Choosing Your Crank Length

CranCmCrank2_A_1346

Our Compass René Herse cranks are available in three lengths to cover the needs of nearly all cyclists. The lengths we offer are a bit unusual, but there is a reason for this: Our cranks use dedicated forgings for each length. The “net shape forging” makes our cranks stronger than if we machined them to length. Our cranks are the only classic models that pass the most stringent EN “Racing Bike” standard for fatigue resistance.

However, this also means that we need a new forging die for each crank length. The investment is substantial. We thought hard about which lengths we need, so that nearly all cyclists would find the most biomechanically efficient cranks in our program. We selected 165, 171 and 177 mm.

Other makers may offer more lengths, but they either are huge companies (Shimano, Campagnolo) who amortize their forging dies over much larger numbers, or they machine their cranks to length (virtually all small makers). Machining the pedal eye weakens the area that is most likely to break, so that wasn’t an option for us: All Compass parts must meet or exceed the performance of the world’s best components.

We settled on three crank lengths (and three forging dies), because a millimeter or two really does not make a difference in how a cranks feel or perform. Here is how our crank lengths translate to the more common ones used by most cyclists:

Herse_lengths

For example, if you currently use a 175 mm crank, we recommend a 177 mm. It’s just 1.1% longer. (Consider that the tolerances of crank lengths are about 1 mm anyhow, so if you measured your 175 mm cranks carefully, they might actually turn out to be 176 mm long.)

It’s generally accepted that only differences of more than 5% are significant. The largest difference between the Compass René Herse cranks and the common lengths is just one-third of that threshold. Riders who’ve tried our cranks report that they cannot tell any difference compared to the lengths they used before. This means that 95% of cyclists can use Compass René Herse cranks and get the feel and performance they are used to. (Fewer than 5% of cyclists need cranks that are significantly shorter than 165 mm or significantly longer than 180 mm.)

crank_collage

Apart from the strength and beauty, the main thing we like about our René Herse cranks is the almost unlimited chainring choice. These days, even the big makers offer only a handful of chainring combinations. The Compass René Herse cranks allow you to get the gearing that works best for you. We offer chainrings from 52 to 24 teeth, in single, double and triple configurations, even for tandems.

For example, I use 48-32 rings for Paris-Brest-Paris, 46-30 rings for general randonneuring, and 44-28 rings for cyclotouring. They are easy to swap, if needed – you don’t even have to remove the cranks. This means that the Compass René Herse cranks can be tailored to your body and riding style more than any other crank on the market.

Further reading:

  • Blog post on how to choose your chainrings.
  • Click here to find out more about Compass René Herse cranks.

About Jan Heine, Editor, Bicycle Quarterly

Spirited rides that zig-zag across mountain ranges. Bicycle Quarterly magazine and its sister company, Compass Cycles, that turns our research into high-performance components for real-world riders.
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31 Responses to Choosing Your Crank Length

  1. Sebastian says:

    Hello Jan,

    so the molds already position the hole for the pedal threads and only these are machined afterwards to a 9/16″ right?

    • The raw forgings come out of the dies without holes. Forging holes would be very complex. However, the outside of our cranks already has its final shape with “net shape forging”.

      • Jason Miles says:

        A lot of crank forgings are made to be slightly longer than needed and the threaded holes are just drilled in two locations. This allows crank manufacturers to offer 2.5 or even 5mm length adjustments on the same forging. MFG a crank this way does not compromise strength and the compromise to weight and ground clearance are extremely minimal.

      • On a modern crank with a slab-like arm, it doesn’t compromise strength if you cut off the ends to make shorter arms. However, on a classic, lightweight crank, the arm is more slender than the pedal eye. Unless you accept an ugly oval pedal eye like some cheap 1980s cranks, you also have to cut the arm near the pedal eye to get the shape right. It’s there that many cranks break, and cutting through the grain of the forging is a problem.

        It’s interesting that most modern cranks are either made from carbon (where the arms have to be huge to make up for the lower strength of carbon) or, in Shimano’s case, from hollow aluminum to keep the weight down with the huge arms. Other modern aluminum cranks are incredibly heavy, because the arms are as wide as the pedal eye.

  2. 47hasbegun says:

    It was only a few years ago that only the 171mm cranks were available. Thank you for providing more options.

