For those buying a new machine... disc or rim?

Discuss light weight issues concerning road bikes & parts.
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Calnago
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by Calnago

C36 wrote: TA came to solve the issue of the braking forces that could move the front hub in the fork (or outside in extreme cases). If we have no relative mvt with a QR and none either with the TA then the stiffness difference would remain the same unless the fork is structurally different.
That’s the point, with a rim brake the braking forces are equal on each side, not skewed to one side as in discs, so you can not only get away with a light and super easy to use quick release skewer, but the fork legs could be lighter as well, to a point of course, since they still have to resist the twisting forces from simply turning the bicycle etc. With the assymetric forces of the disc brake at the hub, added stiffness has to come by way of stiffer fork legs, more support between the fork legs at the axle (thru axle), or a combination of the two. Either way, things needed beefing up with discs.
Last edited by Calnago on Mon Nov 19, 2018 5:11 pm, edited 1 time in total.
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wheelsONfire
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Location: NorthEU

by wheelsONfire

It seems more spokes on wheels should be needed to using disc brakes.
There is no way around the fact that a disc brake frameset (frame + fork) needs to be more heavy because it requires more reinforcement.
I also suspect you'd need 1 1/8 - 1 1/2 fork and headset to handle the stress at lower bearing.
If ultimate lightness is the goal, rim brake still will be the way to go.
I am soon to build Ax Lightness Vial EVO Race. It has some updates in layup and internal reinforcements compared to my old Vial EVO D.
I know both Ultra and Race had the last revision during 2018.
I guess this will be the last tribute to rim brake design for me.
Bikes:

Ax Lightness Vial EVO Race (2018.12.21)
viewtopic.php?f=10&t=156137
Paduano Racing Fidia (kind of shelved)
Open *UP* (2016.04.14)


Ex bike; Vial EVO D

by Weenie


blutto
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Joined: Thu Jun 21, 2012 5:09 pm

by blutto

RocketRacing wrote:
Mon Nov 19, 2018 2:55 pm
Rim brake vs disc brake (lets assume hydraulic disc) is tough to compare.

People are making a lot of generalizations. So it is time for me to generalize. It is like comparing brakes on my daily driver, to a ferarri. At street speeds, the brakes on the daily will feel smooth, and well balanced with lots of modulation. Thr ferrari will feel far to grippy, and it will be hard to be smooth.

At 100km/hr the daily driver will have good power and modulation, but on heavy use, it will be a bit more off/on in respose. The ferrari will still feel easy to overpower (too much braking) in response, so you still need to work to be smooth, but modulation is increasing.

At 200km/hr the daily driver struggles to stop the car. Braking is “all in” to hope to stop the car. There is no modulation. Hit the brakes and pray. The ferarri is now in it’s design element... at this speed, the brakes have as much, or as little power as you wish. You have modulation for days and the brakes feel incredible... like engineering perfection.

My lesson here is an oversimplification, but it is a reminder that brakes have a design for intended use... or rather mechanical characteristics that make it perform worse or better in certain circumstances. A carbon rim brake will perform differently from a dura ace rim brake vs a two pistom caliper, vs four piston trail focused caliper. performance, and modulation will depend on bike speed, rider weight, rim surface (lets simplify to wet or dry), and the degree of incline.

To cut to the chase, the carbon rim brakes in the dry, on a flat, at low speeds with a light rider may feel just great for modulation. The four piston trail brakes... will be an on/off switch trying to throw you over the bars if you use the same level of brake lever input. Now, put those same brakes on a heavy bike with heavy rider flying at high speed down a wet mountain, and the four piston setup now has far more modulation, and the carbon rim brakes are nothing more than clamp and pray.

Yes, some brakes/pads/braking surfaces are better than others, but my point is that every brake will have an intended performance sweet spot, and not all brakes were created (flex is bad), or set-up equil. It is less about which is better, and more which performs better (or is good enough) for your specific riding situation.

I am 60kg, so rim brakes are fine by me. I could probably get away with weight weenie flexy carbon rim brakes. If i were 160kg living in a wet hilly region... disc brakes would be an easy sell.

What is best all depends. Especially when you factor weight and and aero.
A couple of things....why on earth would a heavy rider be hurtling down a wet mountain, wouldn't it be prudent, nay sane, to exercise some caution....and lets remember that that there is a tire heavily involved in the braking equation ....so heavy man hurtling down a wet mountain is in danger so matter which brake set he chooses to use, because my money is on the scenario where the tires will most likely let him down before the brake system, and, not necessarily under braking.....or pushing the tire issue up a notch, is it conceivable that hurtling down a mountain in a snow storm with the road covered in black ice could show discs to be superior in some fashion?....I mean discs have all this magic modulation that is a solution to every braking problem don't they, and the tire is now neatly taken out of the equation....

Bottom line, heavy man shouldn't be hurtling down a wet mountain..........
Last edited by blutto on Mon Nov 19, 2018 7:25 pm, edited 1 time in total.

