Crank Arm Length

turkeytickler said:

Hi there

I would appreciate some advice about crank arm length. Im currently using 172.5 cranks, simply
because I got a good deal on them at the time but would like to establish the correct length for
my size and style of riding. I am 5'11 and of pretty normal proportions, and generally ride for
leisure, on the sunday morning club run and the occasional TT.

What is the effect of using longer/shorter cranks. I am riding the etape this year so would like
to get a good mountain ready setup (trying to avoid the expense of going triple).

Any advice gratefully received.

Cranks should be half your thigh length. Try measuring it accurately, though!

turkeytickler said:

Hi there

I would appreciate some advice about crank arm length. Im currently using 172.5 cranks, simply
because I got a good deal on them at the time but would like to establish the correct length for
my size and style of riding. I am 5'11 and of pretty normal proportions, and generally ride for
leisure, on the sunday morning club run and the occasional TT.

What is the effect of using longer/shorter cranks. I am riding the etape this year so would like
to get a good mountain ready setup (trying to avoid the expense of going triple).

Any advice gratefully received.

Thanks

Chris

This is an interesting question, maybe try rec.bicycles.tech for an answer, they seem to love
debates on topics such as this. FWIW I have three bikes that I use regularly, until last summer two
had 172.5 mm cranks, one 170. I am 6'2" tall with long limbs. In preparation for the Raid Pyrenean I
fitted a cheap triple to one bike making it also a 170 mm one. I trained for the first half of the
year on this and got used to it. When I arrived in France I found that my chainset had been damaged
in flight so I got a new (used) one fitted at a LBS in St Girons, it is a 172.5 mm one and once into
the hills of the Pyrenees I felt no difference ! What does that tell us ? I have no idea !

turkeytickler <[email hidden]> wrote:

: What is the effect of using longer/shorter cranks. I am riding the etape this year so would like
: to get a good mountain ready setup (trying to avoid the expense of going triple).

Depends how long you legs are rather than your height. 172.5 would be pretty typical for someone you
height. I'm 6' 1" and have very long legs and ride 175mm (which I found a noticable improvement on
the 170s I had before).

For the etape, my advice would be to get a triple though. If you haven't ridden in the mountains
before you can't understand what it's like. There are no rides in this country that are that hard.
Then remember that you'll be doing the hardest climbs on the route after 100 miles.......

YOu *might* be ok with somelike a compact double 34/50 and a 13-26 cassette (I'm considering this
for La Marmotte) but you are going to have to sacrifice either your top gear (best plan I think) or
have jumps in the cassette (bad plan when you are knackered after 130 miles)

You can convert to a triple reasonable cheaply. It might involve putting on lower quality components
that you usually do, but that seems fair enough to me.

I did the Etape in 2001 (Aspin -> Tourmlet -> Liz Ardien) on 39/53 13-26 and was *way* *way*
overgeared on the last climb when I was tired. I would have got a silver medal with a triple (I
wasn't far outside the time and having to stop to let my legs recover from the effort of riding at
5.5mph on 39x26 wasted lots of time on the final ascent).

The one certainty in all this is that changing your crank length is not a suffient substute for low
gears. Crank length is a small change (esp 2.5 mm which is what you are looking at) and is not going
to suddenly ride up hills any faster.

Arthur

--
Arthur Clune clune.orgclune.orgOpen ↗ "Technolibertarians make a philosophy out of a personality defect"
- Paulina Borsook

On Sun, 11 Jan 2004 12:09:54 -0000, turkeytickler <[email hidden]>

Quoted message said:

Im currently using
172.5 cranks, simply because I got a good deal on them at the time but would like to establish the
correct length for my size and style of riding.

If you are happy with your speed and your knees don't hurt and you can spin when you need to, then
your cranks are the right length :-)

Guy
===
May contain traces of irony. Contents liable to settle after posting.
chapmancentral.demon.co.ukchapmancentral.demon.co.ukOpen ↗

Quoted message said:

Cranks should be half your thigh length. Try measuring it accurately, though!

Outside or inside of thigh (or front/back)? To top or middle of knee joint?

Zog The Undeniable <[email hidden]>typed

Quoted message said:

Cranks should be half your thigh length. Try measuring it accurately, though!

I don't think that's right! My thighs are more than 400mm long I've never had 200mm cranks!

