Crankset question

gary said:

i need to replace my crankset (Ultegra 6500). it's length is 172.5mm with
53/39 chainrings.

nashbar has a great deal on them but they only have 170mm or 175mm.

would it be better to get the longer one or shorter one?

i'm about 5'7" and my cadence is around 80 if that matters.

if you have a suggestion i would be interested in it along with an
explanation as to why.

thanks!

Dear Gary,

The shorter crank is a tiny bit lighter, gives a tiny bit more
clearance in turns, produces a tiny bit higher overall gearing, and
might be a tiny bit closer to where your legs are on some arbitrary
scale of bicyclist's legs.

175.0/172.5 = 101.45%
172.5/172.5 = 100.00%
170.0/172.5 = 98.55%

You're only going up or down 1.45%.

If you didn't know which crank you bought, it's unlikely that you
could tell whether you'd switched up or down 2.5 mm from your current
172.5 crank--it's only a tenth of an inch.

Supporting this theory are posts from a number of riders who . . .

Er, they accidentally installed mismatched cranks and didn't notice
for quite a while. (Hey, it could happen to anyone.)

Other posters insist that they can tell whether they're wearing
different. (They may, however, be riding unawares on mismatched
cranks--how would they know?)

The biggest normal gearing difference would be for a 53x11 connected
to a 2100 mm rear tire . . .

crank overall
length rear-tire-to-pedal-travel
mm rato
----- ----------
175.0 9.202-to-1
172.5 9.335-to-1
170.0 9.473-to-1

The cadence, of course, remains the same at the same speed, since your
foot just moves once around circles of slightly different diameters.

Prejudice probably plays the biggest role when we worry about whether
we need 170, 172.5, or 175 cranks. I doubt that I can tell the
difference, but I'm damned if I'll order anything except god-fearing
175 mm cranks.

Of course, I've never measured how long they actually are . . .

Cheers,

Carl Fogel

gary said:

i need to replace my crankset (Ultegra 6500). it's length is 172.5mm with
53/39 chainrings.

nashbar has a great deal on them but they only have 170mm or 175mm.

would it be better to get the longer one or shorter one?

i'm about 5'7" and my cadence is around 80 if that matters.

if you have a suggestion i would be interested in it along with an
explanation as to why.

thanks!

If you made the change to either, would you raise or lower your saddle 2.5 mm to compensate??

"gary" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

i need to replace my crankset (Ultegra 6500). it's length is 172.5mm with
53/39 chainrings.

nashbar has a great deal on them but they only have 170mm or 175mm.

would it be better to get the longer one or shorter one?

i'm about 5'7" and my cadence is around 80 if that matters.

if you have a suggestion i would be interested in it along with an
explanation as to why.

thanks!

(172.5-170) / 172.5 = 1.4%
Do you think anyone can feel that difference?

Get out a ruler and look at how small 2.5 mm is compared to your thighs,
lower legs, feet, shoes, cleat position etc. Assuming that the soles of
your shoes are rigid as most road shoe soles are, moving you cleats fore or
after 2.5 mm will have the same effect as changing the crank arm length.

BobT

gary said:

i need to replace my crankset (Ultegra 6500). it's length is 172.5mm with
53/39 chainrings.

nashbar has a great deal on them but they only have 170mm or 175mm.

would it be better to get the longer one or shorter one?

i'm about 5'7" and my cadence is around 80 if that matters.

if you have a suggestion i would be interested in it along with an
explanation as to why.

thanks!

If you're only 5'7", unless your legs are disproportionately long, you
should probably go with the 170s. My husband is 5'10", with long legs/
short upper body and he recently saw a physical therapist/bike fitter/
cycling coach who said that for his leg length he should be with 170
rather than 172.5. He made the switch and LOVES the 170s! He never
had a problem with the 172.5s that he was aware of, but the shorter
170s seem to help him spin more and make his legs less tired on longer
rides. Ditto for my friend who recently switched down, as well.

Jenn

gary said:

i need to replace my crankset (Ultegra 6500). it's length is 172.5mm with
53/39 chainrings.
nashbar has a great deal on them but they only have 170mm or 175mm.
would it be better to get the longer one or shorter one?
i'm about 5'7" and my cadence is around 80 if that matters.
if you have a suggestion i would be interested in it along with an
explanation as to why.

