Fallingwater

I've just received the Avid BB7 calipers and G2 rotors I ordered a few weeks ago, and mounted them on my new bike in place of the old brakes it had, whose performance I judged entirely unacceptable.

The situation is now a lot better, owing in part to the ease with which I can adjust both pads, and I think I can get it a bit better still by truing the rotors a slight bit more and adjusting the calipers' mounting brackets better.

So all is good under the sun.

Except... my old MTB's V-brakes still stop faster.

When I brake with them, the lever goes in for a little bit with no braking whatsoever, then the brakes engage. At that point, the pressure needed on the lever to go from "only slightly braking" to "wheel now solidly part of the frame" is not very much. In fact, if going at a good clip, were I for reasons only ascribable to madness decide to pull the levers for all they're worth, the bike would instantly flip me over and land upside down behind me. And then probably crash right on me as I rolled on the ground.

I like it this way, because it makes it a lot easier to lock the rear wheel (I slide a lot during city riding), and for those occasions when risking to endo is better than risking to crash by braking with less force.

But the disk brakes don't work like that. Even set so that the pads are a hair's width from touching the rotors, going from no braking to full power takes quite a bit more lever travel.

Are my disc brakes in fact being outperformed by my V ones, or am I taking a problem for a desired feature? I see many people speaking of how some brakes are better over others because they can be better modulated... is this just my old brakes having bad modulation? Is it very wrong on my part that I appreciate that?

jimc101

Have you bedded the pads in? as this will make a difference to the stopping power.

For outperforming V's, in the dry, the cable discs will be similar, but it's in the wet that you should find discs are a lot better at stopping you.

For locking the rear wheel and sliding, you need to learn how to brake properly, as if sliding / skidding, you are not in control of the bike

Mark Kelly 

You're not by any chance using road BB7s with mountain levers are you?

Infidel79

You can adjust the cable pull ratio, and thus the modulation, with Avid Speed Dial levers. Problem solved. This is the setup I have, and I can easily modulate between just feathering the brakes to endo force, and everything in between, with one finger on the lever blade.

LarDasse74

Additional info required: What brakes did you have before? What brake levers do you have?

Fallingwater

I learn now that there is more than one version of BB7. I guess I should have gotten more information...

Anyway, mine are these:


I'm using them with the levers that came with the original brakes - and yes, the bike is a MTB. I don't have it here with me now so I can't tell you what the levers are, but I do remember they're Shimano, and shaped to fit together with the gearshifters. Can I replace just the levers on a system like that? I *really* don't want to mess with the shifters too, especially since I actually like how they work...

Cheap brakes. They did have their own brand (not Shimano or, I think, anything famous), but I can't remember it right now. I also remember googling for them and not finding much information at all.

dabac

Yep. There's one version to go with short-pull, canti/caliper compatible levers, another to go with long-pull V-brake levers. Getting the mix wrong may or may not be critical, but it will mess with the expected brake response.

Unfortunately I can't ID road/MTB calipers on looks only.

Doesn't really say anything. Brifters have been around long enough to be available in both canti/caliper as well as v-brake versions.
If you bike came prepared for disc brakes, and those are the originals brifters, then odds are that they're v-brake levers - which together with road calipers would make braking require more force.

No. If you insisted, you could run a Travel Agent in reverse though.

Mark Kelly 

They should be marked on the swing arm - they'll say either BB7 Road or BB7 MTN.

With your Shimano levers, check the internals. Some Shimano levers have two actuation slots for the cable pull - one marked V which is further from the pivot, one marked C-R which is closer to the pivot. Usually there is a piece of red plastic which holds the cable end in the appropriate slot. If this is so and yours are set up on the V brake slots, pull the piece of plastic out (be careful !), move the cable end to the other ( Canti / Road) slot and re-insert the red plastic bit (Be careful !).

The plastic part is the bit labelled "4" in this exploded view PDF : https://techdocs.shimano.com/media/te...9830612364.pdf which otherwise doesn't show much of the brake lever internals.

If you look carefully you'll see that compnent 4 is marked V C-R.

Infidel79

Just so I'm clear, this procedure should only be done if the OP determines that he/she has the Road version of the BB7, right? Otherwise, the V position at the lever pivot should be used for BB7 MTN calipers...is this correct?

Mark Kelly 

I assume so but I haven't done it myself.

