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Technical FAQ: Dropped ‘cross chains, discs vs. cantis

Dear Lennard,
Why does Wout Van Aert always race now with a SRAM double-chainring setup and cantilever brakes? He used to race on CX1 with disc brakes and switched back to old school. When he was the U23 world champion, SRAM said he won the 2014 Superprestige Gavere on disc CX1.
— Frank

Dear Frank,
Like all SRAM ’cross pros, Van Aert has the option of Red 22 or Force 1, and SRAM generally won’t try to convince a pro one way or the other (witness Zdenek Stybar winning CX world’s in 2014 on SRAM 10-speed when the company would have loved to instead have him on 11-speed so it could have advertised that he was on the latest SRAM 22 equipment). I don’t know why Van Aert switched, and given that it would require him to compare different products of his component sponsor, we might get an overly bland answer if we were to ask him. However, I’m willing to conjecture. I also did a conference call with a few product managers at SRAM about this question, as well as the two letters that follow this one.

Regarding Van Aert eschewing the Force 1 (same as CX1) X-Sync chainring and X-Horizon clutch rear derailleur setup in favor of a Red 22 ensemble for the entire 2015-2016 season, I wouldn’t be too surprised if his dropped chain at the 2015 world championships with SRAM CX1 factored into his decision. That said, he insists it was not the dropped chain that cost him that race but rather a crash and other bobbles. And SRAM product managers, whose collective cringe when he dropped his chain could be felt worldwide, checked his bike and found that the chainring was very worn. When worn, X-Sync chainrings are more prone to chain drops, as the teeth don’t fit the chain as tightly and thus can’t control its movement as well. Pros tend to go through a few sets of chainrings every year on each bike, and single rings get more wear than each ring on a double and thus have to be replaced at least as often.

SRAM road product manager Daniel Lee also explained that Van Aert likes the big 10-tooth jump on the front derailleur, from 36 to 46 teeth. At some points on some courses, he wants to rapidly change gearing.

Lee went on to explain that when it comes to equipping CX athletes with 1X systems, “the only difficult group to deal with are the pros.” This is because they demand a 46×11 top gear, which they use on the start of many European courses and never use later in the race. No other category demands such a high gear. The biggest available SRAM Force 1 cassette is 11-36, and on some courses, a 46 X 32 gear is not low enough. Perhaps eventually SRAM will resolve this issue by offering XD 10-32 cassettes compatible with both disc-brake and rim-brake wheels.

On the disc brake vs. cantilever brake issue, weight is certainly involved. So is the fact that Van Aert is Belgian; Belgian pros overwhelmingly prefer cantilevers.

There is no question that the SRAM hydraulic disc brakes offer better braking than any rim brake across all CX conditions, even the sweet Avid Shorty Ultimate cantilevers that Van Aert uses, so sheer performance can’t be the issue. (Although some actually seek reduced performance; at Cross Vegas in 2011 when he was the under-23 world champion, I overheard Lars Van der Haar — who now uses discs in every race — insist that disc brakes are a bad idea in ‘cross because they work too well! His contention was that, to avoid over-braking, it was critical to have a brake that doesn’t stop very well.)

But if performance doesn’t play a role in Van Aert’s brake decision, weight probably does. I recall from measurements I did two years ago on otherwise identical bikes that the weight penalty of hydraulic discs vs. cantilevers was about a kilogram, when you take into account the additional frame and fork weight, hub weight, weight of more numerous and longer spokes, as well as the weight of the levers, calipers, rotors, and mounting hardware. I know the numbers usually quoted are not that big — you often hear half a kilo bandied about. However, other than flat-mount disc calipers, and the possibility of slightly lighter rims lacking braking surfaces, I don’t think much has changed this equation other than the increasing difficulty of comparing apples to apples. Many bike manufacturers don’t make elite-level frames and forks in both disc and cantilever variations, or they focus more on the disc model (since that’s what now sells) and take weight out of them that could have also been eliminated from the rim-brake version but was not. So on an apples-to-apples comparison, I still believe it’s about a kilo (2.2-pound) weight penalty for disc brakes vs. cantilevers.

This weight issue can be exacerbated or reduced depending on the frame involved, and in Van Aert’s case, it is exacerbated. While disc frames do require some added weight for the brake mount area, the Colnago disc frame available to him was considerably heavier than the cantilever model; SRAM’s Lee believes it is on the order of 1.5 pounds more for just the frame.

Even Sven Nys, after racing almost all of this past season on hydraulic discs (Shimano), reverted to cantilevers near the end of the season — and that was when the races were at their muddiest and when disc performance would have far surpassed cantilever performance. I’m sure the discs would have stayed cleaner and braked better, but he already had 15 years on a lot of the guys he was racing against, and I’m guessing he didn’t want to also be at a weight disadvantage to the cantilever guys in the world championships and other final important races of his career. And perhaps the fact that he is about to embark on a new career as manager of Telenet – Fidea, a big club with lots of mechanics and riders exclusively on cantilevers, played into his decision.

