Crankarm Lenght

The charts say that I should be using a 170mm crank lenght (5'7", 30"
inseam), however I'm using 172.5mm.
Should I replace the crank for a 170mm?

--
Tony

On Mon, 11 Aug 2008 02:48:06 GMT, Tony wrote:

The charts say that I should be using a 170mm crank lenght (5'7", 30"
inseam), however I'm using 172.5mm.
Should I replace the crank for a 170mm?

Dear Tony,

In crank length threads, posters often admit that they've ridden with
mismatched cranks for months without noticing.

Other posters insist that a tenth of an inch can make a huge
difference.

But if you're riding comfortably with your current cranks, what can
you expect to gain by shortening them a tenth of an inch?

The approval of some chart?

Presumably you like your leg extension as is, since you aren't
complaining about pain.

The change would be that your feet would rise only 340 mm instead of
345 mm from the bottom of the pedal cycle.

That's ~1.5%, a whole fifth of an inch less rise.

Your hip-knee-ankle joints would bend a tiny bit less.

The good news is that a 170 mm crank isn't likely to cause any
problems if you decide to replace your 172.5 mm crank.

Cheers,

Carl Fogel

I looked at the various charts, and they all seem to have different
values. Is there any one reliable chart?

Andy

On Mon, 11 Aug 2008 04:46:44 -0700 (PDT), Andy Evans
wrote:

I looked at the various charts, and they all seem to have different
values. Is there any one reliable chart?

No.

On Aug 11, 5:46*am, Andy Evans wrote:
I looked at the various charts, and they all seem to have different
values. Is there any one reliable chart?

Andy

No. Put three people in a room and ask about crank lengths, get 4
opinions. Subjective mostly with teeny differences in length meaning
little, nothing.

In article
,
Andy Evans wrote:

I looked at the various charts, and they all seem to have different
values. Is there any one reliable chart?

Andy

No.

On Mon, 11 Aug 2008 12:05:33 GMT, John Forrest Tomlinson
wrote:

On Mon, 11 Aug 2008 04:46:44 -0700 (PDT), Andy Evans
wrote:

I looked at the various charts, and they all seem to have different
values. Is there any one reliable chart?

No.

Just for fun, I'm currently experimenting with 140mm cranks as against
the 175mm that I usually use (I'm 6'1", so most of the 'charts' would
probably say I need the 175s) Gear ratio is adjusted to give a
consistent gain ratio on my fixed gear TT bike

So far, the difference is - nothing at all. To within a few seconds, I
do the same time on the same 10 mile TT course with either set up.

The short cranks feel odd when out of the saddle, and I haven't got
used to where the pedal is when clipping in, but at 100rpm on 175s or
125rpm on 140s I'm making the same power at the same HR and either
feels completely natural after only a couple of weeks of using the
140s.

Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary
** Posted from http://www.teranews.com **

On Mon, 11 Aug 2008 04:46:44 -0700 (PDT), Andy Evans
wrote:

I looked at the various charts, and they all seem to have different
values. Is there any one reliable chart?

Andy

Dear Andy,

They tend to recommend longer cranks for longer legs and shorter
cranks for shorter legs, but the underlying details seem to be
borrowed from astrology charts.

Most riders will fall within six inches of 5'10", meaning 5'4" to
6'4".

That's 64 to 76 inches, with the middle at 70 inches.

If leg-length varies roughly like height, then we'd expect to find
legs varying about the same, and therefore cranks varying the same,
which is only about 8% above and below the middle value.

Most cranks are available in a range from only 165 to 180 mm, with
172.5 being a common middle choice. (You can get bigger and smaller,
but darned few charts recommend them and it's hard to find such
cranks.)

The chart below assumes only two things:

1) A 172.5 mm crank is somehow ideal for a normal-leg-length rider who
is 5' 10" high.

2) Leg and crank length should vary proportionally with height.

64/70 = 91.43% 160.0/172.5 = 92.75% 5' 4"
162.5/172.5 = 94.20%
165.0/172.5 = 95.65%
167.5/172.5 = 97.10%
170.0/172.5 = 98.55%
70/70 = 100.00% 172.5/172.5 = 100.00% 5'10" possibly ideal?
175.0/172.5 = 101.45%
177.5/172.5 = 102.90%
180.0/172.5 = 104.35%
182.5/172.5 = 105.80%
185.0/172.5 = 107.25%
70/76 = 108.86% 187.5/172.5 = 108.70% 6' 4"

If the chart is correct, most riders aren't fussy enough.

If the chart is wrong, then something lets short riders use long
cranks that bend their legs more and lets tall riders use short cranks
that bend their legs less.

Or maybe the chart is neither right nor wrong, and most riders just
adapt to the commonly available 170.0, 172.5, and 177.5 mm cranks,
which are probably commonly available because that length happens work
just fine. (And the riders would be quite happy with shorter or longer
cranks, too.)

Cheers,

Carl Fogel

wrote in message
...
On Mon, 11 Aug 2008 02:48:06 GMT, Tony wrote:

The charts say that I should be using a 170mm crank lenght (5'7", 30"
inseam), however I'm using 172.5mm.
Should I replace the crank for a 170mm?

Dear Tony,

In crank length threads, posters often admit that they've ridden with
mismatched cranks for months without noticing.

Other posters insist that a tenth of an inch can make a huge
difference.

But if you're riding comfortably with your current cranks, what can
you expect to gain by shortening them a tenth of an inch?

The approval of some chart?

Presumably you like your leg extension as is, since you aren't
complaining about pain.

The change would be that your feet would rise only 340 mm instead of
345 mm from the bottom of the pedal cycle.

That's ~1.5%, a whole fifth of an inch less rise.

Your hip-knee-ankle joints would bend a tiny bit less.

The good news is that a 170 mm crank isn't likely to cause any
problems if you decide to replace your 172.5 mm crank.

Cheers,

Carl Fogel

Carl,

The "Princess and the pea" effect:

http://childhoodreading.com/Edmund_D...d_the_Pea.html

Many people have one leg longer than the other and most go through life
totally unaware of the condition.

Chas.

On Sun, 10 Aug 2008 23:50:59 -0400, wrote:

On Mon, 11 Aug 2008 02:48:06 GMT, Tony wrote:

The charts say that I should be using a 170mm crank lenght (5'7", 30"
inseam), however I'm using 172.5mm.
Should I replace the crank for a 170mm?

Dear Tony,

In crank length threads, posters often admit that they've ridden with
mismatched cranks for months without noticing.

Other posters insist that a tenth of an inch can make a huge
difference.

But if you're riding comfortably with your current cranks, what can
you expect to gain by shortening them a tenth of an inch?

The approval of some chart?

Presumably you like your leg extension as is, since you aren't
complaining about pain.

The change would be that your feet would rise only 340 mm instead of
345 mm from the bottom of the pedal cycle.

That's ~1.5%, a whole fifth of an inch less rise.

Your hip-knee-ankle joints would bend a tiny bit less.

The good news is that a 170 mm crank isn't likely to cause any
problems if you decide to replace your 172.5 mm crank.

Cheers,

Carl Fogel

Thanks Carl (and everyone who responded). I've put 4k miles over the past
2 years with the 172.5mm cranks and didn't give it a thought until I saw
"the chart". Since I'm comfortable with the 172.5's I'll "leave well
enough alone"

--
Tony