Choosing a 170mm or 175mm crankset ?



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D

D T W .../\\...

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My little brain can't remember.

What are the advantages? Why would I choose one over the other?

I'm 5'9", 165lbs, with a 32" inseam. Do mostly xc riding.

--
DTW .../\.../\.../\...

I've spent most of my money on mountain biking and windsurfing.
The rest I've just wasted.
 
A

Anonymous

Guest
"D T W .../\..." <[email protected]> wrote in message
news:[email protected]...
> My little brain can't remember.
>
> What are the advantages? Why would I choose one over the other?
>
> I'm 5'9", 165lbs, with a 32" inseam. Do mostly xc riding.
>
> --
> DTW .../\.../\.../\...
>
> I've spent most of my money on mountain biking and windsurfing. The rest I've just wasted.
>
The 170s make you 5mm less likely to smack your crankarms/pedals on rocks and roots.
 
C

Cliff Holloway

Guest
I'm 6'4" and I use 180mm cranks on my Cannondale to make use of my 36" inseam, this lets me use the
proper stroke for my longer legs (more torque) of course I have to watch my rock clearance a bit
more. By the way I often use a 11.5m on my Bic Formula Board on those light days <grin>...

"D T W .../\..." <[email protected]> wrote in message
news:[email protected]...
> My little brain can't remember.
>
> What are the advantages? Why would I choose one over the other?
>
> I'm 5'9", 165lbs, with a 32" inseam. Do mostly xc riding.
>
> --
> DTW .../\.../\.../\...
>
> I've spent most of my money on mountain biking and windsurfing. The rest I've just wasted.
 
Z

Zeeexsixare

Guest
> Torque = force x radius

That doesn't mean a shorty like me could effectively use 180mm cranks.

--
Phil, Squid-in-Training
 
M

Mark Hickey

Guest
"D T W .../\\..." <[email protected]> wrote:

>My little brain can't remember.
>
>What are the advantages? Why would I choose one over the other?
>
>I'm 5'9", 165lbs, with a 32" inseam. Do mostly xc riding.

I'd recommend a 175mm crank for you, but I would also suggest not losing any sleep over the
decision. After all, we're talking about something less than a whopping 3% difference - something
that many riders wouldn't feel, and that would make very little difference to your riding.

The 175mm cranks would give you a little more leverage for getting up the tough stuff and the 170's
would give you a little smoother spin. To keep the comparison exact, you'd have to compare turning
the 170's 3% faster to produce the same output - essentially going from a 32 tooth cog to a 33.

Remember that the 3% difference covers a range of human size that varies by more than 25%, and not
many complain about their cranks not fitting.

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
T

Tom Purvis

Guest
> "D T W .../\..." <[email protected]> wrote:
> > My little brain can't remember.
> >
> > What are the advantages? Why would I choose one over the other?
> >
> > I'm 5'9", 165lbs, with a 32" inseam. Do mostly xc riding.
> >
> The 170s make you 5mm less likely to smack your crankarms/pedals on rocks and roots.

The other key reason to use shorter cranks is that they let you spin a higher cadance. Are you a
spinner or a masher?

At your leg size, it would be fairly appropriate to go to a shorter crank, especially if:

-you generally choose low gears and sit and spin when climbing -riding clean through rock gardens is
a big deal for you

As far as the torque losses to using a shorter crank arm are concerned, I wouldn't lose too much
sleep about that. I bought a second-hand bike last Fall, and it is now temporarily my main ride.
Little did I know, it came with 172.5mm crank arms. I'm 6'1" with a 35-36" inseam. These cranks are
short for me, and I'm a bit more of a masher than a spinner these days. But I can ride the bike. And
I can climb steeps. The bike has a *really* low bottom bracket, so the shorther cranks are surely on
it to improve pedal clearance. But I smash pedals on every rock within 3 feet of the trail anyway.

So I'm doing an experiment. I'll ride this temp bike for another month or so, then I'll get the
replacement and put my 175 cranks on it. I'm curious about whether I'll be able to feel anything in
terms of pedaling power by going back to my normal crank length.
--
Tom Purvis - http://www.arkansasvalley.net/tpurvis/
Salida, CO
 
Z

Zilla

Guest
ZeeExSixAre wrote:
>> Torque = force x radius

This is science!

>
> That doesn't mean a shorty like me could effectively use 180mm cranks.

This is applied science! :)

--
- Zilla Cary, NC (Remove XSPAM)
 
R

Ryan Cousineau

Guest
In article <m9e7101rq0vkum6i6hbba29cb5jlo[email protected]>,
Mark Hickey <[email protected]> wrote:

> "D T W .../\\..." <[email protected]> wrote:
>
> >My little brain can't remember.
> >
> >What are the advantages? Why would I choose one over the other?
> >
> >I'm 5'9", 165lbs, with a 32" inseam. Do mostly xc riding.
>
> I'd recommend a 175mm crank for you, but I would also suggest not losing any sleep over the
> decision. After all, we're talking about something less than a whopping 3% difference - something
> that many riders wouldn't feel, and that would make very little difference to your riding.
>
> The 175mm cranks would give you a little more leverage for getting up the tough stuff and the
> 170's would give you a little smoother spin. To keep the comparison exact, you'd have to compare
> turning the 170's 3% faster to produce the same output - essentially going from a 32 tooth cog
> to a 33.
>
> Remember that the 3% difference covers a range of human size that varies by more than 25%, and not
> many complain about their cranks not fitting.

