Discs or no discs for pros

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Mr.Gib
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by Mr.Gib

LeDuke wrote:
No one is forcing anyone to have disc brakes. It's simply an option now.

I don't know how this is hard to understand.

Although, I'd bet Joseba Beloki wishes he had had disc brakes.


Not quite true. Many frame options from many brands are disc only now. You want the rim brake version? Sure it's available if you are happy with the low end aluminum version, or if it is carbon the fork will have an alloy steerer.

Beloki would have likely locked up a disc brake also. That's what you get for grabbing too much rear brake in that situation.

And what's with people thinking it's possible to descend faster with discs? With rim brakes you can lock up your wheels anytime which suggests maximum late braking is always possible and limited only by the traction of the tire not the performance of the brakes. Not really that different in the wet either. The problem is always tire traction, not brake force.

I have a decent disc set up - a cross bike fitted with road tires. I like how it avoids trashing rims during winter training. What I don't like is the wider rear end. The impact on chain line means with certain drive trains when in the small ring, the chain will hit the teeth of the big ring when in the 11, 12, or 13 tooth sprockets. Same hardware on normal road frame and it is only a problem in the 11.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

pushstart
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by pushstart

Mr.Gib wrote:And what's with people thinking it's possible to descend faster with discs? With rim brakes you can lock up your wheels anytime which suggests maximum late braking is always possible and limited only by the traction of the tire not the performance of the brakes.


I think the theory here is that brakes with better modulation, more linear delivery of braking force help you avoid locking up your tires -- let you brake right up to the point where tire loses traction, but not cross that threshold.

That said, you have to know your equipment and road conditions pretty well to have that play out in practice. I slid out on a wet corner on my road disc bike the other day. Simply was going to fast, maybe grabbed too much brake or maybe any brake was too much for the road surface. So it isn't a silver bullet.

The argument about rub in cross-chaining is valid. I can't use two smallest cogs in my 10sp road setup. In practice isn't really something that I would do anyway, so not a big deal. But it is a legit concern. My chainstays are 410mm.

The other issues like rotor spacing tolerances and axle standards and neutral support sound easy to overcome with tighter standards. This is simply new territory, but it is easy to have disc brake wheels that can be quickly and easily interchanged. And in general once those tolerances are tightened, disc brakes open up flexibility for running different rim width/profiles etc with zero adjustments. I don't miss adjusting calipers when swapping wheelsets. And out of true wheels are a non-issue, as others note.

by Weenie


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LeDuke
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by LeDuke

pushstart wrote:The other issues like rotor spacing tolerances and axle standards and neutral support sound easy to overcome with tighter standards. This is simply new territory, but it is easy to have disc brake wheels that can be quickly and easily interchanged. And in general once those tolerances are tightened, disc brakes open up flexibility for running different rim width/profiles etc with zero adjustments. I don't miss adjusting calipers when swapping wheelsets. And out of true wheels are a non-issue, as others note.


Good points, particularly this last bit.

I've finished an XC race missing 3 spokes (from a 28h wheel) and CX race missing 2 spokes (from a 24h front wheel).

That wouldn't really be feasible on a non-disc wheel.

CulBaire
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by CulBaire

LeDuke wrote:
pushstart wrote:I've finished an XC race missing 3 spokes (from a 28h wheel) and CX race missing 2 spokes (from a 24h front wheel).


Tacos anyone? :beerchug:

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LeDuke
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by LeDuke

The wonders of modern carbon reinforced plastics. New spokes, good as new.

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Mr.Gib
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by Mr.Gib

pushstart wrote:
I think the theory here is that brakes with better modulation, more linear delivery of braking force help you avoid locking up your tires -- let you brake right up to the point where tire loses traction, but not cross that threshold.

That said, you have to know your equipment and road conditions pretty well to have that play out in practice. I slid out on a wet corner on my road disc bike the other day. Simply was going to fast, maybe grabbed too much brake or maybe any brake was too much for the road surface. So it isn't a silver bullet.



Yes in theory but in practice maybe not. Modulation may not be the limiting factor when comparing with top quality rim braking. Assuming identical traction, the sense of road feel or feedback from the tire/road interface is more important IMO. I do notice that some disc forks are impressively overbuilt. Amazing products but does this sturdiness limit critical feedback? I actually decided against one disc bike I was considering for purchase because the fork was so solid it actually made the ride too harsh for my tastes and I am a big guy. I also wondered how this would affect road contact and feedback.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

bombertodd
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by bombertodd

I'm not sure how much tire pressure has on braking but the rim brake heats the rim which heats the tube and increases the temperature/pressure in the tube.

