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Colnago c59 disc

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Colnago c59 disc

Old 03-07-12, 05:36 PM
  #51  
gregf83 
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Originally Posted by merlinextraligh View Post
Road bike brakes should need higher capacity than MTB brakes.

Road bikes are travelling at higher speed, have less aerodynamic drag, and much less rolling resistance.

We've already seen that brakes that are acceptable performers for CX bikes can be problematic on road bikes.
I think you have that backwards. You are much more likely to encounter a situation where you need to limit speed on a steep descent for an extended period on a mountain bike. The worst case scenario for any braking system is a slow speed steep descent. That doesn't happen very often on a road bike. On a road bike you generally get to take advantage of wind resistance to dissipate most, if not all, of the potential energy loss while descending. Normal descents on a road bike involve mostly coasting with hard braking for corners. The coasting sections allow the brakes to cool.

Depending on the terrain and rider skill, it's much more likely you'll be descending slower on a mountain bike which means no help from wind resistance and less coasting.
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Old 03-07-12, 06:32 PM
  #52  
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Higher speed = much more kinetic energy to dissipate on a road bike for any given speed adjustment. Scrubbing off (say) 5mph from 35 requires dissipating almost twice the energy as scrubbing off 5mph from 20.

Or, making everything proportional scrubbing off 5mph from 40 on a road bike vs. scrubbing off 2.5mph from 20 on a mountain bike (assuming equal weights for simplicity because the rider represents most of the mass) requires dissipating 4 times as much energy through the brakes.
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Old 03-07-12, 06:46 PM
  #53  
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Originally Posted by gregf83 View Post
The worst case scenario for any braking system is a slow speed steep descent.
This is just totally wrong. Ek = (mv^2)/2. If you're a common 80kg (176lb) man going 18m/s (40mph) and you need to get down to 13.4 m/s to make the turn you're entering, that means your brakes have to convert 5.78 kJ of kinetic energy to heat.

The same rider going 13.4 m/s (30mph) that needs to drop to 8.94 m/s (20mph) only has to dissipate 3.98kJ.

That's a 30% difference to shed 10mph just because one rider was going slower.
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Old 03-07-12, 07:02 PM
  #54  
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Originally Posted by nhluhr View Post
This is just totally wrong. Ek = (mv^2)/2. If you're a common 80kg (176lb) man going 18m/s (40mph) and you need to get down to 13.4 m/s to make the turn you're entering, that means your brakes have to convert 5.78 kJ of kinetic energy to heat.

The same rider going 13.4 m/s (30mph) that needs to drop to 8.94 m/s (20mph) only has to dissipate 3.98kJ.

That's a 30% difference to shed 10mph just because one rider was going slower.
But the rims/pads/discs are already hot for the slow rider.
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Old 03-07-12, 07:02 PM
  #55  
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Originally Posted by nhluhr View Post
This is just totally wrong. Ek = (mv^2)/2. If you're a common 80kg (176lb) man going 18m/s (40mph) and you need to get down to 13.4 m/s to make the turn you're entering, that means your brakes have to convert 5.78 kJ of kinetic energy to heat.

The same rider going 13.4 m/s (30mph) that needs to drop to 8.94 m/s (20mph) only has to dissipate 3.98kJ.

That's a 30% difference to shed 10mph just because one rider was going slower.
Slow is relative. I mean one where the wind resistance doesn't play a significant role. Clearly it doesn't take any braking to go down a 6% hill at 60kph. But if you want to go down the hill slower it will require braking. Somewhere between 0 and terminal velocity is the worst case scenario and you are more likely to encounter it on a mountain bike vs a road bike.

edit: Sorry I didn't read the rest of your post. Braking for corners is not the issue. Any of the brakes should be able to handle that just fine. The problem occurs when you try and limit your speed on a descent. Some people do this on road bike because they are uncomfortable at speed. On a mountain bike because the terrain can be difficult it's more likely you'll need to restrict your speed on a straight long descent.

further edit: If an 80kg rider descends a 15% slope at 30kph his brakes need to dissipate close to 1000W (I did this quickly so my math may be off). Maybe 200-250W will be dissipated by wind resistance the rest needs to go into the brakes. In your example above the rider going 40mph can burn off his 5.78 kJ in 10 Seconds using only 600W. Clearly the slow (30kph) steady descent is a tougher scenario for brakes.

