Short Crank Database
Written by: Greg Kopecky
Date: Wed Jun 20 2012
Now that we covered the disclaimer, let’s get on to business. Once people understand why they may want to use a shorter crank, there is a second question that comes up: Who makes them, and where can I get them? And after that: Will they fit on my bike? These are the questions I intend to address. In general, the beginning of the “short” range is agreed to begin at about 170mm, so that is where we will start. Consider this to be your guide to all-things-bicycle-crank, below 170mm.
A Crank is Born
As we well know by now, the “standard” crank lengths of modern day are 170, 172.5, and 175mm. It’s generally agreed that these lengths came about after about a hundred years of bicycle evolution (but well before the aerobar and subsequent aero position came about). Outside of these three lengths, you’d see very little. Lucky for you, manufacturers are catching on to the new trend, albeit somewhat slowly. The Big Three (Shimano, Campagnolo, and SRAM) all offer cranks down to 165mm, but below that range your choices become substantially slimmer. To add to the confusion, there are some wrenches that get thrown in to the works – the biggest one being your lowly bottom bracket.
If there was ever a giant white elephant in the proverbial room of the bike industry, this topic is it. The rate at which bottom bracket designs become “obsolete” seems to quicken with every passing model year. Will your brand-spankin’-new $10,000 bike work with short cranks? What about short cranks that measure power? Will the bike work with new cranks that come out in two years? The answer to all three questions is – unfortunately – maybe.
The only saving grace on this topic is the fact that there are some very smart minds out there coming up with a variety of adapters to fit cranks on bikes that really shouldn’t work together. Think of this as the Apollo 13 “square peg round hole” problem. Yes, you can often make these odd combinations work. However, understand that when you do this, you are not getting the intended benefit of the new system. For example, take the relatively new BB30 standard. Say you already own a Shimano Dura Ace crankset in 165mm length, and want to use it on your new BB30 bike. Technically, these two should not match. But – lucky you – there are several adapters on the market that will convert your BB30 bike to accept a crank like the Dura Ace, which is intended for use on a standard threaded BSA frame. Super. Great. But – you do not get any of the ‘benefits’ of the BB30 system any more. Specifically, BB30 intends to be lighter and stiffer than a threaded-BB system. Unfortunately, you just gained that weight savings back with the adapter, and you don’t have the extra stiffness, because that comes from having a BB30-specific crankset with the associated 30mm aluminum spindle. While this scenario is not truly a deal-breaker (in my mind), it is just one example of many possibilities. Do your research before you purchase a new crankset or frame to make sure you know what you’re getting in to.
Brands and Styles
While the table at the bottom of this article is your technical resource for all of the nitty-gritty, I’ll cover some things of note for the short crank brands that exist today.
Origin 8 and Sinz
Some of the truly short cranks out there are not even road-intended designs. They are BMX cranks. Brands such as Origin 8 and Sinz offer options down to 115mm. Go ahead, Dad, optimize the crank length for your soon-to-be child triathlon star (and watch out, Brownlee brothers). The issue this brings up, however, is limited chainring sizing. Most of these cranks are of 110mm bolt circle diameter (BCD), which does end up limiting your ring sizes to some degree.
As well, you have some problems that arise simply by virtue of these cranks not being intended for a road application: chainline and chainring spacing. Chainline is largely dependent on the bottom bracket spindle length you choose, as all of these cranks require either a square taper or ISIS drive BB. In addition, there have been reports that some of these BMX-style cranks are built to be very robust, which includes thicker-than-normal chainring spiders (which is where your chainrings bolt to). What that does is place the chainrings further apart than they’re supposed to be, resulting in poor shift quality, dropped chains, or chainsuck (having the chain get stuck between the chainrings while downshifting).
There are some one-off or small manufacturer cranks out there, including Zinn Cycles, Lightning, and Bikesmith Design. The latter is a machine shop that will cut down some other manufacturers’ cranks to a shorter length, such as SRAM Apex or the FSA’s Gossamer model. Zinn Cycles is headed up by none other than Lennard Zinn, who has long specialized in bicycles and components for both the big-and-tall and the… shall we say - small-and-short? While his offering used to range down to as short as 135mm, it appears that they have since changed the minimum to 160mm (but continue to cater to the long-end of the crowd, with models up to 220mm). Lightning is a small outfit in California that specializes in recumbent bikes, but also offers a carbon crank down to 160mm, for a variety of bottom bracket styles.
