Some Basic Wheel & Brake Questions
 

I've been putting a mountain bike together from a 1997 Marlin frame as a learning project. At this point I have a RockShox XC30TK - Coil 80mm 26-Inch 9mm fork installed. Now I'm focusing on the wheels. I've been told that my frame will support a front wheel that is disc brake compatible, so I went ahead and purchased an Eastern Nighttrain wheel. I now have several questions that I hope you folks will help me with.

1) Would a Mavic 2011 Crossride UB rim brake mountain wheel be okay/compatible for my rear wheel? I've been told the only way that both wheels could have disc brakes is if I installed an adapter on the rear--something I'd rather not deal with.

2) What size disc rotor should I get for my front wheel. I don't really understand what the different sizes mean. If it's relevant I'll primarily be riding this bike on the street, maybe some mild trails occasionally. I'd like to keep the weight as low as possible without compromising safety.

3) Why is there such a range in the price of disc brake rotors? I've seen anywhere from $20 to $150. What may be gained by purchasing a higher end one?

Thank you for your time.

Your frame doesn't care either way about how you intend to brake your front wheel, that's determined by your fork. ANd the fork you linked to can indeed take a disc brake.
Have you read the spec?
it says:"•No braking surface or disc rotor mount"

Seems a bit odd, but that'd make it impossible to brake in any way.
On top of that it says:"•20mm thru-axle compatible" And it doesn't say what kind of axle it comes with. You need a wheel, or the bits to this one, to make it fit in a fork with the regular 9 mm setup.



Compatible - yes. Suitable - not really.
First of all it'll look a bit funny running a 32-spoke, round stock front wheel and a 20-spoke bladed rear wheel.
Next is that Mavic use proprietary spokes.
Should you pop one, by snagging a branch or something, expect some hassle to have it replaced.
Next is that is if you discover that you like biking, and decide to go for a newer bike further on, that bike is likely to be disc compatible front and rear - and you won't be able to use your old wheels on it.
Try finding a wheel with disc-ready hubs but with brake rims and you'll have the best of both worlds. Rim brake now, and a compatible spare wheel should you ever get another MTB.

They're not that bad actually.

I'd go for a 160 mm one. Means you can run the caliper straight on to the fork, w/o needing an adaptor at all. Bigger rotor basically means more braking at equal finger force, or the same braking at less finger force. And for hard riding, better heat dissipation.

Usually a more expensive rotor is lighter, on account of having more material taken out of it. Then there's a theory that various patterns of cutouts do a better job of being self cleaning from dirt and dust that might otherwise foul your rotors.

Then there's bling value of course.

I didn't doubt you, but that sounded too dumb to be true. Even on Fixie, no front brake is a poor option. About the only thing this might make sense for is a coaster brake beach cruiser. Even there I'd like a front brake so I don't skid into a collision.

It's nice to know that after 45 years in the bike industry, I can still be surprised by the levels of stupidity in the offerings.

To the OP, cancel this purchase, and buy something suitable.

Agreed, but that is what it says. One could assume some sort of typo, but with something as readily available as wheels, I would go for one with a spec that made sense instead. And the rim's suitability for rim braking (poor) can be judged by the pic. There's a slim chance that there'd be a disc brake center mount on the other side of the hub, but why guess? I thought center-mount wasn't compatible with 20 mm thru-axles anyhow.

As far as usage goes, it is an odd combo. Thru-axle is heavy duty, and (to me) usually associated with riding that calls for brakes. Mabye some sort of overgrown BMX/ vert bike?

Seems like the kind of wheel meant for serious downhill guys who only use their rear... Seems sketchy as hell to me, but I'm not a mountain biker so I don't know. I'm sort of bewildered by the idea of a front wheel without a disc mount or rim brake surface...