Although some riders prefer one or the other, there isn't much objective
difference. It's a spoke's thickness. I ride 167.5 primarily but also
165 & 170 and can't feel a difference. Others swear by 175, 180.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

gary said:

i need to replace my crankset (Ultegra 6500). it's length is 172.5mm with
53/39 chainrings.

nashbar has a great deal on them but they only have 170mm or 175mm.

would it be better to get the longer one or shorter one?

i'm about 5'7" and my cadence is around 80 if that matters.

if you have a suggestion i would be interested in it along with an
explanation as to why.

thanks!

I have 2 bikes with 170s, 2 with 175s, and 1 with 172.5. I would not
be able to tell the difference if you put a gun to my head.

And FWIW, one of those bikes had a 170 left and a 175 right from 1985
to 1988 and I never noticed.

"gary" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

i need to replace my crankset (Ultegra 6500). it's length is 172.5mm with
53/39 chainrings.

nashbar has a great deal on them but they only have 170mm or 175mm.

would it be better to get the longer one or shorter one?

i'm about 5'7" and my cadence is around 80 if that matters.

if you have a suggestion i would be interested in it along with an
explanation as to why.

thanks!

thanks to everyone who replied. i agree that 2.5mm would most likely not be
noticed
by an average cyclist. i just wanted to make sure that the 2.5mm would not
be noticeable,
sort of a sanity check.

i ended up going with the 170mm.

thanks!

the question given original equipment is does the stock bike fit you
and if not which direction to go when modifying. you spin and are
short so the 170mm could be positive. I'm too large and from Nbar
bought a deore 172.5 up from 170. I wuz asked why not the 175's? well,
caws I use ply caps over the pedals furmuhbigfeet, enjoy pedaling thru
corners.
RBT scuttlebutt before foot was 2.5 is a big deal and it is - the 2.5
helps spinning faster with more power over the top. Counterintuitive
but that's it.
I'll bet you find another 15 rpm with more knee durability from a
flowing over the top knee movement and less straight down crushing
meniscus movement.
Breaking the knee in slowly is a good idea as a new size produces new
over the bone ligament tendon paths.

Hank Wirtz said:

And FWIW, one of those bikes had a 170 left and a 175 right from 1985
to 1988 and I never noticed.

Riding around in circles should have tipped you off (although not over).

<eg>

A Muzi said:

Although some riders prefer one or the other, there isn't much objective
difference. It's a spoke's thickness. I ride 167.5 primarily but also
165 & 170 and can't feel a difference. Others swear by 175, 180.

I used to think that I couldn't distinguish between cranks that were
only 5mm different from each other-- and maybe I can't. The
differences are subtle without a doubt. But lately I have been
regularly riding bikes with 170, 185, 190, and 205mm cranks. I now
think I can feel the difference between 185 and 190, though I don't
have a clear preference one way or the other.

When I spend a few days riding the 170mm cranks and then switch to the
205mm cranks, or vice versa, it feels wrong. Either way it just feels
really weird/not-good for a mile or two. Then I get the hang of it,
and by the time one ride is up, it's back to feeling like a regular
bike again.

I have a passenger sidecar with 165mm cranks, and it just feels weird
all the time. I don't think it's the cranks.

Chalo

On Sat, 22 Sep 2007 05:37:10 +0000, Chalo wrote:

<snip>

Quoted message said:

I have a passenger sidecar with 165mm cranks, and it just feels weird
all the time. I don't think it's the cranks.

You can't make a comment like that and not supply a picture.

On Sat, 22 Sep 2007 01:54:29 -0500, Gary Young <[email hidden]>

Quoted message said:

On Sat, 22 Sep 2007 05:37:10 +0000, Chalo wrote:

<snip>

Quoted message said:

I have a passenger sidecar with 165mm cranks, and it just feels weird
all the time. I don't think it's the cranks.

You can't make a comment like that and not supply a picture.

Dear Gary,

http://chalo.org/

Cheers,

Carl Fogel

gary said:

i need to replace my crankset (Ultegra 6500). it's length is 172.5mm with
53/39 chainrings.

nashbar has a great deal on them but they only have 170mm or 175mm.

would it be better to get the longer one or shorter one?

i'm about 5'7" and my cadence is around 80 if that matters.

if you have a suggestion i would be interested in it along with an
explanation as to why.

thanks!

