ColonelSanders

I'm hoping to get some input from those of you with a "good engineering mind" about the benefits and drawbacks of switching from a 175mm crank to a 165mm crank.

I'm currently a heavy bastard(i.e. a Clyde) and I was looking for ways to improve my capacity to make it up hills in a more timely fashion.

Is it correct that if a 175mm crank seems comfortable enough for me, that when it comes to improving my ability to ride up hills, that a shorter crank like a 165mm, will be of some benefit here?

As part of my refurbishment of my old bike, I am amongst other things, looking to put a new crankset on and before I do, I thought I should check with the people here what would likely work better for me, out of a 175mm and a 165mm crank.

I'm 6 foot tall, and I don't feel as though the 175mm crank is cramping me up or anything, just looking for a better setup.

If the shorter crank helps with going up hills, does it hold you lose out with a shorter crank on flat ground?




Now for another possible benefit from a shorter crank, besides going up hills easier, what about being able to lower my centre of gravity by 10mm, with going to a shorter crank?

My seating position would be lowered by 10mm, would it not?

Is this an actual benefit that also comes with a shorter crank, or is it not a noticeable benefit to one's ride and their maneuverability?

Ronno6

Hmm, I would have to opine that your assumptions about the shorter cranks are about 180° out of phase.

First, hill climbing.
You would lose mechanical advantage by switching to shorter cranks.
Think of it as a shorter lever to move a load.
The only possible advantage here is if you spin up hills at a rapid cadence, the shorter cranks would facilitate that.
But, again, you lose mechanical advantage.
The above reasoning would also apply on the flats.

Now, as for center of gravity, I would think you would actually have to RAISE your saddle 10mm in order to maintain the same lag extension with the shorter crank.
Think about it: the pedals are closer to the spindle at the bottom of the stroke. Hence, you would need to RAISE your saddle 10mm.

I believe these principles even apply south of the Equator..........

Most crank arm length recommendations are derived from your femur length.
Search around the web for the various formulae........

dabac

Shorter cranks would have you put your saddle HIGHER, not lower.
Not that it matters much.
Which just also seems to be a good summary on the influence of crank lengths in general. While there are elegant theories and formulas about what's good and how to calculate it, there are also tests that seems to show that the riders adapt, and manage to generate very similar amounts of output power regardless. Still, we're not all created equal. I spin better, manage an overall higher cadence on shorter cranks. Which means I need less post-ride painkillers.
OTOH, I'm faster on longer cranks. But frequently in pain.

Bandera

Crank arm length on road bikes is intended to compensate for the rider's leg length.
A person of 5' 3" will turn a comfortable powerful 165mm circle while one of 6' 3" will feel just as at home on a 175mm.

Going shorter gives up leverage for climbing and time trialing but may help develop a higher cadence, as for fixed gear use.
"Back when" a 2.5mm difference for road vs. time trial was all the tuning we did.

Make sure that your position is correct and ride more hills to climb hills better, going to way shorter cranks likely won't help.

-Bandera

Jed19

^Without knowing how long your femurs are vis-a-vis total leg length, I'll almost wager that a 172.5mm is the appropriate crank length for you. I am 5' 10" tall, 34ins cycling inseam, and a 175mm on my road bike was a tad too much for me. I changed to a 172.5mm road crank a long time ago, and it is perfect. I do ride a 175mm crank on my mountain bike however, but that is a bike I rarely ride.

fietsbob

I gained the illusion of a little more setback with the 180 cranks, on one bike with a 'sporty-agressive' geometry..

Shorter cranks wont hit the upside slope side of a Velodrome banked track.

its why they are on Track Bikes ..

ColonelSanders

I'm glad I started this thread.

You are right, I was only thinking about the crank when my knee would be near the top tube of my bike, not below the bottom bracket when as you say, I would need the same lag extension.

Ronno6

In my heyday was 6'6" and had a 36" inseam. the various calculators indicated that I should have been turning 220mm cranks!
They exist, but, as I have a fleet of bicycles, I couldn't afford to modify then all.......So, I never tried that length.
Ground clearance would suffer dramatically as well, but I would bet I could pedal up a wall !!

