crank arm length

[Lee]

I built a new bike two years ago, and since my previous bike had 170mm crank arms, I put a set of
170mm arms on my new bike.

Seems everyone else is now riding longer crank arms, I'm thinking about trying out a set of 172.5
crank arms.

I'm a relatively short rider with a moderately short inseam. Good leg strength, just moved up to Cat
4, mostly criterium racing. I spend most of my time on the big chain wheel (again, due to old
habits, I'm riding a 42-52).

Will I see any benefit with a longer crank arm? Will the difference in leverage be noticeable? Any
drawbacks?

Thanks!

Lee

 

[Mike S.]

"Lee" <[email protected]> wrote in message news:[email protected]...
> I built a new bike two years ago, and since my previous bike had 170mm
crank
> arms, I put a set of 170mm arms on my new bike.
>
> Seems everyone else is now riding longer crank arms, I'm thinking about trying out a set of 172.5
> crank arms.
>
> I'm a relatively short rider with a moderately short inseam. Good leg strength, just moved up to
> Cat 4, mostly criterium racing. I spend most of my time on the big chain wheel (again, due to old
> habits, I'm riding a 42-52).
>
> Will I see any benefit with a longer crank arm? Will the difference in leverage be noticeable? Any
> drawbacks?
>
> Thanks!
>
> Lee
>
>
Go do a google search of bicycle crank length. There's going to be enough information to either a.
answer your question, or b. confuse the hell out of you.

Damon Rinard (?) did an article that I found very interesting, but I can't find it right now.
Basically, it told me that according to his theory, my "ideal" crank length is 167.8mm (based on my
30" inseam) My track cranks are 165s, and my road cranks are 170s. More spin at the track, more
leverage on the road for when the road tilts upwards (@#$%$ hills!).

My recommendation is that if you're gonna race crits, keep using the shorter cranks. More cornering
clearance and a faster spin out of the corners is going to help more than the higher
leverage/slower spin.

Next pundit?

Mike

 

[Crystal]

Just because "everyone else is now riding longer crank arms..." doesn't mean that you should too! Do
some research to get your answer or better yet, click on this link... the research is already done
for you...

http://www.airborne.net/eready/janette/store/sizing_step3.asp

Crystal

"Lee" <[email protected]> wrote in message news:[email protected]...
> I built a new bike two years ago, and since my previous bike had 170mm
crank
> arms, I put a set of 170mm arms on my new bike.
>
> Seems everyone else is now riding longer crank arms, I'm thinking about trying out a set of 172.5
> crank arms.
>
> I'm a relatively short rider with a moderately short inseam. Good leg strength, just moved up to
> Cat 4, mostly criterium racing. I spend most of my time on the big chain wheel (again, due to old
> habits, I'm riding a 42-52).
>
> Will I see any benefit with a longer crank arm? Will the difference in leverage be noticeable? Any
> drawbacks?
>
> Thanks!
>
> Lee

 

[Sheldon Brown]

Lee wrote:

> I built a new bike two years ago, and since my previous bike had 170mm crank arms, I put a set of
> 170mm arms on my new bike.

Good move.

> Seems everyone else is now riding longer crank arms, I'm thinking about trying out a set of 172.5
> crank arms.

Save your money.

> I'm a relatively short rider with a moderately short inseam. Good leg strength, just moved up to
> Cat 4, mostly criterium racing. I spend most of my time on the big chain wheel (again, due to old
> habits, I'm riding a 42-52).
>
> Will I see any benefit with a longer crank arm?

No.

> Will the difference in leverage be noticeable?

Probably not. It will be equivalent to replacing your 52 chainring with a 51.

> Any drawbacks?

Yes. Possible knee injury (though such a small difference is unlikely to cause problems) Possible
pedal clearance issues, could be an issue especially for crits.

See my article on this http://sheldonbrown.com/cranks

Sheldon "Spend Your Money On Something Worthwhile Instead" Brown
+-------------------------------------------------+
| To stay young requires unceasing cultivation | of the ability to unlearn old falsehoods. |
| --Robert A. Heinlein |
+-------------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

 

[Andy Coggan]

"Lee" <[email protected]> wrote in message news:[email protected]...
> I built a new bike two years ago, and since my previous bike had 170mm
crank
> arms, I put a set of 170mm arms on my new bike.
>
> Seems everyone else is now riding longer crank arms, I'm thinking about trying out a set of 172.5
> crank arms.
>
> I'm a relatively short rider with a moderately short inseam. Good leg strength, just moved up to
> Cat 4, mostly criterium racing. I spend most of my time on the big chain wheel (again, due to old
> habits, I'm riding a 42-52).
>
> Will I see any benefit with a longer crank arm?

Not in terms of performance.

> Will the difference in leverage be noticeable?

