Advice for new crankset

[Gabster]

I am putting a new groupset on order tommorrow and need help determining the optimum crankarm length. I am having trouble deciding between 172.5 and 175.0. Here is some more data to consider:

I am 35YO/6 feet tall/190 lbs/in decent physical condition.
I have a 34.25 inch cycling inseam.
I am an aggressive rider but not really a racer (unless you count hard club rides)
I split my time evenly between group and solo rides.
I sometimes mash big gears but have in recent years developed an average cadence of about 95-100 rpm.
I am currently using 172.5 cranks

I understand the advantages/disadvantages for having longer/shorter crankarms, but am concerned that having longer crankarm length will significantly lower my average cadence, and unsure how much leverage/power would be gained.

Which length should I buy?

I appreciate in advance any inputs that would help me make a better buying decision.

 

[benkoostra]

I'm about the same size as you, and I use 170's. I've thought about trying bigger cranks too, but what I have works well, so why switch?

You may have already done this, but go have a fitting by someone knowledgable. That will tell you a lot more than you can learn on an internet forum for this problem.
Your seat height is very important for spinning; more so than crank arm length in my experience. A fitting will help with that.

What is the problem you're having with 172.5?

 

[capwater]

Go measure 2.5 mms and when you stop laughing you'll have your answer. Got a couple of bikes with 175s, 5 with 172.5s. For the life of me I can't tell the difference.

 

[Gabster]

That was precisely the feedback I was hoping to hear. Wasn't sure if it would adversely effect my ability to spin at high cadence.

 

[Gabster]

No problem with 172.5. I am just trying to optimize performance/efficiency and I don't have any experience with 175's.

 

[alienator]

My inseam is about an inch longer than yours, and I use 175's. When I moved to 175's from 172.'s, my cadence didn't change, but I did feel a bit more comfortable. It was a subtle difference.

 

[Gabster]

I have spent considerable time researching the subject matter online. Probably much more than it warrants. Here is what I have learned:
1. From www.rollanet.org I found this: "In general, if your inseam is less than 29 inches, use 165-mm crankarms; 29-32 inches, 170 mm; 33-34 inches, 172.5; and more than 34
inches, 175 mm." I also found the same information in a chart on sonicchicken.net for setting up a touring bike.
2. USCF Bike Fit instructions determine crankarm length using riders height as follows: "This distance is generally dictated by the following rule: A rider
with a body height of 175 cm uses a 170 mm crank length. Each 5 cm of body
height makes a difference of 2.5 mm in crank length. For example, rider of
180mm height may use a 172.5 crank length. A rider of 170 cm height may use
a 167.5 mm crank length." (www2.bsn.de/Cycling/articles/uscf-bikefit.txt)
3. Colorado Cyclists determines crankarm length based on size of frame with most frames south of 61cm using 172.5cm cranks.
4. One scientific study used different crank lengths and measured the power output of several subjects under lab conditions. It showed that different crank lengths provided better Maximum Peak power, maximum mean power output; and minimum power output and graphed the results. Leonard Zinn disputed the results saying that the test was flawed in many ways and had a test of his own. (I'lll dig up the references if you are interested)
5. Finally, from www.racersready.com/science_and_technology.htm, "The results of the study demonstrated that crank arm length did affect economy and that optimal crank length does vary from one individual to another. However, no relationship was found between each subject's optimal crank length and his leg length. Thus, it does not appear that optimal crank arm length can be determined by a rider's leg length."

What I really wanted to know was how my cadence would be affected in the real world if I went to a slightly longer crank, and I think I got my answer in this and another forum. Thanks Alienator, capwater, Toyota, rruff and everyone else for your inputs.