Last edited by gregf83; 03-07-12 at 07:16 PM.
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Old 03-07-12, 07:06 PM
  #56  
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Originally Posted by znomit View Post
But the rims/pads/discs are already hot for the slow rider.
And this is exactly why race cars need tiny brakes but cars in stop and go traffic need monsters.
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Old 03-07-12, 07:24 PM
  #57  
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Originally Posted by svtmike View Post
Higher speed = much more kinetic energy to dissipate on a road bike for any given speed adjustment. Scrubbing off (say) 5mph from 35 requires dissipating almost twice the energy as scrubbing off 5mph from 20.

Or, making everything proportional scrubbing off 5mph from 40 on a road bike vs. scrubbing off 2.5mph from 20 on a mountain bike (assuming equal weights for simplicity because the rider represents most of the mass) requires dissipating 4 times as much energy through the brakes.
As i mentioned, the issue with brakes overheating is not scrubbing off speed for corners it comes from limiting speed below the terminal velocity you would otherwise descend at.
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Old 03-07-12, 07:29 PM
  #58  
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Originally Posted by svtmike View Post
And this is exactly why race cars need tiny brakes but cars in stop and go traffic need monsters.
Terrible example.
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Old 03-07-12, 07:30 PM
  #59  
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Originally Posted by gregf83 View Post
Terrible example.
Intentionally so. It wasn't in response to your cogent argument.
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Old 03-07-12, 07:38 PM
  #60  
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Originally Posted by gregf83 View Post
Why is that an issue? If you're travelling at 70kph you're probably not riding your brakes. There's probably more need to ride the brakes on a MTB than there would be on a road bike.
Cuz of the corners and cars dood. If you can come down out of Cypress or Seymour without braking, good job! But I can't.
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Old 03-07-12, 07:45 PM
  #61  
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Originally Posted by Commodus View Post
Cuz of the corners and cars dood. If you can come down out of Cypress or Seymour without braking, good job! But I can't.
Cypess but not Seymour. I do sit up for corners though and have been known to break the yellow line rule
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Old 03-07-12, 07:46 PM
  #62  
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Heh you're still better at it than I am. The idea of my brakes getting all boily coming down either gives me the willies. I have had this experience on an old Suzuki Katana and it was a bit erm, stressful.
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Old 03-07-12, 08:07 PM
  #63  
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for those worried about having to swap levers to change over to hydraulic brakes..Trp makes a master cylinder that works with standard levers..it uses the cables to actuate the master cylinders..I think disc will be the future
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Old 03-07-12, 09:50 PM
  #64  
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Originally Posted by Steve90068 View Post
It's going to be fun to pull this thread up in a few years when any road bike over $1,500 will have disc brakes
Wonder if someone said the same thing a few years ago about Colnago's split stays?
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Old 03-07-12, 10:06 PM
  #65  
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I don't understand why anyone would want this on their road bike. Braking is not like shifting where extra precision makes the difference between a shift or a misshift. I don't see how anyone could possibly have a problem with modulation using standard road calipers. If you need more stopping power, you pull the freaking lever more. You have infinite modulation because you can feel what's going on through the lever feedback. Disc brakes are just too powerful for a road bike application where the contact patch between the tire and road is very small. Also, the extra braking power of a disc doesn't give you any advantage considering it's very easy to lock up a rear wheel with standard road calipers, even in the rain.

