spelger

i wouldn't mind getting a power meter and used is ok. wondering what the effect of having slightly different crank arm lengths would have physiologically. anyone do this for whatever reason? can you even notice say between 170 and 172.5?

Leisesturm

Even if you did notice, 2.5mm would only feel strange for a few days or so. 5mm would take longer to get used to, but it could happen. More than that, probably not. But ... whhhyy?

MarcusT

Yes, I saw a few articles about shorter crack arms being the new fad. Science or marketing gimmick?
Th arm length discussion has been going on for a century.

zaje

Last couple of summers I rented bike in Germany with 172.5mm cranks and both times I used my 175mm crank with 4iiii powermeter, I didnt notice anything strange or different when riding.

Canker

Are you talking about one arm being different from the other on the same bike? Or different size cranks on different bikes?
For the first 2.5mm probably wouldn't be noticeable but I'd know they were different so any time I felt any discomfort I'd always wonder. I'm sure there are bike fitters out there that do it to make up for leg length differences. For the 2nd I just switched to 165mm cranks on my full suspension bike while both my hardtail and road still run 175mm. I noticed the 165mm cranks for about 5mins the first time I road them and haven't noticed a difference since.

veganbikes

If I had different length legs I would probably run different length crank arms on either side but if I didn't have that problem, I probably wouldn't. It is maybe tough to notice a couple MM but I think the knowledge of it would have a psychological effect if nothing else. It would also visually look weird but I have a feeling at least up to a point it would probably be noticed physically.

A power meter is fine if you desire that data just get the proper size or replace other parts to get it correct if that is your goal. I would just get the right stuff and not just try and get a bargain that is not right.

PeteHski

So which manufacturers are marketing shorter crank arms?

MarcusT

SRAM, Shimano, Race Face, Hope, Truativ.
When I built my first road bike in the 80's, there was 170mm and on special order, 172.5mm and it was pretty much solely based on leg length

esasjl

174 mm could be optimum, but I suspect that once used to them anywhere between 140 and 200 will be fine (use gain ratio to determine gearing). I'm using both 150 and 170 and can switch between them without issue.

I think TA and Stronglight had a wide range of crank sizes for decades.

spelger

ok. kinda figured that with two diff crank lengths i would not notice a diff. and yes, at the same time, 170 one side, 172.5 on the other.

CrimsonEclipse

It really depends on what your optimum crank length is.
If your optimum crank length is 170mm, then 165mm - 175mm will work. and 167.5-172.5 you might not notice
The farther your stray from your optimum length, every 2.5mm makes a bigger, and bigger difference to your ride.
If your optimum crank length is 170mm, and you've been riding 180mm for a while, then increasing only 2.5mm to 182.5mm will be a huge difference to you and will be brushing or exceeding your envelope or limits on what's comfortable.

For me, optimal is 160mm, 165 is fine on certain geometries, 170 is 'eh' and 175 is out of the question.
On the other side, 155-157, is tolerable with specific rides, and 150 is not great.

So if you're near your physical optimum crank length (roughly proportional to your inseam), small crank lengths are relatively insignificant.

NOTE:
riders that are super tuned to their bikes (racers or hyperfocused individuals) will definitely notice a difference.

Turnin_Wrenches

Shimano now offers 160mm crank length as a standard off-the-shelf option. SRAM only goes as short as 165mm.

Turnin_Wrenches

Shorter cranks offer significant advantages without any disadvantages. The biggest advantage is a more open hip angle. Some will argue that shorter cranks = less power, but I have seen no evidence to support that claim.

Kapusta

Due to a significant leg length discrepancy mostly in my femur, I typically run a drive side crank 5mm longer than non-drive on bikes that I put a lot of time on.

To be honest, when I go between a bike that has the different length cranks and one that does not, I don’t notice it, unless they are both 175, which is getting too long for my shorter leg. But in my case the mechanics on each side are always a little different for me.

At one point when building a bike for my wife (with normal legs), I inadvertently used a crankset with two different lengths (one of my sets). She did quite a few rides before I realized what I did but she never noticed.

I seriously doubt most people would detect 2.5mm.

However, just because you don’t notice an imbalance does not mean it is not affecting you long term.

noimagination

My experience:

I went from 172.5 mm to 175 mm cranks (so the circle my feet (nominally) made went from 1084 mm to 1100 mm, or an increase of approx. 1.5%).

The difference was not perceptible to me, but it was measurable. With the longer crank my cadence was lower in a similar gear and level of effort than with the smaller crank. This is easily explained: my feet were moving as fast as they had been with the smaller crank, but since the circle was larger the number of full revolutions per unit time was lower.

That's the only measurable I noticed, I did not attempt to quantify the difference in cadence, nor did I attempt to determine what effect this had on speed (flat/climbing) or any other parameter (heart rate, power [I don't have a power meter], etc.). Nor did I feel any difference: I did not feel the larger range of motion that my knees, ankles or hips may have been experiencing, I did not feel that my saddle was too high. I did not feel that I had more leverage with the longer cranks. Etc.

Basically, I was cycling along on the new longer crank and looked down to see that my cadence was lower than I expected.

Kapusta

Shorter cranks have been getting more common on MTBs recently.

It started as a way to help with pedal strikes as BBs got lower, and this was accompanied by much wailing and gnashing of teeth. But then what most people found was that once they adjusted it worked just fine, and some prefer it.

Kapusta

Canfield makes MTB cranksets ranging in length from 150-170mm in 5mm increments.

easyupbug 

When osteoarthritis came to town in hip and knee my previous riding with all 172.5 and 175 changed after lots of trials to 165.

Yan 

SRAM also goes down to 160mm, but only in Apex and Rival. Force and Red stop at 165mm. I'm guessing they sell way less volume of the higher end groups so they couldn't justify the tooling cost on a niche within a niche.

SharpByCoop 

I am 5'6" and have 30" length pant size.I modified a pair of 175mm arms to 155mm with drills and taps.

It was VERY positive and kept me flowing in a circle.

I stopped hopping on my seat.

My Zwift results indicated about a 5w gain right away.

Totally a fan.

Turnin_Wrenches

Kudos to you for the DIY crank modification . Going from 175mm to 155mm is a big change all at once, but at 5'6" with a 30" inseam those 175mm cranks were way too long. I'm also 5'6" with a 29.5" inseam and have been on 160mm cranks for about 3 years. They're awesome! . I think people are gradually becoming aware of the benefits of shorter cranks.

PeteHski

I know they all offer a choice of different crank lengths, but I haven’t seen any marketing gimmick in relation to shorter cranks. Shimano doesn’t care what crank length you choose.

Breadfan

I went from 170 to 160 because my knees were killing me from old injuries. Big difference. The worst problem is finding 160's. Shimano only makes them in 105 and up so going the cheap route was not an option for me, I had a set of Tiagra 170's. However, the 105's are lighter which is nice.

MarcusT

Google 'shorter crank arms'
Dozens of articles even one from Shimano
I like to read

SharpByCoop 

ISO 9/16" x 20tpi LH and RH thread taps are available on Amazon for about $15. A drill press and way to keep or clamp them PERFECTLY true is paramount. Mine had a wide flat for the original bore and that was my index.

The 175's had a LOT of extra room. Each MFG crank arm is different, yet this took advantage of a SPARE Shimano 175mm set I had (way too big for me) and it worked like a champ.

This is 155mm length.