Please don’t make this a rim vs disc bloodfest. Stage 17 won with rim brake

Discuss light weight issues concerning road bikes & parts.

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vinny
Posts: 123
Joined: Sun Nov 17, 2019 5:17 pm
Location: california

by vinny

how about discs are better for descending cuz it doesnt heat up the wheel and cause the resin to heat up and soften.

here in northern california there is a hill mount umunhum where friends with rum brakes and clinchers had there carbon wheels soften and loose all pressure.

this has happened to at least 2 people i know personally, and others that i heard about.

luescherteknik has a video describing this, pros mostly run tublar wheels which are thicker etc....

tjvirden
Posts: 540
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by tjvirden

blutto wrote:
Wed Aug 11, 2021 2:52 pm
To expand a bit on the above response....

I've been riding/training/racing for well over 4 decades now and have in that time logged an awful lot of miles....and with a fair amount of riding, and even racing, in the wet....During that time I have had occasion to apply my brakes on a whole lot of times....and frankly I cannot remember an instance where in applying my brakes I ran out of braking power....I did however on numerous occasions run out of tire ( see that tire patch thingee dilemma mentioned above )...yup lots of experience with that...

And those miles and miles have also given me some experience in regards destroying rims....now I have gone though scores and scores of rims, and yet never have I worn out a rim....have bent numerous rims in race related crashes, stupid riding decisions, have pulled spokes thru rims but have never ever worn out a rim on the brake surface...

So my question is...how much riding does one have to do in the rain ( which apparently is the key to destroying rims ) to total a rim....and how much braking does one have to perform in those rides to destroy a rim....my experience is that braking is a very short series of intervals during riding ( though I understand that some people often revert to dragging the brakes for long periods of time....which is really bad form but that is how some people use their brakes...)....and from reports on this site apparently carbon rims have also been destroyed thru braking in dry conditions as well...and why use carbon wheels in crap conditions....in the old days we used what we called training wheels, lesser quality and kinda sorta understood to be disposable, in crap conditions...

Now the experience that I drew upon to make the comments above was from riding mostly on alloy rims ( though I have used carbon wheels in the last decade or so ...and btw with no problems either with braking or wear in either wet or dry ). Which got me thinking....maybe these rim problems are simply showing that carbon wheels, while they are seriously bling and are de rigueur requirement for true cycle stylin', are not the most ideal material for rim construction for all applications ( as in application, application, application ) ....and that discs are simply an overly expensive band-aid to paper over that problem....

Cheers
With respect, I think that although you may have a lot of experience, what you say indicates that it's narrow experience. I still use rim brakes in 'bad' conditions sometimes (cold and wet) and then it's not uncommon to be limited by the brakes, not the tires. That's using either Swissstop BXP/Koolstop [Salmon] pads on a variety of alloy rims. The braking is good enough, almost all the time, for me to keep using those setups, but I have had some "oh sh*t" moments. Anticipation is of course the best course of action for any braking system.

You appear to have explained why you've never worn a rim out from braking - they're damaged in some other way first; that's very common for someone doing plenty 'performance' riding.

As for how much braking in the rain to wear out a rim - well, Jobst Brandt gave an estimate for that (0.1mm off the rim coming down from an Alpine pass). You can read about it here: https://yarchive.net/bike/rim_wear.html

In my experience biggest factor is the amount of grit on the roads one rides on; I can get through a rim in 6 months of Autumn/Spring/Winter in a rural, agricultural area without significant hills - just undulations and junctions. About 5000 Km.

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tomato
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by tomato

iheartbianchi wrote:
Wed Aug 11, 2021 9:49 am
tomato wrote:
Wed Aug 11, 2021 8:51 am
iheartbianchi wrote:
Wed Aug 11, 2021 8:03 am
Speaking of Porsche's, I kind of see a parallel in the rim/disc debate to the manual/PDK debate. Anyone who has kept up with Porsche knows that the manual option commands a significant premium among the aficionados.
Anyone who has kept up with Porsche also knows that the PDK transmission outperforms the manual transmission, and it outsells the manual tranmission by a wide margin. So, yes, there is a parallel between manual/PDK and rim/disc.
Long-time Rennlister here.

