Disc Brakes

[Steampunk]

Question born out of total ignorance: why is there a UCI ban on disc brakes for cross bikes? I would imagine that they would be rather useful...

 

[Master50]

tradition and and an extremely conservative governing body.
Disk brakes work much better than cantelevers so riders can wait longer to slow which can create an advantage and the UCI has said that unlike mountainbikers, CXers run tighter packs and the disks are a hazard in a crash.

Mostly I don't agree with the hazard and if the brakes actually are more effective than I think they would all switch and the playing field would level.

 

[RDV4ROUBAIX]

Yes, the UCI rule is for safety reasons, which I don't agree with either, but a disk set-up for CX bikes doesn't make sense anyway. They're much heavier than a regular canti set-up, and you don't need that much stopping power to slow down a 17lbs carbon cross bike. I don't recall ever in a race where my cantis were not performing like they should in the worst wet, snow, rain, ice, mud. Disk is just plaine and simple overkill IMHO, not only is a disk brake set up heavier, the frames are too since you have to add more material to anchor it on the frame. Hubs are heavier as well.

 

[dsut4392]

Yes, the UCI rule is for safety reasons, which I don't agree with either, but a disk set-up for CX bikes doesn't make sense anyway. They're much heavier than a regular canti set-up, and you don't need that much stopping power to slow down a 17lbs carbon cross bike. I don't recall ever in a race where my cantis were not performing like they should in the worst wet, snow, rain, ice, mud. Disk is just plaine and simple overkill IMHO, not only is a disk brake set up heavier, the frames are too since you have to add more material to anchor it on the frame. Hubs are heavier as well.

All true, but in the MTB world we all went through the same thoughts - "who could _ever_ need more power than cantis", then "who could ever need more power than v-brakes", now it's "why in hell would you use anything other than a disc brake?"
The three main advantages I see are:
- consistency of performance in the worst conditions (mud, rain). It's not all about power, having a predictable response is worth a lot in terms of letting you get maximum braking without the tire losing traction and sliding out.
- ability to keep riding with a rim clogged up with mud or out of true (e.g. broken spoke), when cantis would mean totally disconnecting the brake to get enough clearance (if that is even enough).
- no wear on the rims, so your light, expensive wheels last much longer.

As far as the weight difference, an extra 200 gram at the hub is negligible - less than 0.3% of 68kg rider + 6.8kg bike, even less for big guys riding bikes that weigh more than 6.8kg.

 

[RDV4ROUBAIX]

All true, but in the MTB world we all went through the same thoughts - "who could _ever_ need more power than cantis", then "who could ever need more power than v-brakes", now it's "why in hell would you use anything other than a disc brake?"
The three main advantages I see are:
- consistency of performance in the worst conditions (mud, rain). It's not all about power, having a predictable response is worth a lot in terms of letting you get maximum braking without the tire losing traction and sliding out.
- ability to keep riding with a rim clogged up with mud or out of true (e.g. broken spoke), when cantis would mean totally disconnecting the brake to get enough clearance (if that is even enough).
- no wear on the rims, so your light, expensive wheels last much longer.

As far as the weight difference, an extra 200 gram at the hub is negligible - less than 0.3% of 68kg rider + 6.8kg bike, even less for big guys riding bikes that weigh more than 6.8kg.

Not entirely unschooled in the realm of disk brake wheels as I build wheels for a living. I know the advantages of disk brakes, just built a couple custom sets for a friend's Salsa, Ambrosio F20's to DT hubs, and Stan's ZTR Crest rims to Hope hubs. I'm talking about racing at elite levels where every gram counts though. Let's forget about the UCI rule for a moment and assume that disk systems would be available to use at the elite level, most, if not all would stay with cantis just because of the huge weight difference. It's not just the hub that's heavier, it's the whole system, brakes, rotor, hubs, and frame, which comes to roughly 700g per wheel. That adds about 3 lbs to the total weight of the bike, not that big of a deal for the average rider, but the nature of CX racing, am or pro, that is totally unreasonable. Until disk brake systems can get down to around 150g, which is the average weight of canti calipers per wheel that the pros use, you won't see disk in CX anytime soon.

