catgita

This is a topic that receives far too little attention. Tradition and industry discourage it. But for those who have legs outside the average male, 30-32" inseam range, you may be riding with cranks wildly disproportionate to your size. For any one individual it may make no difference at all, or it may be a revelation, as it was for me.

I am 6'6" with an inseam of 37". If a 175mm crank is proportional for someone with a 31" inseam, then a 200mm crank would be proportional to me (same range of motion at the knee, hip, etc). Quite by accident, I found a 200mm IRD crank commonly available for $150. After 40 years on 175-180mm cranks, it was worth a try.

The result was a 20% increase in speed, and greatly reduced stress on muscles and tendons. Clearly the cranks I was using were a serious performance bottleneck. If you are also outside "average", haven't experimented with crank length, and want to get the most out of your ride, then I highly recommend reading up on this topic.

Bicycle Crank Length About
Bicycle Crank Length Calculating

SHBR

Good luck pedaling your 200MM cranks through a fast corner.

I use 175MM cranks, even then there are times when I get pedal strike.

Once your up to typical cruising cadence, (90RPM) I highly doubt there is 20% speed increase for most riders.

For many riders, such as my wife, would be at a major disadvantage with 200MM cranks.

catgita

200mm cranks would not be proportional to most people. Longer or shorter, in proportion to leg length, simply makes more sense than one size fits all.

Me on a 175mm crank is like an average height man riding a 145mm crank. You simply would not expect to ride well on a crank from a small child's bike. A small woman might be the other way around.

The bike I am using has a slightly tall BB, plus 38mm tires. It has the pedal clearance of a pre 1990 touring bike, so nothing crazy. I usually ride custom frames, so next time I may up the BB height so clearance is more like what I am used to. For now, a little caution, and no crit racing!

AnthonyG

I'm all for proportional cranks but heres the rub. I wouldn't recommend 175mm cranks for a 31" inseam. Too long. I'd recommend 165mm cranks. If you like 200mm cranks then they work for you. The same ratio that would have me recommend 165mm for 31" would put a 37" inseam on 197mm cranks. Not that much different.

I think that 180mm cranks could work for you as well. I think that what's really missing is that you can't sit far enough back to make the 180mm cranks work for you. Given that your sitting too far forwards then I understand that the longer cranks feel better.

Carbonfiberboy 

I have a 6'8" friend who has ridden PBP, etc., on a custom TI bike. He should be riding 220 cranks but as others have pointed out, he'd need a custom BB height. I don't know why his builder didn't customize his BB height but he didn't. He looks kinda odd pedaling with his tiny 175s. OTOH there are those who claim that we all pedal with cranks which are much too long, so I don't think there's one solution. My friend is plenty fast on his bike. The limiter is always lung capacity/weight anyway, not any equipment spec.

catgita

180mm cranks (which was my previous standard) were clearly better than 175 in feel and performance. So it would make sense to try something longer to see if the up slope in performance continued, which it certainly did. I don't see where you get the idea that my saddle position had any limit. I didn't assume the KOPS would feel right with the extreme change, so went by feel, adjusting out on the road over a few days. It also feels great transitioning out of saddle, which is the other main benchmark for saddle position. In the end it actually wound up in the same 1cm behind KOPS I have always preferred previously.

Clearly not always. Most people would say I am fast too, but a lot faster now! I can hardly get winded on a 175 or 180s, even turning crazy rpm or out of the saddle, but 200mm, certainly. I read a study that looked at efficiency at a fixed low output, which of course favored a very short crank. Efficiency is not the same as performance. Riding fast is not efficient, by any stretch. Spec a 145mm crank on your bike and see if it makes no difference. Regardless of what the "best" ratio of leg length to crank is, it makes no sense that a very tall person would be best served by a 175, while a very short legged person would be best served by a crank just 3% shorter, but that is what conventional fitting would have us believe. Cranks should come in 10mm increments, not 2.5mm.

AnthonyG

If your a really long legged guy using cranks that are proportionally short for you then you need to move the saddle back to achieve KOPS. Its just the geometry involved and an off the shelf frame isn't designed for such a long legged rider.

Moving closer to KOPS and even being behind it is what I would expect to happen with longer cranks.

Carbonfiberboy 

This has all been very interesting. So will you build a custom bike with a higher BB to accommodate longer cranks? Zinn Cycles makes them up to 220mm. I'm 5'6" and ride 170 on my single and 175 on our tandem. Because of low volume, most tandem captain's cranks come only in 175. I don't much notice the difference. I think cranks come in such small increments because BB heights are standardized.

UniChris

Well, I ride on 125's myself... not because of short legs, but because of 1:1 gearing.

