CX Brakes: The obvious superiority of discs…er, cantis

Feb. 17, 2016: Lars Van Der Haar was incorrectly allocated to the canti group in the data. Shocking error, I know, but fixed now (numbers and plots updated). The effect of moving this #2 ranked rider actually served to move the canti and disc groups closer together in all analyses. 

Feb. 17, 2016: Cyclocross Magazine was lovely enough to mention my post. Thanks guys!

 

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The familiar orange and blue at the front of the race at 2016 CX World Champs in Heusden Zolder, Belgium (photo: DRR).

Anyone who knows anything about cyclocross knows that the best brakes are the ones that don’t get used.

But I digress (if that’s possible before I even get started).

Since both the Elite Men’s and Women’s races at the 2016 Cyclocross World Champs were won by riders on canti brakes, I’ve seen several posts lauding the clear superiority of cantis (or at least questioning the supposed superiority of discs).

Twitter was also all aflutter with people posting various quips loaded with their pre-conceived notions of brake superiority:

 

One notable blog post made the astute observation that “about half the bikes [were] cantilever- (and carbon-rim) equipped” but also found it notable that the two Elite winners were on cantis. But that simple analysis is a probabilistic oversight: all things being equal, we would expect two canti winners drawn randomly from an equal pool of cantis and discs about one quarter of the time (1/2 x 1/2). In fact, the more riders that cling to cantis, all things being equal, the more cantis will end up on the podium, thus appearing superior.

But of course, all things are not assumed to be equal. We assume that discs, like all major technological advances, should be, well, better. No question, the industry propagates this, and why not? They’re usually right about major tech advances. Think about 1x gearing, STIs, carbon, suspension forks, etc. (and don’t think about Biopace…but then again).

But rather than hash out the perceived benefits (e.g. power, modulation, mud clearance) and drawbacks (e.g. weight, wheel swapping) to discs in ‘cross, I thought I would just crunch some numbers instead. Admittedly, most analyses here rely on good old-fashioned, outdated, misleading frequentist null hypothesis significance testing. Oh well. It serves the purpose and the Bayesian disc brake analysis will have to wait.

Methods

I have a real job, so the data had to be pretty quick and easy prepare but representative. I decided to pull the top 20 men and women by points in the 2016 Elite CX fields. The UCI had this information handy, complete with ages and nationalities. Then, assuming that riders used similar bikes all year or at least that World Champs was representative (a big assumption, but it should come out in the wash anyway), I used the sophisticated data repository of Google Images to assign them into either the canti or disc brake class. Using the season rankings rather than a single race ensures that we get a more general sense of whether cantis or discs are “better” (since most non-pros probably have to decide on one or the other). A keen person could look at finishes in each race and class the races according to weather or conditions, but today I am not this person.

Using the top 20 riders should limit the sample to groups of riders who are not limited by physical fitness (as level a playing field as possible). That said, there’s probably a wider range of technical ability in the women’s field simply because the general sample of women who go into CX is smaller*. Technical ability may be something that interacts with brake choice too. For example, a very good technical rider can still perform well in wet and muddy conditions with degrading canti brake performance whereas a less proficient rider may suffer even when braking performance changes only slightly.

Stats note: WC points data were positively skewed, so I log transformed them. Ranks are tough to use because ordinal data kind of sucks. So today I’ll stick mostly with WC points data.

With these data, we’ll first test some expected trends:

  1. Belgians will tend to ride cantis. It is popular cyclist wisdom (which we all know is never wrong) that Belgians are sticklers for tradition.
  2. There is a difference in disc use between men and women. First, if we accept that the technical ability range is wider in the top 20 women than men and that discs are more help to less technically proficient riders, a difference should be reflected here. The counter: discs are heavier and bike weight is of more importance to women than men (as higher proportion of body weight). Or maybe female riders are less likely to jump on-board the latest equipment fad because [insert invalid cultural expectation here]. Or maybe it will all even out.
  3. Younger riders will tend to ride discs. With less technological inertia to cling to, the kids may be less likely to be retro grouches.

Then, we’ll test the big hypothesis:

  1. Faster riders will tend to ride discs. This one is straightforward and should be true if the industry hype is to be trusted. Given that pros can choose their equipment and that they have ample time to test out a variety of bike setups, we can assume that they’re always riding the bike that’s fastest.

