Preface: everyone speaking better english than poor me, is invited to help me fixing the language mistakes in this site.

The® Optimum Cranklength...
... is a quite complex subject and can be discussed even more complex and often is so confusingly.
But size of the crank should be ("first order") simply related to the size of the bikers legs.
If you need reasons for this assumption you can read here.
Now let's have a look at some "workaday life bikers."

The following analysis suggests, that with an average 20,5% inseam cranklength it is already possible to ride at a decent speed.
Also note the remarkable scattering ( 19,5... >22 %) indicating indiviual preferences of +/- 10mm(!) (shortcrankers vs. longcrankers).

Fahrer und Kurbellänge

Important hint for crank elongation: Adaption is required!

crank elongation enables and requires (in most cases) growth of otherwise not (or little) used muscle areas.
Especially with (on shorter cranks) very good trained bikers the well trained "round pace" is disturbed, till muscle adaption has been achieved! 1)
Adaption - depending on how much elongation - needs some time! 2)
(And this, BTW, also may be the main reason, why many of test based analyses are inconclusiv or contradictiv)
Do NOT compensate performance slump by applying too much force!!
While adapting pay attention to your knees. If you get signales from there, probably you are trying to compensate. Reduce the pedalforce!
Efficient adaption training is with high (even exaggerated) cadence and low to medium pedal force.
Not until you have reached "harmonic motion" apply the full power.
From what is said above, it should be clear, that an only occasional elongation (e.g. for the big race!) will not work!

Crank shortening
On the other hand the change from longer to shorter cranks should be always uncritical.
There is no need for musclegrowth (some muscleareas are not longer required - but that's not a problem).
The only need is for coordinative adaption. Depending on the biker, this can be reached in a matter of houres or even minutes. 3)

Optimum region
Everyone has ("somewhere") his/her optimum (at a given time (for a given purpose:-)).
Near the optimum, the influence of small deviants is only small.
If your cranklength is in the optimal region,
then you should'nt waste time and money, trying to optimize the last half millimeter,
because this simply makes no sense!
Cranklength is biomechanicaly very relevant - but no panaceas.

Some considerations and tendencies when choosing cranklength,
 depending on...

  shorter <= less - ambitous sport - more => longer

 Long distance / Time trial => longer
frequently starts, cycling in standing position, climbing => longer
 shorter <= circuit race

...Body sizes
  shorter <= rel. long tibia || rel. long femur => longer
 shorter <= smal foot || Bigfoot :-0 => longer
shorter <= full figured |(belly!)| lean => longer
shorter <= aerodyn |ears| distant => longer

SingleSpeed => longer

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Corner clearence
When elongating the cranks, bear in mind, that cornering clearance is reduced.
While deeper pedals may be an aerodynamical advantage (Cyclist sits also deeper) too little cornering clearance is dangerous.
For mountainbikers, fatter tyres can increase the ground clearance.

* * *

You may tell us, if you have questions or think, there should be (even) more sense in this site. :)


1)    Walking and running is not biking. Muscle adaption is typical for every good biker. And every good - but nonbiking - athlete will reach significant improvement after only some days of bicycle training. Fast (and maybe only small) adaption effects may be seen with gymnasts, because they regularly train a very broad range of movements and muscles.
2)    A 2.5mm Elongation is hardly noticible even to well trained bikers and certainly not for the casual biker. The author of this site (with an inseam of 95cm) has made a 20mm leap from 180mm to 200 mm. This resulted in a very obvious performance slump on the first day. Not less obvious muscle ache the next day. Better performance than ever before was reached about 14 days later (but for this it can not be ruled out, that psychological factors where not less important than the actual size of the crank)
3)    The author of this site has no problems in casually using 175mm bikes though he mainly uses 200mm cranks. The change is always noticeable, the performance is lower than with long cranks but there is no performance slumb like in the opposite direction of (occasionally) change and no muscle ache.