 

[icefire]

UCI just changed the rules for next season:

http://www.cyclingnews.com/news/uci-to-allow-disc-brakes-in-cyclo-cross-competition

We'll see how it goes

 

[RDV4ROUBAIX]

UCI just changed the rules for next season:

http://www.cyclingnews.com/news/uci-to-allow-disc-brakes-in-cyclo-cross-competition

We'll see how it goes

LOL ! Ha,... OK, forget what I said.

 

[RDV4ROUBAIX]

..... and to top it all off, I just ordered my new CX F&F without disk brake mounts, even had the option to. Oh well, just have to get another. Had to rethink this one, and I really believe that D-brakes are going to take over cycling. It'll eventually be accepted for pro road too, just a matter of time before the systems get lighter, more compact, and consequently safer for the UCI to change their minds. Heck, if racers are willing to ride with the extra weight of a PT hub today, why not d-brake system.

 

[avanti]

33 mm tire rule

Max tire width now 33 mm. Do my 35 mm Conti Cyclocross Speed tires meet the requirement? I just measured them and they are 33 mm wide so I hope officials don't rely on the manufacturer's stated size.

How is it that the UCI seemingly changes rules without input from the cycling community?

 

[barn yard]

..... and to top it all off, I just ordered my new CX F&F without disk brake mounts, even had the option to. Oh well, just have to get another. Had to rethink this one, and I really believe that D-brakes are going to take over cycling. It'll eventually be accepted for pro road too, just a matter of time before the systems get lighter, more compact, and consequently safer for the UCI to change their minds. Heck, if racers are willing to ride with the extra weight of a PT hub today, why not d-brake system.

yep i agree re pro road racing.

the whole 'they are too heavy' thing has some merit at the moment but the 'they are unsafe and will lock up at 60km/h because they stop too fast' hysteria is completely unfounded and ridiculous, presumably from people who have never used disc brakes at length.

 

[rgmerk]

..... and to top it all off, I just ordered my new CX F&F without disk brake mounts, even had the option to. Oh well, just have to get another. Had to rethink this one, and I really believe that D-brakes are going to take over cycling. It'll eventually be accepted for pro road too, just a matter of time before the systems get lighter, more compact, and consequently safer for the UCI to change their minds. Heck, if racers are willing to ride with the extra weight of a PT hub today, why not d-brake system.

What would be the advantage of disks on a road bike?

Wet braking when using carbon rims? Not having to worry about overheating tires on long descents?

On the upside, would the improved aerodynamics and lighter weight of a wheel that didn't need a braking surface make up for the drag and extra rotating weight of the disk?

 

[philcrisp]

most, if not all would stay with cantis just because of the huge weight difference. It's not just the hub that's heavier, it's the whole system, brakes, rotor, hubs, and frame, which comes to roughly 700g per wheel. That adds about 3 lbs to the total weight of the bike, not that big of a deal for the average rider, but the nature of CX racing, am or pro, that is totally unreasonable.

Couple of thoughts having made the switch on MTB.

The brakes are a prime collection area for mud. Once conditions get bad enough in an XC race the reduced mud collection is going to get your average bike weight for the duration under the rim braked bike. Probably not a big issue for the pros but pertinent at club level.

Disc specific frames are going to trade one set of braking forces for another therefore may trade some material thus reducing total weight gain.

At pro level every bike change is a potential fowl up and a small time penalty. If disks save changes in poor conditions fewer potential fowl ups and a small time saving.

However nothing is going to stop Sven Nys taking six bikes to a race if Colnago are prepared to pay for it.

 

[Cloxxki]

700g? Maybe for the whole bike. Yet not as an increase, but as a total disc brake figure on elite bikes.

I never got my Zipps to offer any kind of braking. I had only one bike, and basically gave up on CX because of this. The one easy flat race I had, I got a regional elites-without-contact title Nice bragging right, but me and 2 pro's were the only fast +23 riders present.

They changed max tire width from 35mm to 33mm. This to me makes CX even more of a small skinny guys sport. Cost reduction? Forbid carbon rims then, those are the #1 cost in CX gear, IMO. Of all the cash I put into CX (3 bikes), half is represented the one Zipp race wheelset I got. And my race frame was a custom one even.
Also, forbid tubular tires.

