Fox Farm

For most of my biking life (I am 66) I have used 175 crank arms. I am 6'2" and ride a 59 or 60 center to center frame. I have no hip problems, etc. For those of you out there who have gone to slightly shorter crank arms, how much of a difference will 2.5mm make in how they feel? I use compact rings 50 / 34 due to the hilly terrain where I live.

PeteHski

You probably won't even notice. I have bikes with both 175 and 172.5 and I can't tell any difference.

delbiker1 

I have one crank set that has 172.5 mm arms, the rest are 170. When I first start to pedal the 172.5 I definitely notice a difference, it feels like the rings are out of round. After a short while, that goes away. However, I do believe the longer arms give me sore knees after x amount time and miles.

shelbyfv

I've used 172.5 and 175 w/o preference, can't tell the difference.

joesch

2.5mm difference will change your ability to spin into leaning turns if your at this level.
Spinning work is very minor for most to notice.
Spinning a little faster for hills with 172.5 is a consideration if this is your style

noimagination

I agree that I don't feel a difference. I recently switched from 175 to 172.5, but I switched bikes as well so any difference in the crank length was undoubtedly lost in the other changes (position, weight, etc.).

When I switched the other way a couple of years ago (172.5 to 175), that was on the same bike but, again, I did not feel a difference. Looking at my cycle computer, however, I did notice a drop in cadence going to the longer crank. I'll emphasize that I did not feel like I was pedaling at a lower cadence, but that's what the data showed.

(I switched form 172.5 to 175 because I needed a new crank on my old bike anyway, and my other bike (tandem) is 175. My new bike has 172.5 because that's what it came with, and from my previous experience I knew that I wouldn't really notice a difference, so I didn't bother to have the bike shop switch to the longer crank arms.)

mstateglfr 

On my 6 drop bar bikes, 2 are 175mm, 1 is 172.5mm, 2 are 170mm, and 1 is 180mm.

I could not care less what I use for crank length. The 180mm is the only one I can tell is different- all the others feel the same in that I dont think about them ever. Once the saddle height is adjusted for the varying crank length, it just doesnt matter to me if its between 170 and 175.
The actual rotational size difference between a 170mm crank arm and 175mm crank arm is less than 0.5", but I have long accepted that I have lower standards than many and just dont care/notice a lot that others observe.

beng1

I have ridden bikes with 165, 171, 175 and 180 in recent weeks. I can notice the difference in the bikes when I ride them, but that does not mean everyone will be able to.

I think about the science. If you ride in a certain gear it should be harder to pedal with a shorter lever. Also a lot of people agree that sizing a bicycle is important for a serious rider, so the crank arms should be just as important to size as the seat-tube, top-tube, stem, bar width etc.. If you think about proportion, a short stocky person should certainly be more comfortable with short cranks than 180mm cranks. If you switch to longer or shorter cranks, I am sure they need to be gotten used to. If you are on the same bike and using the same gear ratio with both a long and short crank, and you are tall enough to make use of the long crank you should be able to generate more torque with that long lever, and that means more power to pull a higher gear at the same rpm you were using with the short lever.

I am over 6'2" tall and I have gone fast with 165mm cranks, but I have never gone faster than I did when I was on a bike with 180mm cranks. And I have done many hundreds of laps timing myself on a local 12 mile flat loop.

I just switched one road bike from 165mm to 171 and as soon as I got on the bike I knew I forget to lower the seat, then when riding the bike I could feel the leverage, and also felt like I was pedaling more slowly. Feelings are one thing, testing is another.

In the end if you are having fun that is all that matters, if you are in any sort of competition or are interested in power and speed, then I think any rider should use as long a crank as they are able to.

Polaris OBark

(175-172.5)/(175) x 100 = 1.43%

torque = F x lever arm, so at 90°, the torque will be reduced by 1.43%, which should be undetectable for most people. At 0° and 180°, there won't be any difference. So you are decreasing the angle your knee and/or hip will need to make, with a neglegable performance hit.

I switched to 165mm cranks. It helps with off-road pedal strikes.

