delay

I have been tossing around the idea of using a BB7 "road" disc brake... with the 140mm rotors in the rear. Is there any reason why I couldn't/ shouldn't do this?

ProFail

Becuase you need disc brake mounts on the bike to be able to do it.


Disc compatable fork, add road BB7's, caliper in the back=Win. Unless, of course, you have a road bike with disc mounts in the back.... Which is unlikely.

pyroguy_3

I'll assume you mean on a mountain bike. Less stopping power, really. I don't personally know if this would be too disastrous because I've never tired it. I'm not sure if you would be able to do this anyway, because of the way the disc mounts are positioned, with respect to the axle of the rear wheel. For instance, I believe if you want to use the 180mm rotors a different bracket must be used to compensate for the extra 20mm added to the rotor.

ProFail

Crap....

markhr

Other than rim brakes SUCK (not really a reason but, hey, any chance to knock crap rim brakes ) there's no reason why you shouldn't. It's an excellent idea.

Please post pictures of the complete build.

M_S

Wait, on a mountain bike? Why use the road version? What levers are you using?

delay

The road version "comes" with a 140mm rotor and adapter for mounting it to the frame. Other than that I don't think there are any differences.

Honestly, what I really need is for our trails to dry out so that I can just start riding and stop worrying about changing stuff on my bike.

pyroguy_3

I hear ya, I've started a list of summer upgrades already. I'm getting real antsy to get out and ride something besides my fixed gear.

C Law

Road bb7 calipers are designed to work with road brake levers. They pull a smaller amount of cable than most modern MTB levers, which are designed to work with linear pull (AKA 'V') brakes.

MTB bb7's are designed to work with MTB levers.


So, like m_s asked above, what levers are you using? If you have MTB levers they won't work properly with the road version of the BB7

pinkrobe

Oh, they will too! Mtn levers pull more cable than standard road levers. Road levers + road calipers is a decent combo, but mtn levers work well [if not better] because they achieve more pad travel with less lever travel. This allows you to set the pads farther away from the rotor, reducing the chance of rotor drag and giving you a smooth, quiet ride.

My road BB7s came with 160mm rotors stock, if it matters.

slvoid

Or you can run STI road levers on a MTB...

ProFail

Oh you.

As a side note, drop bars+MTB=Win

ghettocruiser

From the road forum



Nobody hurt themselves.

BearSquirrel

Do realize that this reduces the leverage of the system. OP, there should be mountain versions available in 140mm.

pinkrobe

How would this reduce the leverage of the system? The road version of the BB7 requires less cable pull because the helix in the caliper moves the piston inboard to the rotor contact point with less rotation of the arm that the cable connects to. Most of Avid's levers have some way to adjust their leverage [i.e. the Speed Dial], so you can fine-tune the feel [power vs. modulation] of rim brakes. The BB7 should have a pretty linear response to cable tension and would therefore not be affected by the type of lever. So there.

Oh yeah, Avid doesn't make mtn cable-actuated disc brakes with 140mm rotors. The 140s are only available for the ROAD version and only in the rear.

C Law

I understand that the road bb7's would work with the mountain levers, i am not disputing that, but it is still not setup correctly.

in essence, you just have more lever movement before the pad engages. which is ok if you like that feeling.

But in addition, you have the caliper setup for x amount of cable pull and you are pulling 1.5x. And not just bringing the outerpad to the disc (which you said was a benefit since you could run more clearance) but bringing the pad through the disc and to the inner pad. I think you would be losing out on alot of modulation even with speed dial adjustments.

Again I am not doubting it would work, but I would think you would have more on/off braking than a nice smooth system.

I have used Linear pull levers with cantilever brakes and have had similiar experience. You can get it to work, but you might as well use the right levers unless you are stuck.

pyroguy_3

I believe this is in reference to a 160mm versus a 140mm rotor. The extra 20mm of rotor that extends from the center of the wheel provides more stopping power because it is essentially a longer lever opposing the rotational motion of the wheel. It has been a while since my last physics class, but analysis of the vectors should prove this. I don't feel like dredging up all that centripetal/-fugal force crap anyway. But common sense should allow one to arrive at this conclusion also.

Ted Danson

That thing is insane.

pinkrobe

Well, since I have this setup on one of my bikes at present, I'll give you my take on it after 6 months of daily riding.

• Pad standoff from rotor - awesome, much better than with road levers [no drag, even with a warped rotor]
• Modulation - great, the harder I press the lever, the faster I stop
• Ease of setup - awesome, even when swapping between wheelsets that don't exactly match
• Power - they're discs, and I use continuous housing for front and rear, so it's predictably good

dminor 

Fixed.

Trekbikedude

Ultimate cross bike?

Phatman

have you ever heard of mechanical advantage?

take a see-saw. put the fulcrum closer to you. less movement on your part=more movement on the other side, but more force is required to push down the see-saw. This is leverage, and applies to brakes as well. The less cable pulled for an equivalent lever travel=more braking force.

markhr

Am I the only one who remebers Tomac's drop bar mtbs?

REPLICA

pyroguy_3

How the hell is that rear wheel laced?

slvoid

That's not a wheel, that's a disc! for aerodynamics.