Educate me re longer crank length please

[Fiertetimestwo]

I am looking for a Campagnolo UT compact crank (for a mountainous ride- the Audax Alpine Classic- coming up later in the southern summer) in 172.5 arm length, which is what I am used to. I am about 179 cm tall.

I thought I had found one (in the UK) but have been told they are out of stock of the 172.5's, but that they do have one in 175 mm arm length.

Will the difference between 172.5 and 175 help or hinder my climbing? Or should I stick with what I am used to and just keep looking?

[Louis]

I am about 179 cm tall.

= 5' 10.5"

I'm 6' tall and years ago found that going from 172.5 to 175 helped on rolling hills. It felt easier to maintain cadence and "get over the top" of small hills while staying in the same gear, compared to before, when I may have been more likely to shift. I have no idea if they made me any faster.

Unless the cost is an issue, I'd try the 175's and see what happens.

[jtakeda]

I've heard that longer crank arm lengths are better for climbing.

Not sure.

[EricEstlund]

The difference is less then the thickness of an Australian dollar coin.

While there are ideals, there is also some wiggle room in your fit. Different shoe soles or cleat interfaces will have a more noticeable influence on crank feel, all of which will be less then the impact of the gearing change to a compact ring set up.

[Louis]

The difference is less then the thickness of an Australian dollar coin.

It may be my imagination, but I'm pretty sure I felt an improvement.

[EricEstlund]

I'm not saying you didn't, just that it's a relatively small variable, and compared to not running compact gearing for a climbing trip, it's a fairly small difference.

[rustychisel]

I doubt you'd notice a difference*

As you know, I ride 167mm [fixed], 170mm [fixed], 170mm geared and 172.5mm geared.

*caveat says if you exceed the comfortable leg extension allowed by the extra 5mm radii you'll feel it in the hamstrings mostly

[carpediemracing]

I've been bouncing around crank lengths for a bit. I was on 167.5s for forever, like 1985? to 1997 or so. I went to 170s when my 167.5s were all worn out.

In 2003, after going faster on my mountain bike (2" knobbies, blown suspension fork, 175 cranks) than my road bike (Campy 9s?, FiR rims, 700x23 clinchers, 170 cranks), I bought 175 cranks for the road bike. I ended up going way faster in one of my test spots, 4 weeks after a dismal test on 170s. Although there were way too many variables, the 33% improvement in speed told me that something somewhere helped me at least a little (I'm saying that you will NOT get a 33% improvement in speed by going 5mm longer, I'm just saying that the difference was so big that at least part of it had to be the cranks, since it was the only thing I changed on the bike, other than the saddle going down 5mm).

Since then I was on 175s for all but 2008 (got an SRM with 170s) and this year (thought that 170s would improve my sprint speed).

In 2010, on 175s, I upgraded to Cat 2. Not a big deal for some but for me, having raced as a 3 for 25 years (and a 4 for a few years before that), it was a huge deal to have finally qualified to upgrade. All my places were in field sprints.

The kicker is that I have very short legs - I rode a 52 Cannondale, size S Giant, and currently my saddle height is 66 cm to the center of BB. My inseam is in the 29" range, and my quads are short.

My power curve starts high and drops off dramatically. My peak power is okay, in the 1400-1550w range, but my FTP is 210-220w. I rely on short bursts of power to adjust my speed when on a wheel, i.e. a hard downstroke to tighten up a tiny gap. I think the longer cranks work well with my power profile, my pedaling style (I tend to spin but I will push also).

When doing power climbs, standing, big gear (53x15-14-13), the 175s are great. When doing long climbs (1-2 hours long) it makes no difference for me, I'm suffering no matter what. Steep climbs, standing, 39x25, 40-50 rpm, no difference. The shorter cranks seem to help on climbs where I can sit and spin and where the climb is too long for me to climb out of the saddle in a huge gear.

Crank length is really individual. They tailor your usable power/cadence curve a bit - you can adjust how that curve looks. In general longer cranks will let you do more standing power climbs, reduce your high speed spin. As someone that doesn't train that much, does crits, the long cranks work better for me most of the time.

My friends who are much taller than me, ride 60-63 cm frames, they run 180s and love them. One had, at one point, led out and beaten two 7-Up pros, one of them a sprinter. The other was my leadout man. They still make a point of getting 180s, and they've tried 175s in the interim.

Finally Leonard Zinn had an interesting test using some pivoting pedal mount. The effect was to alter the crank length as the crank turned. He tested against a shorter crank (equal to the shorter length) and a longer crank (not quite as long as the long reach of the weird pivot mount). He very casually says that the short cranks reduced his power, as expected, and the long cranks were better. I forget what the weird pivots did but I think it improved his power even more. What struck me is how casually he stated that the shorter cranks reduced his power output.

[bewheels]

Geeking out with Zinn...

http://velonews.competitor.com/2003/11/bikes-and-tech/technical-qa-with-lennard-zinn-a-question-of-crank-length_5257

http://velonews.competitor.com/2011/06/bikes-and-tech/technical-faq/technical-faq-with-lennard-zinn-when-it-come-to-crankarm-length-no-easy-answers_178528