The Big Three
This includes Shimano, Campagnolo, and SRAM. As of today, the shortest crank you can get from any of these is 165mm – but you have a fair amount of choices at this length. You can get BSA, BB30, compact, standard, triple, and just about every other configuration out there. I was sad to see that the new slick-looking Campagnolo TT crankset is only available down to 170mm, but perhaps they’ll expand that in the future to satisfy our desires.
Rotor brings the heat
Rotor is, in my personal opinion, the single modern road-and-triathlon components manufacturer to really embrace the short crank movement, on a larger scale than a custom shop operation. They have lengths down to 150mm, and can accommodate all types of bottom bracket styles – a claim that no other single company can make. But, what if you don’t want to use their Rotor ovalized chainrings? Not a problem; you can use nearly any standard 130 or 110BCD chainring with ease. What they don’t have is a short-road-triple option, but that is admittedly a small piece of the pie.
Power measuring cranks
There are surely some of you who want to use a short crank arm set, and also want to use an SRM or Quarq system. For now you have a few options here, but it’s somewhat limited. The unique thing with these two companies is that they’re largely at the mercy of their suppliers… so if Campy doesn’t make a 160mm arm, SRM can’t use it. Both SRM and Quarq told me they’re aware of the new-found popularity of shorter cranks, and are asking for more options upstream in their respective supply chains.
After all the intro, it’s time for the gravy. Before we can get to all the action, however, there are a few caveats that must be explained:
1. This table is a representation of products that are selling on the open market as of right now - today. The intent was to only list items that you can walk in to a retail shop and buy (or buy online). Several manufacturers voiced new options that are “coming soon”, but I omitted them for the time being. As you’ve all seen, product launches in the bike industry aren’t always smooth or on schedule. Fifty percent of the time – they work every time.
2. This table does not include user or manufacturer-made one-off systems. For example, you see that Rotor makes a 3D crank in 155mm, and SRM makes a version of their power meter using the 3D crank… but only down to 165mm. What gives? Due to the current low demand for the shorter lengths, SRM does not stock the shortest options. But – you can buy a 155mm Rotor 3D and send it to SRM to be made in to a power meter. As stated above – this chart is only for items that you can buy off-the-shelf. Quarq stocks the shorty Rotor cranks, so they made it on the table. But - there is not yet a 165mm SRAM Red Quarq… because it’s not ready yet… even though there is a non-Quarq 165mm 2012 Red crank. Just trust me on this one.
3. Adapters. There are LOTS of bottom bracket adapters out there. Here’s how it works. If crankset X is compatible with bottom bracket Z, the result is “Y” – Yes, it is compatible. If X is not compatible with Z, the result is “N” – No, not compatible. But… and this is where it gets tricky… if crankset X is compatible with bottom bracket Z with an adapter - the result is “A” – for adapter.
To drill down further, there are several options for adapters. If the crank manufacturer makes their own adapter – or if there are just too many options to list – the result is simply “A”. But, if there is a specific adapter that is recommended or required for the combination to work, that manufacturer is listed. For example, to use an Origin 8 square taper crank and bottom bracket in your BB30 bike, you must use the SRAM BB30 adapter (which effectively converts your bike permanently to a threaded BSA shell). You cannot use an FSA or Rotor BB30 adapter. Still with me?
4. BBright. As you may know, BBright is the new BB standard that Cervelo started. But what you may not know is that there are actually two different versions of BBright. The “standard” version is BBright Pressfit. However, there is another version called BBright DirectFit that is used on their R5ca bike. The BBright column in my table is for the former – the Pressfit version. To make a long story short, I’m not putting a whole separate column for a BB standard that exists on one bike. And it’s not even a triathlon bike, so the chance that someone will want to use a 150mm crank is pretty slim. If you own that bike, I’m sure your local Cervelo dealer would be more than happy to help you.
After all of the details, caveats, and explanations, here it is – your 2012 guide to short cranks.
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