In the road bike market, you may have noticed that nearly every manufacturer is offering bikes with compact double crankset, ie road cranks with a 110mm chainring bolt-circle typically mounting a 50 and 34 tooth chainring combination. Bike companies have toted the compact double as the ideal way to gain most of the benefits of a triple crank (namely better low range gearing) while having a better chainline and lower weight. This is mainly true, but before you decide that the compact double crank is right for you, you should understand its real advantages for you as a user as well as the motivations bike companies have for selling it to you.
Ultegra SL standard double (top) and compact double cranksets. Notice the size difference between the compact double’s rings.
First, let’s back up a few decades to the days when Campagnolo Nuovo Record was the king of component groups. Back then crankset dimensions generally were 144mm bcd (bolt-circle diameter), and typical chainrings were a 52/42 tooth combo. On the other hand, freewheels of that era were usually 6-speed units. A tight ratio for flatland racing and criteriums might be a 13-19 straight block, meaning single tooth jumps between gears, while a touring cluster might be 14-28. Racers would always prefer freewheels that offered the smallest jumps between gears while still offering the lowest gear necessary for a given race course. The small jumps allow racers to stay at their most efficient pedal cadence as much as possible. Non-competition riders would generally prefer wider range clusters, since they wouldn’t have the luxury of a team mechanic setting up their bike specifically each day. Having a broader gear range gives those riders more flexibility for widely varying terrain.
You”ll notice that with a 6-speed freewheel, to have close jumps between the gears (“close ratio”) you must accept a narrow overall range. That’s why the 52/42 chain combination made sense: the ten-tooth jump between the rings creates a useable overlap between the gearing combinations. This would change over time, and when 7-speed became firmly established, most manufacturers moved to a crank with a 130mm bcd (or 135mm for Campagnolo) that allowed a 39 tooth inner chainring (though racers stil preferred a 42 tooth ring). Combined with a 53 outer ring, every rider could take better advantage of the extra cog in the cluster.
Seen above: Regina America six-speed freewheel 13-19 and a Shimano Dura Ace 11-23 ten-speed cassette.
Later still the industry moved to 8, 9, and today’s 10-speed cassette style cog clusters. A cassette construction, wherein the cog clusters slide onto a ratcheting body integral to the rear hub, also allows an 11-tooth cog, which was not an option with freewheels. Now a racer’s cassette choice might be an 11-23 or 12-25, and a touring rider can have a 12-27 or 13-29 while still having plenty of single-tooth jumps within that range. Thus, even today’s narrowest overall range ten-speed cassette is still significantly broader than a six-speed straight block of 13-19 while still maintaining mainly single-tooth jumps.
Right about the time that nine-speed drivetrains were becoming the standard for road bikes, road bikes enjoyed renewed sales presence, particularly at the high-end. Call it the Lance Effect or whatever, people were willing to shell out cash for high-quality stuff. And it wasn’t just young racers who wanted the good stuff. Shimano and Campagnolo began offering triple cranksets in their top-of-the-line groups to tap into the disposable incomes of touring riders and older riders either new or returning to the sport.
Triple road cranksets were/are structurally akin to the existing double cranks. Usually the third chainring is a 74mm bcd mounting inboard of the other two chainrings. The right triple crankarm is often minimally different than a double with the left being identical; the width of the bottom bracket spindle is greater so that the 74mm innermost ring is far enough away from the from the seat tube to sit properly in the front derailleur’s arc. Triple cranks require special derailleurs and often front shifters. A matching rear derailleur with longer pulley wheel cage accommodates the increased chain slack caused by the wide range between the chainrings. The front derailleur of course needs to deal with the increased swing across three chainrings as well as the innermost ring’s tiny diameter. Depending on the design, component manufacturers might choose to create a modified front integrated shift/brake unit specifically for triple (ex. Shimano Dura Ace). Initially the triple cranks had 52/42/32 chainring set that had almost become a standard combination choice, but eventually a 53/39/30 set became the preference. This combo is exactly a racing double’s 53/39 with an extra chainring (wags will call it a “granny gear”) thrown in.
So, the market had finally reached nirvana: he-man racers got doubles, and a triple crank solved every other problem. Simple, yes? But then on the heels of the new 10-speed drivetrains came the compact double crank featuring 50/34 tooth rings.
Though double cranks with 110mm bcd had existed in the past, they were never really common for road bikes nor did they have the 16-tooth jump between the rings typical of today. An important hurdle to overcome was chainring design that would allow smooth shifting with the chainring size difference, which is greater in the modern compact double than ever before. Sophisticated ramps and pick-up pins (and sometimes compact specific front derailleurs) were necessary to help lift and guide the chain during front upshifts. Shimano had been an industry leader in this technology going back a decade or more, but another company beat them to the punch in marketing similar techniques in a compact double.
Starting about 2002 or so, FSA made huge gains in the OEM market as well as the consumer aftermarket because of their innovative carbon cranksets, attractive pricing, and range of product. At the time of their compact double crank introduction, their modular chainring spider allowed them to easily adapt from existing standard double and triple production.