Have any of you actually descended for > 20 miles on standard road calipers? I don't know about you guys but I sure don't use my brakes much when I'm enjoying the thrill of going downhill for 25 miles. When I do have to brake because I'm approaching the back of a car, they work perfectly fine. I've never experienced brake fade before because I don't hold my brake down like an idiot. IMO if you own multiple wheelsets (which every serious rider should), there will never be a problem with standard road calipers. If you are going climbing for the day and know you will be descending, go with a low profile, low weight aluminum wheel. If you are riding on flat ground and there isn't much wind then go with a deep carbon wheel. Heck, even modern carbon clinchers won't have a problem descending 20+ miles if you know how to use your brakes. I'm a huge fan and advocate of electronic shifting, but disc brakes on a road bike serves no purpose.
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Old 03-07-12, 10:16 PM
  #66  
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Hindsight is 20/20, but I 'aint gonna lie. I thought that disc was a fad on Mountain bikes, now I wouldn't have it any other way.
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Old 03-07-12, 10:32 PM
  #67  
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Originally Posted by StanSeven View Post
Wonder if someone said the same thing a few years ago about Colnago's split stays?
No, but they said it about 10 speed, carbon wheels, carbon frames, etc. roadies have a rich history of fighting innovation only to give in later. disc brakes will be on the overwhelming majority of high end bikes in 3 years or less
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Old 03-08-12, 01:53 AM
  #68  
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Originally Posted by Erzulis Boat View Post
Hindsight is 20/20, but I 'aint gonna lie. I thought that disc was a fad on Mountain bikes, now I wouldn't have it any other way.
There are still those that say discs on mountain bikes are overkill, for whatever reason. They'll always persist. The reason? "They rode fine without 'em back in the day."

Uh-huh, have you SEEN the way pros ride now? It's a completely different sport.
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Old 03-08-12, 06:54 AM
  #69  
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Originally Posted by ESW116 View Post
There are still those that say discs on mountain bikes are overkill, for whatever reason. They'll always persist. The reason? "They rode fine without 'em back in the day."

Uh-huh, have you SEEN the way pros ride now? It's a completely different sport.
What will disc brakes on road bikes allow the roadie pros to do in the future that they can't now?
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Old 03-08-12, 10:02 AM
  #70  
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Originally Posted by svtmike View Post
What will disc brakes on road bikes allow the roadie pros to do in the future that they can't now?
Use a much lighter carbon wheel without fear of heat erosion or failure to the wheel at the braking pad juncture. Ever try and brake at high speeds using carbon wheels with the current system in wet weather? The list goes on.. The innovation is needed in this area imho now that carbon plays such a huge role. It wont be long before we see ceramic brakes and the like as well.

Last edited by WarLordZ; 03-08-12 at 10:05 AM.
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Old 03-08-12, 10:15 AM
  #71  
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Originally Posted by svtmike View Post
What will disc brakes on road bikes allow the roadie pros to do in the future that they can't now?
Now? better braking in the wet, less brake fade, lighter wheels (less rolling resistance, faster acceleration), more tire options (don't have to fit them inside the brakes)

Soon? Integrated rear brake light (i figure 3 or 4 LEDs on the rear brake). all-internal cable routing.

Future? ABS.
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Old 03-08-12, 10:17 AM
  #72  
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Originally Posted by WarLordZ View Post
Use a much lighter carbon wheel without fear of heat erosion or failure to the wheel at the braking pad juncture. Ever try and brake at high speeds using carbon wheels with the current system in wet weather? The list goes on.. The innovation is needed in this area imho now that carbon plays such a huge role. It wont be long before we see ceramic brakes and the like as well.
At the expense of a heavier fork, hubs and braking system.

Disk brakes make complete sense on MTBs, with all the dirt, mud, and other debris issues. Plus they have the forks to take the forces of the disk brakes.
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Old 03-08-12, 10:27 AM
  #73  
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Originally Posted by RJM View Post
At the expense of a heavier fork, hubs and braking system.

Disk brakes make complete sense on MTBs, with all the dirt, mud, and other debris issues. Plus they have the forks to take the forces of the disk brakes.
I'll take a reduction in rotational weight for an increase in non-rotational weight any day
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Old 03-08-12, 10:49 AM
  #74  
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https://www.bikeradar.com/road/news/a...59-disc-33359/
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Old 03-08-12, 10:52 AM
  #75  
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Originally Posted by Steve90068 View Post
I'll take a reduction in rotational weight for an increase in non-rotational weight any day
That is certainly a way to market disk brakes. I am not totally against them, just really wonder what we would have to give up to get whatever benefits disks would bring.

I do hope they fix the scraping sound every bike I have ridden with disks has. It is hugely annoying.
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