Crank arm length for the taller rider — I’m going big!

Posted by SuperClydesdale on May 9, 2010 under Cranksets, Road Bike Components | 4 Comments to Read

Man on tiny bike

Cranks too short?

If you’ve ever been to a circus, you may have witnessed a clown riding a tiny bicycle, with his knees way out to the side, and the massive-looking clown towering over the contraption trying to keep it moving.  This is obviously supposed to be ridiculous, as though the clown does not realize how incredibly inefficient the bike is.  The audience sees immediately that it would be much faster and easier to simply walk than ride that tiny bike.  I have, at times, felt like that clown on the bike.   I hate clowns.

I’m wide, but for a Clydesdale, let alone a Super Clydesdale, I am probably at the lower-end of the height spectrum.   I get e-mails from riders who are 6’5”, 6’6”, 6’7” and I’m not accustomed to being the shortest guy in the room.   This site attracts the attention of a lot of big dudes.    So, while far from being the tallest of cyclists, I’m taller than average – at 6’3”, which puts me in the top 5% of American men in height.     I have often felt that the crankset in particular reveals that most bike manufacturers are ignoring the upper end of the market.   Like any market (and political campaign, and collective bargaining negotiation), the manufacturers want to focus where the money is – the average.  In this case, it’s the average-sized rider.  It’s expensive to design, test, manufacture, distribute, and sell a massive range of products that will accommodate all sizes and shapes of riders, so manufacturers simply make what 95% of the market requires.  Everyone else is supposed to try to make what’s available work for them.  That’s fine for recreational use, but when you are racing or riding with extremely fit, competitive riders, you start searching for all means possible to improve performance, or in my case, to level the playing field.  I want to keep up with the little guys on the hills as best I can.

The resistance I get when discussing this is amazing.  I don’t  really understand it, as any thinking person should realize that the length of a rider’s legs should dictate the proper length of the rider’s ideal crankset.  So there you have it – if you disagree with me, you are not a thinking person.  I think I’ve summed that up rather nicely.

From a simply mathematical point of view, there should be no argument.  As height increases, everything else should scale up as well.  There are excellent arguments against using cranks that are too long, primarily the impact that it has on cadence, and the resulting strain it puts on a rider’s knees, and the loss of efficiency.  But, how long is too long?  Correct crank length is entirely based on a rider’s legs, not made-up anecdotal or emotionally-based arguments, or those meant to hold us Clydesdales back.   The guy at the local bike shop is just jealous because he needs you to reach up and grab the helmet from the top shelf (he can’t reach it), or to open his jar of Accelerade (his hands are too small), so don’t listen to the little guy about proper crankset length.

Crank length directly impacts the amount of leverage that a rider can impart on the drivetrain.   Longer cranks, more leverage.  More leverage, easier climbs.  If your body can handle the longer crank arms, there is no reason at all to not use them.  It puts a cyclist at a disadvantage to use cranks that are proportionally shorter than their competition’s.  I think that this could go a long way to leveling the playing field for a Clydesdale when it comes to climbing.  It allows larger riders to play to their strengths (longer legs) to confront their primary challenge (gravity).  Even if I take back some of the advantage that a smaller rider enjoys, It doesn’t mean that I cannot complain, shout expletives, or otherwise belittle smaller riders while climbing.

Anyone who disputes that there’s defacto discrimination going on in the cycling market need only to look at crank arm length for validation.  Bikes are designed by and for smaller riders – it’s all part of the grand conspiracy to get back at us well-to-do Clydesdales.   Most cranksets come in sizes from 165-180mm (Dura Ace 7900s come in 165, 170, 172.5, 175, 177.5, and 180), which is fine for the average-sized rider.  The only way to get a Clydesdale-appropriate crankset is to go to someone like Zinn Cycles, or High Sierra Cycle Center and order one.

The main reason that I want to get longer crank arms is my weight.   The height (or, more specifically, leg length) of the cyclist is really only needed to determine the capacity of that rider to handle larger crank arms.  So, if you are 6’3” but weigh only 180 pounds, then you may not feel near the benefit of longer crank arms, as the wattage that a 180-pound rider needs to put out on a climb is far less than the 6’3” 220-pound rider.   A 230-pound rider is — trust me — desperate to find any means possible to make the climb easier.  The solution:  proportionally appropriate crank arms.