Eric F 

My road and gravel bikes have 172.5mm cranks. My MTB has 175mm cranks. I don't really notice a difference when switching between bikes. However, when I bought my MTB it had 170mm cranks, and I felt like I was missing the torque of a longer crank in high-torque/low-rpm situations. I switched to 175s and everything felt right.

canklecat

I ride bikes with 170, 172.5 and 175 cranks. For years I didn't notice any difference.

But with age (65) and arthritis I do feel more discomfort and less smoothness with 175 cranks. I'm 5'11" with normal proportions, so I was always on the low end of the range for 175 cranks. For now I have 172.5 cranks on two older road bikes with square taper cranksets and plan to replace those with 170. I might try 165 on my older steel road bike since it's not too difficult to find a variety of square taper cranks.

My 2014 (approx) carbon fiber bike has a 175 Ultegra crankset and I can feel the strain in my hips and knees, and choppy sensation of pedaling squares now. I'll replace that crankset after settling on the length I prefer with the other two bikes.

PeteHski

That’s not necessarily the best idea. For example Bradley Wiggins switched to shorter cranks for his World hour record.

Tests have also shown that power is not significantly affected by crank length. Basically the changes in both torque and cadence cancel out. Power = Torque x Cadence.

Not to mention that most bikes have multiple gears to manipulate torque and cadence accordingly. So crank length only really has any effect in your lowest and highest gears.

172.5 vs 175 is pretty insignificant unless you are already right at the limit of your leg range of motion.

zaje

Last year I rented bike when I was on vacations in Alps; brought my left crank with powermeter and pedals; the rented bike had 172.5 cranks and I installed my 175 crank on one side; didnt feel anything wrong those 10 days.

Camilo

I've used 170, 172.5 and 175 without any noticeable difference in any way. I do always set my saddle height and setback from the pedals the same, so that gets adjusted a bit. But pedaling, no difference for me.

botty kayer

I've got 175 on 2 bikes and 172.5 on 6 bikes.

I find the differences marginal but noticeable. For overall top speed, flat out sprinting type riding the 175's edge it, but I find the 175's more fatiguing on longer rides, so my preference for longer rides is to ride 172.5's, which is why I've got them on most of my bikes.

RJC1811

I’m 65 with shorter legs. I just went from 172.5 to 165 on my road bike and can feel the difference. I couldn’t really feel the difference from my old road bike at 170 to my current bike at 172.5 before I changed. The incentive to change came from having knee replacement surgery in January. So far the positive changes, it’s easier to spin a higher cadence, easier to have a smooth pedal stroke and I feel my pelvis is more stable resulting in less lower back pain after a long ride.

As far as I can tell there are no downsides. I think the research shows that any loss of leverage is only applicable to high power sprinters. For the rest of us, your power output could actually increase due to a smoother more consistent pedal stroke.

I’m not sure it’s worth changing for 2.5mm but I’m very happy with my 7.5mm change.

ljsense

Longer cranks will position your saddle 2.5 mm lower and bring your pedal spindle forward 2.5 mm, which might give you just the edge to relieve numbness or put your pedal spindle just far enough under your kneecap to relieve pressure.

On the other hand, if you have problems with your hip flexors or lower back, a shorter crank might help.

But the standard 2.5 mm between sizes is slight.

For those about 6'2" and up, I'd say cranks are generally undersized -- the rare 177.5 and 180 are worth trying.

easyupbug 

Same here but arthritis in knees and at 73 losing the replacement battle with the left knee. My 175, 172.5 bikes and a 170 are gathering dust and the two 165 are all I am currently riding.

Fox Farm

Thanks everyone. I will report back once installed.

Mtracer

My latest bike came with 175's and I had been using 172.5's up until then. There was a difference and it gave me some knee pain. But, the weird thing is the pain was when riding out of the saddle. I think the difference was just a bit too much causing my knee to have to bend just that little bit more. Though when you think about it, it makes for a net 2X or 5 mm difference between one pedal and another. So, when standing out of the saddle, when one foot is at the bottom, the other is 5 mm higher.

For this reason, I switched out the cranks pretty quickly.

I agree with the others, when sitting and pedaling, it seemed the same to me.

georges1

I have 172.5 on all my road bikes as itwas what I was using the past and 175 on my mountain bikes. Will stay with 172.5 for my next road bike projects