bb7 160 front on 29er

hobiesmith said:

is bb7 and 160 front rotor going to be enough to stop a xc 29er rig with 175lbs rider?

anyone know and can you suggest the best rotor?

if not bb7, how about juicy ulitmate?

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I weigh 180 and ride and race 29"ers outfitted with BB7s and Alligator Windcutter rotors 160mm front/140mm rear. I was using 180mm Alligator Windcutters front and rear in 2008, but found that to be too much resulting in a lot of sliding and rear wheel lock up. This season I raced the 160/140 combo in Iowa, Wisconsin, Minnesota and Nebraska with plenty of braking power and great modulation compared to the larger rotors. I've ridden out in the Black Hills (actual mountains) with the smaller rotors as well and everything was fine and dandy.

So again, it all depends on your riding style and where you ride. I've found 160mm up front to be plenty of brake for my needs on the 29"er. The Alligator Windcutter (or serrated rotors) are a nice inexpensive "weight weenie" rotor that work very well with the Avid BB7's and sintered pads (Avid or EBC Golds).



BB

I'm using a 185mm BB7 front rotor on my Gary Fisher Rig 1x9 conversion and feel that it's definitely improved the bike. I'm probably around 200 pounds,when I'm completely kitted up with knee,elbow and wrist pads and Fox chest protector.

Another question I have is how fast do plan to go? When I travel with my Giant Xtc 29er 1 I'm usually road riding and doing steep ascents and steep descents. Although I can't be sure I'm quite positive that I'm probably hitting 40 mph. At that point the 185mm Code 5 brakes on the bike really come into to play if I need to go from 40-20 in a New York Minute.

The Gary Fisher 1x9 conversion on the other hand seems to top out at 30-32 mph and I'm really lucky to even hit 32 mph. At that speed the BB7's with 185 mm front rotors seem to be more than enough.

To me it's really a question of speed if you're doing 40-45 mph and need to stop within 200 feet then your brakes definitely need to be upgraded but if you're keeping things under 32 mph I think a 185mm BB7 front rotor should be more than enough.

I'm curious to know more. Have you tested the BB7/185mm combination to be good for 32mph and specifically not for 40mph? Is that one stop or repeated stops in rapid succession? How do you reconcile your observation with the fact that tire traction is typically the limiting factor? Are you claiming that the BB7/185mm cannot lock up a tire or just that it can't about 32mph?

I don't have too much experience running the BB7's above 32 mph. I tried one steep downhill run that may have hit the mid 30's with the 160 mm front rotor and I thought the rotors certainly stopped the bike. However this run was done at night in an a hilly neighborhood without lights or even a helmet so I wasn't exactly eager to push things 100%.

I've done far more urban downhill runs with my Elxirs and Code 5's and know they work for that speed. Of course I was riding pavement so traction conditions in dirt may vary.

So far I have never pushed the BB7's to their limits. I've pushed the Elixir's to 100% on a few occaisions and know they're capable of. The Code 5's are awesome I have yet to experience a situation where I thought I used up 99% of their braking power.

So you would say that BB7s, even with on 160mm rotors, are fine beyond 30mph. Why did you suggest the opposite in the previous post?

Any brake can stop you at any speed, you just need enough distance. That's the real question. Yes I was certainly going fast but I was in no particular hurry to stop and had plenty of distance. I wasn't in a situation where I was testing the brake or needed to stop in a set distance.

That's the real question, how fast do you need to stop? Stopping is critical to rider safety, it can be the difference testing your protective gear and medical insurance and simply avoiding an obstacle.

I'll give you another example. I was going down a narrow trail at high speed when I saw a man and his dog,I stopped inches from the dog. Did the Elixir's work yes. Did they do their job yes. However would I have wanted more braking power: absolutely! Sometimes even when a brake works you want some room for error. The same stop wouldn't have been an issue with the Code 5's.

I think the question is far more nuanced than can you stop at a particular speed. Even if you can stop at a particular speed running something at 100% isn't a good idea.

It goes back to the question that started this whole thread: are the BB7's good or bad on a 29er. Well for my 1x9 conversion they are more than enough. Every rider has a different style and it depends on how fast they like to brake and how much they like to hang loose.

mefistofeles said:

Any brake can stop you at any speed, you just need enough distance. That's the real question. Yes I was certainly going fast but I was in no particular hurry to stop and had plenty of distance. I wasn't in a situation where I was testing the brake or needed to stop in a set distance.

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If you haven't tested the brake at speed then why have you condemned it as inadequate? Are you saying a BB7 can stop you, just not as fast as another brake?

mefistofeles said:

That's the real question, how fast do you need to stop?

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Let's say you have identical bikes at identical speeds but with different brakes. If the brakes are all capable of locking the wheels, which ones offer the shortest stopping distances?

mefistofeles said:

I'll give you another example. I was going down a narrow trail at high speed when I saw a man and his dog,I stopped inches from the dog. Did the Elixir's work yes. Did they do their job yes. However would I have wanted more braking power: absolutely! Sometimes even when a brake works you want some room for error. The same stop wouldn't have been an issue with the Code 5's.

