ruftytufty

I’m in the process of getting a new gravel bike, and trying to decide whether I should go with an extra long crankset. This will be my first new bike in many years, and the first where I’m getting properly fitted before choosing a bike.

I’m 6’4”, with very long legs. Every bike I’ve ever had either 170 or 175mm cranks, because 175 is the largest generally available blue.

During a bike fitting I did, we tried a 180mm length, which felt completely comfortable. Didn’t try any longer lengths, b/c the fitter thought 180 would be the longest available. But, later research turned up that there are places that make cranks up to 210mm (!) - e.g. Zinn Cycles/Big and Tall Bikes.
Zinn Cycles also has an article on the “why” of longer crank arms for long-legged folks (sorry, I can’t post the links).

They recommend crank length = 21% of inseam length, so I measured my inseam (using the book-in-crotch method): approx. 36.5", or 927mm.

21% of that is 195mm, so that would be the recommended length for me according to Zinn’s guidelines.

I’m wondering if there are long-legged people here who’ve gone the long crank arm route, and what your experiences are. The reviews on the Zinn web site are of course from people who love their long cranks.

I can probably go back to the fitter and try longer crank lengths, but that’s going to be a pretty short test. And, I don’t know of any easy way to fit an long crankset to my current bike for a real test.

There’s a potential that this could be a real improvement for me, for all the reasons given by Zinn. Plus, a longer crank arm would probably take some weight off my hands - hand numbness has always been a problem for me (hopefully helped by a properly fitted bike).

Finally - anyone had experience with Zinn’s cranks (or custom frames)? And, any other long crank makers you recommend? The other one I found (so far) is Lightning Cycle Dynamics, which goes up to 190mm, but is quite expensive.

Thanks!

Polaris OBark

If you are going to ride gravel, be aware that pedal strikes are a significant issue with longer cranks.

Iride01 

What size crank have you been riding? If you haven't been riding much, then go with what the bike comes with and then after you figure out some reasons why it's not working for you then you can change cranks and see what they do for you.

base2 

Zinn isn't wrong. But it's easy to get the idea that every leg length needs the exact size to cycle at all. Big Crank has a stranglehold on the industry or some such 😉

Generally his ideas are sound, in my opinion. I tried 170mm. Pedaled fast in a bigger cog & felt "bound up." I tried 175. It felt moreorless fine for a while as my pedal stroke was a bit torque-y/lumpy. But, I injured my hip as a tendon rubbed across a bone-y protrusion in my pelvis. In the end, 172.5mm exactly confirmed to his formula.

170, 172.5, 175 are just the most common, most profitable, middle ground with broadest appeal to the most customers. The further towards an outlier size the less the production numbers or market become. Not any different than shoe size or clothing production runs, really. That's where Zinn comes in. He's the "Wide Shoes" shoe store for bicycle cranks.

I say: "Go for it." What's there to lose?

As long as we're on the subject of longer cranks: Just make sure the bike builder takes into account the greater toe overlap. Don't accept toe overlap. Not that it's a bad thing in general, necessarily. But, to many it's it's considered a fault. A custom frame builder exists in business to customize. He is being paid for fault free design & has the opportunity to make it right in a way a production factory can't/won't or isn't expected to. If your custom bike builder accommodates tall riders by simply making the bike taller, find a different builder. A good bike will be proportionally longer too.

79pmooney

Big crank barely has a toehold on the cycling industry. I've had exactly one bike with a BB high enough to race with 180s and the number of 180 cranks I've seen in my lifetime is small. I used to be 6'1/2" with (still) a 3-3/8" inseam (899mm. Fortunately for me, 175s work very well but any shorter is a real compromise.

There are a lot of folk with longer legs than me. I ride a traditional horizontal top tube 59 cm with the insertion line of an old school (short) Campy post well hidden. Any time I go on a group ride I see bigger bikes and higher seats but many still have 175s or shorter.

Riding gravel or other pedal strike places? Pick pedals that can handle hard strikes. Shimano MTB SPDs are indestructible as far as I can tell. Deep enough that first contact is there, not the crank end, is a plus.

Charles Lathe

As Polaris OBark points out, pedal strikes are a concern. I am a six footer — well was before old age started me shrinking — and I dropped down to 165 mm cranks because the pedals on my touring bike sometimes hit the ground when I rode on trails or into fields. It turns out that I like the 165 mm crank length.

All this got me interested in crank length and I did a lot of reading. Several writers referenced a study that showed that at extreme lengths — 120mm and 220mm I think — there was a noticeable effect on efficiency, but from 160 mm to 180mm there wasn’t much difference partly because shorter cranks usually raise cadence and longer ones slow cadence so that power comes out about the same. Longer cranks move the hips and knees more and this can be a problem for some. There weren’t many downsides to shorter cranks except that smaller chainrings might be wanted.

For myself, I fed my numbers into several equations that suggest crank length and Zinn’s gave me the longest crank length suggestion.

I wouldn’t have tried the 165 mm cranks if I wasn’t trying to get my pedals up, but I’m happy I did. And if money and trouble wasn’t an issue, I might try 160 mm cranks. If pedal strikes aren’t going to be an issue, you might find longer cranks suit you. After all, you are outside of the parameters that bicycle designers design for.

base2 

I meant "Big Crank" in the large overpowering mega-corp, conspiratorial, boogie-man forcing 1 of 3 sizes to the masses sense. Not the long crank arm sense. Hence the "wink" emoji indicating jest.