Longer than 180mm cranks for long legs could mean a higher power output, but to use that effectively, in addition to the clearance issue it would seem that you'd either need to be fairly heavy and climbing hills, or to be setup on a bike with taller effective gearing than normal.

In terms of bikes for tall riders with large tires where ground clearance would likely not be a problem, Coker Tire doesn't seem to mention the stock crank lengths of their 36er bike (though with a 40" stand over height it's not aimed at the short).

Dirtysixer however does, and says they offer from 180-220mm, in effect agreeing with the premise of the thread.

There are 32" bikes out there now, too. Of course, both varieties of larger wheels do complicate transport and storage, and many parking racks won't work, and the typically 2.25" tires are more "all terrain" than "road".

catgita

What is good gearing for a long crank? I bought a cadence meter to keep an eye on things. Zinn says keep the same foot speed (though his own tests contradicted this). Others have suggested that if the cranks are 10% longer and you pedal 10% slower, there is no benefit. Also that acceleration would be slower. I would say they have not actually tried riding a crank 10% too short. I don't walk the same step or cadence as would a shorter person, so why should I pedal the same?

At first my cadence was lower, averaging about 83, but my speed was still way up. So clearly the simple math doesn't explain it. One day on long cranks made the cranks length I had ridden for 40 years feel totally wrong, so I ordered up a long crank for my daily commuter. Two weeks later and spinning feels normal again, but I haven't been back on the cadence meter yet. I have broken all my previous best times and averages to and from work, even taking it easy due to heat.

So far I would say I don't need higher gearing due to longer cranks; I need higher gearing due to higher speeds.

Would a lighter rider benefit as much? Hard to say, since I am pretty slim for someone 2m tall. Should rider weight be a factor in crank length selection? Maybe a bit. Many of the worlds best climbers are small and very light, but typically ride cranks about 1cm longer than proportions would suggest. I would argue that tall people would not fall so far behind on climbs with proportional cranks. On my second ride I looked at my cyclometer on a climb where I could go 14mph on a good day, and was going an easy 20.

For now I need base miles on long cranks before tackling big climbs, but based on the greater power, I expect excellent results.

Leisesturm

Well... just to stir the pot... where does this all square with the 'normal' inseam riders going down to 155mm and even shorter cranks? Especially on recumbents. As for gearing... a bike set up with a 24/39/53 triple and a 12-2? 9sp/10sp already has about as wide a range of gearing is is practical. Changing crank length wouldn't change much but rather the cyclist should instead focus on cadence and the maintenance of an efficient one.

dynawolf

I am 6'1" with a 34" inseam. I ride 175s and thinking about 170s. I do spin class in the winter and the spin bikes all have 170. My knees hurt in the Spring when I switch back to the road bike. I guess it is a small change compared to what you are discussing.

Flinstone

Whatever you did made things better for you so great. However a 20% increase in speed if you were already fast? If you're already fast then you're fighting mostly wind and a 20% increase in speed requires a 72% increase in power if air is the main factor and assuming no wind. Even if we just say it's a 20% increase, wow. Sustained 20% increase?

Every decent study I've seen on crank length and performance shows fairly mild effects at best. Several are summarized in the second comment here.

How much torque/power do you lose going to shorter cranks? | Cyclingnews Forum

I've changed my crank length significantly just based on what was available at a good price, and seen no impact at all on my power output. Physiologically there is no immediate obvious reason why, within reasonable ranges, crank length must matter. I mean it could. Are the muscles more efficient in one part of their range of motion than another? I could imagine an effect on muscle fatigue, but that's not the same as power output or efficiency. I think there's a tendency for people to do the math on the gears and say, wow, for the same force and rpm, I get more speed with longer cranks. Yes, but power is force times distance, your legs are moving farther, and your heart and muscles still need to pump out the power.

Many things about bikes are not proportional, primarily because wheel size doesn't change, and as I understand it this creates compromises in handling and weight distribution as frame sizes change.

Personally, I'd rather have a lower C.G. and safe knees than cranks too long, even though I do grind up many hills. If the pros are missing out on 72% or even 20% power gains, wow, watch out, that would be the biggest change probably ever in the sport.

Flinstone

oh, and all this is from a 14% change in leverage.

catgita

This discussion isn't for people who are in that middle average range of 29-33" inseam, who could basically use any common crank length with little difference. I suspect that many taller and shorter riders have already self selected themselves out of cycling. If more people had the opportunity to try correctly fitted bikes, including crank length, we would likely see more people enjoying the sport.