Fallingwater

I'm back at my mom's place, so I can give you more info on the bike.
The brifters are Shimano ST-EF 60L (pictures here). I can't see any plastic parts as described.
The brakes I had before are Promax DSK-400 (pictures here).
The Avid BB7 I have now are the mountain-bike version (they have MTN printed on them).

cyccommute 

Let's be careful about terms here. Brifters are the common name for road brake/shifter levers. Those are only available for use with cantilever brakes, road caliper brakes or road specific disc brakes. Because the brake lever and the shift lever use the same lever arm to both shift and brake, they are called brifters. Mountain bike shift lever/brake lever pods aren't really the same mechanism. The shift lever is separate from the brake lever (with one unpopular exception) and we should call them something else to avoid confusion.

Fallingwater implies that he was using the brake levers as he was with the v-brake and since the calipers are marked 'MTN', he's using the proper levers.

Fallingwater: You've run across what I have been saying for a long time about disc brakes. I'm not popular for saying it but I don't see the allure. I don't think that disc are all that much better than a good set of v-brakes. I don't even think that a good set of v-brakes are all that much better than a good set of properly adjusted cantilevers.

Your issue may be related to a difference in the way that the brakes operate. It sounds like you have a bit of travel on your v-brakes before they engage. Disc brakes have very little lever throw between off and engaged...much less than is usual for v-brakes...because they are set closer to the rotor. This makes them engage faster but you also have more cable run from lever to caliper on disc brakes. A longer cable can make the brakes mushy since you have more housing to compress and more cable to stretch. You might try anchoring the cable in more places down the fork leg so that the cable can't bow out under pressure. If it can move, you've got that much more mushiness built into the system. Ziptie the cable to the fork leg just above the caliper and at least at the top of the leg. You may want to tie it down in the middle of the leg too. This will keep the cable and housing from bowing out away from the leg of the fork and should improve the braking.

Infidel79

Nashbar sells Jagwire-style compressionless (axially stranded, kevlar jacketed) brake cable and housing kits for about $10. For the rear brake, run full-length housing. This will actually result in less total friction, as the point where the cable enters the housing allows water and dirt to enter, and contributes to friction on its own. Also, FWIW, when comparing disc to rim performance, assuming each system is performing optimally, one must account for rigors of technical trail riding to appreciate the differences. A stream crossing or muddy puddle, just prior to a technical descent, provides a clear example of where discs out-perform any type of rim brake. An out of true disc rotor produces negligible drag against the pad, whereas an out of true rim can make v-brakes very tiring to ride back to the trail head. Just sayin...

cyccommute 

Probably a good idea. Couldn't hurt but still tie the cable to the fork leg.

Been riding mountain bikes on techical descents since the end of the last ice age...or at least how it seems. Honestly, I bought my first mountain bike in 1984. Cantilever brakes, no suspension and I've ridden through enough mud and muck to fill a swamp. I've even done high speed descents in pouring rain and never found that I lacked for brakes. A slightly less powerful brake has its place like on ice or wet slick rock.

Rim brakes also clear quickly after intermittent wetting.

Huh? Have you looked at the gap between a pad and a disc brake rotor? There's a only about a millimeter clearance on either side of the rotor. If the rotor is bent only slightly out of true, you'll have to straighten the rotor or walk.

With a rim brake, you can always open them wider if the rim is out of true and still have effective brakes. I've had to ride for miles on a wheel with a broken spoke - probably the most out of true you can get a wheel and still have it rideable - and all I had to do was reposition the cable on the brake caliper so that the calipers ran a bit wider open. You can't do that with a disc.

Infidel79

Ok, you've got about 6 or 7 years of mountain biking on me, which is duly noted, but I've never wished I had slightly less powerful brakes, so I just don't view that as a disadvantage of disc brakes.



Sometime quickly is not quick enough. In my experience, this is a major advantage of discs over rim brakes. Mind you, the bulk of my riding has been in New England, which is fairly technical, and fairly wet. Maybe that's a factor.

Have you ever had this happen? I have not, nor do I know anyone who has had this experience. I'm talking about a slight rub, which happens, but is still a relatively rare occurrence. No adjustment necessary, just ride normally. On a rough trail ride, wheels can get knocked out of true much more easily than disc rotors. It's actually a bit of a moot point, because this is far from my favorite aspect of disc performance.