And yes, you are correct. Longer crank arms on a properly proportionally sized bike would force a higher bottom bracket. I once got my eccentric in upside down so the bb was "low" instead of "high" when I was running a 175mm crankset. The pedal strike launched me into a juniper bush & I had a big welt on my thigh from the top tube. It sucked.

ruftytufty

I had thought of that, but didn’t want to make my original post too long.

I probably wouldn’t be riding very extreme terrain, but definitely will keep this in mind. Especially if I go for the longer end of the range, this would argue toward a custom frame, where I could have a higher bottom bracket to compensate for the crank lengths.

Polaris OBark

I had to go to 165mm cranks with my 650b wheels. With short legs for my height, it wasn't an issue.

ruftytufty

“Going for” the really long cranks tends to force other design decisions (e.g. possibly custom frame with higher bottom bracket) that can’t easily be undone. So, it’s a big decision, unless I find some way to do some proper test riding with longer cranks, even if the bike I do that testing on isn’t optimal (e.g. too low BB for off-road riding).

Thanks for the tip regarding toe overlap - I hadn’t thought of that, and I agree that it’s important. Fortunately my feet aren’t as proportionately long as my legs, which would make that problem even more likely.

ruftytufty

Mostly 175mm, on my road bike - simply because there was no option for a longer option. It feels OK to me, but I have no comparison except for a few minutes at 180 on the fitter’s adjustable bike.

If I get a frame with a standard BB height, then switching to much longer cranks later will likely lead to pedal strikes - so if I want longer cranks, I have to at least allow for the possibility when choosing/designing a frame.

I think it’s a given that my max cadence, and even average cadence will drop with longer cranks. I’m not sure that’s a bad thing - larger athletes/animals tend to have lower “cadences” (running, flying, whatever). Zinn’s tests indicate that his climbing speed increased noticeably with longer cranks - that would be of more value to me than spinning fast. The fitters commented that I looked a little weird pedaling on 175’s, since my feed were making such a small circle relative to my leg length, and definitely didn’t look worse at 180. I wish that I had suggested trying longer lengths at the time, but had no idea that really long cranks were even available, till I got home and started researching.

Carbonfiberboy 

I'd say definitely don't go over 180 w/o a custom frame. I ride with a guy who's 6'7". He rides just fine with 175s, did PBP twice. It looks a little odd, but he's fine with it. There have been several threads here and there on BF where folks have advocated strongly for shorter cranks than the formulas say. In general, one can train to be able to put up with most anything and get quite good with it. We get good at what we practice. Without considerable training with each length, it's really impossible to say if one crank length will be of more benefit than another. Spend a year with each length, see what your power is like. Of course that won't work either, because every year is different somehow.

I have a 30" inseam and ride our tandem just fine with 175s. I don't really notice the extra length - my singles have 170s. Zinn's formula says 160. Eh.

Iride01 

I think you have to consider the riding Zinn was doing. I haven't read his take on the crank lengths though. Zinn does a lot of off road riding doesn't he? If that's the case then I can easily see longer cranks and slower cadences. Maybe even for gravel too.

While you say you are getting a gravel bike, is most of your riding going to be in gravel or will it be on paved surfaces? If most of your riding will be on paved surfaces then I'd just go with the normal size cranks for that size frame and try not to let yourself obsess over this one thing that is marginal gains and personal preference along with the type of riding surfaces and terrain being actually ridden on.

And especially don't get so infatuated by this one thing that you design your bike around this one idea of super long cranks and forsaking all the other reasons of fit and bike stability that BB's get put at the height they are put at.

And again, expounding on what I said in a previous reply, once you have some good experience and performance data saved from a year or so worth of rides, then you might want to try other cranks if you still desire to know. That way, like Zinn you'll have some data to compare to and know if it's a difference for you instead of just believing you have some advantage.

If you were on a road bike riding all pavement, even in hilly conditions I'd be on the side of the shorter crank. A good range of cadence on a road bike will do more for most people IMO than will the leverage of a longer crank. How short is a short crank and how long is a long crank? Well, from everything I've read here on this forum of personal opinion that depends on the individual. You might be able to keep a higher cadence with a longer crank than others or you might not. And that is something that only your own data will be able to show you.

oldbobcat

Many riders at all levels are going to shorter cranks anyway. I'm not one of them, but I won't argue. Eddy and I have about the same leg length, 89 cm. Eddy used 175s and that's what I've gotten used to. I think my position is a little better with that length and I appreciate the leverage when climbing. Miguel Indurain, who was taller, used 180s. I don't think you'll gain anything by going longer than 180 or 177.5.

PeteHski

One potential downside to longer cranks is injury/pain if you don't happen to have the range of joint motion required. I've discussed this with 2 local fitters (both very experienced) and they both recommended going relatively shorter on cranks, particularly for endurance riding. At 6'4" with very long legs you could well get away with longer cranks, but don't expect some kind of miracle gain. Stock 175mm cranks are extremely unlikely to limit your cycling performance in any way. Extra long cranks on the other hand could cause issues with pedal strikes and joint pain if you went too far.

In your shoes I would go with standard cranks and forget about it.