I won’t post the R code here, but I’ll put up the data at the end of this post.

Results

Hypothesis 1: Belgians will tend to ride cantis. 

Yup, no question. Whether it’s because they’re traditionalists or because discs are somehow incompatible with motors, they definitely favour cantis, with 14 of the 15 Belgian riders (93%) in the top 20 men and women opting to stay off disc brakes. By percentage, they’re beaten by the French and the Czechs, each with all their top riders on cantis (100%), but the small sample from these countries makes this result a bit suspect (we should have an equal draw from each country for this, but I have a job).

1a. Belgians Ride Cantis (Plus-Minus Barchart)

And apparently they’re a wee bit dominant in the sport (in case you didn’t know). 15 of the top 40 men and women are Belgian (38%). While I expected the Dutch to be a strong second, they’re actually just beat out by the Americans with 7 in the top 40 (18%) to The Netherlands’ 6 (15%).

Incidentally, this American showing is largely driven by the women, who make up 5 of the top 20 women (25%), just beating out Belgium’s 4 (20%). Also, the only American rider in the top 20 on cantis is also a woman, and this was Ellen Noble who, at 20th place, just barely got a set of American cantis into the cut (and as a Focus rider certainly would have the option to ride discs).

1b. Belgians Ride Cantis with Sex (Plus-Minus Barchart)

Another note from the sex breakdown: I hadn’t realised the disparity between the Belgian men and women. While still accounting for 1/5 of all female riders, the women’s dominance is nothing compared to the men. Country-wise, the women’s is a much more even field.

Hypothesis 2: There is a difference in disc use between men and women.

Maybe not surprisingly, there’s no real evidence for this. While the extremely weak trend is for men to choose cantis more often (65%) than the women (55%), given the sample, neither of these proportions are significantly different from 50% (p=0.26 for men and p=0.82 for women).

2a. Women Ride Discs (Plus-Minus Barchart)

Hypothesis 3: Younger riders will tend to ride discs.

This one had the potential to be interesting as it weakly trended counter intuitively: the older riders seem to be more prone to switch to discs. The mean (median) age for disc and canti riders respectively is 28.0 (28) and 27.7 (27) years.

3a. Younger Riders Ride Discs (Boxplot)

But alas, this effect too is not even close to significant (p=0.87). After all, both the youngest rider (Eli Iserbyt, BEL) and oldest rider (The Sven Nys, BEL) were on cantis. And both Belgian. Of course.

Just as a fishing trip extended analysis, I also considered any potential interaction between age and gender in brake selection. Perhaps we would expect the young males to adopt the new tech because of [insert invalid cultural expectation here]. But this trend doesn’t emerge. Rather, the visible trend is just that of having younger men than women in the top 20.

3b. Younger Riders Ride Discs by Sex (Boxplot)

An ANOVA suggested that the interaction between brakes and sex (p=0.19) was more important than the effect of brakes (p=0.96) or sex (p=0.27) alone on determining age, but it’s still a long way from a significant result.

           Df  Sum Sq  Mean Sq  F value  Pr(>F)
Sex         1    38.0    38.02    1.232   0.274
Brakes      1     0.1     0.08    0.002   0.961
Sex:Brakes  1    54.4    54.41    1.762   0.193
Residuals  36  1111.3    30.87

When plotted, the interaction is there, but its definitely non-significant. I know, boring.

3b. Younger Riders Ride Discs by Sex (Interaction Plot)

Hypothesis 3: Faster riders will tend to ride discs.

Okay, FINALLY, we get to what we really want to know. If you’ve been paying attention, you should have a pretty good idea how this is going to play out. If not, here it is, in one three handy plots:

4a. Slower Riders Ride Discs (Boxplot by Points)4a. Slower Riders Ride Discs (Boxplot by Rank)

It doesn’t matter if we’re talking about World Cup points (top, note log10 scale) or World Cup rank (bottom), there is no significant difference between disc and canti riders (p=0.54 by points and p=0.75 by rank). Yes, there’s a slight trend in medians towards faster riders on cantis, but we can’t infer (from this small data set anyway) that it’s anything more than would be expected at random. After all, the fastest and slowest riders in the top 20 are both on cantis.