That Belgian pros overwhelmingly tend to ride cantilevers actually goes much deeper than simply tradition and resistance to change; there is a whole mechanics issue. On a big club like Van Aert’s, with lots of riders in lots of categories, it is very challenging for a manufacturer to keep all of the team mechanics up to speed on new parts. Cantilevers are a no-brainer for any Belgian cyclocross mechanic, but that is not the case with disc brakes.
― Lennard

Dear Lennard,
At my last cyclocross race of the season, in mid-December in Colorado, I had big problems with dropped chains on my SRAM 1×11 system. It was below freezing, the course was entirely mud, snow and ice, and there were some deep, muddy puddles. I had left my 2×11 bike in the pit, because I figured I was less likely to have drivetrain problems in those conditions with my 1×11 bike. But after five dropped chains, I switched to my front-derailleur bike. Even though that bike was all muddy from the pre-race course inspection, I had no problems with it. One bike has Force 1 with an X-Sync chainring and a Rival 1 clutch rear derailleur. The other bike is all Force 22 with a Rival 22 rear derailleur.

Having dropped a chain once before on the 1×11 bike, I realized the alternating tooth shape and no chain guards made it impossible to pedal the chain back on. In this case, pulling over and manually placing the chain back on wasn’t enough, though. I knew to take the time to make sure I was putting the chain on so that the wider spaces in the chain were going onto the fatter teeth on the chainring. But I noticed the fat teeth didn’t want to go in because of the icy mud in the chain. The third time it dropped I had to realign it probably half a dozen times, because after setting it on the chainring, it would drop again with a quarter pedal stroke forward. It seemed clear to me that because the ice had built up in the chain, it would ride up above the long, fat teeth. It occurred to me that the long teeth were actually causing the dropped chain when paired with buildup, rather than preventing dropping as claimed.

Afterward, when washing the bike with the race’s power washer, the exact same thing was happening — the ice was preventing the fat teeth from going into the chain, and the chain was derailing while I was simply turning the crank. And it was pedaling off when I was pedaling forward by hand to try to set the chain, not by turning the crank backwards or something.

Have you heard of this before?
— Em

Dear Em,
I have SRAM Force 1 with hydraulic discs on my own cyclocross bike, and I have dropped my chain in muddy and snowy conditions, but I never figured out why it was happening and thought it was a fluke. I do know that pairing the X-Sync chainring with the clutch rear derailleur is critical to chain retention without chain guards or guides, as the chain can bounce wildly on bumpy trails without it. After seeing Jeremy Powers and Steven Hyde be so dominant stateside and seemingly problem-free mechanically on SRAM Force 1, I second-guessed myself when I dropped my chain. Was I hitting bumps too hard? Was the chain too worn?

But I have seen others with SRAM 1X11 drop chains at our Wednesday morning group CX training rides. I thought at the time that if I were still racing I would put on an inner chain stop and an outer chainring guard like I used to use with a single Rotor chainring. But after what you described, that likely would not cut it in freezing-mud conditions, and it also wouldn’t solve the problem mentioned in the following letter, either. What is required is a chain guide with not just walls but also a roof.

Indeed, the SRAM product managers I spoke with conceded to me that freezing mud is the most challenging condition for the system and can cause the chain to ride up and derail. In conditions like that, they recommend chain guides.

It’s the lift of the chain that has to be stopped to keep the chain on in those conditions, and even though its product description only mentions controlling lateral movement of the chain, K-Edge’s CX Single Ring Chain Guide keeps the chain down on the teeth if it’s set low enough on the seat tube. Another K-Edge chain catcher, the Cross Single XL Braze-on shown on Ben Berden’s bike in this article on the subject might also do the trick, but it lacks an outer stop that might sometimes come in handy. MRP makes one that should work well; scroll down to “CX Seat Tube 34.9” to find it. For bikes with 28.6mm or 31.8mm seat tubes, the Problem Solvers Chain Spy or Chain Spy 2 for 34.9mm seat tubes might do a similar trick.

I should note that, while you have a round chainring, there are a number of non-round 1X chainrings on the market with long, fat/thin/fat teeth. One of these chain guides will only hold the chain down to its proper height in two places on each revolution of an oval chainring. That might be enough to still retain the chain in conditions like you describe; I don’t know. I recently got a Wolf Tooth oval single ring but have not ridden it much, and I know riders who have dropped chains with Rotor QX1 chainrings.

