tomato coupe

I ignored the weight of the bolts and/or lock rings and any extra weight in the hubs because they don't significantly change the moment of inertia. You could double (!) the weight of the hubs and the moment of inertia of the wheels would increase less than if you added 1 g at the rim.

OBoile

The time to change disk brakes is like 1-2 seconds longer. It's not really a persuasive argument anymore.

Dave Mayer

So I took your posting that rim-brake bikes have won 8 of the 9 Tour stages so far. As best as I can, I count 5 teams running rim brakes out of 22 starting teams.


So I ran a statistical analysis to quantify the probability that with 22 evenly matched teams, that 8 of the 9 stages would be won by these 5 select teams. 100,000 simulated Tours over 9 stages. I came up with a maximum outcome that 10 of these 100,000 times we would have experienced the 2020 results to date. So if all of the Tour teams are evenly matched, with equivalent equipment, then what we've seen to date in 2020 should happen less than 10 out of 100,000 years.


So obviously, discs are a significant handicap in race conditions. Or possibly the strongest teams are also making smarter equipment decisions.


The insurmountable disc handicap?... the higher rotating mass of disc wheelsets. Since braking forces on disc wheels have to be transmitted through the spokes, and spoke holes in the rim, and then the end of the fork, in contrast to the far more sensible path in rim brake bikes, all of these components have to be bulked up, adding mass at the worst possible places on a bike. Plus the constant rub rub rub and squeal squeal squeal.

MinnMan

(muffled laughter)

Maybe you should talk to someone who builds wheels or something.

Dave Mayer

I've built dozens of wheels.

MinnMan

Oh really? And when you build them with disc brakes, you "bulk up" the rims and spokes? So for example, when I buy two sets of wheels, one rim brake, one disc brake, and they have identical rims and identical spokes, I'm in trouble?

Dave Mayer

Radial-lace some disc-brake wheels and report back on the results.

tomato coupe

6 stages were won on rim brakes, not 8.

The teams in the Tour de France are not evenly matched. B&B Hotels - Vital Concepts clearly does not have the same chance of winning a stage as Jumbo Visma. Your statistical analysis is useless.

This is as bad as your statistical analysis...

Dave Mayer

6 disc teams only? Are you sure that you are counting the teams that advertise their disc-brake fleet of bikes before the big race, and then quietly slide onto rim-brake bikes before wheeling up to the start line?

Same thing happens with clinchers/tubeless. Big advertising before the race, but on the start line, everyone is on tubulars on every stage in every race.

Regardless, if (only) 6 rim-brake teams have won out of the first 9 stages, then the chance of this happening should only be 5 times out of 1,000 years.

Listen: the pro tour exists to sell beer, sketchy lotteries and banks (same thing) and bike bling to dentists with gold cards. So here is a solution: that all bikes be fitted with functional concealed rim brakes (like on TT bikes), but also kitted out with lightweight (cosmetic) carbon fibre discs that look like the real thing - for marketing reasons. Win-win for everyone: the racers and mechanics are back on what they actually want, and the marketers have a chance to showcase the latest tech.

tomato coupe

Watch the stages.

More bad statistics.

Doge

I see the point of being pro athlete is total compensation / how much you get paid. It may be doing a wheelie off the back, a long break away in front of cameras etc. Their job is to get the most money. A great way to do that is winning. Someplace down the line is speed and further down the line is stopping speed. I have no doubt disc brakes wheels stop speed better than rim brakes wheels. I have a lot of doubt they help winning. They may help you get paid more.

To your winning calculation also add the last few races with the big names. In Milan-San Remo, the disc guy lost the sprint to the rim braked guy. The then Criterium du Dauphine 2020 top two on the podium used rim brakes.
The argument might be that they are just better riders. I'll accept better riders use rim brakes.
Looking at actual results, now that UCI does allow disc brakes, weighs higher for me than calculations. If all teams go disc, then it doesn't matter, but for now we have good data to look at.

Doge

It depends on what you buy. For what I buy, yes. The disc stuff weighs more and is heavier.
I bought a 20 hole rear hub ax-lightness tubular race set. 16 hole rear hubs are also options in various brands - Internet search.
In trying to use these same rims on the new S-Works disc braked Venge, there are no 20 hole (let alone 16 hole) disc braked rear hubs. I'd love to be wrong, so if you know of any, please post. That is another 4 spokes and nipples, or 8 if you came from a 16 hole rear that you need to get a disc brake build. The disc braked Venge weighs in a bit under 17lbs in SRAM eTAP. The 2014 (or 15) Venge with rim brakes and some tuning is 13lbs in Di2. I used lighter cable (power cordz) housing on the rim braked Venge. It also has lighter wheels. I don't know how to lighten the hydraulics. I'd expect with similar tuning for seat, stem bars they'd still be 2-3# apart.

tomato coupe

Ummm ... how about an apples-to-apples comparison? A 2015 rim brake S-Works Venge with Di2 weighs in at 7.7 kg (17 lbs.) off-the-shelf. A 2020 disc brake S-Works Venge with Di2 weighs in at 7.1 kg (15.6 lbs.) off-the-shelf.

Doge

Because you can't do with the disc bikes what you can do with the rim braked bikes. There are lots of ways to play with weight other than brakes. But the disc brakes and supporting materials will weigh more.
You cannot buy the lightest wheels - 16 and 20 spoke rears.
You cannot cut cable weights by almost half using Power Cordz or other.
I believe the forks are heavier - I have not weighed them.
The brifters are heavier.
I had to add ballast to my rim braked builds for UCI after finding the heaviest skewers,

I have under 12lb Di2 builds with steel BB spindles and pedals that would be 2# heavier if disc braked. Disc brakes mean heavier cables, heavier forks, heavier brifters, heavier wheels (hub, spokes, bolts, discs).