The articles listed either do not contradict, or in some cases support what I am proposing. These studies were of mostly average size riders, where all of the cranks tested likely fell well inside the bell curve of the optimal range. The extreme change test using 120 and 220mm showed a power drop off as you would expect for average size riders. The test with women indicated that 175mm was getting over the top of the bell curve, again as you would expect from a shorter demographic.

Within reasonable ranges is what I am talking about. An average size man riding 145mm cranks would not be reasonable. This is equivalent to me riding 175mm cranks, and is equally not reasonable. Would I see a difference between 195 or 205mm? Probably not. Even less so if I tested 172.5 or 177.5mm cranks. No surprise there.

The C/V system can't reach its full potential if the legs can't reasonably be expected to spin faster or harder. It was painfully clear on short intervals this was the case for me. I topped out in speed very early before, but now continue to accelerate to exhaustion. And on endurance rides, I now end feeling strong with the bike leaping forward easily, where before my legs and knees were simply dead long before my body was ready to quit.

Many things on large and small bikes are compromised for reasons that have nothing to do with what is possible geometricaly. I design my own bikes, so they handle really well with no compromises, but that is another topic.

I would not want to have cranks that are too long either. A 31" inseam on a 200mm crank would be like me on a 240mm crank. But for me, 200mm is actually quite conservative, low risk affair. Knee pain is a risk at either extreme of crank length. Too long, and the knee experiences excessive range of motion. Too short, and the knee experiences excessive forces at excessive cadences, as in my case. Clearly I am recruiting the gluteus and additional muscle groups that were underutilized previously.

You CG is fixed relative to the pedal at the bottom of the stroke, not the spindle, so a long crank will either lower your CG, or if considered in the frame design, will make no difference at all.

Long cranks have already made an impact in racing. Miguel Indurain used 180mm, but kept this secret during his career because he was ridiculed for it. Other tall riders are now using longer cranks, but they are limited by the requirement to use production frames with BB that are too low for them. Leonard Zinn regrets not having his 203.3mm cranks during his pro career. But for most riders, they are pretty optimized already on 170-175mm cranks.

But what of those taller riders who never turned pro, because fitters told them that everyone over a certain height should ride 175mm, and anything longer is at best no benefit, but at worst may destroy their knees? And told them tall people can't climb or sprint?

Flinstone

You make some good points. You're right about the C.G. The women's study didn't show any negative impact of short cranks. the 145 to 170 study did but you mischaracterized it. They only showed issues at 120, not 145. So yes, they seemed to conclude that an average size man riding 145 is reasonable. That's a 17% range where nobody in the study had enough issue for them to take notice I guess. No details in the summary about details there. Maybe it was one slightly less than average size man. Maybe I'll grab the article.

Your 37" inseam is about 19% higher than a 31, which I guess might be about average, possibly a bit below average (I think 29 is less common than 34 maybe but whatever). So yes, you might be pushing that range slightly. I would tend to think a 175 or 180 would still get you in a pretty good situation, but maybe not.

Still no way I'm buying 60% is power increases. I think you had a headwind the first day you tried the new cranks. Oh, and yes, there are some 6'6 riders in the pros, probably in proportion to population but who knows. Are they on 200mm cranks? Being some are in the world tour, I'm sure they aren't missing 60% of their potential power.

I'm not saying you didn't find any improvement though. I'm just not buying that there's some huge factor that hasn't been discovered. Maybe some minor tweaking. Certainly mass produced bikes aren't designed for the tallest and shortest. That's clear just by the fact that the reach of some expensive bikes hardly change at all in their entire size range (like Trek as I recall).

Flinstone

And yes I'm aware that the geometrical constraints related to wheel size are also related to mass production cost cutting or at least corner cutting constraints. Constraints none the less.

fietsbob

Lennard Zinn Cycles has a specialty bike line for tall people , he is in Colorado his market is the custom high end..

but he has a source for cranks longer than 180.. He Also writes a monthly column in Velo News.




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McBTC

Cannot think of any reason why why a person with a longer leg would experience better performance with the proportionally higher foot-speeds per revolution that would result from using longer crank arms... although it is not well-studied, the few that do exist support the finding that increases in performance are obtained using shorter not longer cranks.

Flinstone

Higher foot speeds don't result from longer cranks. Higher foot speeds result from moving your feet faster. Ok, ok, maybe you mean for the same RPM and same power, you need higher foot speed and less force. The question is does RPM matter independently of foot speed? If anything I would think getting higher foot speed at lower RPM would be less neurological stress/fatigue. That would seem to be a point in favor of longer cranks.

McBTC

...higher foot speed at lower rpm results in less neurological stress/fatigue-- okay, good to know...

