https://www.bsn.com/Cycling/cranks.html

by the way, their calculator ain't working.


I like this quote, even though the article seems to be kinda old, and I've just bought 2 pairs of 180s:

"If you look at elite cyclists, despite an increasing number of long femured (tall) competitors, you will see that 175mm is pretty much the longest crank (other than for time trials) that is used. I would not, as has often been suggested, put this to conservatism. On the contrary, the fierce competition and prizes of professional cycling are substantial and bring a willingness to quickly adopt what might appear to provide some form of advantage -- which more often than not is at best psychological. In a realm where high tech voodoo and strange science abound, I can't accept the arguments to the contrary...

Ya gotta admit, this sounds more than reasonable. Despite the image that Euro cycling is sometimes smothered by tradition and conservatism, like he said, if the riders thought they would get an advantage from long cranks, I reckon there'd be more using them.

Interesting, thanks for the link.

but wait, there's more......


https://www.myra-simon.com/bike/cranks.html
https://www.peterwhitecycles.com/fitting.htm
https://www.cranklength.info/
https://www.billbostoncycles.com/crank_length.htm

ya know, 53-11 is probably gonna have either
a coronary or a nervous breakdown when he reads
the first article.

Wow! I guess the best way to calculate the "correct" crank length is to take the average of the results from all of these formulae and charts.

You haven't even been reading my stuff lately then. For the last 4 months I've been saying this "proprtional" crank length theory is all a bunch of BS becasue the bikes aren't made "proprtional" (and I'm not talking about BB height either)

Look at how seat tube angle changes drastically as you move up the size range in a road frame. Heck just becasue some guy with a 28" inseam can ride a 170mm crank doesn't mean I'll be able to ride a 195 mm crank with my 36" inseam. Easiest explanation (BB height non-withstanding) is that I'm not riding a 76 degree seat tube angle (which decreses distance to pedals and compensates for shorter femeur) like the guy on the smaller frame.

yeah, there's a bit of variation. There seems to be the "street smart" view and
the "proportional view" -- the latter seeming to put people on pretty long cranks

Frames are made with compensation for long legs already built into them. (seat tube angle)

Since the compensation is already built into the system you can't go compensate again by lengthening the crankarm.

If you try try to put a long crank on a factory frame you'll end up moving the seat forward (it will be forward and higher). You can only get away with so much of this with a slack seat tube angle.

I doesn't sound reasonable to me. I do R&D for a living, and I hear lame arguments like this all the time. People can come up with endless reasons for not changing. If bikes specifically designed for tall people were very commonly available, and anyone could easily try one, then he would have a point. But that's not the situation.

By the way, proportional crank length is not a theory any more than proportional femur length is a theory. The only "theory" I see is that 170 mm cranks are right for everyone, and it's an incorrect theory!

CAAARMON!! Nobody says that anymore.

I would say this is the current "doctrine":


"Popular Guides" https://www.bsn.com/Cycling/cranks.html

..Height......Inseam.....Crank length
under 5'.....<=70 cm.....165
5' to 5'2"....<=74 cm.....167.5
5'2" to 5'7".<=80 cm.....170
5'7" to 6'....<=86 cm......172.5
6' to 6'5"....<=93 cm......175
over 6'5"....<=99 cm......177.5 - 180.0

But they ARE saying it, and your chart proves it. 165 is only 3% smaller than 170, and 175 is only 3% larger than 170. I see the doctrine as "170 mm (give or take a tiny variation) is right for everyone."

Biggest problem in my opinion is the pedal at the top of the stroke. In fact, that can make the longer crank worse than the shorter crank unless you compenaste for this.
The only way to compensate for the decrease in power at the top of the stroke is to move seat forward and higher. (if you don't do this the longer crank is worse IMO)

Like I said before smaller frames already do this via the steep Seat tube angles and long top tubes they have. Look at tall frames? They are the reverse: shallow seat tube angle and shorter top tube. They ain't proportional.

I restate this: You can't apply "proportional" theories to things that aren't "proportional". (Simple)

aaaah, you thrown in that little caveat....so, I guess so, but my 180s feel heaps bigger that the 165s I used to have on my track bike

Anyway, I'm with ya...I just forked out $1200 AUS for 2 pairs of 180mm Dura-Ace cranks and BBs, based mainly on the "Zinn" and "Crank length Info" sites, and my inseam is "only"
89.5cm, at 5'11.65 (182cm).

Enjoy your cranks! I have been riding with 180mm cranks for the last 15 years. If I had the money to spare, I would have Zinn make a complete custom bike for me.

Will do.

It's just that the first link I posted mentions a few things that I think aren't really explored by guys like Kirby Palm, who, by the way, ain't no athletic veteran of the pro circuit. Check him out: https://www.nettally.com/palmk/resume.html

I ride 180mm cranks too, but I just think people need to have a deeper understanding of what is really going on with their frame before they buy into Zinn's theory.

Differences in frame seat tube angle through the size range are not just for KOPS. It is also done to keep the fore-aft center of gravity relatively constant through the size range. But, there are also plenty of manufactures who use 73 degree seat tube angle though the whole size range and let people fiddle with seatposts if the want too.

I think associating crank length with leg length just makes sense, but I think it most likely benefits the short riders who have been using cranks that are to long more than tall riders who have been using cranks that are to short.

I know about the wheelbase being held constant and I agree with that, but I maintain that longer cranks only work as well as shorter cranks if the knee at the top of the stroke isn't closer to the trunk.

Steeper seat tube angle helps keep this hip angle relationship. The longer top tube on the smaller frames in turns lets the cyclist rotate his body forward about the BB to make it all work.

KOPS is BS anyway. I think there is an ideal knee to spindle relationship, but it has nothing to do with KOPS. It has to do with how the levers and pivots that make up the leg are oriented around the BB. You rotate the trunk of the cyclist forward about the BB and the ideal position of the knee to spindle is also rotated forward.

Only LOOK does this. Maybe a couple of manufacturers I don't know about, but the main thrust of the industry is to adjust tube length and STA throughout the range (makes sense too considering there is only a token 5mm spread in crank length, but a huge variation in leg length).

Tall cranks need high forward seat(to maintain hip angle- think "saving your knees" too) with long top tube to compensate for forward rotation. Industry has been doing this for years to help small riders with short legs adapt to 170mm cranks.

Now how are you going to apply a "proportional" crank theory to tall riders when they don't ride their bikes in this position? You can't.


P.S. I agree with you Galen that taller riders would be better served with longer cranks, but making this happen would require some drastic frame changes (not just BB height) that might even change the wheelbase too.

Actually, I have.
I was jus' funnin as they say down here.

I agree with Galen, probably makes more difference
to those of us that are vertically challenged
than taller riders.

Marty

The biggest problem (besides BB height) with a tall cyclist trying to use a proprtional crank is likely to be balance on the bike or excessive wheelbase. Take your pick?

If I were to use a 195mm crank that would result in a very significant forward shift in my center of gravity (if properly compensating for hip angle, etc)

Just going from a 170mm to a 180mm I noticed this already.

So what does that mean in laymans terms? Bigger cranks can cause a bike to be more wobbly as one puts more force into it (such as when climbing a steep hill)?

I think by "balance" he means a balanced postion on the bike.

Body weight has to go WAY forward before the handling characteristics of a bike are changed much.

long cranks will not make your bike wobbly