Mep
Posts: 487
Joined: Fri May 28, 2004 4:11 pm

by Mep

wheelsONfire wrote:It seems more spokes on wheels should be needed to using disc brakes.
There is no way around the fact that a disc brake frameset (frame + fork) needs to be more heavy because it requires more reinforcement.
I also suspect you'd need 1 1/8 - 1 1/2 fork and headset to handle the stress at lower bearing.
If ultimate lightness is the goal, rim brake still will be the way to go.
I am soon to build Ax Lightness Vial EVO Race. It has some updates in layup and internal reinforcements compared to my old Vial EVO D.
I know both Ultra and Race had the last revision during 2018.
I guess this will be the last tribute to rim brake design for me.
Good luck on your build! I'm a weight weenie at heart and ultimately couldn't justify the weight penalty and additional hassle of disc brakes. It feels like it may be the last rim brake bike, but I hope not.

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taodemon
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Location: Massachusetts

by taodemon

Calnago wrote:
Wed Nov 14, 2018 7:23 am
I don’t quite know how Specialized seems to be getting around these rules... maybe they release a few to employees and call them “the public”. Same with the rim brake Roubaixs (?) that were made special for the likes of Boonen a couple years ago yet the production model was only available in disc. Did the rim model ever see availability to the public?... I didn’t see any. That’s a good question. It does seem like they’re making some special “allowances” here and there. No manufacturer has been on more of a mission to push discs than Specialized.
https://www.specialized.com/us/en/s-wor ... 801-170388

It took them long enough to release it but they did as a frameset only with the 2018 models. No idea on how many they made or are still available. You can only find it on their site now by going through the bike archive and doesn't show up when looking at current models. I'm sure most people didn't even realize it was available (whole out of sight out of mind thing). I doubt they even had their reps inform the shops as my local shop had no idea it existed until I mentioned it to them.
C36 wrote:
Mon Nov 19, 2018 2:28 pm
KevinM wrote:Interesting that you found the rim brake version to be more snappy since the disc version has thru axel. Really cool that you got to ride both side by side on a real ride to compare! That’s the best way to make your decision.
Counter intuitive maybe, but consistent with all the comparisons that exist I keep posting this capture from the french magazine Le Cycle
I had a friend just go from an Sworks Tarmac SL5 disc (DA di2 hydro) to an expert SL5 (DA mechanical) and he reported the same thing with the non disc bike feeling a lot snappier and responsive. Sounds like they haven't been able to engineer that out of the SL6 from what you are saying too even if it is diminished from the SL5.

RocketRacing
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Joined: Thu May 10, 2018 2:43 am

by RocketRacing

blutto wrote:
Mon Nov 19, 2018 5:34 pm

A couple of things....why on earth would a heavy rider be hurtling down a wet mountain, wouldn't it be prudent, nay sane, to exercise some caution....and lets remember that that there is a tire heavily involved in the braking equation...
Yup. For Most good brakes, they are only as good as the tire, which is only as good as the surface they are on. Without a contact patch to the road, there is no braking. Looking at the brakes only is an oversimplification.

But if buying all new gear, i would still rather brake on a cheap replacable rotor, than 3000$ carbon wheel that does not work so well in the wet. (Fwiw i bought a very nice used rim brake bike and sunk savings into weight weenie and tech upgrades, and i try to avoid rain).

Here is one i wonder about... do wider tires allow for a larger contact patch under braking (aka better braking). Lets think about why wider tires have less Rolling resistance.

And the wuestion about the fat man flying down the mountain in the rain on a bike? Here is his response: “my mates dared me to do it.”

Natural Selection usually weeds out most who lack that type of common sense.

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

by maxxevv

The guys who advocate rims obviously ride in climates that are dry far more often then its wet.

If there's a 50% chance of rain on every ride you go on, I'm pretty sure the preference for rim brakes in view of weight savings wouldn't be so heavily advocated.

blutto
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Joined: Thu Jun 21, 2012 5:09 pm

by blutto

RocketRacing wrote:
Tue Nov 20, 2018 3:04 am
blutto wrote:
Mon Nov 19, 2018 5:34 pm

A couple of things....why on earth would a heavy rider be hurtling down a wet mountain, wouldn't it be prudent, nay sane, to exercise some caution....and lets remember that that there is a tire heavily involved in the braking equation...
Yup. For Most good brakes, they are only as good as the tire, which is only as good as the surface they are on. Without a contact patch to the road, there is no braking. Looking at the brakes only is an oversimplification.

--------------------------------------------------------------------------------

Here is one i wonder about... do wider tires allow for a larger contact patch under braking (aka better braking). Lets think about why wider tires have less Rolling resistance.
Hmmm....most excellent point about the role of various tire widths and their various contact patches.....the accepted view is that the wider tires provide a smaller contact patch ( and what diagrams I have seen to illustrate the contact patch difference seem to show that ) and then there is the contribution that hysteresis differences make.....and we can agree that a wider tire corners better but is that a function of contact patch shape or a function of hysteresis.....so the question is will the wider tire stop give more stopping power.....does better cornering ability translate into better braking potential....I'm thinking not ( wide tires on hard water, as in snow, are just sleds....and in deep snow taller and narrower are generally the better option...)

