Why no love for direct mount rim brake?

Discuss light weight issues concerning road bikes & parts.
User avatar
ProfessorChaos
in the industry
Posts: 725
Joined: Tue Dec 20, 2011 3:10 am

by ProfessorChaos

pdlpsher1 wrote:
The problem only occurs when the gravel is sticky. If you ride normal gravel roads there's no chance for the gravel to end up near the brakes due to gravity.

There are more reasons to not get one....like the cost of a new frame. But if you are shopping for a new frame anyways why not consider as an option? And the DM is not about weight savings. It's about being aero, better modulation, higher power (leverage), zero chance for going out of center, etc.


There are also some advantages to the way the frame is manufactured as well. Loosing the brake bridge in the back, and removing the need for a center mount hole in the fork, open up options that were previously not possible with standard center mount rim brakes.

by Weenie


pdlpsher1
Posts: 1324
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

ProfessorChaos wrote:
pdlpsher1 wrote:
The problem only occurs when the gravel is sticky. If you ride normal gravel roads there's no chance for the gravel to end up near the brakes due to gravity.

There are more reasons to not get one....like the cost of a new frame. But if you are shopping for a new frame anyways why not consider as an option? And the DM is not about weight savings. It's about being aero, better modulation, higher power (leverage), zero chance for going out of center, etc.


There are also some advantages to the way the frame is manufactured as well. Loosing the brake bridge in the back, and removing the need for a center mount hole in the fork, open up options that were previously not possible with standard center mount rim brakes.


Yes, indeed. And I forgot to mention the biggest advantage....the ability to run very tall and wide tires. With DM brakes the tire clearance will be limited by the fork and frame, and not the DM brakes themselves.

jeffy
Posts: 1242
Joined: Sun Oct 05, 2014 11:51 pm

by jeffy

@froze. have you ridden road hydraulic discs?

Lieblingsleguan
Posts: 152
Joined: Mon Mar 23, 2015 9:47 pm

by Lieblingsleguan

jeffy wrote:@froze. have you ridden road hydraulic discs?

Oh, come on, the old BS that everyone who criticises road hydraulic disc brakes could never have ridden them... I have and I found it underwhelming.

fromtrektocolnago
Posts: 980
Joined: Sat Dec 07, 2013 10:15 pm

by fromtrektocolnago

pdlpsher1 wrote:
fromtrektocolnago wrote:that would be a very good reason for not wanting to get a pair in my book. I would not want to stop and remove gravel from the brakes.


The problem only occurs when the gravel is sticky. If you ride normal gravel roads there's no chance for the gravel to end up near the brakes due to gravity.

There are more reasons to not get one....like the cost of a new frame. But if you are shopping for a new frame anyways why not consider as an option? And the DM is not about weight savings. It's about being aero, better modulation, higher power (leverage), zero chance for going out of center, etc.


When I read the marketing aero is what comes up most. I'd think about the other talking points except I don't view my Dura Ace brakes as a problem in search of a solution but if I did what you tout about the direct mount calipers would be more true of disc according to the proponents. I also like standards and non-proprietary solutions one reason among many I'm still on a BSA bottom bracket. Any of the bikes offering direct mount brakes are targeting aero from what I've seen.
Colnago C-59 (Dura Ace)
Firefly(Ultegra)
Trek 5200(ultegra)

lowside67
Posts: 62
Joined: Sat Apr 23, 2016 5:34 pm

by lowside67

I sure wish Trek would make direct mount brakes available on their non-SLR level frames!

Mark

pdlpsher1
Posts: 1324
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

lowside67 wrote:I sure wish Trek would make direct mount brakes available on their non-SLR level frames!

Mark


They probably did it on purpose so those who want DM brakes will have to pay more $$$.

There's a lot of aero hype being marketed by Pinarello on their F8 and F10 high-end bikes. But I'm surprised they didn't include DM brakes. Someone had suggested that it's because Campy doesn't have DM brakes, and that Pinarello won't make a frame that only accepts Shimano :D Has Campy introduced DM brakes yet?

