Disk Brakes Again

On Monday, May 27, 2019 at 3:46:16 PM UTC-7, Tom Kunich wrote:
On Monday, May 27, 2019 at 1:47:35 PM UTC-7, jbeattie wrote:
On Sunday, May 26, 2019 at 9:23:45 PM UTC-7, Frank Krygowski wrote:
On 5/26/2019 9:52 PM, Tom Kunich wrote:
On Friday, May 24, 2019 at 10:07:31 AM UTC-7, jbeattie wrote:
On Friday, May 24, 2019 at 9:27:51 AM UTC-7, Tom Kunich wrote:
I don't know how many of you watched the Amgen Tour of California but I think it was a Frenchman that got way hell and gone off of the front on Stage 5 I think.

As he was descending a rather long and steep climb he looked like an absolute beginner. All of his lines were screwed up and he almost went off the road several times. On one occasion he ran off of the road and up onto the sloped dirt siding.

I could not understand how someone that could ride 7 minutes off the front of a 140 mile race was so amateurish descending. He wasn't tired because he kept his lead for a very long way after the descent finishing with a full 7 minute lead.

Two days ago during some rain I was looking at videos and ran across one of them by a pro that showed himself descending almost identically amateurishly. The same bad lines though the corners and the same very dangerous lines.

He blamed this entirely on his disk brakes. He said climbing they drag and make noises and descending they cannot be relied upon to slow you properly. The upshot is he said that NO PRO would choose disk brakes over rim brakes and that this was just another gadget to up the price of a bike.

When I was talking here about how too F-ing powerful the large disks were and how much better the V-brakes were on a cross bike I got a whole lot of static. Well it appears that the same problem is on road bikes with the smaller disks.

They also have an aero disadvantage and I can tell you that the new bikes are so aero that you have to be careful descending in a group because you keep closing up on those in front.

The original idea was to have an alternate way to brake so that you wouldn't wear out the braking surface of carbon wheels. But using the artificial cork brake pads allows you to use a set of carbon wheels as long as you can the super-light aluminum wheels with standard brake pads.

Although we are presently in a trade dispute with China I don't expect that to last long and carbon wheels from China only seem to have one problem - they do not have much spoke tension and so move around too much in side winds. And they are spectacularly cheap.

While the US made carbon wheels are slightly more aero it isn't by much and unless you're riding TT's it isn't worth paying six to eight times the price.

Another problem - rim brakes put all of the braking forces at the strongest portion of the bike. Disks put the forces at the weakest. This forces manufacturers to make much heavier forks and rear stays. And the axles have gone to much larger sizes that cannot be used with quick releases. Pro mechanics no long change out wheels on bikes but make entire bike changes and that costs a lot more time than it used to.

All in all I think that disks are nothing more than something different to buy if you're a non-mechanical enthusiast that is likely to go with the flow.

Here is what some pros say: https://www.youtube.com/watch?v=OX_EPa0ZuSM

Discs do give better braking with CF rims, they don't heat rim glue, so you don't get sew-ups squirming around on the rims. If I were doing a long descent with lots of braking on sew-ups, I might prefer a disc. Otherwise, on a rapid descent on a racing bike with clinchers on aluminum rims on dry pavement, there is no a whole lot of difference between the two, assuming both are properly adjusted and the pistons lubricated. I own both and don't find much difference, except in ways that are equally bad, e.g. rim brakes grabbing at seams or with contaminants on the rim and discs shuddering or grabbing or screaming.

If disc brakes are juiced up to the point where light braking locks up the wheel, then that's a problem. If one is used to the requisite heavy hand to get good rear braking with a cable caliper brake, then that can be a problem with discs. I had to adjust after a couple of fish-tailing experiences.

Discs are the clear winner in wet-weather riding, but on dry pavement, it's just a matter of feel and personal preference. In professional racing, there are other considerations.

-- Jay Beattie.

I have had very long rides in the rain though not by choice. I never had a single problem with the brakes but with the tires. Stronger brakes would make that problem worse yet.

Since aluminum rims actually conduct heat a lot more directly than carbon wheels what would make you single out carbon wheels?

I have been thrown over the bars - WAY over the bars on my cross bike when I was braking and a trail bump locked the front wheel solid and releasing the brakes doesn't release the disk brake the same speed.

On my other cross bike I have TRP 9.0 brakes and they are so superior I have told that story more times than necessary.

I think that team mechanic summed it up - "The industry wants it and it is coming whether we want it or not. So we might as well get used to the idea."

The industry wants it for racers because a significant number of
ordinary cyclists will want whatever the racers use - as I said earlier.

Maybe, but unlike some equipment first seen on racing bikes -- SIS, step-in pedals, electronic shifting, X + 1 speed, etc. -- the pro peleton seems to be following the consumer market. My 2006 Cannondale CX was sold with discs when they were still prohibited by the UCI -- totally ruining my Euro pro CX career. The Trek Portland had discs. Phil Wood had a disc brake in the mid to late '70s. Small rotor hydraulic discs were introduced by Shimano in 2013 and not seen in the TdF until five years later. Yes, putting them on TdF bikes stimulates the market, assuming consumers pay attention to what's on TdF bikes, which is a questionable assumption. Most people don't follow pro racing and just go into bike shops and look around.

And for Tom, carbon rim wheels are hard to stop when wet and they are poor at dissipating heat. Discs fix a lot of problems with carbon wheels. I've been riding on cable or hydraulic road discs for 13 years and have never thrown myself over the bars. I have locked up a rear wheel because rear braking is so much more positive, so I avoid being ham-handed. Discs have their own set of problems and aren't perfect, but like I said, they're great wet weather brakes, and you don't grind your rims into oblivion.

-- Jay Beattie.

That isn't clear Jay. While normal old Carbon Fiber conducts heat up to half as good as aluminum, the unidirectional stuff conducts twice as good a aluminum.

The problem is that carbon fiber itself is a good conductor while the resin isn't. So depending on the construction technique you could have a pretty heat conductive rim. And if they were to put it together with graphene strips that a whole other ball game since graphene conducts heat 30 times better than aluminum.

Also, they had this really great test of aluminum vs carbon fiber bars in YouTube. The final result was that aluminum has a fatigue limit while carbon fiber fatigue limit was so high they never reached it in three days of constant running. However - in a crash that exceeded the strength of the material carbon fiber would break while aluminum would bend.

I know that modern designs are better with heat dissipation. My son has some Vision CF wheels that were OE on his Emonda. His major complaint is braking with wet rims -- or the lack of braking. He also complains that the brakes scream when the rims are hot. He's shopping from some new aluminum wheels. He's moving back to SLC and is going to resume his former life of climbing and descending canyons. His comment is "why own them." His words, not mine. He'd probably miss having really stiff wheels, but the braking issues are important to him -- and they should be on the twisting, steep roads in the Wasatch. Shimano C40s would probably be a good choice.

-- Jay Beattie.