Was this on a mountain bike? Under this scenario, how effective the brakes remain, as well as how rideable the bike remains, is open to interpretation. One of my riding buddies tacoed his front wheel about 10 miles from the trail head. He was able to straighten it enough to clear the fork, but the rim was cracked, so he wrapped a length of inner tube around the cracked rim section, tire and all. Stuffed the tire with leaves and grass. Remarkably, he was able to ride back to the car (gingerly) with a fully functional front disc brake. I suppose there will always be a scenario, real or imagined, wherein one type of brake is superior to the other. However, in my 20 or so years of mountain biking, the last several of which have been with discs, I can say that discs suit my riding much better, especially when I'm not grinding my expensive-to-replace rims with mud.

cyccommute 

I've ridden in New England. With a v-brake equipped bike and a disc brake equipped bike. Not noticeable difference in performance of the brakes. If anything the discs were a bigger pain in the butt because the calipers had to be realigned each time I removed the wheel to put the bike in a car...which I was doing a lot. Other people have had the same problem with alignment and have mentioned it on these boards.

And New England isn't any more technical than Colorado. Depending on where you go and what time of year it is, it can also be as wet.


To me personally? No. However I was with a person on a ride who managed to jam a 1.25" diameter stick between the fork, through the disc and into the wheel. Mangled the disc. I know of others who have bashed the disc on rocks and logs. That bends them too. I can true a wheel in a matter of seconds. Truing a disc is much more difficult.



Yes. Mountain bike. The wheel wobbled 5 to 15 mm out of true which is enough to hit the brakes without opening them up. Open the brakes, reduce some tension around the broken spoke and ride gingerly to the trailhead. The woman above walked back, pushing the bike on the rear tire because the front wheel wouldn't turn. Yes, a tacoed wheel can make a rim brake bike just as unrideable but a bent and jammed rotor isn't rideable either.

Infidel79

I've never had an issue with caliper alignment, but will happily concede on this point; fact is, most riders I know in N.E. use wheel-on style roof or hitch racks, mostly to accommodate through-axle forks and to avoid putting muddy bike wheels in the car.

I was also thinking about the examples we each cited, and the fact is, those are both somewhat catastrophic events to occur on the trail (trashed rotor, trashed wheel) which could have been a lot worse, and at which point one's choice of rim or disc brakes is probably among the least of one's concerns. Myself, I was late to jump aboard the disc band wagon; using some of your arguments, I even convinced a friend of mine not to "waste" his money on discs when buying a new bike. I have now changed my position and he has since converted to disc brakes (he now prefers them), which was costly, mainly due to the necessity of a new wheelset with disc-compatible hubs.

jchabalk 

i had a similar experience to yours with the avid mechanical disc brakes.

My mountain bike with V-Brakes still has the best stopping power when compared with my mechanical disc equipped bike and my canti equipped bike. Hands down, no questions asked. (the bike with cantis probably out-performs the bike with discs too)

In dry conditions.

The thing about the discs is that even when they're soaking wet the stopping power is pretty much identical to when they're dry where as with V-Brake and Cantis I lose a significant amount of power when they're wet.

I wouldn't say I'm necessarily sold on the mechanical discs and if i had a mulligan on the decision to buy my frame with disc tabs instead of canti studs i can't say i would make the same decision but the mechanical discs do work pretty well in all weather and the others not so much.

EDIT: My Disc brakes are the BB7 Road with Road pull brakes. That bike and my canti equipped bike both have the same 700c tire on them and a similar rim. Both are built up in a pretty similar fashion too

MichaelW

To bed-in disc brakes, find a big, steep hill.
Ride down at normal downhill speed. Apply the brakes firmly but DO NOT SKID. Release the brakes, gain speed and apply brakes again. Repeat 8-10 times.
Some people recommend cooling the brakes down by pouring water over them. They will be hot (do not touch) and water will steam off.

Flying Merkel

+1 Worked for me.

I bought a set of Nashbar mechanical discs. After bedding in, they stop as well as my Shimano LX V-brakes. No more funny noises after riding through wet sand. Using them with a shift/brake lever combo, also from Nashbar.

Discs are a little harder to adjust, but require less of it. If you bend a rotor on a ride, you can open the adjust up or pull off the rotor. No brake system is perfect

Fallingwater

This makes me wonder... if I were to assault the pod with a Dremel, it should be possible to cut the brake lever apart from the shifter. It'd ruin the lever, but as the objective is to replace it, that isn't much of an issue.

Flying Merkel

That's along the lines of knitting your own shoelaces. It's an accomplishment, but not efficient

electrik

Avid bb7 aren't much stronger(you can get a larger rotor) than my parallel push rim brake, but they blow them away in the wet.

If your brakes aren't engaging at the correct point you need to adjust the pull.

fietsbob

160's 0n a 20" wheel they are positively grabby..

cyccommute 

I agree. It can be done but it would be difficult and uggggggllllllllyyyyyyyy. Shift pods and separate levers aren't all that expensive depending on what level of components you have or want. On the other hand, if you components are lower level and you have the time and patience, hack away!