KS59

Anyone around my height have experience using 170mm crank arms? Are there any benefits/disadvantages to using a longer crank instead? I know there's probably not a notable difference but just wanted to see what opinions people had.

ypsetihw

I'm 5'11", had 170s on my first single speed, now I have 172.5 on my FSA crankset, it changes the leverage a little bit, and if you have a longer lower leg you might like something longer. I have these because they came on my bike and have not yet been upgraded.

Shorter cranks are somewhat easier to spin at extremely high cadence, longer cranks give you a little better leverage. I say "a little" because we are probably talking a few percent here, depending on how much you ride, you might not even notice, or it will be different from another bike but perhaps not annoyingly so.

If you have a low bottom bracket geometry or do any hard fast cornering on the regular (like racing) or generally want more ground clearance, you may consider a shorter length to give you more pedal clearance while pedaling through a corner or riding uneven ground.

Unless you have a specific reason not to, and they work, and you like them, then it's fine, use them!

rjones28 

woodcraft

I went from 175 to 172.5.

At first it felt inefficient- less torque,

but then felt more efficient- faster spin & easier to hold a low position.

soom

I am 5'10 and 3/4 inches tall or as my doctor said let's just put you down as 5'11. I also ride with 170mm cranks!

Here is my conclusive answer to OP: There are indeed certain benefits to both short cranks / long cranks but those attributes are subject to certain constraints.

If you want to read a possibly boring spiel on this knock yourself out! *you've been warned*

I want to notate my thought that these performance benefits, or a lack thereof, are largely rooted in our brain's ability to recognize these definable benefits or not. This changes when the brain recognizes the ability to quantify with a degree of confidence/validity as an improvement on personal performance. This probably sounds very abstract but let me explain in further detail.

A novice cyclist will not recognize the subtle nuances of a change in crank length (after all the standard delta in crank length is usually +/- 2.5 mm) due to the fact that their brain is incapable of recognizing 165 mm vs 170 mm with only one bicycle. If a second identical bicycle were to be introduced with the only differentiating factor being a longer crank they *might* be able to discern that 2.5 mm jump. However I am in the camp that says this will introduce no beneficial gain for said novice cyclist.

The brain of novice cyclist simply cannot discern what a change in crank length will do for them. They may feel they're pushing a longer revolution perhaps (pssst. its almost pi day ) but this introduces the concept of body mechanics and measurements. Body mechanics/measurements add the layer of complexity which is why topics like this come up so often. Also note that a change in crank length is usually offset by a change in seat post length or not. What this inherently does is change the bodies center of gravity in a minute, yet potentially definitive, manner. This is very important in terms of body position on a bicycle and even more important when say cornering.

In comparison a pro cyclist will be able to capitalize on these subtle nuances due to their brains recognition ability to adjust / compensate / eliminate certain factors when the math (center of gravity in relation to crank length / seat post height, etc) is adjusted. Essentially this is the compounding effect of having experience. A pro may be able to consult engineers in producing the next level high performance product due to their brain's ability to decipher changes in numbers / quality / quantity / materials / etc.

If you were to run a mathematical / physics simulation of two bicycles with a change in crank length only, then the position of the cyclists center of gravity will most likely change. My thought here is that the determination of performance gain or not is purely based on your body's ability to accept or disqualify the change in a beneficial technical maneuver such as cornering, maintaining an aerodynamic position, or accelerating. Essentially this would apply in any situation where seconds count in a defined situation like racing where skill/victory is measured chiefly by a time factor.

Here's a logic formula:

Let NewCrankLength = OriginalCrankLength + Random(+/-2.5mm)

If NewCrankLength > OriginalCrankLength = CenterOfGrav1,
else CenterOfGrav2

If Brain* > CenterofGrav1, PerformanceGain = 1
else PerformanceGain = 0 AND CenterOfGrav2

*Brain is the ability to compensate for the change in center of gravity (CenterOfGrav1) and whether it can use it to shave time, hence a performance gain of +1. If the change in crank length is too great and the brain cannot handle the gravitational force of the new position (CenterOfGrav2) the cyclist will either fall or be unable to attack as aggressively in a corner, hence a performance gain of 0.

This is an overly simplified physics representation of what's going on. This is really splitting hairs because the brain is rather intelligent (or is it ..? insert philosoraptor meme) and I believe it is capable of accepting a certain level of variance where such small microscopic changes are insignificant for probably 80%** of the population.