A Rotor representative told me that with early versions of the QX1 cyclocross rings “some — but not all — chains had trouble landing perfectly on the chainring teeth and the error would start small within a pedal rotation and increase until the chain was out of line and would consequently drop. This error would increase even more when contaminants like mud and snow entered the drivetrain.”

Rotor has since revised the design so this issue won’t occur with any 11-speed chain on the market.

It’s one thing if you’re getting a new bike every lap. But for riders who don’t have pit crews and multiple bikes who race ’cross in freezing mud, the investment in the correct chain guide is a must to be able to successfully use a 1X system with fat/thin/fat chainring teeth.
― Lennard

Dear Lennard, 
I managed to drop the chain on a CX-1 drivetrain a few times and I know others who have too. In my case, the bottom valley between teeth on the chainrings packed up with mud and lifted the chain until it fell off. It seemed that there was no way for mud to evacuate from between the teeth, and it kept compacting and building up.

The other cases I have heard of were more conventional situations of the chain bouncing off, even though a clutch derailleur was in use.

What to do?
— Michael

Dear Michael,
Using a chain guide with a roof as I described above should alleviate this problem. Additionally, too long of a chain creates more opportunity for dropped chains. So while measuring the chain length is always critical, the issue easily arises in cyclocross with 1X riders who have multiple chainrings of different sizes. Switching chainring sizes affects chain length (the chain’s the same length, but you know what I mean — the derailleur jockey cage rotation changes). Since nobody is likely to switch to a different chain with each chainring size change, a chain guide becomes even more important.

This particular issue of mud buildup in the tooth valleys seems to me one that could also be exacerbated with an overly worn (elongated) chain and/or a worn chainring.

As the chain gets longer due to wear, the tooth at the bottom of the chainring (the one at 6-o’clock — the last tooth the chain engages before heading for the bottom jockey wheel of the rear derailleur) is carrying an ever-higher percentage of the load. The longer space between chain rollers means that each subsequent roller trailing the one contacting the bottom chainring tooth is riding up progressively higher on the tooth behind that roller and less in the bottom of the valley between teeth. This would allow mud to build up in those valleys and give it a chance to harden in there a bit before it passes the six-o’clock position. And using a worn chain on the chainring also pushes out the aluminum on the leading flanks of each chainring tooth, making the teeth hook-shaped and providing a wider platform for mud to collect on. This could still give it more chance to collect mud even after replacing the worn chain with a new one.
― Lennard

Feedback regarding SRAM 10- and 11-speed compatibility

Dear Lennard,
Your recommendation to try Jtek Shiftmate is a good one. I’ve been using the adapters for years to flawlessly shift Shimano derailleurs with Campy shifters. It takes a little longer to install a new cable with them, but that goes with the territory. I highly recommend them.
— Thomas

Dear Lennard,
I read your article about using 11-speed SRAM shifters with a 10-speed cassette, and I must be a minority because I’ve done it twice now without any adapters. The first time was with SRAM Red hydro disc shifters on my ’cross bike. I was waiting for an 11-speed freehub body on my DT Swiss 350 hubs and set it up with 11-speed Red hydros, no FD, narrow-wide front chain ring, and an 11-32 rear cassette with a XO 10-speed clutch derailleur. It worked perfectly. It later was changed to a double for winter training on the road. I have the parts for 11-speed but just haven’t gotten around to it, and it shifts perfectly.

The other setup is for my CycleOps Silencer trainer for my road bike. It came with a 10-speed cassette and my bike is 11-speed. I just mount it up; add six clicks of tension to the rear derailleur to align the shifting and off I go. It shifts every gear perfectly.

I’ve also seen it done on at least two other bikes.

Even by your measurements, we are still just 1.8mm out of spec for nine shifts. Use fifth as the place to adjust and it’s 0.9mm out at the top and bottom. And I think Shiftmate Y isn’t made. I think it is to say what works without an adapter, like Shiftmate X are examples of what can’t be made.
— David

Dear David,
Well, knock me over with a feather. If it works for you, more power to you! And I clearly did not read the Jtek page very carefully!
― Lennard

Dear Lennard,
Responding to your VeloNews Technical FAQ response to Hans, SRAM does offer 10-speed hydro road shifters, called S-700 DoubleTap Shifters, available with either hydraulic disc brakes or hydraulic rim brakes. See here and here.

I upgraded my 10-speed gravel bike in early 2015 to the S-700 Hydro shifters as I too wanted to remain 10-speed compatible with numerous wheels. Sticking with 10-speed at the time also allowed for a wider choice of ultra low gear cassettes and long-cage derailleurs that could be mixed/matched from the MTN product lines.
— Bryce

Dear Bryce,
Good catch; I ought to have mentioned that!
― Lennard