    Funny enough, I’ve been riding 175mm cranks ever since I got my first adult bike as it’s the ‘standard’ today for bikes in my size, but I’ve been switching to 170mm cranks for better spinning for my sensitive knees—just as the Herse cranks gained the longer 177mm length option.

  3. Guy Jett says:

    I’ve been riding a half-step + granny for the last 40 years and see no reason to change. My current ideal setup uses a 24-41-44 chainset over a 12 to 36 cassette. On the two largest chainrings this avoids duplicates, allowing me to dial in my cadence in a narrow range. Right now I am limited to TA for odd-toothed chainrings, running a TA 41 on a Sugino crankset. It would be nice if Compass offered such odd-toothed rings, but I know there are limits to production costs and inventory for items with limited demand.
    Thanks for all your research an resulting innovative products.
    GAJett

    • Half-step is a neat system. The front chainrings usually are spaced 5% apart, and the rear cogs 10% (or some other combination where the steps in the half as large as in the rear, hence the name half-step). If you need a big (10%) change in gearing, you shift in the rear. For a smaller change (5%) you shift in the front. Or sometimes both. The result is that all your gears spaced 5%. However, the double-shifting means that it’s best used for big mountains, where you’ll stay in the same gear for a long time, or for loaded touring. The small ring doesn’t have “half-step” – all gears are spaced 10% apart.

      To set up half-step, you need to choose chainring and cog combination carefully. Nothing is worse than “almost half-step”, where you shift both on the front and the rear, only to end up in the same gear as before, because you have duplicate gears.

      I wish we could offer uneven-sized chainrings, but we already offer more chainrings than any other maker except TA. And even TA only offers even-numbered chainrings now. However, you can do half-step with our cranks, too, for example, by running a 48-44 with a 14-28 5-speed rear (the classic half-step). More about half-step is in the big gearing article in Bicycle Quarterly 40.

      • nickskaggs says:

        “Almost half-step” is definitely the worst. Now that I think about it, I’m pretty sure the last bike I had with a half-step crank was set up with the incorrect freewheel in the back. It was not at all a joy to use.

        Thank you for the more technical explanation of half-step gearing. Maybe I’ll try it again someday, but I’ll set it up with more attention to detail.

      • B. Carfree says:

        Having ridden about a quarter-million miles with a half-step plus granny (just about the amount of miles a Phil Wood hub lasts, as it turned out), I find that I disagree about it being a big mountain arrangement. A great many of those miles were in the pancake-flat Central Valley where I found it very nice to always have the right gear for a tightly-controlled cadence to respond to the constant small slope and wind changes.

        It’s really not difficult to shift the front when there are only three or four tooth differences between the rings, so I just marched up and down the gear run with every other shift being a double shift. Sure, compared to today’s shifting hardware it might take a bit more touch, but the learning curve was pretty quick, as I recall.

        The only difficulty I remember was when I was using Regina freewheels. They were the only six-speed freewheels I could get that allowed for 12-14 teeth on the two smallest rear cogs. I think I wiped out the west coast warehouses in the early ’80s by breaking every single one of them. Fortunately, the warranty was for more time than it took me to make them fail.

      • I agree that for flat terrain, half-step is great, too. Basically any place where you use the same gear for a long time. In hilly terrain like Paris-Brest-Paris or the Puget Lowland, you are constantly shifting, and thus by the time you’ve got to the new gear with half-step, it’s already out of date, so to speak. So a simple system where you shift almost always on the rear is better here.

        In fact, that is the appeal of 1 x 11 – sequential shifts, all on the rear, without any double shifts that break your rhythm. What I use is similar – most of my riding is on the big ring (48, 46 or 44, depending on the purpose), and I only use the small ring for those few very steep hills. So 95% of my shifts are on the rear… It’s like a 1×7 system with a granny. I get the same gear range and almost the same convenience without the need to go to extreme chainlines and 11-speed.

  4. B. Carfree says:

    The Compass site says the cranks are compatible with 5-10 speed driver trains. Does that mean that the spacing between the rings is too wide for an 11-speed chain, or was that written before 11-speed was around?

    • The cranks are currently designed for 5-10-speed drivetrains. Customers and builders report that 11-speed Shimano chains work well, too. However, we need to do more testing before we can officially recommend this. (We never release anything we haven’t tested ourselves.)

