MTB technology - ignorant roadie

[kieran]

Can anyone help - my knowledge of MTB tech is set at the pre 2000 rigid MTB v-brake era. I have just bought off ebay a hardtail disc brake only frame so I need to update my brain.

Disc brakes:

mechanical (e.g. Avid BB7) v hydraulic (e.g. Formula oro k18)
what are the parts for a disc brake? rotor, pads, cable etc?
Are they left/right handside specific - due to frame fixing points?
How does the diameter of the braking surface (the disc?) affect brake power

Can you mix'n'match brands?

could I mix front v-brake (i.e. buy a fork with fittings for both disc and v-brakes) with rear disc brake? (saves money as could then use current front brake and only need to get a new rear disc brake.

Also currently my old bike has 24 gears, i.e. 8 speed on the rear, should this fit ok onto new wheels, spacing wise?

[Sylv]

Disc brakes:

mechanical (e.g. Avid BB7) v hydraulic (e.g. Formula oro k18)
I'd go hydraulic if you buy both discs front and rear (more power + if you have a front vbrake you might as well do without the "hassles" of hydraulics just for the rear (bleeding mainly). If you just get one end I'd say maechnical would be a good choice (Grahame swears by his Avids)

what are the parts for a disc brake? rotor, pads, cable etc?
Disc brake system should include everything yes, including the lever. Hydraulic ones will be all built up so you just have to fit it and don't worry about the bleeding.

Are they left/right handside specific - due to frame fixing points?
If you buy a rear disc system it will generally come with a left lever in the uk (unless otherwise specified). Some brands you can run the left lever on the right but not many (Hayes I think)

How does the diameter of the braking surface (the disc?) affect brake power
Yes it does. 160mm is the most common and is fine for uk mtbing, you can get 180mm and sometimes 140mm (rear only)

Can you mix'n'match brands?
I wouldn't.

could I mix front v-brake (i.e. buy a fork with fittings for both disc and v-brakes) with rear disc brake? (saves money as could then use current front brake and only need to get a new rear disc brake.
Usually if you are going to mix you would do it the other way round as the front brake does 75% of the job, so it makes sense to have a disc there. I'd rather have one single system as otherwise you could possibly get the worst of both worlds (bad points of vbrakes + bad points of disc brakes).

Also currently my old bike has 24 gears, i.e. 8 speed on the rear, should this fit ok onto new wheels, spacing wise?
yes no difference in cassette width

PS be aware there are two mounting systems on the frame: International Standard (most common until recently) where the bolts are perpendicular to the frame/forks and Post Mount where they are parallel (becoming the norm).

[Dombo]

Sylv has covered everything except I would only add you should get sintered pads as they last longer in the current wintry conditions.
Regarding running a rear disc and front V, I did that for a while as although 75% of braking power is on the front, I tend to use the rear more on the mtb to reduce the risk of an endo. I also find the 160/140 combo to be fine for my style and weight ie x-country at 65kg.

[Sylv]

Forgot - I have a spare used Shimano front disc system (XTR caliper, XT lever, all built but no rotor) if you want to buy it from me. it's international standard

BUT it's a LH lever

[Grahame]

Pretty much agree with Sylv. With the following additions:

Yes, I pretty much swear by my Avid BB7 mechanical disc brakes, whereas I used to swear at every hydraulic disc brake I ever owned.

If you already own a set of mountainbike V-brake compatible levers, then that would make up my mind for me - Avid BB7s. Cheaper than hydraulic systems, easy to set up, easy to repair and you can replace the pads mid ride with only your hands (no tools required).

If going hydraulic, go for a mineral oil system rather than DOT brake fluid. Hayes, Shimano, Avid all fit into this category. Mineral oil doesn't absorb water, and in an emergency, you can run them on cooking oil. And it doesn't melt the paint off your frame when they leak.

I'm a *bit* heavier, so I use a 185mm disc at the front and a 160mm disc at the rear. This works fine for me, even in the Rockies.

<pedant mode>
Bigger discs don't mean more power, but the do mean more stopping torque, and that's what really matters.
</pedant mode>

[kieran]

[quote="Sylv"]Forgot - I have a spare used Shimano front disc system (XTR caliper, XT lever, all built but no rotor) if you want to buy it from me. it's international standard

BUT it's a LH lever

[Grahame]

This is another advantage of the Avid disc systems (both hydraulic and cable actuated) the calipers are designed for post mount, but come with an adapter to IS mounts as part of the package.

Have I mentioned before that I really like Avid brakes, especially the BB7 cable system?

[kieran]

So Graham, what brakes would you recommend then?

Is it also true that I can use existing v-brake levers with the BB7 disc brakes?

[quote]Can you get adaptors to fit IS barkes to PostMount and vise versa?

[quote="kieran"]So Graham, what brakes would you recommend then?

Is it also true that I can use existing v-brake levers with the BB7 disc brakes?

[Elliot M]

ah, but grahame you were wrong on one point - hydraulic avids use DOT not mineral oil.

i have the corroded paint, fingertips and brakes seized after being left in damp garage to prove it.