Comparing cycling to the auto world short cranks would be like a car in the LeMans vs long cranks for the car in the Indianapolis 500... taking advantage of A.I., for us older folk dealing with a range of joint problems, shorter cranks may offer some advantages, e.g.,

Joint Health & Smoothness: They reduce the range of motion for your knees and hips, decreasing joint stress and preventing injury over long distances.

High Cadence: Like a Le Mans engine that must balance high power with long-term reliability, short cranks favor a higher, smoother cadence over raw grinding torque.

For any who may be interested.. beginning with 165 mm cranks (which are not hard to come by and relatively inexpensive) you can easily experiment with even shorter cranks by fitting the 165mm cranks with crank length shorteners, e.g., some studies have a lot of positive things to say about going as low as a 145mm crank length but going even shorter is possible if a joint issue demands it. Using crank shorteners does increase the Q-factor but I never found that to be an issue and may be of some benefit if you ride in ordinary shoes which generally have a wider heel than cycling shoes.

The downside of short cranks for us older riders is that higher cadence at the same speed equals higher HR for that speed. As my max HR has dropped, so has my most effective cadence. Those posting in this forum are not 25 y.o. super talented riders. It takes some experimentation to figure out what cadence range produces the fastest time on long hilly rides. I'm still pushing my limits, though they are a lot lower now. I have about a 30" inseam and run 175s on our tandem, no problem. My stoker OTOH uses custom made short cranks. the rule is that everyone's different. Our most effective cadence is around 85. I have 170 cranks on my singles and spin a little faster, no big deal. I ride by HR and don't notice the difference. My wife and I have been gymming for, I don't know, maybe 40 years, full body workouts. Full body might not be the most effective for cycling, but we don't get injured and we backpack and do whatever we want. I split stovewood for our tiny vacation cabin. Love doing that, all about accelerating the maul head, increasing the kinetic energy while maintaining accuracy.

Exactly right! I haven't ridden for years now, but still read occasional postings here.
When I was still riding I preferred lower gears, aka higher cadence for speed.
This didn't make sense to me as I had a 31 inch inseam.
Kind of like a big block Chevy that revved like a small block. This will make sense to gear heads. I was fast but never competed.

Everyone's different but as regards shorter vs longer cranks the feedback from A.I. is fairly direct on the matter of impact on heart rate, i.e. not much if any and probably none but maybe for some.

I asked A.I. as follows: in bicycling the current Trend even in the Tour de France is for shorter cranks does the use of shorter cranks at the same speed which of course increases RPMs increase heart rate or are they not related to one another.

Shorter cranks generally allow for a higher, more efficient cadence with a smaller range of motion, which often results in similar or sometimes lower heart rate at a given speed, rather than an increase. While higher RPMs can sometimes increase heart rate, shorter cranks reduce the oxygen requirement of the pedaling motion, making them more efficient.

Key Findings on Shorter Cranks: Heart Rate and Efficiency: Studies indicate that shorter cranks do not typically cause a significant increase in heart rate and may improve gross efficiency at the same power output, largely because they reduce the restriction in hip and knee joints.Reduced Oxygen

Cost: While a higher RPM can raise heart rate, shorter cranks mean the pedal travels a smaller circumference (lower pedal speed). This often leads to a lower or similar metabolic cost compared to longer cranks.

Adaptation is Key: While they facilitate higher cadences, it takes time for riders to adapt, meaning immediate tests might show temporary, small heart rate differences, but they are often inconsequential.

Comfort Benefits: Shorter cranks reduce the range of motion for knees and hips, decreasing fatigue, improving comfort, and allowing for a more aerodynamic position without sacrificing power. In summary, at the same speed, you are usually not increasing your heart rate with shorter cranks; rather, you are reducing your body's, specifically the joints' and muscles', energy expenditure to maintain that speed.

My own personal assessment is that it is possible going to shorter cranks will increase HR but not because the smaller cranks are the direct cause but because oftentimes the rider will feel more natural to shift to a lower gear and end up riding in a lower gear without any feeling of extra effort. But obviously that will increase mph and going faster does take more energy and will effect heart rate because the rider is actually working harder even though feeling fine in doing so.

As I have gotten older, I have slid down the gear range to lower gears. To go to shorter cranks would be like spitting (or something) into the wind.

–>an analogy in bicycle riding of going to shorter cranks is similar to two shovelers of coal– if you have a bigger shovel (longer cranks) it's like having a shovel with a bigger shovel... You get a bigger load of coal but you can only shovel so fast and you get worn out a lot quicker than going to a smaller shovel load but in doing many more shovel loads in the same amount of time you'll actually be shoveling more coal...

To that, A.I. says...

That is a spot-on analogy for pedal cadence versus torque.

In cycling terms, switching to a "smaller shovel" (shorter cranks or a lower gear) allows you to increase your cadence (RPM). While each individual stroke carries less "weight," your cardiovascular system handles the high-speed, low-resistance movement much better than your muscles handle the heavy, grinding "big shovel" strokes.

In the real world ... it's spinning a smaller gear vs mashing a bigger one. All in all, you end up accomplishing the same thing but in actual practice, there ends up being a benefit to shorter cranks overall according to some of the research and apparently the research has validity as, that is what the pros seem to be gravitating to, even in the TdF.

I switched from 170 mm to 165 on my commuter bike, the bike I ride the most. I don't feel a dramatic difference, but I might have done a good thing.

I have a fixed gear bike I sometimes commute on, and it has 155 mm cranks. I do feel the difference there, and it's not bad at all.

I've noticed that I'm uncomfortable with 175 mm cranks.

My jeans inseam is 30 inches FWIW.

According to Amazon the Ride2 crank shorteners are not currently available but the spec is that they (two versions to fit narrow or wide crank arms) 'shorten' cranks by 24, 41, 59 and 76mm. So, starting with 165 mm cranks, the first shortening adjustment stop of '24' results in a '141' mm crank length which is not much different from the 145 mm length that that a seminal study found to be the ideal length for maximum performance.

A relatively small 4 mm difference could easily be made up by the variance in the thickness of the sole of typical bicycle riding shoes. With a typical 175 mm crank length, the first adjustment stop would result in a 151 crank length.

It might seem odd but when you think about the typical stair step being 7 to 7-3/4 inches which is less than 200 mm, to ride a bike that would approach the exercise junkie who runs stairs would be a crank length of less than 100 mm.

Both LeMond and Armstrong were spinners although both were able to do so using 175 mm cranks so my thought is, it isn't the length of the crank so much as it is the effect of the length of the crank on the ability to spin for the individual rider– that's the important factor, i.e., spinning vs mashing or RPMs vs torque.