**You are probably the 20% that does discern to this frustrating level of detail following Pareto optimality.

Therefore a pro may be able to use the shorter crank length to maintain a better cornering position versus another athlete of equal ability who feels the bicycle is too awkward when handling in corners and prefers the longer crank length. Your brain has to constantly fight, adjust, compensate, cope, and calculate against negative factors present when cycling.

Negative factors like:

Ever hit a head wind? Its much different than riding on flat land with next to zero wind movement.
Ever had a burn in your thighs going up a hill? Your bodies responding to the stress / gravitational strain you're putting it through.
Ever descended and saw a sudden curve ahead? You need to figure out to slow down or adjust your position to successfully corner.

These negative factors have been addressed with say:

Aero wheels for windy conditions
Triple chainrings for the most grueling mountain grades
And perhaps you can say stiff frames / quality grade materials used to instill confidence on descents

Overall yes there is indeed a benefit but again one must look to see if the brain can be cognizant of the change. Also the question largely becomes will this be a deciding factor or the sole factor in determining your own success or enjoyment in this particular sport. If you feel confident that a change in crank length is the only thing holding you back from victory, change your crank length. If you're not comfortable and the crank length is the only thing holding you back from enjoying the sport, change your crank length. The questions and resolutions are infinite. The choice is ultimately yours.

/end

k_kibbler

Wiggo is 6'3" and apparently gets on with 170mm cranks (I think he used to ride 175mm). Point being, at least one really tall dude has no problem with shorter cranks, YMMV.
https://www.youtube.com/watch?v=Vl3xgFw-u8A

I've nothing to add personally, I'm a short 5'7" and ride 170mm.

jsk

I'm 5-11, 32" inseam. I have 172.5mm cranks on my roadbike, and 170mm on my TT bike. I would probably go with 170mm if buying a new crankset for my road bike today. It's not a hug difference, but it's there: a little more ground clearance, a slightly more open hip/knee angle. Plus I tend to prefer a fairly high cadence. Extra torque for mountain ascents isn't something I have to worry about here, the short rollers we have don't even require using the small chain ring for the most part.

Lazyass

Your height is irrelevant, your inseam is what matters. You could be tall with short legs and vice versa. 170mm used to be pretty much standard. Seems the industry went to 172.5 in the 90's when the MTB scene exploded. Almost every vintage bike from the early '90's and older I've owned had 170. I have a 33 inch inseam and I'm fine with them.

PepeM

I went from 172.5 to 175.

At first I felt nothing.

but then I felt nothing.

Jiggle

6', I'll buy a crank with 170, 172.5, or 175...I have no preference.

WalksOn2Wheels

I'm 6'2" with a proportionately sized inseam, 80cm seat height if that helps at all. I think my first bike had 175mm cranks, and then on a build I did, I got a screaming deal on a 172.5mm crankset, so I decided I didn't care. Ever since then, I've gotten 172.5mm cranksets on all my bikes out of happenstance or convenience.

But then again, I'm not a rider who is training seriously, so any marginal gains/losses aren't really noticeable.

fietsbob

Spinner or a Masher ? spinner the shorter arm has advantages ..

ptempel

Haven't used 170mm but am still curious to try. Went from 172.5 to 175mm a while ago. Can't say that I noticed a difference, honestly. I recall reading an article saying that shorter cranks can be more efficient. Can't find it at the moment. Use what turns you on. There may not be an easy answer to the efficiency question.

bleui

probably this article Are shorter cranks better? - Cycling Weekly
My inseam is 33" and currently using 170 mm but considering a 165mm one

jdjones

I'm 5'10" and had 172.5 mm on my last bike. I just built up my current ride with 165 mm which I found to be easier on the knees. It's a subtle difference but I notice it.

Doug28450

splain please.

soom

Spinner = higher rpms, less power delivery to complete a full revolution
Masher = lower rpms, more power delivery to complete a full revolution

It is in reference to whatever your natural tendency is on a bicycle. Some prefer one over the other. I hate spinning rapidly as I feel like I'm a blender but studies have shown a similar cyclist can be MORE efficient and gain an increase in average speed spinning a higher RPM over a period of time. The concept is instead of pushing potentially a taller gear ratio (masher) you might be better off with a slightly easier lower gear ratio (spinner) and edge out over a masher.

Having shorter crank length allows you to spin up faster (beneficial to have a shorter crank) to keep your RPM's consistent to what you want. Having longer ones means more travel distance to complete the same distance. Think of a donut and the travel distance on the inner circle is smaller than the outer circle right?

Doge

5'11" 170mm cranks.