koger

I'm going insane. I've read quite a lot of info about crank length

https://www.cptips.com/crnklth.htm
https://www.nettally.com/palmk/Crankset.html
https://www.stevehoggbikefitting.com/...gth-which-one/
https://bikedynamics.co.uk/FitGuidecranks.htm
https://www.plan2peak.com/files/32_ar...gTechnique.pdf

I currently use 175 cranks. My inseam is 91cm, from the above sites (even though not in total agreement) I have come to the conclusion that I can use 180mm cranks.
But will I actually benefit from it?

180mm cranks are 3% longer, so the theoretical max. power increment is 3%.

I think I understand the basics. When I increase the crank arm 3%, I increase the torque 3%, so with the same cadance I should be able to choose a 3% bigger gear (if available) and get a 3% power increase.

But that doesn't take into account the downsides with increased cranks, such as less smooth pedaling because of bigger deadspot.

What's an realistic power increase, if any?

spectastic

the greater leverage provided by the longer crank is offset by the greater distance you have to push the pedals. There is no advantage other than preference.

carpediemracing 

I use long cranks for my leg length, 175mm and about 74 cm (I just measured since I didn't remember, but it's in that vicinity). I used to ride 170 (3-4 years), 167.5 (12 years?), 170 (8-9 years?), 175 (6 years), 170 (1 year), 175 (1 year), 170 (1 year), 175 (2 years).

I tried really, really hard to go back to 170s. I committed an entire season (with pre-season training), trying to utilize the 170s, trying to find some speed. Unfortunately my top speed, in ideal conditions, is 2-3 mph higher with the long cranks but 5-6 mph lower than it was 20 years ago. I wanted to find some of those missing 5-6 mph but no dice.

I think that as I got older my power curve changed a bit. My peak power dropped dramatically (and definitely my power/weight ratio) but my slightly more sustainable power (3-5 minutes) went up a bit. My sustainable power always stunk so that isn't a factor (my best TT is 23.5 mph for an hour, all aero equipment, etc, and I always got dropped on hills no matter what my weight, from under 100 lbs to over 200 lbs).

So for me, as someone that is maybe 80-90% of what I used to be, the longer cranks allow me to use more of what I have. The long cranks really, really help on power hills (standing, big gear possible hills). For example on a 150m hill I do all the time (in Bethel) on the 170s I'd have to sit and spin a larger gear (53x17, 53x19); on 167.5s I'd be in the 54x21 regularly. On 175s I could stand and roll over pretty effortlessly on a 53x14, 53x15. Although technically I'm putting down the same watts (same hill, same types of speeds) nowadays I can do it more comfortably with the 175s. I've done literally thousands of race laps on that course, 6-7 weeks a year, up to 85 laps a week so for about 10 years I was doing 500 laps a year, for 21 years, so the hill is pretty familiar to me.

On the other hand for sustained climbs, like 7-120 minutes, the longer cranks don't make a difference. Remember that the wattage is the same for a given hill/speed/conditions, so longer cranks only alter the effort, they don't change it. With longer cranks I'd usually use one gear larger (39x23 instead of 39x25) and pedal at a lower cadence. I suppose my foot speed would be about the same; my speed is about the same (awfully slow), that's for sure, and my power output is virtually identical.

Two of my best friends are former teammates, former coworkers at the bike shop, and very tall. They both ride 60-63 cm frames, they wear something like 35" inseam jeans, and they both swear by their 180s.

I'm a fan of using longer cranks, obviously. There are others who would disagree. I don't disagree with them - your experience may not reflect mine.

datlas 

I think spinners do better with shorter cranks.

Mashers do better with longer cranks.

In the tri community, there is a movement towards much SHORTER cranks. NTTAWWT.

I suppose the only way to find out what works best for you is to try them and do a field test with a power meter to see what works best for you.

patrickgm60

89cm inseam, here. My road bikes are 57/58 frames with 175 arms. I didn't look at your linked articles, but I suspect they contain the same formulae I've seen - 21% of inseam, 41% of tibia length, etc. Those lead me to want 177.5 or 180s; however, besides the cost of experimentation, I'm concerned about ground clearance in turns and my knees slamming even harder into my rib cage, when I'm in the drops.

link0

You don't magically get more power from a longer crank arm. You get more torque but must travel a longer distance.

cycledogg

This brings up the question as why do most TT bikes have longer crank arms the their road bikes. I use a 172.5 and have done so for almost the entire time I have been road riding. But when I purchased my TT bike, the shop insisted I use 175 on the TT bike.

fstshrk

Does it have something to do with your position on the TT bike. Maybe you are farther forward and lower? I use a 172.5 mm crank on my road bikes and a 175 on the MTB.

koger

Thanks for a great reply

Ice41000

There is no power increase.

RollCNY

I am no expert, but will regurgitate what I have read:

TT and tri guys ride solo, so they don't have to plan for attacks. They look for constant effort, consistent or improving splits, and the means to hit grades without standing or breaking stride. So they went slightly lower cadence, longer arms, bigger front rings. The longer lever arm gave more torque to let you apply it without standing, as that aero penalty is worse on the long hall. All of the really good tri guys that I ride with do long crank arms and cadences of 65-70 (as a visual guess).