It seems that mountain bikers are way less picky about crank lengths than road riders: roadies can
generally find cranks from 165-175mm in 2.5mm increments (though the majority are 170 or 172.5).
Almost all the mountain cranks I see are 175mm.

Moreover, "leverage" seems to be a false god. You can get the same leverage with a smaller
crank by lowering your gearing (thus requiring the same amount of torque at the pedal to move
the bike forward).

Furthermore, shorter cranks have two minor advantages and one huge advantage for most MTBers: the
minor advantages are that they can be made slightly stronger and lighter, and the major advantage is
better obstacle clearance.

I ride 165mm on my road bikes (5'6", 156 lbs.) and I'm looking for shorter cranks for my good old
94mm BCD rings, as it has 175mm on there now. This is completely rideable, but I hit things with my
pedals too often and I think my pedalling would be more comfortable with smaller cranks.

--
Ryan Cousineau, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club
 
B

Bbense+Alt Moun

Guest
-----BEGIN PGP SIGNED MESSAGE-----

In article <[email protected]>, Ryan Cousineau <[email protected]> wrote:
>
>
>I ride 165mm on my road bikes (5'6", 156 lbs.) and I'm looking for shorter cranks for my good old
>94mm BCD rings, as it has 175mm on there now. This is completely rideable, but I hit things with my
>pedals too often and I think my pedalling would be more comfortable with smaller cranks.
>

_ Try Ebay, I found a pair of 165mm deore XT's with the 5 arm spider.

_ Booker C. Bense

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M

Mark Hickey

Guest
Ryan Cousineau <[email protected]> wrote:

> Mark Hickey <[email protected]> wrote:

>> Remember that the 3% difference covers a range of human size that varies by more than 25%, and
>> not many complain about their cranks not fitting.
>
>It seems that mountain bikers are way less picky about crank lengths than road riders: roadies can
>generally find cranks from 165-175mm in 2.5mm increments (though the majority are 170 or 172.5).
>Almost all the mountain cranks I see are 175mm.

Isn't THAT the truth! I sometimes ride my wife's bike with it's 170mm crank (a Suntour XC Pro
gruppo), and really don't notice the difference. If anything it's easier to climb since it has a 20
tooth granny.

But I CAN feel the difference between a 170 on my tandem and the 172.5 on my road bikes. It's not a
big thing, and I don't worry about it... but when you're spinning real circles on smooth roads it's
more of an issue than when you're bouncing over rock gardens.

>Moreover, "leverage" seems to be a false god. You can get the same leverage with a smaller crank by
>lowering your gearing (thus requiring the same amount of torque at the pedal to move the bike
>forward).

Exactomundo.

>Furthermore, shorter cranks have two minor advantages and one huge advantage for most MTBers: the
>minor advantages are that they can be made slightly stronger and lighter, and the major advantage
>is better obstacle clearance.

They've done studies on biomechanical efficiency and found that there's basically a HUGE range where
the crank length doesn't really make a real difference. I think it's just what you're used to. If
the S-monster only built cranks in 150, 152.5 and 155, I'm sure we'd be having the same discussion
about the 150 vs 155.

>I ride 165mm on my road bikes (5'6", 156 lbs.) and I'm looking for shorter cranks for my good old
>94mm BCD rings, as it has 175mm on there now. This is completely rideable, but I hit things with my
>pedals too often and I think my pedalling would be more comfortable with smaller cranks.

The XT and XTR cranks do come in 165mm (as well as 180), but of course they're set up for 64/104mm
rings. I'm not aware of any 58/94mm crank that comes in 165mm length.

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
 
B

Bbense+Alt Moun

Guest
-----BEGIN PGP SIGNED MESSAGE-----

In article <[email protected]>, Mark Hickey <[email protected]> wrote:
>Ryan Cousineau <[email protected]> wrote:
>
>>I ride 165mm on my road bikes (5'6", 156 lbs.) and I'm looking for shorter cranks for my good old
>>94mm BCD rings, as it has 175mm on there now. This is completely rideable, but I hit things with
>>my pedals too often and I think my pedalling would be more comfortable with smaller cranks.
>
>The XT and XTR cranks do come in 165mm (as well as 180), but of course they're set up for 64/104mm
>rings. I'm not aware of any 58/94mm crank that comes in 165mm length.
>

_ What about this?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=%203655749121

_ I don't think 64/104 comes in 5 arm does it? Plus you can get custom spiders for the newer XT
crank, I've only seen them for
75/110 though. You might look for old RaceFace cranks as well.

_ Besides you both missed the biggest advantage of shorter cranks.

Your thighs don't whack your beer belly.

_ Booker C. Bense

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S

Slacker

Guest
> _ Besides you both missed the biggest advantage of shorter cranks.
>
> Your thighs don't whack your beer belly.
>
> _ Booker C. Bense

lol I like that :) less whacking is good!

--
Slacker
 
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