Dbl to Trpl conversion: crank length

[Pau11y]

I'm curious on this one, would you go longer or shorter when converting to a triple from a double? I mean crank arm length is dictated by your leg length. But when you goto a triple, your rpm (in theroy) can speed up which means a shorter length will get you the same amount of torque from the increased rpms. But, you typically goto a triple to make climbing walls easier which a longer crank arm will also help. Gimme some logic behind this madness... :mumble:

[LordOpie]

I think crank length is totally independent of gears.

But if you are going to new cranks, then might as well explore the issue. That said, I've heard the best way is to measure your femur, but hell if I know how to do that.

If you've put good miles on your current length, then it's safe to stay with 'em. I tested bikes last week that had 175s and had no issue eventho I've been on 170s, so I asked about it and was told that it can take a while before issues show up.

Sorry, no advice, just a warning to not take a chance on something different without knowing for certain that it's okay. And if you do go with different length, you'll have to change your saddle height to compensate.

[Wumpus]

http://www.sheldonbrown.com/gain.html

http://www.velonews.com/tech/report/articles/5257.0.html

http://www.nettally.com/palmk/crankset.html

Rode a friends 177.5 some years back. I didn't notice any difference at all over 175. They were identical bikes accept for that. It was mostly a flat ride, though.


Mountain bike(but crank related)
I have 190s on my XC HT running a 1x9 setup, dropped down to 177.5 for awhile and didn't like it all.

Put the 190s on the FS but didn't like it and went to a 175 and a granny to be able to spin the climbs seated. Much better.


Note: 6'3" w/ a 37" inseam

[Pau11y]

Had 180mm on a FSR Enduro Pro w/ 24/34/46 and 11-34. But, I bottomed the cranks on rock too often so I decided to go w/ a set of 175 w/ 22/32/44. So far, no rides yet as we're still hip deep in snow and the fork needs an oil change. With road, I have a set of 175mm and a set of 172.5mm. I did notice a slight advantage w/ the longer ones in extended climbs which makes sense. What I'm thinking is in extended climbs, I go back to mtb form w/ high torque and low rpm. In this situation, the longer will be more effective. But this kills the spin; the longer the arms the more likely you're to bounce when the rpms gets to 100 or higher. My observations.

Edit: wow, following the idea of femor length in inches = crank length in mm, I come out at 190mm!

[Pau11y]

Oh hey Lord Opie, I've figured out the compact thing. My Profile carbons come w/ removable spider. I can just bolt on one of those old XTR 4 to 5 bolt conversions from Hershey and I'll have the right bolt pattern for the 50/34 or 36 w/ 110 BCD. Won't need to go triple after all :D

[LordOpie]

awesome!

[Pau11y]

LO: What compact rings do you run, specifically the teeth count? I'm thinking of the 50/34 or 48/34. You know this area so I'm thinking you might have some good insights.

[LordOpie]

I have a triple -- 30-42-52.

If I ran a compact, it'd start with a 30 and go as big as possible (46?).

If you're in decent fitness condition and have good knees, just go with a standard compact 34-50.

Serial Midget has ridden these mountains, but he's in great shape, so he'd probably tell you to go with a standard double 39-52 :D

[JRB]

I have 34-50 now, with no mountains. I did mountains on 39-53 in December and it killed me. :dead:

[Pau11y]

I have a triple -- 30-42-52.

If I ran a compact, it'd start with a 30 and go as big as possible (46?).

If you're in decent fitness condition and have good knees, just go with a standard compact 34-50.

Serial Midget has ridden these mountains, but he's in great shape, so he'd probably tell you to go with a standard double 39-52 :D

I've ridden 39/52 and 12-25 up Rabbit Ears (twice) and DAMN OUCH! 34/50 it is then, thanx.

[LordOpie]

I have 34-50 now, with no mountains. I did mountains on 39-53 in December and it killed me. :dead:
dude, you need to come out here this season. We'll take you to some great pavement. Yes yes, bring your mtb too. Pick a time window and I'll find an organized century that we can all do.

My place is only 700sq.ft, but you're welcome to crash in my place.

I've ridden 39/52 and 12-25 up Rabbit Ears (twice) and...
I'm impressed. I assume that was from the west (Steamboat side)? Isn't that steep?

[Pau11y]

I assume that was from the west (Steamboat side)? Isn't that steep?

Yeah, average of about 5% or so, but starts at something like 7500, and goes to hi 9s in 7 or so miles. Friggin' painful!

[Serial Midget]

I have a triple -- 30-42-52.

If I ran a compact, it'd start with a 30 and go as big as possible (46?).

If you're in decent fitness condition and have good knees, just go with a standard compact 34-50.

Serial Midget has ridden these mountains, but he's in great shape, so he'd probably tell you to go with a standard double 39-52 :D

Back in the day... early 80s anyway. :cool: We would have two sets of wheels and/or coggs (no cassettes yets) with chains specific to the road grades we would ride. My two 6 cog freewheels where something like 14/26 and 12/21 with 53/41 rings. With friction shifting we didn't worry too much about short or long cages - I don't even know if there were such things back then anyway.

I couldn't do it now because of the altitude and my current fitness level but back when I was 20 and 145 LBS we rode the front range all the time. The wind seemed to be more of an issue... add 20 years and 20 pounds and I'm sure I would be suffering.

I still wouldn't run a triple... only girlie-men do that. :D

[JRB]

dude, you need to come out here this season. We'll take you to some great pavement. Yes yes, bring your mtb too. Pick a time window and I'll find an organized century that we can all do.

My place is only 700sq.ft, but you're welcome to crash in my place.


I'm impressed. I assume that was from the west (Steamboat side)? Isn't that steep?
Certainly an option for late summer if I can get out for a week or so. It's our busy season though.