Between men and women, the same statistical result emerges, with no significant difference in World Cup points between discs or cantis among the men (p=0.89) or women (p=0.45).

4b. Slower Riders by Sex Ride Discs (Boxplot)

For interest, the high-point outlier in the men’s disc group is Mathieu Van Der Poel (NED). Without him, the canti group has (just barely) significantly more World Cup points (p=0.04), but only if we don’t talk about multiple comparisons, etc. (which we won’t).

Now that’s a wide mouth bass convincing result if I’ve ever seen one.

Edit Feb. 17, 2016: Van Der Poel is no longer a high-point outlier now that Lars Van Der Haar has be correctly re-allocated to the disc category.

Conclusions

I could find no significant differences between disc and canti riders, either in demographics or, more importantly, in performance. There are some suggestive trends, but nothing conclusive, at least within the top 20 male and female riders. Sorry, I know that’s a lame result. But it’s a result all the same. I’ve made some assumptions and used a pretty small and potentially biased sample, so it may not be perfect. But it’s a hell of a lot better than the prevailing “hey, look at all the cantis on the podium” argument.

When we expect discs to be superior performers, we risk affirming the consequent when we see cantis on the podium. In fact, there may be no (significant) performance advantage to either. From the data, we should see roughly the same proportions of cantis and discs on the podium as line up at the start line.

Pro riders can choose their equipment, probably on a race-by-race basis too, so they’ll pick what is faster for them individually. And this is almost certainly where the advantage to discs comes in: another equipment option to match to a rider’s skill set on a particular day. Of course, for the rest of us non soon-to-be pro racers, we have to pick a bike and go with it for at least a season or two. For me, I’ll take discs, even at a slight weight or performance disadvantage, just so I never have to set the toe-in of my G. D. canti pads ever again.

Homework

See if you can count the riders in this video that raced on cantis at World Champs!

Data

Use it freely and wisely (and let me know if you do so I can check it out). Data errors? Post a comment and I’ll see what I can do. But remember, I have a job!

Sex Rank Name                   Country        Age Points Brand       Brakes
M   1    Wout VAN AERT          Belgium        22  2360   Colnago     Canti
M   2    Mathieu VAN DER POEL   Netherlands    21  1860   Stevens     Disc
M   3    Kevin PAUWELS          Belgium        32  1835   Ridley      Canti
M   4    Lars VAN DER HAAR      Netherlands    25  1810   Giant       Disc
M   5    Sven NYS               Belgium        40  1620   Trek        Canti
M   6    Laurens SWEECK         Belgium        23  1263   Stevens     Canti
M   7    Tom MEEUSEN            Belgium        28  1203   Ridley      Canti
M   8    Jeremy POWERS          United States  33  1094   Focus       Disc
M   9    Clément VENTURINI      France         23  1086   Look        Canti
M  10    Michael VANTHOURENHOUT Belgium        23  971    Ridley      Canti
M  11    Eli ISERBYT            Belgium        19  842    Ridley      Canti
M  12    Marcel MEISEN          Germany        27  819    Focus       Disc
M  13    Francis MOUREY         France         36  815    Lapierre    Canti
M  14    Stephen HYDE           United States  29  785    Cannondale  Disc
M  15    Toon AERTS             Belgium        23  770    Ridley      Canti
M  16    Radomir SIMUNEK        Czech Republic 33  760    Stevens     Canti
M  17    Gioele BERTOLINI       Italy          21  740    Guerciorn   Disc
M  18    Quinten HERMANS        Belgium        21  700    Ridley      Disc
M  19    Tim MERLIER            Belgium        24  696    Colnago     Canti
M  20    Klaas VANTORNOUT       Belgium        34  674    Ridley      Canti
F  1     Sanne CANT             Belgium        26  2142   Stevens     Canti
F  2     Caroline MANI          France         29  1540   Raleigh     Canti
F  3     Nikki HARRIS           Great Britain  30  1525   Ridley      Canti
F  4     Eva LECHNER            Italy          31  1520   Ibis        Disc
F  5     Pavla HAVLIKOVA        Czech Republic 33  1424   Ridley      Canti
F  6     Katherine COMPTON      United States  38  1405   Trek        Disc
F  7     Ellen VAN LOY          Belgium        36  1381   Ridley      Canti
F  8     Helen WYMAN Great      Britain        35  1298   Kona        Disc
F  9     Kaitlin ANTONNEAU      United States  24  1190   Cannondale  Disc
F  10    Sophie DE BOER         Netherlands    26  1175   Wilier      Disc
F  11    Thalita DE JONG        Netherlands    23  1136   Giant       Canti
F  12    Jolien VERSCHUEREN     Belgium        26  1086   Ridley      Canti
F  13    Sanne VAN PAASSEN      Netherlands    28  839    Giant       Canti
F  14    Amanda MILLER          United States  30  782    Focus       Disc
F  15    Loes SELS              Belgium        31  768    Ridley      Canti
F  16    Maud KAPTHEIJNS        Netherlands    22  760    Scoppio     Canti
F  17    Alice Maria ARZUFFI    Italy          22  754    Guerciorn   Disc
F  18    Crystal ANTHONY        United States  36  681    Focus       Disc
F  19    Christine MAJERUS      Luxembourg     29  661    Specialized Disc
F  20    Ellen NOBLE            United States  21  656    Focus       Canti