The Cayenne and Macan are Porsche's best sellers by far, and they don't have manual as an option - means nothing.

Super high-end models and the Porsche VIP program caters to the buyers who demand manual. Porsche 918, Carrera GT, GT3 models, GT4, 911R. Interesting that people will pay a significant premium for the much slower manual gearbox. Hypercar manufacturers like Pagani are also making their cars with manual transmission. The hardcore aficionados for whatever reason prefer the slower manual, although the ordinary consumer and racers will of course use dual-clutch.
For the record:

Macan: PDK only
Cayenne: PDK only
Boxster: PDK outsells manual
Cayman: PDK outsells manual
911: PDK outsells manual

Some of the specific models you mentioned:
Carrera GT: Manual -- predates introduction of PDK.
918: PDK only.
GT3: PDK outsells manual. Some older versions were PDK only.
911R: Only 911 variant (of 24?) available as manual only.
GT4: Only Cayman variant available as manual only.

Yes, some hardcore afficionados prefer manual transmissions, but most prefer the PDK.

Mcdeez
Posts: 318
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by Mcdeez

iheartbianchi wrote:Did someone actually say that rim saves 10w? Maybe in an awful crosswind, maybe.
C36 did

"The gain is there on a complete system. 10 W+ are not in the marginal territory how much do you need to train to increase your FTP by 10W? When the race heat up and they become 15?"

openwheelracing
Posts: 289
Joined: Thu Jan 28, 2021 6:41 am

by openwheelracing

iggg wrote:
Wed Aug 11, 2021 3:02 pm
openwheelracing wrote:
Wed Aug 11, 2021 2:23 pm
Nah most people here prefer rim over disc. So clearly your claim is specific to you. Yes, some of the fastest riders in the World live here too.
It doesn't even matter what you mean by "here", you are almost certanly wrong - most (and by most I mean 90+%) cyclists prefer disks brakes, including "here"
You would be wrong cause most people "here" and "there" where I Ride prefer rim brakes.

Like I said, YMMV. Go to Taiwan KOM and see how many people ditch disc like ditching COVID.
Last edited by openwheelracing on Wed Aug 11, 2021 6:05 pm, edited 1 time in total.

openwheelracing
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Joined: Thu Jan 28, 2021 6:41 am

by openwheelracing

Again, PDK is not current gen disc brakes. False equivalency. Stop the silliness. Current gen disc brake allows feather light modulation and better wet braking performance at the expense of weight, cost and climbing speed.

PDK actually faster and is actual "technology" advancement.

rudye9mr
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Joined: Wed May 01, 2019 12:01 pm

by rudye9mr

Those who still opt for the manual prefer the sensory appeal that it gives vs a PDK....

Not sure how that applies to rim brakes..

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C36
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by C36

Mcdeez wrote:
iheartbianchi wrote:Did someone actually say that rim saves 10w? Maybe in an awful crosswind, maybe.
C36 did

"The gain is there on a complete system. 10 W+ are not in the marginal territory how much do you need to train to increase your FTP by 10W? When the race heat up and they become 15?"
Boy, you guys need to keep track of a conversation Image… one guy said that “10% of a bike was marginal”. I said that even 10w is not
marginal, guess I need editing to help people following a conversation Image

Now, almost all the measurement showed that rims brake have some aero advantage anywhere between few to 10w (the GCN case being quite a surprising one when we know how advert-oriented they are). Edit: to keep a link with original topic, it’s at least in some cases part of the reason we saw some rim brakes in major races…
Last edited by C36 on Wed Aug 11, 2021 6:15 pm, edited 1 time in total.

Perp
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by Perp

wheelsONfire wrote:
Wed Aug 11, 2021 2:10 pm
Perp wrote:
Tue Aug 10, 2021 6:24 pm
I must be doing it wrong. I have 2 rim brake and 2 disc brake bikes. All top end (Wilier zero, s-works tarmac, v3rs disc, Time ADH disc) with top groupsets (shimano, sram, campy)

Rim brakes bikes are under 7kg with the wilier at 6.3kg. Disc brake are 7.2 and 7.5kg. Flat, climbs, mix, I'm fastest on.... the heaviest bike - v3rs. 4w/kg FTP rider at 65kg. Must be something wrong with my lighter rim brake bikes with similar depth wheels (45mm).