I have been riding a bike with 177.5 cranks for about 2 years now.  I have come to the conclusion that this is way too short for me.   I have decided to take the plunge and try a much longer crankset.

From what I can determine, the crank arm length, while generally best determined by a rider’s inseam, is most precisely predicted by the length of a rider’s femur.  The femur is the bone from the hip to the knee.   The femur length is largely what determines how much leverage a rider can impart on the pedal.   I created the following table, based on the crank arm lengths in use by the general cycling population, and scaled it up for man-sized cyclists.  The femur length to height was determined based on established data for estimating femur length in Caucasian males, and is really just to show the ranges.  While you might find this a useful guide, you should measure your own.

Recommended crankset length to femur bone

Recommended crankset length to femur bone

This is where the arguments start.  But, the arguments are largely based on a desire for smaller riders to stop us bigger guys from whining about the lack of appropriate equipment for man-sized cyclists, as well as to keep as much of their advantage as possible, as outside of horse racing, there’s not a lot of sports that have much of a use for smaller guys (okay, perhaps as a coxwain).    The average cyclist uses a crank arm that is between 38%-41% of the length of their femur.  Obviously, few, if any people have measured their femur and decided to buy a certain-sized crankset.  Most people just use what came on their bike, and for 95% of cyclists, that’s probably fine.

For those of us lucky enough to call themselves Clydesdales, or for the human genome lottery winners that make up the Super Clydesdale class, this is almost certainly not right.  You are being inadvertently screwed by the bike industry.   You are the clown on the tiny bike.

To pour salt into the wound, using a longer crankset may cause you to have “pedal strike” – where your pedal hits the ground if you try to pedal through a sharp turn.  This can be disastrous.  Make sure that you are comfortable with this trade-off.  Pedal strike can mean instant crash.  Personally, I don’t pedal through sharp turns.  It’s possible to get a frameset with a higher bottom bracket height.

Looking at the chart above , and trying to estimate your femur length, I can see that I would likely be able to handle a 190-210mm crank arm.  I have a 36” inseam (as tested with the technique as described by Colorado Cyclist ), and I estimate my femur is 20” – calculating that while sitting down, and measuring from where I think the hip joint is to the font of the knee cap.  Bill Boston Cycles has a great summary of the argument for basing crank length on femur length.

Zinn Cycles’ “big & tall” approach is based more on inseam — in my mind, a less accurate indicator of proper crankset length, but much better than your local bike shop’s approach, which is “you’re full of crap — use the cranksets that I sell.”  Using Zinn’s recommendations, I created the table below.

Recommended crankset length based on inseam

When using inseam don’t go by what you use for buying clothing.  You need to really estimate the height of your “sit bones” from the ground to get an accurate measure (see link to Colorado Cyclist above).

I’m going big.   Stay tuned..

  • Swedge said,

    pedal strike is a big problem when you are riding in terrain that has lots of roots and rocks. also its even more of a problem on a full squish bike… Not a big deal on a road bike..

  • Swedge said,

    pedal strike is a big problem when you are riding in terrain that has lots of roots and rocks. also its even more of a problem on a full squish bike… Not a big deal on a road bike..

  • kingdavid said,

    SuperClydesdale, your argument is extremely well, well, argued. Very long cranks have never crossed the minds of most riders, even tall ones. Even when I first switched from 172.5mm cranks to 180mm cranks, another guy my height at 6’4″ refused to believe the cranks improved my performance so significantly. He was sure I was suddenly doping! I’d love to see him again when I get my 200mm cranks.

  • kingdavid said,

    SuperClydesdale, your argument is extremely well, well, argued. Very long cranks have never crossed the minds of most riders, even tall ones. Even when I first switched from 172.5mm cranks to 180mm cranks, another guy my height at 6’4″ refused to believe the cranks improved my performance so significantly. He was sure I was suddenly doping! I’d love to see him again when I get my 200mm cranks.

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