Notes

* Okay, before anyone cries foul that I’m slighting the women’s field here, I’m not. There are fewer female cyclists in the world and certainly fewer female cyclists in competition. That means that the sample to draw from is smaller. With the same sample size (i.e. roughly the same number of pros) a proportion of the sample will be drawn from closer to the mean of the “technical ability” curve. I would also argue that this makes for more interesting racing, as results can vary more widely given the conditions, etc.

 

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16 Responses to CX Brakes: The obvious superiority of discs…er, cantis

  1. roder1 says:

    Some interesting statements from FSA’s website that I couldn’t really make fit in the write-up: “Disc brakes have been legal to use in races for several seasons now. In fact, at the 2015 world championships, only one race winner wasn’t using discs. The benefits are similar to those associated with using discs on a road bike. Better clearance is the main advantage, and especially important in muddy cyclocross races where this could save you a bike change (or a few seconds) every lap. By moving the braking surface away from the muddy tyre and rim, you’ll stop more quickly, and therefore, be able to ride faster. Disc brakes will allow you to stop more quickly in muddy conditions, so you should be able to ride faster as a result. In summary, if you’re a regular UCI road racer you’ll probably want to monitor any regulation changes regarding discs and make the move as soon as they become race-legal. If you love to ride your road bike but don’t race, discs are fast becoming your go-to option. And, if you race cyclocross, we’re getting ever closer to having a season where every major race is won onboard a disc brake bike.”

    Like

    • dominicwatts says:

      A very interesting article and good that it provides balance. Your additional post from thE FSA website does not provide the same objectivity which does them little credit. Why on earth you would need disc braking in a UCI road race is well beyond me. The fact that they make it sound as if it is the most obvious thing to do is disingenuous at best. I’m not a ludite in anything but because I have no been convinced by anyone that discs are a good idea on the road I am always perceived as a flat earther. I still remain convinced that discs are not the obvious choice for CX apart from the clearance. I think I will still be CXing on cantis for some more years to come and I can’t ever see me leaving dual pivot caliper braking in road racing and riding.

      Like

  2. Regan P says:

    Plain and simple. Wout rode a 2013 colnago and Thalita won on a giant with cantis…not a Liv. and that bike is probably 2 years old. The industry is pushing it. In my opinion there are maybe 5 course a year that it “might be an advantage”. If strapping and extra pound to your bike can be seen as such. Just wait till they intro a new bb standard and front axle standard. Better crack the Bourbon right now. Great article Dave.

    Liked by 1 person

  3. Extremely interesting article but I wonder whether the wrong question is being asked at the end, “Hypothesis 3: Faster riders will tend to ride discs”. It seems maybe you are really measuring what the disk vs. canti preferences are for top performing riders, not whether disks perform better than canits, all else being equal. The fact that they are faster is not necessarily due to their riding disks or not but perhaps better overall fitness/training/endurance/etc. And I think while pros will tend to choose the fastest bits those choices are influenced a lot by qualitative factors like personal perceptions, traditions in cycling (especially regionally), as well as personal experience. Maybe a big bike mag needs to organize back-to-back shoot outs in a wide range of weather and surface conditions, with the riders, framesets, and tires all as controlled variables. Sounds like a great project for a PhD student…

    Liked by 1 person

    • roder1 says:

      Yeah, I vaguely tried to get at that when I suggested that the pros can basically choose whatever is fastest for their riding style on a given day. The rest of us mortals don’t have that option, so need something that works for us (that may include speed, easy of maintenance, etc.). Different priorities. I agree that a controlled experiment with a variety of riders in a variety of conditions and terrains would be awesome. If anyone would fund this, it would be fun to do!