I like both kinds of bikes but prefer the ride of disc due to ease of braking (modulation and effort) and obvioulsy in the rain. Wilier *feels* the fastest to ride, until I look at the numbers after.
Which bike does feel best to ride? If you picked one of these bikes and could only have that single bike, which would you pick and why?
I prefer the ride of the Colnago the most. I like the geomerty/handling that Colango has the others. It's so smooth/stable and fast. Prior, I didn't think "aero tubing" shapes made much of a difference, but I'm still fastest on that bike. I've used the same wheels/Tires on the Time and Colnago and my bars on the Time are more aero (at least visually) and I'm still quickest on the V3RS. My Time is still very new, only have <200km on it, so still more riding to get a better feel. Wilier is the most "fun" to ride - I think the lighter weight makes accelerations feel better. I find the handling quite twitchy though - I have more trust going max speed cornering on the Colnago and I think I'm only average bike handler.

If I had to pick one... Probably the Time. Colnago is eletronic / internal routing so maintanance would be easier on the Time. I also prefer mechanical shifting (much like I prefer manual tranmission over DCT - BMW M owner). Specifically bought mechanical SR instead of EPS for the Time. EPS shifts "better", just prefer the feel of the cables. Granted, I could move the groupset over, but I love the quality of manufacturing on the Time (plus that weave!). I acsutally have a hard time deciding which bike to ride lol.

For me, the biggest weakness of my Wilier is max tire size. I have 25s on it and the clearances are really tight.

spartacus
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by spartacus

C36 wrote:
Wed Aug 11, 2021 6:15 pm


Now, almost all the measurement showed that rims brake have some aero advantage anywhere between few to 10w (the GCN case being quite a surprising one when we know how advert-oriented they are).
The comparisons are largely invalid though since new bikes are designed for disc brakes, and they aren't just being slapped on a rim brake frame. There may be other factors at play here but is anyone claiming that for example the new aeroad is slower than the old one because it is less aerodynamic because it has disc instead of rim brakes? I don't think the facts support these conclusions.

Ypuh
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Location: The Netherlands

by Ypuh

tjvirden wrote:
Wed Aug 11, 2021 4:33 pm
In my experience biggest factor is the amount of grit on the roads one rides on; I can get through a rim in 6 months of Autumn/Spring/Winter in a rural, agricultural area without significant hills - just undulations and junctions. About 5000 Km.
Wow.

As part of team #savetherimbrake I can confirm that grit/wet weather descents are murderous on rim brake wheels. I've had 1 or 2 rides where I wore through a set of pads in the span of ~200 km's. I've never had to replace a rim due to excessive wear though (clocked about 70.000km in my 5-6 years of riding). Once binned a cheap set that I bought 2nd hand for bad weather riding and never gave any love, but most of my wheelsets have 15-20k on them and still look great.

Note: I live in a flat country. My brake tracks barely see any use and definitely no prolonged braking. It's more likely a spoke fails, crash or damage of another kind than the rims actually wearing out. Disc don't really make sense for me, except for those 2-3 rides in the hills/mountains and it starts raining (in 5 years I can count about 3-4 times I wished I had discs).

Replacing rims after 5k or 15k for that matter would seriously persuade me to look towards disc.
Cervelo S3 - 7.29kg

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cveks
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by cveks

C36 wrote:
Wed Aug 11, 2021 12:09 pm
Leave the forum for like 10 days and 350 messages later it deviated in the “but I like / I have / my experience” I hope we were all better at sticking to the subject (what pro use and why) in high school or exams must have been pretty painful for some Image.