--
Helen D. Vecht: [email hidden] Edgware.

MSeries said:

turkeytickler said:

I would appreciate some advice about crank arm length. Im currently using 172.5 cranks, simply
because I got a good deal on them at the time but would like to establish the correct length for
my size and style of riding. I am 5'11 and of pretty normal proportions, and generally ride for
leisure, on the sunday morning club run and the occasional TT.

Very roughly and generally, 170mm is for average roadies, 175+ is for lankies. You're inbetweenish
so 172.5 is probably fine for you.

Quoted message said:

Quoted message said:

What is the effect of using longer/shorter cranks.

Too long makes spinning more difficult. Too short is inefficient for getting the power down. Too
long or short just may not feel as comfortable to legs and knees, etc. Gearing is altered (longer =
lower) - but only very slightly with the differences we're talking about so it's not an issue to
consider. Cornering clearance is slightly affected as well.

Quoted message said:

This is an interesting question, maybe try rec.bicycles.tech for an answer, they seem to love
debates on topics such as this.

They won't thank you for raising the suject again because it's been done a thousand times already
there. Search via groups.google.comgroups.google.comOpen ↗ . Unfortunately there is no definite answer or evidence
or formular and a lot of people say they don't notice the difference between a few mm. Personally, I
found switching from 170 to 175mm worthwhile.

~PB

Arthur Clune wrote: the etape, my advice would be to get a triple though. If you

Quoted message said:

haven't ridden in the mountains before you can't understand what it's like. There are no rides in
this country that are that hard. Then remember that you'll be doing the hardest climbs on the
route after 100 miles.......

YOu *might* be ok with somelike a compact double 34/50 and a 13-26 cassette (I'm considering this
for La Marmotte) but you are going to have to sacrifice either your top gear (best plan I think)
or have jumps in the cassette (bad plan when you are knackered after 130 miles)

You can convert to a triple reasonable cheaply. It might involve putting on lower quality
components that you usually do, but that seems fair enough to me.

and you can always switch back to your usual set up once you get home and maye even sell the triple
on eBay. I would recommend a triple for real mountains. For years I grunted up Alps and Pyrenees
with 39/53 - 12-27, with
30/39/53 and 13-24 I didn't go up much quicker but was nowhere near as shot when I got to the top !

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

Quoted message said:

I did the Etape in 2001 (Aspin -> Tourmlet -> Liz Ardien) on 39/53 13-26 and was *way* *way*
overgeared on the last climb when I was tired. I would have got a silver medal with a triple (I
wasn't far outside the time and having to stop to let my legs recover from the effort of riding at
5.5mph on 39x26 wasted lots of time on the final ascent).

The one certainty in all this is that changing your crank length is not a suffient substute for
low gears. Crank length is a small change (esp 2.5 mm which is what you are looking at) and is not
going to suddenly ride up hills any faster.

What Arthur said. I thought I would be alright in last year's Etape with a 39/27 bottom gear and
175mm cranks, but I just wasn't up to it. The first half hour or so of mountain ascent was OK but
then it started to hurt. It wasn't so much pain in the legs as a whole body thing. Don't forget the
air is thin up there too. I really thought I was going to pass out and had to walk a few times. I'm
sure I would have had a chance of winding my way up with a triple. Mind you there were people with
triples walking as well. There were people falling heavily when they tried to restart after walking
for a bit; the hill was simply too steep for them to get moving. I had an 85K training route that
included a number of "long" Surrey climbs including Leith Hill and Box Hill, but it didn't prepare
me at all for the Soudet.

--
Dave...

Mark Thompson said:

Quoted message said:

Cranks should be half your thigh length. Try measuring it accurately, though!

Outside or inside of thigh (or front/back)? To top or middle of knee joint?

Precisely!

In article <[email hidden]>, [email hidden] says...

Quoted message said:

Quoted message said:

Cranks should be half your thigh length. Try measuring it accurately,

Quoted message said:

though!

I would appreciate some advice about crank arm length. Im currently

Quoted message said:

using

172.5 cranks, simply because I got a good deal on them at the time but would like to establish the
correct length for my size and style of riding. I am 5'11 and of pretty normal proportions, and
generally ride for leisure, on the sunday morning club run and the occasional TT.

You wouldn't notice any difference going 2.5mm either way. Stick with what you've got, you
won't go wrong.