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But the stop wasn't an issue for the Elixirs in your example, either. You imply that one brake offers more "braking" than another. What makes that so and what makes a BB7 inadequate in that respect above 32mph?

I would suggest that if your criterion is going to be a single panic stop on a trail then you should look at things other than the brakes to improve your margins.

mefistofeles said:

I think the question is far more nuanced than can you stop at a particular speed. Even if you can stop at a particular speed running something at 100% isn't a good idea.

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But you were the one who chose the "can you stop at a particular speed" measure. The speeds in question where your choices. The simplistic argument was advanced by you.

Who's to say that the BB7 is any closer to "100%" than another brake at a particular speed? 100% of what?

If you haven't tested the brake at speed then why have you condemned it as inadequate? Are you saying a BB7 can stop you, just not as fast as another brake?

At this point I think you come up off as being deliberately antagonistic but I'll pretend you aren't. I have tested the BB7's at speed but I wasn't making a fast stop. Sometimes you slow down from 30/40 and it's very urgent to stop and sometimes you can take your time. In this instance I was taking my time. When you have alot of run off area stopping you a few hundred feet doesn't make a difference.

I would suggest that if your criterion is going to be a single panic stop on a trail then you should look at things other than the brakes to improve your margins.

I am in total disagreement. Because the idea behind evaluating a good brake is understand which one stops you faster, all things being equal. This is a legitimate and critical situation, especially if you ride fast. Things happen in New York minute. The faster you ride the more important the brakes are.

Who's to say that the BB7 is any closer to "100%" than another brake at a particular speed? 100% of what?

If you don't push yourself and your brakes to the limit then I don't think you'll ever understand. Being on the limit can be vary dangerous and if you ride hard and fast you'll understand that being at 95% are two very different things.

At this point I'd really like to know what you mean? I think you're trying to be very confrontation. I'm trying to keep it about the brakes and riding you come as being belligerent and confrontational. Whether or not you mean to or not well that's another story. Merry Christmas.

This is getting a little silly.

At a given speed, can a particular brake or rotor lock the front wheel up, i.e. endo the bike/rider? If so, in theory it is capable of stopping the bike AS QUICKLY as a "more powerful" brake or larger rotor.

The point before endo is maximum effective braking. This doesn't change based on brake selection. It's based on speed, terrain and weight and how the rider manages his center of gravity.

The difference is that smaller or less powerful brakes will require a more powerful squeeze of the lever than (a) a "more powerful" caliper with the same rotor or (b) the same caliper with a larger rotor.

At typical mountain biking speeds/rider weights a 160mm rotor is capable of performing this task. In fact, if you want to talk about BB7s specifically, pad spacing can be set close to the rotor such that the brake behaves much like a light switch. By doing so, you've just created a "more powerful" brake -- at the expense of modulation.

What does a larger rotor buy you? Better heat capacity -- it'll take a greater number of panic stops to overheat it. But so does installing a heavier rotor with more material.

The larger rotor will be easier to lock up -- but this is relative. Was the smaller rotor actually "difficult" to lock up? The heavier the rider, the faster the speeds, the more this may be true. I have trouble believing a typical rider at typical speeds will have any trouble applying the lever squeeze necessary to effectively panic stop a BB7 w/ 160s.

Now what about the rider creepy-crawling down a steep and rocky technical section, where the rear brake is all but ineffective and an easily modulated front brake is preferable to a hair trigger wheel lockup device? I'm not saying a 185mm rotor is going to be this, but as rotor size increases, as brake calipers are adjusted to be "more powerful," this is the uncontrollable endo one is trying to avoid.

Brakes aren't about absolutes, they're about balance. So whatever the rotor size, if you can endo your bike with a forceful squeeze, you've got the ability to stop as quickly as possible. The rest is up to the rider, based on how often he needs to do this, and what his other needs are.

mefistofeles said:

Because the idea behind evaluating a good brake is understand which one stops you faster, all things being equal.

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You seem unable to do that. You admit repeatedly you haven't tested the BB7 at speed and you can't answer the first question on what makes a brake "good" yet you've defined and arbitrary speed that BB7s are only acceptable up to.

mefistofeles said:

If you don't push yourself and your brakes to the limit then I don't think you'll ever understand.

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Oh I understand, do you? Perhaps you should push the limits of the BB7 before commenting on their inferiority.

mefistofeles said:

At this point I'd really like to know what you mean?

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You've offered specific claims that I've asked that you to back up with some detail. Rather than engage in meaningful discussion, you've chosen to do a lot of hand waving. People seeking answers are better served with facts than with prejudice. Sorry you found this confrontational but I think your opinion is either poorly informed or poorly expressed. I was hoping you'd prove that it was the latter. I've asked you enough questions for which there are good answers but you have chosen to ignore them.

I have a bike with BB7s and have owned a number with hydraulics as well as plenty with rim brakes. There are clearly differences. If I'm deciding whether to go ridiculously fast on any bike the last thing I think about is whether I have BB7s or something "better". The times I've personally gotten into trouble with braking off-road it has been because of an inability to find traction, not because I lacked brake power. I realize that's not true for everyone in all situations, but you seem to think that braking distances are determined entirely by the brake when it's commonly other factors.