Seen here clockwise from top: Dura Ace 12-27 ten-speed, DA 11-23 ten-speed, and Regina America 13-19 six-speed.
Initially the compact double was considered a special application item, a tool for a hillclimb. This concept was cemented by Tyler Hamilton’s success with an early FSA compact crank during the 2003 Tour de France. A compact double had the chainline and narrower pedal stance of a standard double but almost the same low gearing of a triple crank because the compact’s 34 tooth inner ring split the difference between the two smaller rings of a triple. And a compact double could be lighter than either of the other two options. For racers, the compact double crank made great sense if the race was primarily uphill, but the uphill time trialist segment of the market is very narrow indeed, not enough to seize the OEM market. As much as anything else, the ease of marketing and producing complete bikes with compact doubles would be the reason these cranks are everywhere today.
It’s a two-fold reason. Component manufacturers would rather offer compact double cranksets instead of triples. Even if they could produce a triple version of a standard double with minimal changes to tooling (ex: Shimano Dura Ace 7700/7703 nine-speed and 7800/7803 ten-speed double/triple cranksets), the complexity of producing triple shifters and derailleurs to match far outweigh the cost developing the molds or dies for the compact crank. And for companies offering complete bikes, they know that they can often get away with offering road bikes only with compact cranks, particularly in the entry- to mid-level segments. Reduced variation means easier stocking, which leads to better profitability.
Three years ago, this was more disagreeable to me. At the time, cassette ranges for road bikes did not allow the compact double to properly shine. A compact double needs an 11 tooth start cog for most riders in not-so hilly areas, but in the past most cassettes with an 11 were narrow range with a 21 or 23 tooth bottom end. That didn’t really give much more low end than a 12-27 with a standard double. Now that 11-25 or 11-26 are more common, compact doubles are approaching the overall range of triple cranks. And in 2009, Shimano is introducing an 11-28 cassette in its Dura Ace line, bringing the gap down even more.
However, the downside is that the triple crank is being demoted from top of the line offerings. Shimano’s top-of-the-line Dura Ace 7900 next year gains a “DA” branded compact crank but drops the triple offering. Campagnolo has eliminated triple derailleurs branded to match their upper-end component groups. Even more telling, Campagnolo has yet to indicate that they will develop a triple version of their Ultra Torque style cranksets. And though only in the road market for two or three years, SRAM doesn’t even make a triple crankset at any price point.
Who suffers from this? With the newly expanded cassette ranges, compact cranks are more capable than ever, but I happen to wrench in a shop in a hilly area that caters to special niches in the high-end. Sometimes a 34 tooth inner ring just doesn’t offer a low enough gear even with a 28 tooth cog, particularly for touring riders. Not only are my customers looking for triple road cranks, they would like even more range on the cassettes. We’re putting mountainbike derailleurs on road triples for touring riders. I would like to offer both high-quality road triples and ten-speed cassettes with a 34 tooth bottom-end.
When I toured in Japan, my bike had a road triple with 28-tooth chainring and 27-tooth bottom cog. If a ten-speed 11-34 cassette had been available, it would have given me a comparable gearing range on a compact double, but the actual 12-27 cassette on a triple gave me closer ratios. I don’t think that bigger jumps between gears would have been favourable, but the closer pedal stance might have been kinder to my knees on the ride through Honshu, Japan. The hypothetical reduction in weight is meaningless on a touring bike that weighs 65 pounds loaded.
Seen here clockwise from top: Ultegra SL compact double crank, Ultegra SL standard double, and Ultegra triple.
Finally, the question: will the compact double completely replace the standard double as well? Not very likely. Racers in most cases will need standard doubles because they’ll need that 53-tooth ring to get a big enough gear. ProTour riders use a 53×11 top gear on flat stages and sometimes 55×11 or bigger for time trials. Cassette hubs can’t fit a cog with less than 11 teeth because of the size of the bearings and axle supporting the cassette body, so there is no way to approximate that kind of gearing with a 50-tooth big ring on a compact. Yes, you could just make a 53+tooth ring with a 110mm bcd to fit the compact crank, but such a ring would likely deflect more under power than would be acceptable without the larger 130mm bcd spider to support it. What about normal amateur racers who don’t need an 11-tooth cog with a 53 ring? A compact double’s 50×11 is very close to a 53×12, even a bit bigger. Arguably though, the standard double is better since the 53 tooth ring yields tighter ratios. For instance, upshifting from the 13-tooth cog into the 12 on a 53 ring is a smaller jump than a 12 to 11 shift on a 50 ring. And the racer’s desire for closer ratios was the reason for developing drivetrains with increasing numbers of cogs on the cluster.
So Campagnolo Record and Shimano Dura Ace will no longer be available in triple. On one hand, the traditionalist in me hates progress. On the other hand, before the turn of the century (as in the 21st) neither of those groups was traditionally available with triples.
So…yeah…um…compact doubles are good? Triples were mechanical abominations for weaklings who didn’t deserve top of the line racing components anyways, right?….
Well, those answers aren’t going to please everyone. But I suppose that as long as someone like Shimano at least offers triple cranks and shifting systems at the Ultegra level, the world will be okay.