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Discussion Starter · #1 ·
So here's my thinking:
I have disc brakes on various bikes now including a chameleon SS and a freeride type bike and I love them. But here in colorado it is dry most of the time. My current XC SS is vbrake equipped, and mostly I am happy but on long steep descents I wish I had disc of course.

I have a inbred 29er on the way and have some hayes I could throw on it but;

Seems like discs are less of an advantage on 29ers since the lever arm of the wheel has increased. I've always had a heck of a time keeping 8" rotors true and there is a significant weight penalty.

Also it seems like v's might work better since the rim is moving slower on a 29er compared to a 26 at the same speed.

So am I missing something? I know most of you guys run discs but for a XC 29er in dry climate it doesn't seem necessary.
 

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Cold. Blue. Steel.
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Discs.
Are you really heavy? If not, 6" rotors should be just fine.
Why worry about rim wear and decreased/inconsistent performance with rim brakes?
Unless you live in the Southwest... maybe.
My 02¢

OGG
 

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In FTF We Trust
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"My current XC SS is vbrake equipped, and mostly I am happy but on long steep descents I wish I had disc of course."

You may have answered your own question there. I'm running Juicy 7's with 8" rotors on my Strong and I've been very satisfied with them. (side note: I'm running King hubs and a White Bros. BW.8 fork too, clearance issues be damned-one of these days I'll post pics. with my fix) That said, I'm planning a new 29er SS and I'm seriously considering going back to V-Brakes. I say try V's on the Inbred-you can get them cheap, and if you're not satisfied, slap on some BB-7 mechanical discs later.
 

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I would go for disk brakes, just for the one reason you metioned. Long down hills, better brake pad life, and also what was previously mentioned about rim wear do to v-brakes. If you need more stopping power, you could always split the difference, and go with a 7" rotor.
 

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Discussion Starter · #5 ·
Thanks for the recommendations but;
I have years of experience with both brake systems so I have a pretty good grasp of the pros and cons.

But am more interested in the physics and the pros and cons scale when going to 29er.
 

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I have found rims brakes to be more powerful on 700c wheels than 26" wheels but it does not change the hand effort required very much on the long descents. It is the hand fatigue factor that is the biggest benefit of discs.
 

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being is
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v's are all the same!

wheel size has nothing, NOTHING!, to do w/ v-brake performance. The rim is going the same speed regardless of wheel size. Tire size has a small effect on rim speed since the smaller the tire the closer to the running surface the rim is.

Of course big wheels are doing fewer rpms but the rim is going the same speed cause its got a bigger radius. If this is difficult to grasp just consider that the tire patch is going the same speed no matter the wheel size. It has to be going the same speed. If you are going 20mph then thats how fast your tire is spinning at its circumfrence, no matter how big the diameter.

discs are a different story because the disc size is constant but the wheel size variable.
 

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pseudo intellectual said:
wheel size has nothing, NOTHING!, to do w/ v-brake performance. The rim is going the same speed regardless of wheel size. Tire size has a small effect on rim speed since the smaller the tire the closer to the running surface the rim is.

Of course big wheels are doing fewer rpms but the rim is going the same speed cause its got a bigger radius. If this is difficult to grasp just consider that the tire patch is going the same speed no matter the wheel size. It has to be going the same speed. If you are going 20mph then thats how fast your tire is spinning at its circumfrence, no matter how big the diameter.

discs are a different story because the disc size is constant but the wheel size variable.
Not in my experience.
 

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shiggy said:
Not in my experience.
Could be that you live in an alternate universe. Or maybe the bigger rim doesnt heat up as much? Maybe the slight angular difference in the arc of the rim makes a difference? Maybe the rim had a different surface? Maybe a tear in the fabric of space-time produced an enhanced 29er experience? Maybe the tires bit better?

I don't notice much difference that's due to the brake. The wheel, sure, there is some difference there. But it has noting to due with the friction the brake causes.
 

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pseudo intellectual said:
Could be that you live in an alternate universe. Or maybe the bigger rim doesnt heat up as much? Maybe the slight angular difference in the arc of the rim makes a difference? Maybe the rim had a different surface? Maybe a tear in the fabric of space-time produced an enhanced 29er experience? Maybe the tires bit better?

I don't notice much difference that's due to the brake. The wheel, sure, there is some difference there. But it has noting to due with the friction the brake causes.
I do not try to explain why. I only know that with similar width tires on similar type rims using the same brakes on the same trails overall braking is better for me with larger diameter wheels. The rim is just a huge brake rotor.

BTW the speed of the contact patch of any tire at any pace is always the same (unless the tire is sliding): zero.
 

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I'm pleased with V's on my Mooto-X. I run very light Marta SL/Stan's Rotors on my other bike but went with Pauls Levers and Mag Avids on the Mooto-X to build it extremely light. First time I've run V's in years -- pretty suprised at how well they haul it down and they feel good also....mostly fire roads on the Mooto so the V's will be fine for me.
 

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shiggy said:
I do not try to explain why. I only know that with similar width tires on similar type rims using the same brakes on the same trails overall braking is better for me with larger diameter wheels. The rim is just a huge brake rotor.

BTW the speed of the contact patch of any tire at any pace is always the same (unless the tire is sliding): zero.
Yeah, of course the rim is just one huge rotor. That's the whole point. Rim brakes are the original disc brakes. I just wanted to emphasize that rim brakes work the same for all wheel sizes. Now wheels might brake better, jsut like they might corner better, or get better traction going uphill. Whatever it's a dead horse...

The contact patch thing: I see what you mean. I should have said merely circumference. But I wanted to emphasize the relationship of wheelspeed to ground speed. But the whole concept of contact patch as a fleeting thing is problematic if you think about it. For it to be going zero mph it must be kind of a purely mental concept because it exists outside of time. If its only the instantaneous point of contact it becomes a not very practical concept for discussing dynamics. How can an instantaneous contact patch sipe water? It would require an infinite series of such contact patches to do the actual siping and they would require integrating. I suppose the more workable concept is of a contact patch moving forward in the same way as the axel moves forward.

Or you could say that the tire sipes water at the contact patch.
 

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While Psuedo intellect debates (mostly with himself, although he is correct) the angular blah blah, I'll put in my vote for discs. Not because they stop any better (than a well tuned set of vee's), but because they are so consistant. I am prone to dinging up rims and it was a real problem back in the vee/canti days. Constant thump thump and pulsing levers were a real pain in the a$$.

I highly recommend the cable 7' Avids. I am heavy and brake very hard. They provide more power than I can generally use.
 
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