Disc Brake and Wheel ???'s
 

excuse the newbness of many of these, but up until about two months ago, my only bikes were a 59 Schwinn 3 spd and 61 Schwinn Corvette cruiser :P Now I own a '03 JTS (hehe, new gf is biker chick!) and also have a Nashbar frame, carbon fork and disc brake setup which I'd like to build up, hence the need for some answers.

I did search the forum but haven't found what I am looking for which just might be a FAQ, if there is one please point me in the right direction. OK..sorry, for the longwindedness...
my questions have to do with wheels. I'm reading some confusing info on here as to what 700c wheels are compatible or what characteristics make them compatible with disc brakes? any pointers? also, what makes a road wheel cyclocross worthy? I see some advertising of this type of thing on ebay and CL..."road wheel will also work for cyclocross", etc. Again, what sort of thing should I be looking for to help guide my buying decisions? or do I have to build my own wheelset? (eeks!) The learning curve here seems steep and a bit technical for a newb at times, which is part of the reason I wanted to build up bike in the first place - so I could do some learnin'.

thanks for any info or help.
-Tony O

fyi, I had originally planned on moving everything over from the JTS, but now have decided it would be nice to have second wheel set and will build up Nashbar for more off roading, keeping the JTS as light duty trail and cross town bike.

just get a disc brake hub, a rim and get the shop to build it for you.

You could also buy off the peg spoked, deep section or aerospoke carbon wheels

I went with DT Swiss 240s disc hubs, Mavic CXP33 black rims, DT Swiss stainless 2.0 straight guage spokes - makes for slightly heavier wheels that are relatively bomb proof

thx mark, but you assume too much. I wouldn't even know what type of rim is good for cyclocross and what size it needs to be to fit the size of tires I want to use 35-38mm. Yes, I know that 38 is against official rules but I highly doubt I will be entering any races in this life. I'd probably prefer to buy complete wheelset and since I won't be racing, it doesn't have to be top notch either, just good enough for some fire roads and some single track.

cheers
Tony O

find a good quality bike shop in your area and have them build up a wheel - if you don't know exactly what you need the bike shop guys will be more than happy to help with specifics I'm sure

http://www.yellowpages.com/

haha...thanks for the yellowpages link ;P

I've recently seen a couple of wheelsets for about $200 or so on ebay and may likely buy one of those in due time, but since I am mainly asking questions for knowledge I guess what I want to know is this..

am I correct in thinking it's the HUB that dictates whether a wheel is disc brake compatible or not?
The other half of my question could still use clarifying...is there a certain characterstic of rim that makes it suitable for off roading as well and I guess the thickness of spoke is also important?

I may just do what you suggest though I will go to local bike co-op (we have this place called the Bike Church here in Santa Cruz) and see if they will help me build a wheelset myself. No substitute for knowledge, but I would still like to know what sort of rim to order.

thanks again for helping a noob.
cheers
Tony O

I'm moving this to the mechanics forum to see if there might be some better answers there...

You will definitely need disc brake compatible hubs, since you need a place to attach the brake rotor! I have built several sets of 700c disc wheels, and I have been using Velocity Dyad or Alex Adventurer rims with Shimano XT six bolt hubs. I prefer 36 spokes per wheel, and use DT Swiss Competition 14/15 gauge butted spokes. There are a lot of other parts you could use.

I'm no expert, but I do know that you will need a disc specific hub. The wheels on my Cross Check can be used for disc or rim brakes. The difference is that they have the rotor mount on the hubs - it is a circular ribbed piece that sits outside of the spokes, but inside of the drop out on the frame (I know, that was a rough description). What makes a good CX wheelset? I like a 36 hole rim for added strength, but I run about 225 lbs. Spoke count might not matter if you're one of those skinny guys. You also will need to know the width of your rear dropout on your frame. The Cross Check is set at 132.5mm so it can accept either a 130mm road wheel or a 135mm cross/29er wheel. Hope that helps.

Spoke count does matter when using a disk brake, remember that the brake torque has to go through the spokes on a disk brake, as opposed to through the rim in a rim brake. In both cases, there are other reaction forces going throughout the wheel, but definitely forget about low spoke count (or radial build, for that matter). Add the type of terrain you'll go through compared with a typical road bike, and you'll see the virtue of 32-36 spokes, strong build.

thanks guys...

so it looks like (for those following along at home),

disc specific hub
more spokes=better
pick a quality spoke, assuming thicker is better here too.

and now the rims...
is there a rim design that is inherently stronger?

All this stuff seems ideal for a FAQ since quite a few
cross people are starting to think about disc brakes
and asking some of these very same questions.

cheers
Tony O

Hubs: Must be disc compatible. MOST disc compatible hubs are 135 mm overlock, and thus will need that kind of spacing on the rear dropouts. If you are using the Nashbar X frame (great frame, I built a bike with this) then you're easily covered.

Spokes and count: 32 min, depending on your weight and intended usage. At 150 lbs I go with 32. I'll second the vote on DT swiss Competition spokes.

Rim: Whatever rim you use, I would make certain that it's eyeletted...at least single eyeletted. This is due to the braking forces going through the spokes. Provided you can achieve that, then the rest of the features of the rim will depend on usage. Want light and fast? Mavic Open Pro should work fine with your discs. Want stronger? CXP-22 or 33. (Not 23...not eyeletted.)

Mavic also makes a disc specific rim for 700c wheels, and it's what I use. A317 Disc. What makes it disc specific? It lacks a braking surface, so they didn't go to the trouble to make it nearly seamless, or to machine the sidewalls and reinforce them for breaking. It's also double eyeletted, which made it terrifically easy to build, and is supposed to reinforce the rim at the point of spoke entry to withstand the force of braking. It's a little heavy, but it's a triple hollow rim that can withstand some pretty awful roads.

Provided you get a rim that's eyeletted and will be suitable in weight/construction for its intended purpose, you then need to look at width. A "road" rim will often be no more than 15mm in width, giving it capacity for 28-32mm wide tires, tops. (Though some run wider with no issues.) A317 rims are 17mm wide, with capacity for greater than 40mm wide tires...though no smaller than 25mm.

So.

You must have a disc hub, or else you can't attach the disc.
Competitions are a good double butted all around spoke, and make the count no less than 32.
Rims will depend on intended usage, but I would personally at least stick with eyeletted.

Double-butted spokes are stronger than straight gauge. Thicker is not always stronger.

Higher spoke count helps with strength, as does build pattern. A 36 spoke 3-cross using 14/15 DB spokes should be strong enough for most anything.