wheel question - not as knowledgeable as I thought!

PBo

I've buggerered my rim. It'll cost me £20 for a replacement, and was gonna have a go at building using the current hub/spokes. It's 700c, but with disc hub.

However:
Am I right in thinking that even a 700c rim might have a different internal diameter, so spokes might not be right size? or will it only vary by a few mm and not be an issue.

secondly, seen a whole wheel on ebay, built on the rim I was gonna buy (taurus rigida), built on brand-x hubs - which can't be worse than the unbranded hubs I've got, surely? Only 30 quid, must be worth the extra tenner?

But then I remembered - buying a set of QR skewers t'other week, they had different size rear skewers for road/mtb.

Why? Are disc hubs wider? Or is it do with cassette size? Or the frame? How do i ensure this wheel will fit, if I buy it?

thanx

Blue Meanie

Internal diameter is crucial for spoke lentgh, I've often swopped hubs with no bother, but changing rims... You need to check the ERD (Effective Rim Diameter), best way is with two old spokes and a ruler.
You can often get away with "a few mm", maybe even use 14mm or 16mm nipples?

Hub axles are measured OLD (Over Locknut Dimension) and normally:
MTB Front 100mm
MTB Rear 135mm
Road Front 100mm
Road Rear 130mm
Track Front 100mm
Track Rear 120mm

You can squeeze steel frames, but run the risk of making the drop-outs less than parrell. Not advised on Alu frames.

When in doubt:
http://www.sheldonbrown.com/frame-spacing.html

PBo

cheers - because the hub is for disc brakes, i'm guessing it'll be a MTB hub, 135?

Or do i need to measure something?

edit: just followed the sheldon brown link and seen the answer to my own question about measuring.