On the flip side, can't do this with disc brakes:


But both are pointless examples if they aren't an improvement over last gen rim brake bikes.

Rim brakes are lighter, more aero, and can be designed around all modern requirements (i.e., wide wheels/tires and stronger braking). They can also be designed around the fork crown and frame design of every modern disc brake tri bike besides maybe the Ku and Shiv, neither of which is as fast as a P5-6, anyway.

Both my bikes are disc now and it's where we're headed. I just don't like pretending that it's a better solution for bicycles. We could have better performing bikes released in 2022 if R&D had stuck to rim brakes.

exactly. but they're not pointless if they are an improvement. do you have some knowledge about my example that i don't have?

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Dan Empfield
aka Slowman

Yes, their own data on their website. It's no faster than a P5 disc. Make a P5 disc with rim brakes and it's faster than both.

Your list of points is the same one that usually comes up. But those points are either independent of rim vs disc brakes or not a net-benefit if you look at the system level, as you suggest.
- disc brakes have inherently greater aero penalty due to all the mandatory parts that stick into the wind, so that point doesn't work. Rim brakes can be made larger (see any old bike that isn't a pure road bike) and still come out ahead in aero
- same point as above. can make larger calipers or integrate them into the fork as all superbikes were doing, for no additional drag
- same as precious point
- purely theoretical. Think about this one for a second. How different from parallel are disc brake rims near the tire? Not much, if at all. AND rim brake wheels like SES 7.8 were already anything but flat up to the rim edge. The brake tracks were both angled and convex. Any shape you come up with can still be used with rim brakes. Show me one example of a disc wheel where this wouldn't work.
- disc brake rims being 10-20g lighter doesn't help much when you now need to add a 100g rotor, extra spokes, extra carbon at the caliper mounting point, etc. Disc will always be heavier as a system.
- thru axles are an independent design decisions. Rim brake frames and wheels can be made with thru axles if that's a better solution than skewers.

i don't think that's an accurate representation of their own statements. i have known since 1990 that this fork design offers real aero advantages, because of wind tunnel tests that i attended that surprised everybody at that first test (e.g., john cobb and steve hed). since then other brands have figured this out, but only recently have brands (specialized with the shiv disc, but more recently CADEX and KU) really exploited this. it's only been possible with the advent of disk brakes. in fact, if you look at what canyon did with its disc brake speedmax, you can see this same idea expressed.

but it seems as if you only want to argue. why am i not surprised?

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Dan Empfield
aka Slowman

Looks like you are locked into a rim brake world, despite a lot of other progress happening in the disc world.

All your responses are theoretical, because nobody did them. They could have done them, yet nobody did. It's not like the wind tunnel was invented the same year as the disc brake. Now with disc brakes, anything is on the table and designers are experimenting in wholly new approaches.

It is highly unlikely that anyone will attempt to retrofit things like a wide fork, no head tube, non-straight/flat brake track, etc. into a rim bike design. They could, but probably nobody will. Therefore all of your counterpoints are just hypothetical. (And can you imagine how ridiculous a rim brake would look (and probably perform) on a fork design like Slowman showed with 28 or 30mm wheels & tires?)

We run teeny tiny brake rotors (especially on tri bikes) - my cargo bike is rocking 203mm rotors and regularly handles stopping ~400lb. I don't imagine we're going to start seeing 203mm IceTech rotors with ABS systems on road/tri bikes anytime soon, but I imagine that those would be some really good and sustained stopping power.

It's a fickle problem, because bicycles, especially in tri/time trial have no need for extended braking. But in order to sell a product, it needs to exceed "foreseeable misuse", like strapping on a 100lb backpack onto an already overweight rider and taking the bike down a mountain pass.

I'm actually surprised we're not yet seeing aftermarket forks that entirely encase the caliper for Tri's.

Both my bikes are disc brakes.

The theory argument works both ways, since we are comparing 2022 disc bikes to 2015 rim brake bikes and assigning aero progress to the brake system.

That fork design shared by Slowman is the exception. Canyon, Cervelo, Cube, Argon, Orbea, Pinarello, Colnago, Trek, Ventum, Parlee, BMC, Felt, QR, Scott, Fuji, Lool, etc. all have traditional forks designs that would easily integrate rim brakes into the fork legs as they previously did.

I tried to articulate a counterpoint to each of the "advantages" of disc brakes in bullet format to make it easy to digest and discuss at feature level, since they seem to get echoed without much though (for example thru axles or rim profile flexibility being benefits of disc brakes when they can be applied in rim designs). You responded with a picture of an edge case.

I push it (what you seem to perceive as arguing) because I enjoy breaking these point down. Both to get other people to reconsider their thinking and to elicit a response that gives me a new perspective. I'll admit it does frustrate me when it goes like this:

A1: "Disc brakes allow for more clearance"
B: "Rim brakes can be made in any size"
A2: "No one is making them tho"

A2 it true but is no longer a discussion about which tech is better and can be pushed further, even though that was the theme of what A1 claimed.

Looking at Ganna's printed Pinarello for the 1hr record I found it odd that they didn't go with a wide front fork like the Hope bike or the others you mention, their testing must have proven different?

I thought about editing my prior post from "world" to "worldview" but decided to leave it intact. You are looking at bikes from a traditional rim brake worldview. By contrast, all my bikes are rim, yet I view the future of bikes from a blue sky disc brake worldview.

The point of my comments and Slowman's example are that everything is on the table from frame, fork, and wheel-system points of view because of disc brakes. Rim brakes have been around for a century, yet little has changed in the design fundamentals - we're not just comparing 2022 disc frames to 2015 rim frames; we are essentially comparing disc to all of rim brake history and its innovation plateau. Discs appeared on the triathlon scene a couple years ago, and designers are going wild.