Few of the comments linked to the initial topic
iheartbianchi wrote: Even if a rim bike in a wind tunnel is 5-10% faster, those are marginal gains and doesn't speak to "system gains."
The gain is there on a complete system. Even 10 W+ would not be in the marginal territory, how much do you need to train to increase your FTP by 10W? When the race heat up and they become 15?
iheartbianchi wrote: But a bike will never decide who wins or loses in a 1 hour crit. So it's kind of silly for riders with FTPs below 4.0w/Kg to be beating ourselves over something that will have little to no impact on our lives.
Nonsense, that’s not how physics work… a gain is a gain regardless of your FTP or PMA. Thinking that you need to be 6w/kg to measure the difference is not connected to real word mechanics rules. And if you lose a race by 50cm and you spent 10W more than anyone else (and more at each acceleration) then here are those 50cm. Same applies if you can’t keep the wheels in an attack…
iheartbianchi wrote: I was at my fastest on a CAAD7 aluminum frame on mechanical 7sped dura-ace 20 or so years ago
Typical error mixing physical shape in deferent moments and what different equipment would give you at the same date.

I keep repeating the same. Rim brakes have been measured faster on flats and climbs by some pro teams, independant testing and some brands. Discs brakes haven’t been measured faster descending where we could have expected gains.

Now to avoid the « but I prefer xxx fans », this is relevant for pros, not for each of us, not for marketing or supply chain managers (or LBS). We can debate on sales %, how we reach this point etc. Discs are here to stay, it’s in everybody’s sales interest on the short to medium terms independently of what we / pro like.
Yep great point.Thats why experienced ppl ride rim brake bikes.

You get much higher value, better bike for less money, plus you are superior aginst disc brake lovers.on both hills and flatsnwith same power output.

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cveks
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by cveks

Mcdeez wrote:
Wed Aug 11, 2021 3:12 pm
Rim brakes saves 10watts? LOL

In a 40 min crit you run disc or rim ,there would be no difference, youre almost always at the wheel of somebody, and you really think a rim brake will make you accelerate faster? lol

Discs brake better because of the better modulation, it has nothing to do with the contact patch.

And yes you wear out your rim brake wheel with excessive brake in the long term like a aluminum wheel, same thing.

If you buy an used carbon rim wheelset,you're not gonna inspect the brake track before buying?? Of course yes!!(if youre not inspecting it,not smart) because it wears out in the long run.
Mate you lack information. Pitty for you.

GCN did science research in wind tunnel with Pinarello Dogma F12 2 types same gear - one with rim brakes other with disc brakes. And with rider, rim brake bike was 16 watts faster on 45 kmh . 10 watts faster on 30 kmh. That is A LOT. Ton on pro level.

Rim brake bikes are simply more aero, they produce less drag so you go faster with same power .

Thats why no grand tour was still won on disc brakes. Rim brake bikes give advantage over rim brake bikes on pro level.

Image

Complete info here


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cveks
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by cveks

Science is science. For example I rode bike for years with unshaven legs . Once I find out research which says that you save 10 watts if you shave legs. So I shaved mine first time in my life and that brought me increase in both my top speed, FTP, and level of cycling. Aero rim brake bike, shaved legs, 38 mm deep aero carbon wheels is killing combination for me :)

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cveks
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by cveks

iheartbianchi wrote:
Wed Aug 11, 2021 12:50 pm
C36 wrote:
Wed Aug 11, 2021 12:09 pm

The gain is there on a complete system. 10 W+ are not in the marginal territory how much do you need to train to increase your FTP by 10W? When the race heat up and they become 15?
Sorry, but can you clarify where you're getting the 10W data from? I am aware of tests in certain wind conditions where the disc brake variant will actually be slower, such as in crosswinds, or how in even the most optimal conditions the disc version "only" makes you 0.5 to 1.5 watts faster. Are we talking about the same thing? Mind you I haven't looked up this stuff in a couple of years so there may have been newer research.
C36 wrote:
Wed Aug 11, 2021 12:09 pm
Typical error mixing physical shape in deferent moments and what different equipment would give you at the same date.
No error there - I wasn't trying to say that I was in better shape on old tech therefore old tech is faster (nor would I support such a claim!). I was saying, for most of us, whose racing days are long gone, no amount of gear will make much of a difference.
GCN does science.

Rim brake bikes save from 10-20 watts on pro level races.

Image

Thats huge mate.


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