rcapilli

I'm looking at purchasing a Compact Crank. But I am a little unsure what size I should be looking at. A 172.5 or a 175. I want this crank for climbing mountains. I have a 05 Trek Madone 58cm. No upgrades. I stand 6'-0" at 204 with an inseam of 32". I typically ride hilly courses but nothing horrible. My thought is that when I go ride in the mountains I will just switch out my crank and go, but reality tells me that I will switch to the compact crank and just get too lazy to switch back to my standard. I guess my question is, what is the difference between the two lengths and what so you think would be the best for climbing hills?

Grasschopper

I would go with the same size that is currently on your bike be that 172.5 or 175. You may like a shorter or longer crank based on how youlike to ride. My father and I are pretty similar in size, he like a 175 and I prefer the 172.5...we are both about 5'10" and have 31.75" inseams.

Raketmensch

I'm 5'10" and ride a 56-cm Madone in very hilly terrain. My 50-36 compact has 172.5-size cranks and it suits me fine. My guess is that you wouldn't notice a major difference betweent 172.5 and 175. I certainly wouldn't expect either to offer a particular advantage for hill climbing. If you're comfortable with the length you have now then I agree that it's probably best to stick with that.

rcapilli

That's my thought as well. I cannot imagine that there is a world of difference between the two. I am sure there is some, but nothing that is going to give me a big edge. It seems to me that the 172.5 is somewhat typical. For those of you that have compact cranks, do you enjoy them better then the standard?

Grasschopper

I prefer them over a triple but I have never used a std double.

roadfix

Not only do I enjoy them, but like I mentioned in another compact thread, I instantly became King Of The Mountain the moment I switched to a 50/34 from 52/39....

Switching to compacts were an obvious & easy fix for me to somewhat 're-gain' my performance level of ten years ago than to simply(?) lose the 15 lbs of body fat I've gained over those years....

Raketmensch

I prefer a compact to both a standard double and to a triple. I get better climbing performance out of my old-man legs than I do with a standard double, and it's a simpler, lighter-weight rig than a triple. (And yeah, there's also that granny-gear stigma.) The only downside to a compact that I have found is that the difference between the big ring and the small ring is larger, so you end up shifting a bit more. When you shift the front derailleur the jump is big enough that you have to click through a gear or two in the back to get to where you want to be... more often then with a triple or a standard double. But for me, that's been a small price to pay for the other benefits.

merlinextraligh

At 6" with a 32" inseam, a lot of calculators would tell you to go with 175, or even longer. Longer crankarms equal more leverage, but the pedals have to go in a farther circle to maintain the same rpm. Theoretically, a little bit longer crank would give you more leverage for pushing a gear in the hills. It's largely a matter of preference. I'm slightly taller than you, and ride 172.5, mostly because it's easier to pedal through corners in a crit. I'd stay with whatever cranklength you're used to.
By the way, back in the day, 170 was standard issue.

rcapilli

Sounds like everyone enjoys there Compact Cranks. I have never ridden one so I imagine that it will be quite different. A few months ago I tried to climb a Gap here in Georgia. I quickly found out that I was not able to do it. I hope that the Compact Crank will give me a better advantage when I try for it again.

ac29593

I cant wait to make the switch to a compact double. I love the 42T ring on my triple, and think I am going to love the 50T even more. Im going to go with a 13/26 cassette I think, and have the smaller ring be a 36T instead of a 34T. This might be my ideal setup. I have researched it a lot, just havent tested it out yet. I am going to the Boston bike show this weekend too, cant wait.

bbattle

+1

roadfix

Yes, the 42 is a sweet ring to have. I see many recreational and even some serious riders always on the 42, utilizing the entire cassette range, and rarely touching the 53 big ring.

ggg300

get a fitting...

...your compact can be both a 53/39, 50/36 or 50/34 due to the bolt pattern...just get the rings that go with it...

enjoyhttps://www.bikeforums.net/road-cycling/123238-compact-crank-overload.html

UmneyDurak

I think you might be mixing in two issues here.
172.5, 175 is crank arm length. It has nothing to do with compact/standard. It's usually prefernce, and what inseem you have.
There are a bunch of calculators out there, that make recommendations, but I think most people just ride whatever came with their bike. I suggest getting the same lenght as what you have now.
Now Compact vs Regular is another story entirely. That has to do with how many teeth there are on the ring. Compacts usually come in two major flavors 50/34, and 50/36. Regulars usually come with 53/39, 52/39. Used to be 52/42. There are tons of posts discussing advantages of copacts vs Regular. Just to sumrise, with comapct if you have 11 as the smallest cog, your gear ratio slightly better then 53/12 on high end. On low end of gears you are gainning/retaining some gears, depending on what you have as the biggest cog. So climbing gets easier. Frankly speaking even if you put 12/27 on the back to make climbing easier, it won't be that big of a deal on flats. Unless you are a pro I doubt you will be spinning out 53/12 on the flats, so loosing 50/11 shouldn't make a big differnce. On descents it's more about technique imho.

fogrider

the length of the crank has to do with biomechanics. I agree that there is not much difference of between 172.5 and 175, but it might make a big difference in comfort. the question is what is the comfortable range of your leg motion.

rcapilli

To echo on UmneyDurak, I did notice that there is a 50/34 and a 50/36. Right now I have a standard 10 speed cassette, I think thats a 12/25. What do you think would be a better gear ratio for a Compact Crank either the 50/34 or 50/36?

voltman

There's always the custom chainring option.

roadfix

.....or even the not too common 48/34 or 48/36 combos......
You can still acheive a decent high of 117 gear inches running 48-11....

ac29593

48/34 very interesting

Every time I take a peek in a thread I get new ideas lol. Im in the process of bike shopping, Im taking everything into consideration!

kraftwerk 

I am old school: 170 so when I build my new bike I have to consider this whole topic.
But if you have really big/tall pedals it will effect your crank arm leangth, right?