You perceive that all those brands have traditional forks that could accommodate rim brakes; yet you cannot support that assertion. Just starting with BMC, take a closer look at its new disc fork versus their rim fork on the same bike. Those two are way different, and I do not think that they could adapt a rim brake to that fork without aerodynamic harm. And BMC's fork is not as interesting as the new Canyon disc fork. A rim brake on that bike would definitely alter the aero profile of the fork. And take another look at the Bolide F - good luck adapting that fork design for a rim brake. The brands are experimenting with wholly new relationships between the headset, fork, and wheel that was virtually impossible before.

first, you have to build it before you can test it. did pinarello ever build a bike with that kind of wide blade fork? i doubt it.

second, the reason i suspect they never built it is that i don't see, and never did see, pinarello as a leading tech company. their bikes have never impressed me as being well thought out. what i do think they are great at is styling. i don't expect ferragamo to make a new, world leading, shoe design. i expect them to make the stylish set of existing designs you can buy. same with pinarello.

if you look at the other disc naysayer here, he asks why canyon doesn't make that wide blade design. i would argue they do. if you look at the most recent speedmax, head on, you'll see very wide fork blades. they just aren't as wide as those on the Ku and the CADEX. the speedmax has very wide-set forks and very wide-set chain stays. same idea, just not executed to that degree.

in the testing i've seen, it works to get the stays and blades very close to the wheels. or very far away from the wheels. what doesn't work as well is to place them where they've traditionally been placed. back to the pinarello to that company's credit they chose one of those options for ganna's bike. it appears to me the blades hug the tire and (front disc) wheel, and that's perfectly fine.

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Dan Empfield
aka Slowman

What IS it a discussion about? I don't get the point.

What do you make of the pro peloton locking up on descents and having to change bikes rather than get a fast wheel change? Also what about the bikes being heavier now with disc? Don't remember seeing the peloton locking up on descents on rim. I'm just an oversize walrus on a bike but the big GC dogs fairly late adopters of rim

I don't have information to challenge your view on disc brake bikes being a better platform for evolution, so I will take that as a fact. What I challenge is consumers being "forced" to buy currently inferior bikes at nearly double the price. I would have expected manufacturers to wait until the bikes are, at least, on par with run brake bikes. But it seems we, the consumers, are to easy to manipulate.

And I speak on the basis of having bought what could arguably be the best disc brake road bike or there, a Scott Addict with an HMX SL, frame. Which is inferior in any terrain to the Scott rim brake bike it replaced. To the extent that I bought another brand new rim brake foil, only at half the price.

For a while Dimond offered both rim and disc on otherwise identical models and sales were practically 100% disc, so it’s a ‘the market has spoken’ thing. Dimond’s own testing showed there was a small but measurable cost to the front disc, which is why they sold a few rear disc/front rim bikes, but not many chose this route either. I personally see no benefit and several costs to TT/Tri bikes with disc brakes, have been disappointed to see the transition.

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Dimond Bikes Superfan

Ummmm, we are talking about triathlon bikes here? That is a different use case. There have been tons of debate threads about disc brakes on grand tour road bikes.

Would you like this share the several costs you see? Did you read any of the threads about IMWI this year?

10 years ago when disc brakes starting to appear more and more I read an article where overheating of discs was discussed. At the time that was a problem: sandwiched discs where the adhesive layer would melt in descents.

Is this with disc-brakes still an issue: overheating on long steep slopes when being heavy (I weigh 190 lbs) or have the discs become better in the last 10 years. How is it with the diameter of the discs: can you mount smaller or bigger discs when needed.

 

Never heard of the issue you describe, or even the use of adhesives, vs all-metal construction. Brake rotors may be new to bikes but they have existed in motorcycle applications for much longer.

The overheating danger comes from boiling your brake fluid, not damaging rotors, which may warp but won't fail before the fluid boils. Larger rotors will absorb and dissipate heat better, but enough to make a practical difference.

You can fit different rotor sizes with adapters, to a point. On road/tri frames it is usually limited to 160mm or 140mm. You shouldn't get in trouble with 160mm unless you weigh a lot and drag tour brakes down a long descent. There may be some spacers you can buy to fit larger rotors but it really isn't necessary. The main benefit to larger rotors is brake leverage.

The issue is with Shimano Ice-Tech rotors, in that the aluminum center of the steel-aluminum-steel "sandwhich" reaches a point where the material becomes thixotropic (not melted, per se, but more like a "jelly" state). Tour Magazine in Germany was able to get them to fail...and quite spectacularly, as well IMO. Of interesting note is that the rim-braked bike actually was navigating the course faster than the disc bike...until the disc failed during the simulated "panic stop"...doh!

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http://bikeblather.blogspot.com/

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"I'm thinking of a number between 1 and 10, and I don't know why!"

Oh good...My neighbor got a fat wheeled bike for Christmas that we stored in our garage for 6 weeks waiting for the big holiday. He got a flat and hadn't been able to ride for several weeks so I volunteered to fix the flat for him. None of my bikes have disc breaks so his was the first one I worked on with the disc break. It took me 10 minutes to change the flat tire then I spent 20 minutes trying to get the disc aligned so it wouldn't rub. I got it the best I could but thought that it would annoy him when riding. I thought that I must of bent the disc when removing the wheel or something. He said the bike was fine when he rode it. I am glad to hear that I do work as well as highly rated shops. I feared that I had ruined his bike. If that disc is not perfectly flat it is impossible to get it to not rub.