  5. Waldo says:

    Jan, thank you for offering longer and shorter arm lengths than 171mm. In Compass Cycles web site’s description of the crank, you say: “Today, they [Herse] are among the lightest cranks, while offering a great choice of chainrings: from 52 to 24 teeth” without listing crank weight. Obviously, the weight depends on arm length and chainring configuration, but please provide weights of any of Compass cranksets you choose for your customers and readers interested in component weights.

    Thank you.

  6. Mark Min says:

    Greater availability in crank lengths is good. I use 165 mm because they’re easier on my knees and allow a small increase in clearance. I also used half step gearing for years. With either down tube or bar end shifters it was easy. With modern ten speed shifters (“brifters”) & wide range cassettes, and a 1980s triple crank it was even better. I’ve got a tandem set up with nine speed equivalent. Half step triples would seem natural for modern electronic gears if they made them compatible with triples (ignoring for the moment the Shimano MTB electronics), and I don’t really understand why major manufacturers have eliminated triples (apart from production costs). Surely a small granny gear is better than a heavy extra wide cassette. That said, I bet that with some fettling a Compass crank could be made to work with a Shimano MTB electronic FD. I believe Santana have done something similar with tandem triples. (I know electronic gears go against the philosophy or preferences of most of the people who read this blog (hell, even I resist them), but without wanting to inflame passions, IME with reasonable care & attention they’re superior to cable gears, esp. when under load, and a great boon for those of us with arthritic or otherwise injured hands who want to ride long distances)

    • I am not opposed to electronic shifting. I prefer Di2 over older STI, which requires too long a lever swing to operate from the drops. I found that Campagnolo’s EPS works even better.

      A few years ago, when electronic shifting first came out, Bicycle Quarterly published an article suggesting that it was logical to use half-step and simplify the shift sequence. Just push a button for “bigger” or “smaller”, and have the computer figure out whether to shift the front or the rear derailleur or both. But the big bike companies still think inside the box, with a separate lever for each derailleur. (Rohloff has two gearboxes operated by the same control, but unfortunately, the integration isn’t entirely seamless.)

      • 47hasbegun says:

        I’ve heard that some systems allow customization, and that paddle shifting as you describe is possible, though not default.

      • I think the mountain bike system allows customization. A Bicycle Quarterly reader hacked into the road system and made it work with a single set of commands (upshift/downshift) as well. If can be done, but at least for the road system, it’s not intended by Shimano. Even for mountain bikes, they are going to 1 x 11, which seems like an admission that front shifts still aren’t as smooth as the mainstream press wants us to believe.

      • Tom says:

        Isn’t this (automatically choosing the next gear in the sequence through a combination of front and rear shifts) what Shimano’s Synchro Shift does?

      • Yes, for mountain bikes… We are excited that Shimano finally has adopted our suggestion.😉 In fact, I’d love to try the new system, but most of our test bikes are road bikes, so there hasn’t been the opportunity yet.

        On the road, you still have to shift each derailleur separately.😦

      • Hamish Moffatt says:

        The recently announced Dura Ace 9100 has the option of automatic front shifting (“Full Synchro Shift” they’re calling it apparently).

      • Glad to hear that. For electronic shifting, it makes sense not having to remember where you are on the rear cassette and just pushing a lever…

  7. Austin says:

    Hi Jan,
    I’m wondering what the difference is between inner and outer chainrings? Is it just that inner moves the chainline a little outboard? The reason I ask is that I’m interested in running a 1×10 system with chainring smaller than 42.

  8. Frank says:

    Hi Jan.
    Talking about 1 x 10 and 1 x 11 and I think sram have 1 x 12 now.
    Are you thinking of making some narrow-wide chainrings for your cranks?
    Best, Frank

  9. canamsteve says:

    Somewhat off-topic (as only a single chainring is required) – but in reference to the mention of electronic shifting options – it would seem a no-brainer for someone to make a Rohloff electronic shifter. It would be relatively simple to design and the existing Rohloff shifter options are all compromises. I suppose it goes against the KISS principles but it could be configured so that manual shift was possible with a dead battery

  10. Jim Roberts says:

    Jan,

    I have your crankset on my touring bike and am wondering if you folks sell your crank arms seperatley? I typically ride a 175mm and went with your 171 crank arms as recommended by my local bike shop. I am now thinking I should’ve gone with your 177mm.

    Thanks for all things bicycle.

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