At 33mm, there will be yet less braking traction to work with.

Old men running governing body, nothing really ever changes.

 

[benlondon]

There won't be a weight penalty for disk brakes.

After a couple of years of development there won't be a weight penalty for disk brakes at all. Rims will be made lighter (as they don't need a braking surface) & manufacturers now have the incentive to produce some superlight disks etc. Within 3 years elite crossers will only be riding disks (and won't bother taking a bike with conventional brakes to races) I also predict they'll be legal on road bikes within 5 years and about time too!
As for the dumb remark about not needing decent brakes to slow down a 17lb bike! It's the bike plus the rider so always at least 150lbs.

 

[Master50]

Max tire width now 33 mm. Do my 35 mm Conti Cyclocross Speed tires meet the requirement? I just measured them and they are 33 mm wide so I hope officials don't rely on the manufacturer's stated size.

How is it that the UCI seemingly changes rules without input from the cycling community?

Yes seemingly without consultation but the UCI had a CX committee that did and these changes are from their recommendations.
It would be normal for a committee to include industry and rider input as well as a few old stogy guys that seem too conservative to most.
There are a lot of ex pro cyclists that work in cycling at management levels and to some I expect they wish for the good old days or when they were racing type of comments.

 

[DirtyWorks]

After a couple of years of development there won't be a weight penalty for disk brakes at all. Rims will be made lighter (as they don't need a braking surface)

Nice try, but no way.
Frame/Fork: think about the forces on the very end of the fork (a lever!) with a disc brake. Your fork weight will go way up. If it doesn't, then I'll pass on that fork. Same thing with the rear triangle.

Wheels: gain lots of hub weight. Now, I'll give you that the rotational weight drops, but it is replaced by a much heavier hub and disc. The whole brake track argument is almost null because they are running sew-ups.

Calipers: You are telling me that a disc brake caliper is going to equal a pair of cantilevers? No way.

Race course: the point of 'cross courses is that they just aren't as rough/tough as mountain bike courses. So, the braking power of a disc is just overkill.

Racing: 'Cross is still a Watts/skills test. More powerful brakes just won't upset the average race placing.

Will there be rare occasions where discs provide some advantage? Yes. Will bike manufacturers shout from the rooftops that canti's are dead? Yes. Are they actually dead? No.

 

[durianrider]

Avid BB7's are the ticket. Easy to adjust on the fly, just as powerful as hydro's.

 

[JA.Tri]

Cantis vs V brakes

Sorry for the detour .

Why are cantis currently used in CX rather than V brakes??

Ta js

 

[LugHugger]

Sorry for the detour .

Why are cantis currently used in CX rather than V brakes??

Ta js

Most road brake levers do not pull sufficient cable to enable use of V brakes. Some people do use V brakes by either using specialist levers or using mini-v's or by installing a rollamajig or such like. If you are riding a muddy course, V brakes tend become mud-logged much faster than canti's due to lower clearances.

 

[dsut4392]

Avid BB7's are the ticket. Easy to adjust on the fly, just as powerful as hydro's.

Nah. Hydros are the ticket, just as powerful as BB7's but don't need adjusting!

 

[dsut4392]

Nice try, but no way.
Frame/Fork: think about the forces on the very end of the fork (a lever!) with a disc brake. Your fork weight will go way up. If it doesn't, then I'll pass on that fork. Same thing with the rear triangle.

That argument is specious. The total energy dissipation is the same, so while you need to reinforce different areas with a disk brake compared to cantis, the total frame/fork weight need not differ significantly. Considering the front only, for disc brakes you need to build proportionally beefier lower left fork legs, and tune the flex of the fork differently. For cantis you need to reinforce the fork at the bosses to reduce spreading under braking, and the fork crown needs to be beefier. Properly designed, weight should be equal.

Wheels: gain lots of hub weight. Now, I'll give you that the rotational weight drops, but it is replaced by a much heavier hub and disc. The whole brake track argument is almost null because they are running sew-ups.

Disc hubs are heavy, granted but they can be made lighter - the weight weenies just haven't got there yet. As you say, rotational weight can drop, and that's where it's at in terms of noticing the mass under acceleration.

