cyclinggirl

I'm a 5"4 women, riding a 52 Supersix, 53/39 with a 170 crankarm.
This summer we are planning a trip to Oregon, to ride some hills. I am getting a compact 50/34 for the trip, but should I stay with the 170 crank size or switch to a 165. I don't have a high cadence, but do have endurance.

Retro Grouch 

Are you happy with the 170 mm crank length that you have now? If so, what do you hope to gain by changing?

spdntrxi

sounds like cadence is to gain.. and you will slightly. I also think it will not hurt endurance any.

some reading material
crank length importance discussion

cyclinggirl

So, far I've been happy with the 170mm. It's going to be the first time I'll be doing any major hills, and I'm just looking to make it easier on my lungs, I have exercise endured asthma.

Retro Grouch 

170 mm to 165 mm isn't a real big change so I wouldn't worry excessively either way. You might not even notice the difference.

The next time you go out, think about your top knee. If it feels a little uncomfortable or if it seems to want to point outward slightly, you might benefit from the shorter crank. If you're delighted with the way that your top knee feels now, I'd be reluctant to change.

prathmann

My bikes have cranks of 165, 170, and 175mm, and I hardly notice the difference. I agree with the comments above that if you currently feel comfortable with the 170mm cranks then you might as well stick with that length. The main advantage to going with shorter cranks would be if your knees were bothering you as a result of being bent more at the top of the crank rotation when using longer cranks.

gregf83 

A shorter crank would be helpful for getting into a slightly more aero position but that doesn't sound like your goal. It won't make pedaling any easier as you'll need to apply more torque at a given cadence to maintain the same speed. It might help a little if you were racing on the track and needed to use a very high cadence but again that won't be happening going up a hill. I would stay with what you have.

Going to a 165 from a 170 will feel like you shifted up to a slightly higher gear. If you went from a 170 down to a 155 crank length that would be like shifting from a 23 sprocket in the rear to a 21, i.e. you'll be applying more force to maintain your speed at a given cadence or forced to shift down into an easier gear to keep the same force on the pedals.

fietsbob

extra leverage is good .. as is saving the money spent 'fixing' the unbroken..

think about changing chainring sizes .. there you can make a difference ..

now that the cassette companies go to 11 we mortals really dont need great big chainrings

my touring bike has a 50,40,24 triple and i use freewheels that are no smaller than 13t

perhaps a uncommon double , like VO's 46-30 would be fine..

though since a lot of OEM builds are now offering the 50-34 they are selling pretty cheap .
the lowest gear you can use is the 34 though..
so 1:1 with a big rear cog is About, as low as you can go..

MichaelW

OP is 5"4. 170 is a long crank for a rider that size. Are the riders advising to stick with 170 that short?
160/165 would be a better fit. the chanes in leverage/torque will be taken care of by change in choice of gears and cadence.

tcarl

By way of comparison, I have a 31" inseam and find a 170 comfortable for general use. 175 is noticeably too long for me, but in high torque situations like mountain bikes, loaded touring or either steep or long hills they feel good. If your inseam is reasonably close to mine I'd think the 170 might be really good for the hills. Also consider a 167.5 if it's available.

cyclinggirl

I do have a 30 inseam. So I'm mainly all legs with a short torso.

zonatandem

My wife/tandem stoker is 4' - 10 3/4" 'tall' and rides 170 mmm cranks on our tandem.
She has logged over 240,000 miles on 170 mmm cranks and at age 79 has no issues.

tcarl

With a 30 inseam, lower cadence, and finding 170's comfortable so far, I'd be inclined to stay with that length for Oregon.

cyclinggirl

Thank You I will stay with the 170

xenologer

crank length variation not proportional to leg length variation of riders.
insignificant effect on performance

however 165 cranks still desirable for short riders, for alternate reason
reduces toe strike with front wheel, when relatively huge 622 wheel crammed into xs frame
alternatively ride a Terry, geometry and wheel size sensibly designed to correlate rider size

roadandmountain

Height is irrelevant. Leg length (generally measured by inseam or pbh) is what matters.

Either 165 or 170 would be appropriate--it's a matter of personal preference.

5 mm is less than 1/5 of an inch difference. Not exactly worth sweating over.

roadandmountain

You're doing great with 170. No need to go through the hassle and expense of a new crank.

Little Darwin

Generally agree. Not worth changing the crank for a different length unless one of the following is the case:

1) You have real identifiable issues with the current length. Then change it, and don't hesitate.

2) You are planning a different change (gearing etc), and changing the crank length can be affordable or free in conjunction with that change. (I am currently doing this).

fietsbob

Separate out the crank, to say an Origin 8 110 bcd BMX cranks are made from 140 to 175 long

Product Description | Origin8

they are pretty cheap , you can run a DIY experiment.

https://www.origin8.bike/product-desc...model_uid=1008

these are threaded for a triple ..

carpediemracing 

Hills - to go a given speed on a given hill it takes the same amount of power. In other words if you are going up a hill at 6 mph it's 6 mph regardless of crank arm length, cadence, gear. Your power output will be the same if you're going 6 mph in the same conditions, regardless of crank arm length, cadence, gear. It's just that some combinations may feel easier than others. Also, at extremely high or low cadence there is some other stuff because it gets so inefficient if you go too far one way or another.

It's hard to believe that, I never did, but when I got a power meter I realized that was the case. I tried different gears on a particularly steep hill in the area, one that takes me from 6.5 minutes to about 9 minutes to climb. At the bottom I tried going hard or not-as-hard because I wondered if it would make a difference in the second, very hard half of the climb. I found that I'm redlined for most of the climb so it's quicker if I go quicker at the bottom. Then I tried using bigger gears or spinning little gears. My power at the bottom was pretty consistent and I couldn't really tell if one was quicker than the other.

Theoretically a 53x11 and a 39x25 require the same power overall to go 6 mph the 53x11 will feel harder and will have more significant dead spots.

For any kind of sustained effort, i.e. not a sprint, you'll find some happy/tolerable medium in terms of gear/cadence for a given speed. You just have to get the gearing to somewhere within a good range for you, so you're not in a bad-for-you gear.

FWIW I'm a short legged 5'7", with a 29" inseam. I use 175 cranks and I'm primarily a crit racer. Most would have me on shorter cranks. I used to use 167.5s, then 170s. I tried going back to 170s for a year in 2008, another year in 2011, and both times I had poorer than expected results (I also rode both 170 and 175s during 2009 and that didn't work well either). I lacked strength/power and therefore speed. I was hoping to return to my 167.5/170 crank days but couldn't. The only thing I noticed was that I could spin faster with the 170s. However my power didn't change enough that I could notice.

If you're doing long climbs then your gearing will make more of a difference than crank length. After you get the gearing in the right range then the cranks may change the feel a touch but for me that's about it. From 2004-2011 I visited a good friend and his family in SoCal. I'd try to climb Palomar Mountain each time I went out, a climb that takes me (bottom part as well as the proper climb) about 2 hours. 170, 175, didn't matter. 39x23 bottom gear hurt because I went too slow for it, 39x25 was better; the only thing was that I spent more time in the 23 with 175s because I had more leverage. The only thing that changed my time significantly, by something like 15 minutes at minimum, was losing about 35 lbs compared to the year prior.

Whatever equipment you want to change do it as soon as possible so you are fluent with it when you go out west. Enjoy the trip!