I seriously doubt you'd be able to feel the difference in mechanical advantage...after all, can you
feel a small difference in wheel diameter and hence gear ratio when you go from your fat training
tires to your skinny racing tires? (It's the same thing.) However, I wouldn't be surprised if you
could tell that your feet were moving in bigger circles/that your joints were now covering a greater
range of motion...many people can detect a 2.5 mm difference in crank length (esp. if compared back
to back), and most can detect 5 mm (at least if they think about it).

> Any drawbacks?

Yeah: 2.5 mm less ground clearance, and 2.5-5 mm higher pedal location (and thus greater hip
flexion) when the pedal is at the top of the stroke.

Andy Coggan

 

[Andy Coggan]

"Crystal" <[email protected]> wrote in message news:[email protected]...
> Just because "everyone else is now riding longer crank arms..." doesn't
mean
> that you should too! Do some research to get your answer or better yet, click on this link... the
> research is already done for you...
>
> http://www.airborne.net/eready/janette/store/sizing_step3.asp

I didn't find anything that would pass for research at the link you provided.

Andy Coggan

 

[Squid-In-Traini]

> > Any drawbacks?

Original poster, I'm 5'5" (dunno inseam) and I switched from 175 to 170 and I loved the 170 so much
better. My legs weren't being wound all around and about while pedaling and it "fit" me.

I'm betting that you'll do better with your 170s.

--
Phil, Squid-in-Training

 

[Mike S.]

"Phil, Squid-in-Training" <[email protected]> wrote in message
news:[email protected]...
> > > Any drawbacks?
>
> Original poster, I'm 5'5" (dunno inseam) and I switched from 175 to 170
and
> I loved the 170 so much better. My legs weren't being wound all around
and
> about while pedaling and it "fit" me.
>
> I'm betting that you'll do better with your 170s.
>
..or 167.5s...

Mike

> --
> Phil, Squid-in-Training

 

[Peter]

> Will I see any benefit with a longer crank arm? Will the difference in leverage be noticeable? Any
> drawbacks?
>
> Thanks!
>
> Lee
I'm an old rider with dodgey knees and normally use 170 length cranks. Put longer cranks on a bike
when I changed to using larger rings, for mechanical advantage. Increased frequency and extent of
pain, so after research on net suggested I needed shorter cranks with my 29" long legs, I switched
to 165 length. Easier ride, no pain, no loss of power. peter

 

[Tom Paterson]

>From: "peter"

>I'm an old rider with dodgey knees and normally use 170 length cranks. Put longer cranks on a bike
>when I changed to using larger rings, for mechanical advantage. Increased frequency and extent of
>pain, so after research on net suggested I needed shorter cranks with my 29" long legs, I switched
>to 165 length. Easier ride, no pain, no loss of power.

Similar approx. experience, inseam length, xlent results with switch to 165's, have had them on over
a year now, not going back.

"Power production" less important than happy knees, esp. in the dotage. Stay short, be happy.
--Tom Paterson

 

[Sheldon K. Smit]

I am just under 5'8" and grew up riding 170 length cranks since I was a Junior 25 years ago. This
year I got a new Specialized S-Works bike that came stock with 172.5 cranks.

The first thing that I noticed was the improved leverage, but I had to slide my seat farther back on
the rails in order to keep my knees happy. Subsequently, I also had to ride a 1cm shorter stem than
what I would ride normally to accommodate for the seat being farther back.

With longer cranks, I could not have the seat as forward as I did with 170's. Insofar as being able
to spin, no problems, I just slide forward on the seat.

Rode a couple of training crits with the longer cranks and did not have any problems (other than
speed issues related to my age/fitness <grin>)

-Sheldon

[email protected] (SprintAtBettyRussells) wrote in message
news:<[email protected]>...
> "Lee" <[email protected]> wrote in message news:<[email protected]>...
> > Will I see any benefit with a longer crank arm? Will the difference in leverage be noticeable?
> > Any drawbacks?
>
> Drawbacks would be less clearance. I ride 170s on the road and I have a short inseam--I wouldn't
> consider changing. I use 172.5 on the TT bike...I can tell the lengths are different, but no real
> improvement one way or another.

 

[Andrew Bradley]

Sheldon:

> I am just under 5'8" and grew up riding 170 length cranks since I was a Junior 25 years ago. This
> year I got a new Specialized S-Works bike that came stock with 172.5 cranks.
>
> The first thing that I noticed was the improved leverage, but I had to slide my seat farther back
> on the rails in order to keep my knees happy. Subsequently, I also had to ride a 1cm shorter stem
> than what I would ride normally to accommodate for the seat being farther back.

Backward is a strange way to go, sacriledgeous even. Moving up a full 2cm in crank length has me
nudging the saddle slightly forward.

If you feel comfortable that way then fine, it's just hard to understand why you would. How much
farther back did you slide your saddle for such a small crank length change?

> With longer cranks, I could not have the seat as forward as I did with 170's. Insofar as being
> able to spin, no problems, I just slide forward on the seat.

That's cheating, sliding forward on the saddle defeats the object of spin.