Will there be rare occasions where discs provide some advantage? Yes. Will bike manufacturers shout from the rooftops that canti's are dead? Yes. Are they actually dead? No.

Amen to that (for now), for now canti's are good enough. But disc brakes are getting better (and lighter) all the time, and one day the advantages will outweigh the disadvantages for CX like they have for MTB.

 

[DirtyWorks]

That argument is specious. The total energy dissipation is the same, so while you need to reinforce different areas with a disk brake compared to cantis, the total frame/fork weight need not differ significantly. Considering the front only, for disc brakes you need to build proportionally beefier lower left fork legs, and tune the flex of the fork differently. For cantis you need to reinforce the fork at the bosses to reduce spreading under braking, and the fork crown needs to be beefier. Properly designed, weight should be equal.

one day the advantages will outweigh the disadvantages for CX like they have for MTB.

We generally agree, but a couple of nits to pick.

1. The advantages disc brakes have in mountain bikes exist because of the sum of rougher and faster courses, fatter tires and suspension. A cross course will never be as rough and won't be as fast. The 'cross bike doesn't have fat tires or suspension either. (Suspension tears up the courses too)

2. The UCI also set the fattest tire limit at about a 32c tire. Even if there was some constant benefit to discs, the skinnier tire doesn't make discs an overwhelming good now or in the future.

#1 and #2 are critical issues the ignored in the rush to discs. Boom/Nys/Stybar races will not be tilted for/against because one of them is riding last year's cantilever equipped bike.

3. For the front disc, there is the small matter of the disc brake forces loosening the skewer. Unless they put the caliper in a different position, the same problem mountain bikers had will plague 'cross for a while. I make this point to remind readers that the switch to disc will include expensive design failures for a while.

4. The 'properly designed' argument is perfectly circular. I can make almost any design case and rationalize it with 'properly designed.' Ex. A 'properly designed' mountain bike will have 12" of travel front and rear and weigh 7 kilos. How come I can't buy one now?

 

[dsut4392]

We generally agree, but a couple of nits to pick.

1. The advantages disc brakes have in mountain bikes exist because of the sum of rougher and faster courses, fatter tires and suspension. A cross course will never be as rough and won't be as fast. The 'cross bike doesn't have fat tires or suspension either. (Suspension tears up the courses too)

2. The UCI also set the fattest tire limit at about a 32c tire. Even if there was some constant benefit to discs, the skinnier tire doesn't make discs an overwhelming good now or in the future.

#1 and #2 are critical issues the ignored in the rush to discs. Boom/Nys/Stybar races will not be tilted for/against because one of them is riding last year's cantilever equipped bike.

3. For the front disc, there is the small matter of the disc brake forces loosening the skewer. Unless they put the caliper in a different position, the same problem mountain bikers had will plague 'cross for a while. I make this point to remind readers that the switch to disc will include expensive design failures for a while.

4. The 'properly designed' argument is perfectly circular. I can make almost any design case and rationalize it with 'properly designed.' Ex. A 'properly designed' mountain bike will have 12" of travel front and rear and weigh 7 kilos. How come I can't buy one now?

Sorry to be so combative, no offence intended - it's late here.

Re 1 and 2, the advantage of discs isn't limited to power, they also have significantly better modulation. Yes, they certainly make it easier to brake harder for longer without getting tired hands, but they also make it easier to control your traction...which I believe is what you are getting at regarding the skinnier tyres? OK, CX races are mostly won through acceleration and handling rather than deceleration, which limits the technical advantages for elite racers (just as it has for elite XC MTB which still has linear pull hold-outs, on some courses), but for anyone else, discs are a no-brainer, especially where mud and sand are involved. Just as you say the race won't be won or lost by cantis, I'm sure the weight difference won't be a deciding factor either. And I bet many financially overcommitted privateers would convert - imagine for me the noise of gritty mud grinding against your expensive rims and wearing out the sidewalls of your dugasts and tell me discs are for fools!

Re 3, you're right, it's a small matter. The easiest solution is changing the orientation of the dropout, as a number of fork manufacturers did. While I would be hopeful that lesson has already been learned, I'm pretty cynical about humanity's ability to perpetuate bad decision making, so you have a point!

