PepeM

Worked for me.

I don't ride on that position all the time, but I like being able to achieve it without my knees hitting my torso. Rather not take the aero penalty if I can avoid it.

I'm 140lbs. While losing a bit more is definitely possible, it won't solve this particular issue. My hip angle is pretty closed already when in that position.


My saddle is already pretty high, towards the extreme of what is considered 'normal,' although that was part of the solution indeed.

You are right, there are many solutions. Shorter cranks where part of it (plus lets be clear, we're just talking 165s here, nothing too extreme. If I could easily find shorter ones I would probably experiment a bit with them. I am guessing at some point there would be a length that is too short.) Can't say I've noticed any penalty. Standing starts probably suffered, but I never do those. I've seen the torque numbers given by my power meter and when at max power I am nowhere near my force limit, so I am not sure more leverage would do much for me. Being able to spin 10rpms more would probably be more beneficial to my rather pathetic sprint.

That would be sweet.

I personally see crank length as more of a fit issue than a power/efficiency issue. But I am not expert nor have I done any studies, formal or otherwise on it, which is why I wouldn't tell anyone what they should or shouldn't do. But so far I've had good success with 165mm cranks (they also give better cornering clearance, a nice bonus) which is actually a bit of a shame since they are harder to find, so they limit my options somewhat.

ThermionicScott 

Same here. The impression I've gotten from the studies shared on this forum is that power output is remarkably unaffected by crank length, although some have chosen to home in on whichever length ended up making a 1% difference. I learned from weightlifting years ago that the human leg is strongest nearest to full extension -- that's why you can squat way more if you don't go all the way down. So as long as the bike is set up to allow proper leg extension, and the fit is otherwise comfortable, you should be fine. Although it still stands to reason that if the cranks are way out of proportion to the rider, that won't be optimal.

Cyclist0108

I'm 5'9" with comparatively short legs (30" inseam), am fairly inflexible and have some limits to range of motion due to a four year old injury (in other words, I doubt it will get much better). So I was thinking maybe a shorter crank arm than my current 172.5 mm might be in order. Then I read this on the OP's blog post:

So according to that criterion, my 172.5 mm might be too short.

I definitely tend to prefer a lower cadence than what most consider optimal.

McBTC

Going to shorter cranks will increase rpms in any given gear but being a pusher and not a spinner chances are you'll probably also gear down so for you, it's probably a win-win going to shorter not longer cranks-- i.e., a higher gear at an increased RPM equals a lot more power... don't be afraid to go as short on the cranks as needed to get the mobility you need.

Cyclist0108

OK, that is what I am managing to confuse myself with.

Briefly, I have an 11-32 cassette and a 50/34 crank, and am about to pull the trigger (after about 2 years of vacillation) on a 46/30T crank, with the hope it will help me grind up some ultra-steep hills around here that I find challenging, even with my current lowest gear.

My impression, which it sounds like might be 180° off, was that shortening the crank would effectively cancel the benefit of having one lower gear.

McBTC

You talked about dealing with flexibility and you probably can concentrate on that instead of wondering about the effects of shorter cranks on hill-climbing ability given that you probably cannot go below 165s without spending big bucks. You might try installing Ride2 crank shorteners to see if going to shorter cranks addresses the flexibility issue.

Cyclist0108

If I do experiment with shorter cranks, probably getting an 11-speed 105 in 165mm for $100 on chainrxn would be the way to go. My bike frame was made based on the starting assumption of a 172.5 mm crank, so I also worry that changing the length might de-optimize the custom frame geometry. Too many variables for my tiny mind to process.

wphamilton

Foot speed is sometimes a limiting factor, but most examinations of this find that the faster cadence common with shorter cranks is psychological. To cyclists who are accustomed to a longer crank, it "feels" natural to spin the smaller one faster - mainly because they're maintaining the same foot speed. At least until they've trained with the shorter crank.

McBTC

Possibly... when you consider that-- if you shorten the crank from 172.5 to 165 you'll probably have to raise your seat 7.5 mm, which means you may have to raise the bars a bit, move the seat forward, shorten the stem, &etc.

McBTC

... times pie?

McBTC

radius = 1/2 so the diameter is 1 so the circumference is 1 x pie -- increasing r by 5/100s increases the d by 1/10 so the new c is 1.1 x pie --e.g., (.1 x pie / pie) * 100 or 10%

wphamilton

No ... 1.05 larger radius is 1.05 times the circumference. Times pi would be over three times.

Increasing radius by 1/10 increases diameter by 1/10, increases circumference by 1/10. But why is it an important point? Once we realize that the foot moves a larger distance with longer cranks, for every revolution, you know that foot speed is a factor. Likely, according to several recent papers, the only factor involved in increased cadence.

McBTC

If you increase the crank (radius) by 1 inch, the diameter increases by 2 inches, right?

wphamilton

Yes, the same percentage increase. example: radius is 10", diameter is 20". increase radius by 1 inch, that's 10%. Diameter increases by 2 to 22", that's 10%. What's the point of all this?