Zipp has this on their site: When a wheel with carbon braking surfaces encounters a long, technical descent, spikes in rim temperature and tire pressure can impact braking and handling.


I was speaking with a few engineers from Trek and they said braking distance is improved with discs because of the larger contact patch from the lower pressure. I someone will release data on this. It makes sense, but how much does it really matter? Is it 0.01%, 1% or 10% better? Sometimes I wish I was an engineer...

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Mr.Gib
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by Mr.Gib

bombertodd you have touched upon a critical issue. We know tire pressure can be the difference between life and death in this sport. I do not go into the high mountains without running 25mm or 28mm tires on wide rims at pressures between 80 and 90 psi. Once descending in the Pyrenees in cold rain, I stopped and lowered my pressure down to 70 -75 psi. Chip seal made with shiny round pebbles instead of the usual crushed gravel - absolute slippery terror. Even with discs I still would have stopped and let air out. I find at the pressures I run I never get into trouble even when I am forced to really hold my speed down over long steep stretches, so limited advantage for me. No doubt some riders with less care about tire pressure may avoid crashes because of disc brakes.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

kulivontot
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by kulivontot

So tubeless > disc for descending is the current conclusion then?

pushstart
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by pushstart

A lot of the awesome new wide tubeless rims are also disc-specific -- Pacenti SL25, Velocity Aileron, Stans Grail. I think this just supports that larger point of freeing up rims to be wider, more aero etc. when there are no brake track constraints.

I would take my disc brakes any day over the carbon braking surface of my previous bike/wheels. Heck, I would take them over my alloy rims too. But obviously for success in the peloton, there need to be some tech improvement and tighter standardization. I am quite excited for those changes to trickle down to the rest of us too. The idea of using little rubber pads pressed against the rim to slow a spinning wheel is a little humorously crude compared to calipers and rotors.

Fiery
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by Fiery

Mr.Gib wrote:And what's with people thinking it's possible to descend faster with discs? With rim brakes you can lock up your wheels anytime which suggests maximum late braking is always possible and limited only by the traction of the tire not the performance of the brakes.

Are you actually locking up you front wheel? Going straight on dry pavement, your front wheel locks and slides under hard braking?

hornedfrog
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by hornedfrog

There is a big difference between "you CAN lock up your wheels..." and "I am locking up my wheels going straight on dry pavement and my front wheel is sliding under hard braking". I don't know where you read that Mr. Gib is doing the latter, but you seem to be jumping to conclusions.

Fiery
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by Fiery

Let me rephrase that: Mr. Gib, are you actually capable of locking up the front wheel and making it slide while riding in a straight line on dry pavement? Alternatively, are you capable of consistently braking so hard that the only way to avoid endoing is by decreasing the braking force?

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Mr.Gib
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by Mr.Gib

Fiery wrote:Let me rephrase that: Mr. Gib, are you actually capable of locking up the front wheel and making it slide while riding in a straight line on dry pavement? Alternatively, are you capable of consistently braking so hard that the only way to avoid endoing is by decreasing the braking force?


The simple answer is yes. I have pushed front tires to the limit in straight line braking - hearing the scuffing sound of the tire starting to skid on the road on multiple occasions - it never stopped rotating however. Can't really say what would have happened if I had squeezed harder - maybe endo, maybe slide. I have also had the rear wheel off the ground on several occasion under braking. I prefer not to leave the braking quite this late, but I do like to brake late and hard. In all cases I felt I had a lot more "squeeze" in the left hand available if I wanted it.

And before any less experienced folks get too excited and start testing braking limits, please make sure you understand exactly what to do with your body or you will die. Good mountain bikers seem to have no problem with any of this from what I have seen.

Done this with Sram Red and Ultegra brakes and some TRP mini V's which had wicked stopping power (modulation is tricky with those however.)
Last edited by Mr.Gib on Wed Aug 12, 2015 3:32 am, edited 1 time in total.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

weenie
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by weenie

since all arguments are opinion pieces, here's mine:

you can get my hydro-disc-equipped road bike off my cold dead fingers. ill never go back to "regular" brakes. id venture to say it saved me for a few crashes in the past 2 years ive had them (so yes, sram s700's)

by Weenie


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