Newer school is going back to shorter based on aero penalty of longer cranks. I have not read much about it, but the premise seems to be moving your feet through longer circles exposes you to more resisted travel distance than shorter. It isn't about cross sectional area, but the work that goes into spinning itself. I think.

carpediemracing 

I think the shorter cranks allow the rider to tilt their pelvis forward more, giving them a more aero position. This was one of my thoughts when trying the shorter cranks because I noticed my back would be flatter and I could hold a lower position overall. The longer cranks make me feel like I'm sitting upright. When standing though the shorter cranks seemed less effective for me, and that would make sense - when standing vs sitting the saddle no longer affects things like aero advantage, pelvis rotation, etc.

nhluhr

It's not as easy as this. When you increase the crank arm 3%, you increase the circumference of the pedal circle (and thus pedal velocity) 3% as well. That increased pedal velocity will require higher metabolic output to maintain. So yes, you'll make more power at the same cadence, but it's not free - you're still making that power from your body.

Realistically, you will have exactly the same power output as before.

Eric S.

I have 180mm cranks on my MTB commuter and 2 road bikes, 177.5mm on a 3rd road bike. Once you get used to the feel of long cranks there's no going back! 177.5mm feels really short when I ride the bike equipped with those arms.

As for the cost of experimenting, there was a time that the only way to go longer than 175mm was with Record and Dura Ace from the two main brands out there.

In 2010 I got a pair of 180mm SRAM Rival cranks (new) for $140, and in 2012 got a pair of SRAM Apex (new) in 180mm for $115. They may not be the lightest cranks on the block, but at 6'2" and 200lbs, I don't care about a few grams.

Nick Bain

Key word of this topic "tradeoff" there are a lot of different tradeoffs in regard to crank length. So don't fret over it too much. Any gains or losses will be a result of your body physiology (if that is the right term) and your pedaling style and training/ riding style and not a product of mathematical calculations. But if it feels right then give it a shot as fit is actually more dependant on experimentation than fitting a common mold.

rekmeyata

Actually the reverse is true, you need to look at shorter cranks! See this article: https://www.powercranks.com/cld.html

531Aussie

Yeah, "trade-off" and "preference" are good words for this topic.

Arnie Baker briefly explains the trade-off between torque and force with longer cranks.
https://www.arniebakercycling.com/pub...m%20Length.pdf

Aside from the force/torque thing, while there may be more leverage with longer cranks, they're also a little harder to push at the top of the stroke because of increased knee and hip flexion. This is an extreme example just to make a point, but it's kinda like how it's harder to walk up 2 steps at a time, instead of one; or how it's harder to get off a low couch than it is to get off a dining chair.

In my opinion, the only time there is definitely more leverage is when you ride off the saddle, because this obvious gets around the issue of position, somewhat.

There's a trend in the tri world at the moment of using shorter cranks, coz they can get more aero.

Frank Day (the Powercranks guy) has lots of anecdotes of people generating more power using

Some people say that crank length formulas are as much voodoo are they are science, and I tend to agree.

Long cranks can hurt some knees.

Also, I'd stay away from Kirby Palm's formula, coz it's ridiculous -- it would have me on 190mm cranks, and I'm just under 6ft! I don't know how shorter guys can ride relatively longer cranks. Palm pretty much made up his formula to suit his preference. His website hasn't been updated for about 12 years, so i wonder if he still believes it all.

Both Zinn and Palm are tall guys who were frustrated in the old days about not being able to get cranks longer than 175mm, and when they did, I figure they had a little "hallelujah" moment, and stuck to their guns since.
Long cranks can feel great at first, and this seduces the rider into thinking they've found a "secret" power weapon, so they stick with it,

I delivered a good rant about Kirby Palm on forum somewhere not too long ago, but I can't find it.

I used 180s for a while, but I ended up hating them, even though I loved them at first. Put simply, it was the position that they put me gave me the sh1ts after about a year. I briefly went to 175s, then to 172.5, which is my main length. My inside leg is 89cm.

Having said all that, while I have 172.5s on a few bikes, I still have 177.5s on 2 bikes, 170s on one, and 165s on another. I obviously can barely notice the difference between the 170s and 172.5s; and i sometimes ride the 165s if I have a sore knee, or just for "something to do". Ha.
i enjoy the feeling of being able to really stomp on the short cranks from a 'great height'.

rekmeyata

I think in the article I posted it mentions this somewhere, but it's easier to climb stairs one step a time for long stair climbing then to do 2 steps at a time. And I think the articles study and how they came about the formula is pretty accurate, even Armstrong went with shorter cranks then was suggested by previous thought. I have a 34 inch inseam, all my bikes up until my new one have 175 because that's what the prevailing school of thought was, on my new bike I went to 172.5, not much of a difference in length but I do find it a bit more easier to pedal for longer periods of time. Someday, at least experimentally, I would like to find a 165 or so and see what it's like. Look, you guys talk about high cadence all the time, why? Think about it, it's the same reason of thought that makes the shorter cranks work better, at least for on the road purposes.