      Like

    • roder1 says:

      Further, as I think you allude to, we have to be careful (and I tried to be) not to confuse a tendency for discs/cantis among the top riders with any causal mechanism. Without strict experimental controls, causal mechanisms will be elusive (double-blind CX time trials? I’m in for watching that!). After all, the top riders might not embrace discs BECAUSE they’re fast cyclists (hence the biased sample disclaimer) whereas most everyday riders/racers may find a huge benefit. I’ll apply for a NSF grant.

      Like

  4. Bill C. says:

    Really nice article and analysis, but …. I wonder if one of your assumptions is wrong. You stated “Pro riders can choose their equipment ….” which would imply that the choice of canti or disc is really based on performance. My guess is that – indirectly – riders are being pushed to use disc brakes because that’s where the bike industry wants everything to go.

    Like

  5. Bran says:

    Sanne Cant rode discs more often than not this year.

    Like

  6. crosssports says:

    Folks are way to fixated on weight as the prevailing reason for choosing canti brakes. Contrary to the marketing hyperbole, experience suggests that the major deficiency of disc brakes is that on certain types of terrain, the lifespan of disc brake pads can be counted in minutes. Might I suggest as a follow up a statistical analysis of the pit entries by disc and non-disc racers, see for eg: VdH vs WvA at Zolder.

    Liked by 1 person

  7. Thanks for the detailed analysis. I’m glad you dug deeper than I to get more exact numbers on who rode what. Also thanks for citing, quoting, and commenting on my work.

    I should add that I have questioned the performance benefit of discs elsewhere. http://jralong.blogspot.com/2015/12/cant-stop-disc-brakes.html

    Liked by 1 person

    • roder1 says:

      It was actually your post that first motivated me to look a bit more, as I had the exact same response to the podium that you did. Hopefully you didn’t think I was disparaging it (the contrary, in fact!). And thanks for the link. I didn’t see that post on your site. It’s great.

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  8. joe says:

    for what it’s worth, Laurens Sweeck has ridden discs all season, so I’m guessing he did at worlds. also Kevin Pauwels normally rides cantis, but was on discs that day (unless he pitted to a canti bike at some point, I don’t know). I noted this because I found it odd to change for such a high-level event. unfortunately, you’d likely need to watch video to confirm these…

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    • dominicwatts says:

      It was a great race so I just might watch it again anyway. Although I watched it, as I always do, whilst doing a TrainerRoad session on my Turbo so will probably miss the canti/disc split.

      Like

  9. I’m pretty firmly in the canti camp- my thinking being that discs are too powerful in slick conditions (sure, the modulation is great, but a little too much brake on a slick off-camber and you’re crashing), and overkill for most ‘cross courses. Dry and grassy like CrossVegas is a good disc course, sandy and muddy Belgian courses better for cantis.

    Here’s where I see the skew in any current data: Belgians- it’s what has worked for them for a longer time, and they have wheels and tires already glued for every course and condition. Smaller teams with less money or less pull with their sponsors are riding what the sponsors want them to ride, while also having fewer wheelsets to fully replace when making the conversion. Juniors and women, while in this group of smaller teams and less money, are sometimes left riding last year’s offerings, or on 2-3 year frame cycles! It’s like there’s no hard place (yet) to draw the line of what patterns you might find.

    On the amateur side, those who are newer to the sport in general and maybe don’t have more than one or two sets of wheels- they can move on to discs easier, especially as all new offerings are disc-only.

    I feel like any data set for this comparison are almost always going to be incomplete. If every rider was able to choose what they wanted to ride, with no sponsor or availability input, maybe then you’d have a set of numbers that could give you an accurate picture.

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  10. payalsethi says:

    Really nice article. It was a great race.

    Like

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