Globe199

Hi

I want to replace the stock crankset on my 2011 Trek 3700. It currently has a Shimano 42/34/24 (I think; need to verify) with 170mm crank arms. My old bike (1996 GT) has 175mm crank arms and I feel like I have much so more power with that, like I can take off a lot faster. It feels more like an "adult bike" if that makes sense. So the pedals trace a 10mm larger circle, but it just doesn't seem like that alone could make for the huge difference that I notice.

Today I learned that there are at least three different chain rings that can work on my Trek. I need to count the teeth on the GT's crank, but I'm wondering if the difference I notice between the two bikes is a combination of a longer crank arm and a smaller (i.e., fewer teeth) chain ring. I was told that smaller chain rings allow for faster take-off. Is that correct?

So among these three possible chain rings,

22/32/42
24/34/42
28/38/48

combined with longer crank arms, which is going to give me a more power? My biking consists of 99.9% commuting on relatively flat city streets about 3.5 miles each way.

Thanks so much for any info.

hueyhoolihan

start with googling "gear inches" or search Sheldon Brown's site for gear inches.

onespeedbiker

The feeling of power is hard to quantify so I doubt any comparison of gear inches is going to be helpful; better to consider how you ride. Power comes from the engine (you), not gearing. The difference you feel between a 170mm and 175mm crank is a difference in leverage; all things being equal to achieve the same speed, you will be able to push a bigger gear with a 175mm but your RPM will be slower. However, it may be easier for you to push a bigger gear at a higher RPM (then that that would would be achieved at a constant speed) , than spinning a smaller gear at an even higher RPM. If you rarely use the inner 24t ring with the bigger rear cogs, then it would make sense to go to 28/38/48; while the 28t inner chainring will give up some low end bail out gearing, the bigger large chainring you will be able to pedal faster without spinning out.

cny-bikeman

If the 175 feels better to you then get 175, especially if you have long legs (inseam 34+ inches). As noted power is in you, not the bike, and certainly not in gearing. In 3.5 miles you will barely be warmed up anyway.

Globe199

Thank you for the replies. Maybe my question should have been: which setup will give me more efficiency? I am not a tall person (only about 5'7") but the 175mm bike feels more efficient. I'm almost always in the middle gear on the front, so i guess it's a matter of 32 vs 38 teeth, as 34 teeth with 175mm arms is apparently not available for my bike. (Or at least the phone rep wasn't sure.)

So which of 32 or 38 will seem faster or more efficient? Thanks again.

cny-bikeman

Onespeedbiker gave about as complete an answer as one could expect in a forum post. 175 would be particularly long for your leg length. There is no way to tell what will be more efficient for you, as that is a combination of the bike, your body and your riding style - but here is some info on crank length and efficiency: https://www.cobbcycling.com/articles/...ng-full-circle. You can Google crank length efficiency and research for yourself if you want a more complete answer. As I said before, if it feels better to you then go with it.

AnkleWork

Pretty sure you are confused about the concepts of power and efficiency. None of the variables mentioned materially affect either power or efficiency.

Globe199

Again, I appreciate the replies, but I'm now more confused than I was before. I read the article that cny-bikeman posted. It's interesting, thanks.

I'm going to count the teeth on the GT and see how it compares to the Trek. The problem is that evidently I can't change only the crankarm length, because the same chainring configuration I have now is not available in 175mm, only 170. So no matter what I'll be changing two things, and I'm trying to figure out which direction to go. All I want is the same feel my old bike allows, and not to feel like I'm riding a kids bike.

I agree that it seems like 175mm would be long for my height, but that was the OEM part on my old 18-inch mountain bike frame. Someone at GT thought it was the way to go.

does anyone else know? Is this part compatible with my bike (which is considered a 7-speed)?

Sugino Crankset | Sugino MX34 Black/Silver 42/34/24t 175mm Square Tapered

Nevermind, I found a Shimano TX M171 that is available in 175mm 42/34/24. I'm guessing it's a slightly better product than the Sugino anyway.