I'd say 170s but wht ya gotta replace the crank??

"thejen12" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

If you're only 5'7", unless your legs are disproportionately long, you
should probably go with the 170s. My husband is 5'10", with long legs/
short upper body and he recently saw a physical therapist/bike fitter/
cycling coach who said that for his leg length he should be with 170
rather than 172.5. He made the switch and LOVES the 170s! He never
had a problem with the 172.5s that he was aware of, but the shorter
170s seem to help him spin more and make his legs less tired on longer
rides. Ditto for my friend who recently switched down, as well.

Jenn

If you believe this, try this experiment: change his crank arms back to the
172.5's and see if he notices and report back.

BobT

"Chalo" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

A Muzi said:

Although some riders prefer one or the other, there isn't much objective
difference. It's a spoke's thickness. I ride 167.5 primarily but also
165 & 170 and can't feel a difference. Others swear by 175, 180.

I used to think that I couldn't distinguish between cranks that were
only 5mm different from each other-- and maybe I can't. The
differences are subtle without a doubt. But lately I have been
regularly riding bikes with 170, 185, 190, and 205mm cranks. I now
think I can feel the difference between 185 and 190, though I don't
have a clear preference one way or the other.

When I spend a few days riding the 170mm cranks and then switch to the
205mm cranks, or vice versa, it feels wrong. Either way it just feels
really weird/not-good for a mile or two. Then I get the hang of it,
and by the time one ride is up, it's back to feeling like a regular
bike again.

I have a passenger sidecar with 165mm cranks, and it just feels weird
all the time. I don't think it's the cranks.

Chalo

Feeling the difference between 170 and 190 or 170 and 205 I can believe.
These are different by a magnitude on the order of ten times that of the
difference between 170 and 172.5.

BobT

BobT said:

Chalo said:

A Muzi said:

Although some riders prefer one or the other, there isn't much objective
difference. It's a spoke's thickness. I ride 167.5 primarily but also
165 & 170 and can't feel a difference. Others swear by 175, 180.

I used to think that I couldn't distinguish between cranks that were
only 5mm different from each other-- and maybe I can't. The
differences are subtle without a doubt. But lately I have been
regularly riding bikes with 170, 185, 190, and 205mm cranks. I now
think I can feel the difference between 185 and 190, though I don't
have a clear preference one way or the other.

When I spend a few days riding the 170mm cranks and then switch to the
205mm cranks, or vice versa, it feels wrong. Either way it just feels
really weird/not-good for a mile or two. Then I get the hang of it,
and by the time one ride is up, it's back to feeling like a regular
bike again.

I have a passenger sidecar with 165mm cranks, and it just feels weird
all the time. I don't think it's the cranks.

Feeling the difference between 170 and 190 or 170 and 205 I can believe.
These are different by a magnitude on the order of ten times that of the
difference between 170 and 172.5.

I think you missed my point, which was that even in that context, I
now think I can feel the difference between 185mm and 190mm cranks.

Chalo

Chalo said:

I used to think that I couldn't distinguish between cranks that were
only 5mm different from each other-- and maybe I can't. The
differences are subtle without a doubt. But lately I have been
regularly riding bikes with 170, 185, 190, and 205mm cranks. I now
think I can feel the difference between 185 and 190, though I don't
have a clear preference one way or the other.

I too have a whole range of sizes on various bikes, but I believe I
can discern the difference. As for preference, I find than my 175's
don't feel right, but 165's feel great as do 195's. Strange.

Joseph

Well, it's actually an extra 85 meters per hour for each 2.5mm
difference with a cadence of 90 rpms that your legs have to travel in
a circle. It all adds up! :-)

Of course you could slow down your cadence to 89 to make up for it....

BobT said:

(172.5-170) / 172.5 = 1.4%
Do you think anyone can feel that difference?

Get out a ruler and look at how small 2.5 mm is compared to your thighs,
lower legs, feet, shoes, cleat position etc. Assuming that the soles of
your shoes are rigid as most road shoe soles are, moving you cleats fore or
after 2.5 mm will have the same effect as changing the crank arm length.

BobT

"Hank Wirtz" wrote: (clip) I would not be able to tell the difference if
you put a gun to my head (clip)
^^^^^^^^^^^^^^^
Neither would I. I'd be way too nervous.