Bill Kapaun

I run 165's because I have a limited range of motion in one knee. It was a godsend for that purpose.
IF you have no trouble spinning 175's, stick with them.
IF you have other crank lengths that you can experiment with, I suggest you do so for your own gratification. Give them a couple days and make sure to dial in the seat height.
My length/cadence results were- I'm 5-11. (Used to be almost 6'1", but short legged)
175-60
170-80
165-85
160-80>82 and really felt too short.

BTW- Any "loss of leverage" can be compensated for by a slightly lower gear and faster cadence. You will likely end up producing "more power" with the "correct" length.

ColonelSanders

Without any deep thought on this matter, I recall reading on more than one occasion someone on these forums saying that they were going to go to a shorter crank to help with tackling hills, so I just assumed it must be so.

However due to the information in the responses I have received and some articles I have just read, I think I will stick to 175 for now, as that is the only crank length I've known and I can't say I have any evidence it is giving me problems.

Thank you to everyone who replied.

EDIT: Unless curiosity eats away at me and I go for 170mm cranks.

prathmann

My bikes currently have a variety of crank lengths: 175mm (road bike), 170mm (touring and folder), and 165mm (tandem). I really don't notice much of a difference but I do tend to use somewhat lower gears on the tandem with the shorter cranks than on my road bike. As long as you're comfortable with the 175mm I'd be inclined to stick with them. For some people the longer cranks result in their knees being too bent at the top of the stroke - but that doesn't appear to be the case with you (nor with myself).

ThermionicScott 

Go ahead and try it if you're curious, but there's no reason to think shorter cranks would help you climb hills. It's a simple question of leverage.

lostarchitect 

I think it's a function of leg length, but you won't really know until you try. I was used to 170's and figured, what difference could 5mm make? So I tried some 175's and found them really surprisingly uncomfortable. I now mostly use 165's, having come to the realization that I have short legs and the shorter cranks feel much more comfortable.

davidad

One idea and a good article on fit. How to Fit a Bicycle

Bill Kapaun

Something to also keep in mind is your age.
Older people aren't as "bendy".
Over bending the knee may exacerbate any knee problems you have or are going to run in to as you get older.

Scooby Snax

Want to spin up hills easier, get a smaller chainring, or a mega range cassette which would be cheaper than a whole crank.

scott967

I have 170, 172.5 and 175. Not sure I can really tell a difference, at least I can adapt to all of them.

scott s.
.

ColonelSanders

Thanks for your input.

What you and others have said and linked, has made me want to give 170mm a go. 165mm may be too big a leap that I could come to regret.

Gonna give the 170's a go.

Thanks for that article.

I reckon I have comparatively longer shins, than thighs, to most people, so will give 170 a go.

As I am buying a new crank for other reasons, there isn't an extra cost involved for me, but I wanted to explore what might be the best crank size for me, as now is obviously the perfect time to choose it.

Also thank you to other contributors in this thread that I haven't quoted, I still appreciate your feedback, even if I didn't directly acknowledge it.

McBTC

I swapped out 175 cranks for 165s on a 63c endurance road bike I recently purchased. TKA on right knee so amount of a bend is an issue. But, going on 2 years I've been using a trainer with 165 cranks so everything feels fine so far. I did a bit of research in the process and as it turns out, there's very little science backing up what most people think they know about optimum crank length and a lot of new information that encourages experimentation. Fixie riders traditionally have 165 cranks as do track bikers -- safety is an issue for these riders. Tri-athletes who like the idea of not working the hips as much in preparation for the run are talking about going to 165s. For others, some studies show an improvement in watt production using shorter cranks. I'm pretty sure I will benefit by a modest improvement in cadence compared to what I've been accustomed to over past years. Essentially, anything in the 70s is spinning but I'd like getting closer to the 80s and feeling comfortable.

GuitarGangster

I’ve actually heard that going with a shorter crank you end up raising your seat because your foot doesn’t need to go down as far so to get a full leg extension you need to raise the seat.

DiabloScott

What brings you here Mr. Gangster?

choddo

The noble work of resurrecting a 7 year old thread to repeat what was posted in the first reply?

13ollocks

choose your crank length with biomechanics in mind - whatever length is kindest to your knees and hips is the way to go. Any mechanical dis/advantage will be compensated for by the gear selection. The only time crank length becomes an issue when climbing is when you’re crawling up a slope in your lowest gear - the difference between being able to continue on the bike vs walking could come down to how much torque you can put through the cranks - longer cranks have the advantage here

wheelreason

No.

wheelreason

Zombie AI...