McBTC

Just that your quote says, Increase the cranks by 5% and the circumference increases by 5%; but, the circumference actually increases by twice the increase in crank length.

wphamilton

OK I'm not going to go into this any more, but what is your point? Do you think that OP has it right about cadence correlating with crank length?

McBTC

No, my math sucks. I agree-- he says, when you increase the crank length, you naturally increase the distance around the circle. Maintain the feet per second for the rotation around that circle, and cadence drops. And, vice-versa.

AnthonyG

Based on a 30' inseam I'd recommend you try some 153mm to 160mm cranks particularly since you have flexibility issues. I recommend that crank length should be between 20% to 21.5% of inseam. Roughly, 21.5% of 30' is 164mm so given some rounding is going on then 165mm cranks are right at the top of your range. If you were flexible then 165mm may be ideal for you.

Short cranks are available, Short Bicycle Cranks


With 172.5mm cranks you ARE going to have a slow cadence. You have no choice with cranks that are so relatively long for you.

I take the OP's article with a grain of salt. The bicycle industry has for a LONG time being trying to convince/cajole customers into accepting that they only need a small range of sizes(it wasn't that long ago that the Industry wanted to get EVERYONE on 170mm cranks) and if the industry could somehow get EVERYONE on ONE size of bike (one size fits all) then they would. A small band of enthusiasts (including me) have been proponents of a greater range of sizes to suit the riders better but this is the LAST thing the industry wants. The Industry is still trying to convince consumers that fewer sizes are adequate.

I see the OP article as trying to convince the public that he has the expertise to fit you on a bike with only what is easily available. Being an "expert" who is always recommending that you need expensive custom parts, while CORRECT, isn't much of a business model. A business model that convinces you that you can get a perfect fit with readily available parts is MUCH better for business. A better fit? Not so much.

Anthony

wphamilton

My line of thought is that the shorter stroke induces us to spin faster, but without any particular need to. It's logical that the rhythm is more important physiologically speaking, the timing between contraction and relaxation. OP suggests that shorter cranks means faster cadence, or should mean faster cadence. But maybe he'll come back to the thread and speak for himself on that score.

Cyclist0108

Thanks. One of the reasons I am interested is that I am about to buy a new crank (Sugino 46/30T). They make a lot of shorter ones (perhaps for Japanese riders?), so at least it would be an option. My primary concerns, as mentioned, are (1) I'm after lower gearing, so I don't want to negate changing a 34T to a 30T by losing some lever arm, and (2) I have a custom frame and fitted bike, premised on 172.5. I'm trying to avoid making a costly mistake (either way).

AnthonyG

I ride 125-135mm cranks. My experience with shorter cranks is that they didn't reduce my torque for hill climbing and in fact I climb better with short cranks.

The big issue here is that you need to look at the entire cycle of the crank, not just the instantaneous torque at the 9-3 position, and assess how your leg muscles and knees are moving through the entire cycle.

As your knee gets higher your leg angle close up and you don't have as much torque in that position. When your knee is lower the leg angles are more open and your muscles have more force in that position. A really long crank would give you a LOT of torque just in the 9-3 position but also make it VERY difficult to get through the 12-6 position. On a really steep climb you would likely stall in the 12-6 position. Shorter cranks may give you less instantaneous torque in the 9-3 position however since your knee is lower you have more strength in that position than if your knee was higher with a longer crank and then the shorter cranks make it much easier to get through the 12-6 position.

There is both too long and too short cranks for a particular rider. My two bobs worth is that 172.5mm is too long for you and going shorter will only benefit you.

What's the seat tube angle on your frame? One of the happy consequences of shorter cranks is that you need to push the seat back which also makes the bike more comfortable (less weight on your hands/shoulders) for most riders.

Anthony

Cyclist0108

73.5°

Here is a link to all the measurements: Link (PDF)

Also, is shoe size relevant? I have a 47 (US 12), i.e., big.

AnthonyG

Thanks for the link. Based on that drawing, you inseam has to be WAY more than 30" which means that the advice we are giving is wrong. A 30" inseam is 762mm. That drawing has me estimating that your inseam is more like 880mm (34 1/2"). That's a significant disparity. Based on a 880mm (34 1/2") inseam I would go longer to 175mm cranks.

You need to double check your inseam (or the drawing).

Anthony

Cyclist0108

Every pair of trousers I have has either a 29 inch or 30 inch (762 mm) inseam. Even if you allow for jamming a measuring device right up into my pubic bone, it isn't going to be much more than that. The standover height in that drawing is 775 mm (30.5 inch), and there is zero clearance with my shoes on and feet flat on the ground. (The bottom of my belt buckle is 34" from the floor). I just checked all of this.

How are you arriving at the 880 mm estimate from the drawing?

McBTC

Shoe size won't be an issue, even for a midfoot riding position: a shorter crank would reduce toe-overlap problems. Additionally, your frame has a fairly slack head tube angle.