On the TdF. Is UAE mixing braking methods? Did Tadej Pogačar use rim (at least for some stages) and Alexander Kristoff use disc brakes?

tomato coupe

Regardless of where you stands on the disc vs. rim issue, building ultralight 16 spoke rear wheels and then adding 3 lbs. of dead weight to meet UCI standards is brilliant.

Doge

The bike has a different feel based on where the weight is. If the UCI weights we 3# lighter, I expect we would not see as many discs.
Where do you think the brilliant JumboV is adding that weight? A typical road with rim brakes will be under the 6.8kg.

Not TdF I've lost two disc braked wheels in the last 2 years, and none for rim braked in 5, then 20 years. The pros are good at hiding broken stuff. There is a reason the winning riders are selecting rim brakes and I don't think it is because they are paid to. What do you think the reason is?

tomato coupe

Are you suggesting that Jumbo Visma chooses to ride with rim brakes so that they can build a bike well below the UCI weight limit, and then add a bunch of dead weight in a strategic location?

Doge

1 A standard SRAM Red/eTap/Dura-Ace rim brake build with 23-25mm tires on a painted team frame will be below UCI weight limit.
They will be adding weight if they choose that build.
2 They had a choice on brake type. It appears UAE uses both. Certainly Wout made a name for himself using disc braking in cx.
3 All builds provide a bit of choice on where you put the weight. I think that depends a bit on rider preference and course as to where that weight is placed. You can calculate all day which is better, but riders prefer different feel. While in general they ride what they are given, they will go off brand. TEAM Sky was riding FMB tires, and Froome ax-lightness rims a few years back. I expect that Pinarello needed a couple pounds added.

tomato coupe

You didn't answer the question:

Doge

They may be. I don't think the rim brakes stop better, although they may prefer the feel, I do, and I have both.
So they may prefer the lighter wheels and moving mass to where they want. I assume it is for convenience.

Why do you think they are on rim brakes?

tomato coupe

It simplifies logistics, eliminates some incompatibility issues, and (slightly) speeds up wheel changes. End of story.

79pmooney

Three things I've been seeing more of since disc brakes appeared in the peloton; slower wheel changes, full bike changes instead of wheel changes and more down the road issues with second stops for new bikes. I believe this is happening more when neutral service is involved. If I were a team DS, I'd want the wheels that are simplest to change reliably by any mechanic for the simple reason that if my rider is up in the break or the field splits, my team car isn't going to be doing the wheel change if he punctures. Neutral service might give him a bike, but that bike isn't going to fit very well and might well have less than optimum pedals.

The game is to win races. My best candidate might well be my rider in the break. Handicapping him with a poorly fitting bike simple because he flatted or risking a wheel change where he might well have to stop again and take a second bike. Not good race winning strategy. I highly doubt discs can ever replace the seconds, maybe minutes, lost if those scenarios play out. And yes, that doesn't happen often. But ... the rider who's getting handicapped might well be a smaller team's best chance at a podium. That's a lot to lose.

I see this as mostly - sponsor teams and insist they ride your disc braked bikes because you need to produce the bikes your team races (rules) and discs bring in more money. Get your team on discs, have them shown off and use that to sell bikes. As a rider, unless you have a lot of bargaining power, you have little choice but to ride what is provided, especially when it is as visible as disc vs rim. You are being paid as an entertainer to sell a product.

Ben

OBoile

It's amazing how desperate some people are to avoid accepting the truth: disk brakes work better.

robertorolfo

You know that ABS has become big in the motorcycling world the past few years, right? And yes, I know about contact patch and suspension differences, but the point is that the technology is applicable and of some value for two-wheeled transport.

Do they though? The results so far don't bear that out (more on this below). And even if they did work "better," whatever you mean by that exactly, does the benefit really make a difference in reality? (Again, see below). Lastly, does this so-called "better" compensate for the downsides in both racing and everyday life?

I agree that you can't use the results so far to prove that rim brakes are better, but you can use them to disprove this notion that rim brakes are inferior and might actually be a handicap.

Watching stages 8 and 9, with their pretty intense descents, it was clear that the rim brake guys were at no disadvantage. Indeed, they were there riding in close quarters with the disc guys, and it didn't seem to make any difference to them at all. So what the results do seem to show is that for the best riders in the world, there is little to no difference in performance, so for the average person there is nothing there (or you could say it's a matter of skill).

But, for the average person that doesn't have a mechanic stripping their bike down at the end of every day, there are some real downsides to discs that shouldn't be ignored. Dealing with hydraulics is annoying (at least relative to simple cables), and it only gets worse with age. What I find funny is all the disc worshippers that have as a frame of reference new, or fairly new, bikes and brake systems. Just wait a few years until things start to get some wear and tear, until seals start to dry out or get worn. That's when the real fun begins.

See above. What these results (and the actual racing) do tell us is that rim brakes are NOT some type of handicap. Not even close.

Do you watch MotoGP? Heck, do you watch F1? If you don't think placing mass where you want it is important to racers, you don't know racers...

tomato coupe

Do you think that Jumbo Visma chooses to ride with rim brakes so that they can build a bike well below the UCI weight limit, and then add a bunch of dead weight in a strategic location?