Noctilux.95

I just ordered a Dura Ace 9170 groupset with 165mm crank arms for my Cervelo R5 disk. I'm 170cm tall and all my other road and gravel bikes have 170mm crank arms. To be honest the compact 9100 crank with 170mm arms was out of stock making decision a bit tough for me. I didn't want to go up to the available 172.5 so I decided to roll the dice and try the 165mm. I'm aware the advanatges of using shorter arms for TT/Tri bikes but what about road bikes?

datlas 

It's controversial but any difference of 5mm one way or the other is not highly significant IMO.

I suspect you will be fine with these. If you asked my opinion, I would have suggested 170's but since you have 165 I would ride them as they are.

79pmooney

I ride 175s and was over 6'. (My height's a moving target, steadily down. ) 175s felt right the first time I rode them.

Now. if I scale my cranks to the difference in heights between us, I get 162.5 for your height. That said, ideal crank length varies from person to person and isn't dependent on just height. I don't know the science, but muscle fibers and flexibility certainly add into it.

If you have only ridden 170s, try these 165s. They might be a revelation. (170s are the "preferred" crank length because they work OK for most people and they keep bike design and part stocking simple. If cars didn't have tracks for the front seats, driver's seats would have one standard legroom. Ask yourself if that would be best for you.

Ben

rubiksoval

I ride 165s at 5"11. The biggest benefit is improved positioning (lower front end) that allows for a more open hip angle and pedaling without your knees crushing your ribcage. There's also a slight benefit for tighter cornering (a little more wiggle room for pedaling through turns).

After about 3 seconds you probably won't notice the differences if you don't change your fit too much.

Trsnrtr

I’m 170 cm tall and have used 165s since my Cat 2 days in the ‘80s though I have to admit that whenever I rode a bike with 170s, I couldn’t feel a difference.

MoAlpha

This doesn’t answer the question, but I bought a road bike with 172.5s on it this summer, after using 170s all my life, and now regularly switch back and forth. I notice nothing. I’m about 175 cm.

MidTNBrad

I switch between 175s and 172.5s and don't notice the difference.

RChung

There was a recent podcast on crank length here but the bottom line is that at 170cm in height you're probably fine with 165mm cranks.

znomit

Shorter is lighter and with less drag.

canklecat

I didn't notice much difference between my bikes with 170, 172.5 and 175 cranks until I started getting lower and more aero, including aero bars. I'm 5'11", 150 lbs with about 3-5 lbs of excess baggage around the middle -- not much by most standards but I notice it when I'm in the aero bars on the bike with 172.5 cranks. My thighs bump my gut. So I might swap some stuff around and see if the 170 cranks help. Or it might just be a bike fit issue, since I'm just beginning to get the hang of aero bars. In the drops I don't notice any problems.

Yeah, even when riding upright I think I can feel some differences in crank lengths, but it doesn't seem to show any significant differences over time in my ride data. Sorta like the differences between my road bike with Biopace chainrings and the other with regular chainrings. Sure, I can feel a difference. But it doesn't amount to much in ride data over time.

bpcyclist

Interesting thread. I am 6'1" and 190 lbs, but built long and lean--long arms, long inseam, etc. Have used 172.5s for as long as I can recall, but I may just get some shorter ones and give it a shot. I do think my knees are maybe popping up into my chest a bit when I am riding hard in the drops. Never even thought about it. Great--one more thing I probably need to buy...

u235

No universal advantage to any crank length. It depends more on you. I went down to a 165 for some knee problems and it seemed to help. I really felt the reduced torque from the shorter arms and was shifting a lot more to compensate and became abnormally picky about maintaining a certain cadence. I got used to it after a few rides. Of course all of what I think I felt could have totally been in my mind. Oddly when I switched back to my old 170 cranks for other reasons I noticed no difference. Go figure.

smurfy

165mm feels like peddling a little kid's bike. However I can't seem to tell the difference between 170 and 175 for some reason.

colnago62

the difference is very small. Most of this stuff really only matters when one is racing. Match sprinters are fanatics about position on the bike. For them, a tenth of a second matters. For the casual rider getting home or back to the car a minute sooner doesn’t make a difference.

Maelochs

I am a little over 6 foot and have bikes with 165, 170, and 175. I can't tell much after a couple minutes. I have long legs and prefer 175, but I adapt immediately to whatever I am riding. Even if you are not thrilled with i65s, you will be fine riding them until you can afford a chain set ... but maybe you will love them, or not even much notice.

sdmc530

I have 175 on my daily riding road bike and 172.5 on my "event bike". I have done a ride on both back to back and I can't honestly notice any difference when trying them out either way. 2.5mm just isn't enough. Now if one was 175 and one was 170 or more I can see a noticeable difference but if you only have once size I doubt it will ever have any effect.

I honestly think its a mental deal.

GCN did a video or segment on them and they said it was not scientifically proven to have any effect for most riders.

Carbonfiberboy 

Most folks seem to do best at (crank in mm) = 5.5 * (inseam in inches). That's measured inseam for a bike fitting, not your pants. That said, there's quite a range of acceptable crank lengths and hard to tell the difference in knee wear or power levels between them when one considers all the variable conditions: flat, gentle climbs, steep climbs, gentle descents, etc. Different cranks lengths seem to have different strengths.

bruce19

The radius of the crank is basically a 1st class lever. The longer the lever (radius) the less force required at the pedal. And, the farther the distance to complete a rotation. It's essentially the difference between spinning your 13 cog and spinning your 26 cog given the same crank. This is all theoretical and I suspect 99% of recreational riders will never notice a difference.

cat0020

I change crankarm length according to my flexibility.

In the winter/early spring, I tend to use shorter crankarms, more spin, less mashing the pedals.

During the competitive season, I use longer crankarms, better for a quick jump/acceleration at lower rpm cadence with more leverage.

For more casual riding, I ride 165mm crankarm, pedaling smaller circle reduce stress on the knees.

Metallifan33

After my bike was delivered, I went to a professional bike fitter (I've been hurt way too many times running, that I decided it would be worth my $$ to get started off cycling correctly). The fitter said my knee was too extended at the bottom of the pedal stroke, so he lowered my saddle. When the saddle was lowered, he (and I) noticed that my knees bowed outward at the top of the pedal stroke (this could also be because I have a gut). Anyway, the way he solved this is by changing my crank from 170 to 165. Now the top and bottom of the stroke both feel good to me.... and I have an extra Shimano 105 170 crank if anyone is interested
So I would say there is some merit in changing the crank length to better fit you, but as with many things YMMV.

RiceAWay

It is more relative to leg length and usually taller people have shorter legs for their height. I think that most racers use 172.5 and most of them ride a 54 to 56 cm bike.

Bah Humbug

Shorter cranks give more freedom for fitting to the bike, with very little downside. Over in the tri world 150-155 is common to get very aggressive fits. The odd thing about crank length is the range of common lengths is much smaller than the range of leg length, percentage-wise, so a 165 for a short rider is longer, relatively, than a 175 for a tall rider. And the number of people I’ve seen have issues with it (other than how it affects position) is vanishingly small.