Flinstone

Don't take that as fact. I don't know. If you've done cadence builds and tried to hit 180rpm, you get the sense that just making your legs change direction that quickly is very tiring, but I can't be sure it wouldn't be just as tiring at 10% lower rpm and 10% bigger circles (same foot speed), but if I were forced to guess, I'd guess not. My point really was that it's not clear to me though.

catgita

There isn't much information available on changing to longer cranks, so here is an update with a few weeks on the 200mm cranks.

It felt a little strange on the first ride, for maybe 1 mile, then felt good. The next day, back on my daily commuter bike, the 175mm cranks felt totally wrong. There was no going back. After 40 years on 175 and 180mm cranks, familiarity and muscle memory could not overcome a positive change.

Saddle height is relative to the pedal spindle, so 20mm lower. Same leg extension was fine.

Saddle for/aft position is essentially unchanged relative to the forward pedal. I made this adjustment by feel, testing both seated and standing, then checked the position with a plumb line to the pedal. It was the same as I had set with 180mm cranks. That means my saddle moved forward 2cm, and I switched to a 2cm longer stem. This also means that my feet move 4cm further to the back with each turn of the cranks, which surprisingly feels normal.

It seems that using more of the legs available range of motion amplifies any minor issue. Where I had previously kept my saddle dead straight, now I turn it slightly to the right, which corrects a slight leftward bias in both knees.

Retraining the legs: this has taken some time. I have had some slight inflammation below the knees, in the same way I did after a long layoff from the bike in the late 1980s. My fit is perfect, so it comes down to building some base miles (increasing mileage slowly and avoiding hard efforts). Over all, my knees feel far less stressed due to the lower forces.

Performance: the 20% speed gains I reported earlier have held true on rides under 1 hour. Rides over 3 hours leave my legs feeling far fresher, without the feeling of bogging down as I tire or run low on energy. Average speeds are generally up 1-2mph. I certainly would not expect others to see that much change, since I clearly was up against some physiological limitation.

Cadence: With 180 and 175mm cranks, it was critical to keep the cadence very high, 100+, and push hard to maintain any speed. It took discipline to stay on top of the gear, and it was tiresome. The longer cranks allow a much wider torque range. Loafing at 75rpm is fine, but wind that same gear up to 85-95 and pedaling becomes much easier. The bike begs to go faster. So now I maintain a more normal cadence.

General comfort: No new issues have shown up. Saddle and hand comfort I would say have improved slightly. With less pedal force, I would expect more saddle pressure, but this has not been the case. Maybe there is more blood movement with more leg movement.

Bottom Bracket height: of the two bikes I am using 200mm cranks on, one has 277mm BB height, and the other 280mm. Both were designed for 180mm cranks. The 3mm lower BB has lead to pedal scrapes. It requires caution, and is definitely cause to go custom on the frame. For my style of riding, I think my next frame will have a 295-300mm BB height. If I rode with groups or raced regularly, I might go higher, but UCI regulations limit the BB height to 300mm.

Iride01 

High performance engines built for high rpms typically have short cranks. I don't think proportional sizing makes sense. Sure a longer crank give you more leverage. But that advantage can be easily made up by spinning a lower gear faster.

When younger, my parents had a foot stool with a round top that rotated. I found that the closer I moved my finger to the center, the faster I could spin it. Makes complete sense as you are moving less. Always seemed to me that that applies to pedals too, no matter what your leg length.

I have a 35" inseam. I've tried longer cranks, but I'm happy at 165mm. Longer cranks just equal more leg movement that adds negatively to the physics of rotational forces.... IMO.

McBTC

The industry standard which is in general the norm works for most everyone. Nevertheless, those driven to the peak of performance like triathletes, for example, have experimented with cranks on the short-side of the norm and have written about positive experiences that are in line with what little research has been done on the subject--e.g.,



* https://www.ncbi.nlm.nih.gov/pubmed/11417428
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Your experience comes at it from the long-side of the norm and even appears to be at odds with research that looked at the alternatives on both sides of the norm. From the graph below, the trend is pretty clear although in individual cases, experiences seem to differ. While 170-175 cranks may be the norm, as I understand it, track racing involves powerful riders who oftentimes use 165 mm cranks. So, crank length alone doesn't matter so much as to motivate the industry to broaden the norm even though it is obvious that in individual cases -- even involving high-performance athletes -- the norm arguably is not the ideal, for whatever the reasons. From a power-generation viewpoint, the graph below indicates that 'standard' size cranks are not necessarily the most efficient and for some 145- to 165-mm cranks may actually be a lot better for many riders than 170- to 180-mm cranks and also crank lengths >180.