Andrew Bradley

 

[Sheldon K. Smit]

Well, I think the issue in my situation (but I am no biomechanics expert) is getting the pedals
through top-dead-center (tdc) at the top of the pedal stroke, and bottom-dead-center(bdc)at the
bottom of the stroke in high torque situations such as hill climbing as well as pedaling style. I
dont spin fast, never did, never will, but I can spin fast enough for maintaining speed in crits.

With the seat farther back, one can get the pedal over TDC and BDC easier, as it utilizes thigh
muscles and hamstrings better (while sitting down climbing). Again, in high torque situations such
as hill climbing or gear mashing, but not necessarily in situations such as higher RPM spinning
where I find myself sliding forward on the seat for those situations.

With longer cranks, I found myself having to slide the seat back in order to get the pedals over TDC
and BDC without my knees saying something. Sure, I can move the seat forward like I see triathalon
bikes, but in my mind, that defeats the leverage advantage of longer cranks.

FWIW, I dont think moving the seat back is "sacriledgeous" as I primarily sit while climbing and
time trialing and turn relatively slow RPM's. On steep long climbs (excess of 12%), standing is not
an option as the rear wheel lifts, so one has to sit so that they are evenly balanced between the
front and rear wheels and grind it out. A seat farther back helps accomplish this along with long
cranks. When Davis Phinney first raced pro in Europe with 7-Eleven, one of the first things he was
told was to move his seat back. In looking at pictures of Eddy Merckx climbing, he is pretty far
back in the seat.

That has been my experience but I dont preach it as gospel.

-Sheldon

[email protected] (Andrew Bradley) wrote in message
news:<[email protected]>...
> Sheldon:
>
> > I am just under 5'8" and grew up riding 170 length cranks since I was a Junior 25 years ago.
> > This year I got a new Specialized S-Works bike that came stock with 172.5 cranks.
> >
> > The first thing that I noticed was the improved leverage, but I had to slide my seat farther
> > back on the rails in order to keep my knees happy. Subsequently, I also had to ride a 1cm
> > shorter stem than what I would ride normally to accommodate for the seat being farther back.
>
>
> Backward is a strange way to go, sacriledgeous even. Moving up a full 2cm in crank length has me
> nudging the saddle slightly forward.
>
> If you feel comfortable that way then fine, it's just hard to understand why you would. How much
> farther back did you slide your saddle for such a small crank length change?
>
>
> > With longer cranks, I could not have the seat as forward as I did with 170's. Insofar as being
> > able to spin, no problems, I just slide forward on the seat.
>
> That's cheating, sliding forward on the saddle defeats the object of spin.
>
> Andrew Bradley

 

[Andrew Bradley]

Sheldon:

> Well, I think the issue in my situation (but I am no biomechanics expert) is getting the pedals
> through top-dead-center (tdc) at the top of the pedal stroke, and bottom-dead-center(bdc)at the
> bottom of the stroke in high torque situations such as hill climbing as well as pedaling style.

I don't really follow your biomechanics but a 1cm change in stem length (and presumably seat
position) for 2.5 on the cranks doesn't seem in proportion.

> I dont spin fast, never did, never will, but I can
> spin fast enough for maintaining speed in crits.

Fortunately there are no primes awarded for fast spinning cranks only fast spinning wheels. Don't
worry about spin in absolute terms. It could be that your legs are on the short side which will
handicap you in the RPM stakes on your 172.5.. I'm no sprinter, but I can spin a standard crank
pretty fast 'cos I'm tall. That is of no advantage to me whatsoever in a crit and I've been beaten
many times by midgets on massive gears.

> With the seat farther back, one can get the pedal over TDC and BDC

Mine go over just fine in any seat position.

> With longer cranks, I found myself having to slide the seat back in order to get the pedals over
> TDC and BDC without my knees saying something.

Did you raise your saddle, because sliding back in the seat can be a sign it is too low.

> Sure, I can move the seat forward like I see triathalon bikes, but in my mind, that defeats the
> leverage advantage of longer cranks.

Long cranks don't offer any leverage advantage.

> FWIW, I dont think moving the seat back is "sacriledgeous" as I primarily sit while climbing and
> time trialing and turn relatively slow RPM's.

It is sacriledgeous because KOPs dictates that you move the saddle forward for longer cranks. And
95% of bike fitters and coaches worship this rule (though none of them can explain it)

> On steep long climbs (excess of 12%), standing is not an option as the rear wheel lifts

What sort of a bike are you riding?

> so one has to sit so that they are evenly balanced between the front and rear wheels and grind it
> out. A seat farther back helps accomplish this along with long cranks.

This balance is not normally a big issue on the road, but if it were you would want to move the
saddle forward not back.

>When Davis Phinney first raced pro in Europe with 7-Eleven, one of the first things he was told was
>to move his seat back.

They'll tell you all sorts in Europe.

>In looking at pictures of Eddy Merckx climbing, he is pretty far back in the seat.

Look at some of the great specialist climbers and you'll see fast climbing can be done in other
positions too. And when you are climbing your saddle moves back anyway.

Andrew Bradley