be in the center. With mechanicals it can be a little left or right of center without making any difference as long as you keep the static pad almost touching the rotor and the opposing pad has enough material on it to cross the gap and clamp on to the rotor firmly. Which is why i stick with BB7's on my commuter hybrid as i have about four or five different wheelsets for it and i just couldn't be bothered to faff about with the brakes everytime i switched them over.

ravey1981

Thats a good point about the hydros.... You could find out which of your wheels has the disc nearest the dropout, set up the caliper for that and then shim the disc across to match on any other wheels with those really thin washers used for shimming old IS mount calipers. I can't see a reason why that wouldn't work.

ugo.santalucia

ravey1981 wrote:

Thats a good point about the hydros.... You could find out which of your wheels has the disc nearest the dropout, set up the caliper for that and then shim the disc across to match on any other wheels with those really thin washers used for shimming old IS mount calipers. I can't see a reason why that wouldn't work.

With mechanicals it is a bigger job to swap the wheels than it is to adjust the pads... I think you are making a big fuss out of nothing, to be honest

ravey1981

I had moved on from mechanicals and was thinking about getting around issues that hydros would present in this situation. I like things to work first time, without fannying around adjusting things, which is why I don't really like mechanical brakes. They are ok, but not a patch on the fit and forget hope hydros on my mtb. When hydraulics filter down to the mid-low price range, as they will do eventually, mechanical brakes will disappear. Thanks for you're input.

woolwich

Ravey,

Your idea of shimming the discs sounds good. I think i might give it a try. Unless both sets of wheels are more or less identical, this issue is a headache for hydro's in a competitive setting. When youve just punctured you just want to bang a wheel in and carry on and hope to limit your losses, not start fettling.
Mechanicals were great in this respect, just set them up baggy and no issue. I am not regretting to the swop to hydros though. Apart from this bug I believe they out perform in most respects, no system is perfect.
Thanks for the suggestion.

tgotb

I solved this issue by building all my race/training wheels on the same model of hub. Failing that, shims are the answer, and readily available:
http://wheelsmfg.com/rotor-shims.html
http://www.syntace.com/index.cfm?pid=3&pk=757

Hydraulic brakes *do* have a certain amount of tolerance to accomodate different rotor positions (mine do, anyway) but you have to push the pads out before you put the new wheel in, which would be a pain in a race scenario.

On_What

Shims are the way forward, I encountered this going between wheels and didn't fancy setting up BB7s everytime I swapped. So I took some shim steel and made some washers. I believe 4 clicks on the BB7 inner adjuster is worth around half a mm.

ugo.santalucia

On_What wrote:

Shims are the way forward, I encountered this going between wheels and didn't fancy setting up BB7s everytime I swapped. So I took some shim steel and made some washers. I believe 4 clicks on the BB7 inner adjuster is worth around half a mm.

It's good, but I can't do it on mine that way... I've got a pair of rotors which are new and another which have a couple of tenth of mm worn off, so I have to adjust... call it 30 seconds per wheel is a bit generous