Zakalwe
Posts: 336
Joined: Sun Jun 17, 2012 3:15 pm

by Zakalwe

Yes they have.

Pinarello also stick with threaded BBs, despite Campy offering several pushfit options.

maxxevv
Posts: 1949
Joined: Wed Feb 09, 2005 4:51 am

by maxxevv

Its more of the additional costs in the molds rather than Campag. And amazingly from the grapevines, Pinarello's annual revenue turnover supposedly surpasses Campag ! ( I have no way to verify this, but that's what I heard .)

The F10 will most definitely transit to discs later anyway, its easier to transit to that modifying a mold for a dual pivot caliper frame than one with a DM design.

PureSek
Posts: 22
Joined: Mon Jan 09, 2017 8:17 am

by PureSek

what is the problem with rear DM located under the bb tho?
never a DM user, just curious. painful to clean or to adjust maybe?


Sent from my iPhone using Tapatalk

pdlpsher1
Posts: 1324
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

PureSek wrote:what is the problem with rear DM located under the bb tho?
never a DM user, just curious. painful to clean or to adjust maybe?
Sent from my iPhone using Tapatalk


I've read this and I don't know how true it is. It has to do with the force vectors. When the DM brakes are below the BB the braking force is pulling the brakes out from the BB, whereas the brakes on the seat stays are being pushed against the stays.

Image

maxxevv
Posts: 1949
Joined: Wed Feb 09, 2005 4:51 am

by maxxevv

Its a problem of keeping them clean and adjusting if necessary.

The force vectors are identical to your front fork for such an arrangement anyway.

The location also makes it more difficult to remove/replace wheels.

pdlpsher1
Posts: 1324
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

Sorry I had it wrong. However it does have something to do with force vectors.....on the wheel and not the brakes themselves. I found the post that I saw.

colster wrote:Chainstay mounted brakes do offer a marginal aerodynamic gain, so are great on TT bikes, but for road bikes they may create an additional issue regarding brake rub.

The issue relates to the way a wheel flexes - apparently spoked bicycle wheels flex kinda like a Pringle, that is to say lateral flex is greatest at the point that is 90° from the ground than the point at the top point that is 180° from the ground i.e. flex is greater at the chainstay than at the seat stay, therefore a chainstay mounted brake may be more prone to brake rub, and so may have to be set up wider. This issue would not really affect a rider who chooses a rear disc wheel, again making it wholly appropriate for TT bikes.

FYI the above factoid was gleamed from listening to episode 67 of The Bike Shop Show podcast in which he breaks down all the issues affecting wheel stiffness, and he states the above wheel flex point was learned from seperate tests conducted by Zipp and Damon Rinard. I should also add I haven't personally owned or ridden a road bike with chainstay mounted brakes (and have no intention to) so cannot speak from experience, only theory.

Stormtrooper
Posts: 21
Joined: Wed Mar 30, 2016 3:29 pm

by Stormtrooper

No problems with the bottom bracket dm brakes on my bike. LBS mechanic adjusted it once and no problems since then. Dirt on the rear brake? I clean my bike after just about every ride. Never had gravel get stuck in there. Seems isolated to me. Adjustments on the fly? That should be sorted out before you ride, again take a minute to inspect your bike. Only people I can see complaining about this are pro riders, are any of you that good that you have a mechanic that has to adjust during a ride. Top 1 percent I would say. I can't even count how many times my standard da brakes shifted off center on my old bike. Wheel flex? Get stiffer wheels, not the brakes fault. Sorry for my rant.

by Weenie


PureSek
Posts: 22
Joined: Mon Jan 09, 2017 8:17 am

by PureSek

maxxevv wrote:Its a problem of keeping them clean and adjusting if necessary.

The force vectors are identical to your front fork for such an arrangement anyway.

The location also makes it more difficult to remove/replace wheels.

one thing I am also aware of is the compatibility with crankarm-based powermeter (e.g stages), as the clearance between crankarm and the brake from the above pic doesnt seem to hv enough space for it.


Sent from my iPhone using Tapatalk

Post Reply
  • Similar Topics
    Replies
    Views
    Last post