And this is kinda critical because I have seen the argument put forth that the full potential of the disc brake can only be realized by going to a wider tire ( which is, in a weird way, an admission by the disc crowd that things aren't as magic in disc world as the push from the bike industry would lead us to believe ) ....maybe as someone up-thread was so quick to point out by the time the bike industry is done with us we'll all be riding mountain lite bikes on the road real soon ( if an recent interview with an industry insider on GCN is to believed that takeover of the market by discs will be quite total by 2020....the manufacturing lead times by the bigs are apparently well past the planning stages and into pre-production mode...).

Bb13
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Location: Aix en Provence

by Bb13

maxxevv wrote:
Tue Nov 20, 2018 3:37 am
The guys who advocate rims obviously ride in climates that are dry far more often then its wet.

If there's a 50% chance of rain on every ride you go on, I'm pretty sure the preference for rim brakes in view of weight savings wouldn't be so heavily advocated.
You are right, and also brave to ride in this kind of climate.
I live in Provence and there are maximum 45days of rain per year so this days I rest behind my windows blaming god for his cruelty !
But for the remaining 320 days, i’ m more than happy to save weight when climbing Lure, Ventoux, Espigoulier or in the alps and being used to technical descents the rim brake power is more than enough. If rain suddenly appears I just take my time cause the road is slippery and racing with friends is not important enough to risk breaking my bones.

A friend of mine reported same difference in sensations with Giant Tcr and he returned to rim brakes after a few weeks.

mattr
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Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

maxxevv wrote:
Tue Nov 20, 2018 3:37 am
The guys who advocate rims obviously ride in climates that are dry far more often then its wet.

If there's a 50% chance of rain on every ride you go on, I'm pretty sure the preference for rim brakes in view of weight savings wouldn't be so heavily advocated.
I'm in Scandinavia, near the west coast, so we get a lot of rain, and ice and snow, and gravel roads. So probably into your 50% chance of adverse conditions.

So i have a bike for adverse conditions. That's got rim brakes as well. When i replace it, i'll probably get discs. But i'm not interested in being able to swap wheels from training bike to race bike. As training bike has shit wheels with big heavy tyres and studs for 3 months of the year.

So my next race bike will also have rim brakes. Unless i can't get a frame that fits AND the brakes i want (fit first, everything else second)

modcon
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Joined: Sat Apr 07, 2018 8:32 am

by modcon

I bought a cervelo r3 disc to replace a rim brake r3 that was several years old. It's a touch heavier, and slightly less nimble feeling. It is much more comfortable to ride, same size tyres but wider rims means a larger tyre volume. Braking is much more consistent and powerful everywhere, better modulation especially at the limits such as in rain and fast flowing descents. It feels much stiffer and connected as an overall package. The discs themselves have been pretty good over 8k, but had one issue once where the front rotor rubbed up against the caliper during a sprint in a group ride and made a metallic sound that was off-putting. Learning to set and maintain hydraulics was a slightly larger learning curve than rim brakes, but I've found it okay as I have gotten used to it. I wore a set of zondas concave in one season prior, so the lack of rim wear has been worthwhile for me. Sometimes I feel like rim brakes would be easier, but then when I ride with rim brakes I realise how much easier disc brakes are to use and I don't think I'd go back.

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rexyi1990
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by rexyi1990

I perfer rim brake, because I still think the disk is ugly...

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Calnago
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by Calnago

rexyi1990 wrote:I perfer rim brake, because I still think the disk is ugly...
Very subjective, yet very valid.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

xDOMx
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by xDOMx

I have a disc road bike and will go rim for my lighter build.

There’s a lot of climbing here in Japan, but the weather is usually okay, so rim is almost always more than fit for purpose.

If I still lived in England, though, I suspect I’d hesitate to go back to rim brakes.

by Weenie


MarcFaFo
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Joined: Fri Sep 14, 2018 4:58 pm

by MarcFaFo

bikeboy1tr wrote:
Mon Nov 12, 2018 9:54 pm
MarcFaFo wrote:
Mon Nov 12, 2018 7:04 pm
bikeboy1tr wrote:
Mon Nov 12, 2018 2:49 am
Just purchased a rim brake Colnago V2R and I am happy with it. I have several pairs of rims for rim brake and my area of riding is vertually flat. The V2R has direct mount brakes which is a first for me and I think they are more powerful than my standard but that is just my opinion. My CX bike has disc hyd and the MTB I just got rid of had disc hyd. For me those bikes are best with disc.
Just waiting for my 2019 V2R with discs is comming in.
What color and size are you going with MarcFaFo?
Sorry for my late reply but I completely missed your question. It is going to be the red VJRD version.

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