Re 4, again a specious argument. There are plenty of reasons why you can't buy a 7kg DH bike, and none of them have anything to do with disc brakes.
We're talking cyclocross bikes, for riding CX courses, experiencing applicable forces. There are no extra complicated suspension designs involved, where maintaining strength (and rigidity) through multiple pivot points acting through long levers is critical, and we're not talking about bikes where the normal use parameters include rock gardens and massive gap jumps. All we're talking about is moving the brake from near the crown to nearer the dropout - there is no magical magnification of forces involved, no kinetic energy created.

Do you need to change the design of the fork to cope with the altered stress pattern? Of course you do. Does this mean you don't optimise the design to remove redundant reinforcing where it is no longer required (i.e at the canti bosses, where forks are beefed up to resist spreading and forwards rotation of the bosses under braking)? Why not?

Does a weight-competitive solution to allow a privateer racer to convert from cantis to to discs exist? No, but that doesn't mean it couldn't be built, if there were a market for it.

 

[kiwirider]

Disc hubs are heavy, granted but they can be made lighter - the weight weenies just haven't got there yet. As you say, rotational weight can drop, and that's where it's at in terms of noticing the mass under acceleration.

How do you - and Dirtyworks - define heavy?

I run DT Swiss 240s disc hubs on my MTB - and the "weight penalty" over the non-disc version is 40g each hub. Granted, as a percentage for the front, this is quite a big jump - but only because their front hub is ridiculously light!

As for the mass of the disc itself ... as people have said, you don't need the same sort of braking for cross that you want for (some) MTB racing - and the main advantage would be the modulation that you can get from a disc set up. With that in mind, why go anything bigger than a 140 at each end - and if you run Stans aluminium discs, that's about another 40g per wheel. (And who knows, in the future there may even be 120's or something similar if its demonstrated that they give all of the braking power needed for cross??)

So, that gives a total penalty of about 80g/wheel - granted, that's enough to get the weight weenies mega excited, but when most of the top pro bikes have "lower spec, heavy" parts for reliability (eg., check out the profile of Nys' bike on here from a couple of years back) and the choice of line on some courses can see that much mud being lugged around for a lap anyhow, is that really enough to write home about?

I think it'll be interesting to see what happens with discs in cross. I know there are times where I've wished I had the certainty of braking that they give - I can think of one course in particular where having the ability to carry more speed into a hairpin bend at the bottom of wet slope and do a bit of back wheel sliding to set me up for the nasty uphill pinch on the exit would be a real plus ...

 

[Hangdog98]

Discs

I was one of the first to adopt discs for XC racing in Australia at the National level in my team. Plenty of people said it was a fad, too heavy, too much power, yada yada yada, the rest is history. One rider, now a cycling mag journo told me "only w@nkers use discs in XC". Does he now use discs? err, yes. Am I still a w@nker? err, probably

So the major consideration for me when speccing the new season's frames with disc tabs (we had them custom made because 1kg XC racing frames didn't come with disc tabs back then) was to avoid problems with untrue rims mid race. We'd had a few problems with brake pad drag in the previous season's races when riders had experienced out-of-true wheels and it was enough to ruin their race. The disc brake solution was 100% successful in this regard. Interestingly we used a 160mm front disc and a 135mm rear disc which gave better braking than the XTR V brakes they replaced.

Now I'm sure CX wheels won't suffer the same out-of-true wheel problems that XC riders faced, but the transition to discs will happen. The technology is there and the manufacturers have already made their mistakes on MTB. In 2005 I built a road bike with disc brakes from spares we had left over from those early days and it was great fun and worked really well. The hydraulics were in the caliper which was a twin floating ceramic piston job and the internal master cylinder was actuated by a cable from the STI levers. The 23mm clinchers offered great traction under disc braking, probably the same feel and adhesion as you get with an MTB bike with slicks. The feel at the lever was much lighter and for the first few rides was a bit of an eye opener until I re-set my brain to the power and modulation.

I'm looking forward to the development of hydraulic brake specific STI drop-bar shifters and an 11 speed alfine internal hub race version with Ti, carbon internals and electronic shifting (if they ever make it) for no other reason than it will be interesting.