--
Mark (MSA) 5ft 11", 172.5mm cranks all round.

This post is packaged by intellectual weight, not volume. Some settling of contents may have
occurred during transmission

Quoted message said:

I don't think that's right! My thighs are more than 400mm long

phrwoar

Helen Deborah Vecht said:

Zog The Undeniable <[email hidden]>typed

Quoted message said:

Cranks should be half your thigh length. Try measuring it accurately, though!

I don't think that's right! My thighs are more than 400mm long I've never had 200mm cranks!

If you measure from the middle of your knee to the top of your thigh - not the middle of your hip -
(it's easiest to do this with your knee bent so your thigh is parallel to the ground) the theory is
about right. I think it's one of those meassurements from the 1970s CONI manual.

Helen Deborah Vecht said:

Zog The Undeniable <[email hidden]>typed

Quoted message said:

Cranks should be half your thigh length. Try measuring it accurately, though!

I don't think that's right! My thighs are more than 400mm long I've never had 200mm cranks!

Yup, surely some mistake. Mine are over 500mm and I don't think I'm unusually built.

--
[email hidden] (Simon Brooke) jasmine.org.uk~simonOpen ↗

;; I'll have a proper rant later, when I get the time.

Pete Biggs said:

Very roughly and generally, 170mm is for average roadies, 175+ is for lankies. You're inbetweenish
so 172.5 is probably fine for you.

I ride 185mm cranks. It never did seem logical to me why such minuscule changes are recommended (as
above), after all other aspects of bike fit and size vary so much more with rider size. It seems to
me that it probably has more to do with cost than anything physiologically based.

James

Dave Kahn said:

What Arthur said. I thought I would be alright in last year's Etape with a 39/27 bottom gear and
175mm cranks, but I just wasn't up to it. The first half hour or so of mountain ascent was OK but
then it started to hurt. It wasn't so much pain in the legs as a whole body thing. Don't forget
the air is thin up there too. I really thought I was going to pass out and had to walk a few
times. I'm sure I would have had a chance of winding my way up with a triple. Mind you there were
people with triples walking as well. There were people falling heavily when they tried to restart
after walking for a bit; the hill was simply too steep for them to get moving. I had an 85K
training route that included a number of "long" Surrey climbs including Leith Hill and Box Hill,
but it didn't prepare me at all for the Soudet.

Come off it. Tim Moore just jumped on a bike with no training and rode most of the stages straight
off with panniers on. Your not telling me that he could do what hundreds of experienced cyclists
couldn't surely ;-^)

Tony

In article <[email hidden]>, [email hidden] says...

Quoted message said:

Quoted message said:

Quoted message said:

Cranks should be half your thigh length. Try measuring it accurately, though!

240mm cranks, Octalink compatible.

RSVP

--
Mark (MSA) This post is packaged by intellectual weight, not volume. Some settling of contents may
have occurred during transmission

James Annan said:

Quoted message said:

Very roughly and generally, 170mm is for average roadies, 175+ is for lankies. You're
inbetweenish so 172.5 is probably fine for you.

I ride 185mm cranks. It never did seem logical to me why such minuscule changes are recommended
(as above), after all other aspects of bike fit and size vary so much more with rider size.

The bad logic is concluding that because a limited range is available, small increments can be of no
importance. Other things can vary more: saddle height for example, but you can and do adjust that by
small increments.

Actually no change was recommened above because the OP already has 172.5mm cranks. I personally
wouldn't encourage any uncertain person to change cranks by less than 5mm purely just to get a
different length.

Those familar lengths above are recommended for people in the "normal" size range (although it still
makes some sense to get as short/long as possible if one is outside the available range). Notice the
plus sign above after the "175". 170 is only stated as the starting point for "average" because
shorter cranks are usually hard to find.

In any case, smaller changes are needed with cranks because a smaller section of the body is
affected and in a more subtle way. Bent legs, circles, knee joints, etc, etc. And 2.5mm crank
difference makes 5mm of difference to the pedalling circle, so the changes aren't so miniscule as
first seems. 5mm change to seatpost or saddle is very important, for instance.

There should indeed be more variation in available cranks for those well outside the average, but
like in so many other aspects of life, short or tall people get a raw deal (although with bike
cranks, it seems particularly bad for the shorter end of the spectrum).

Quoted message said:

It seems to me that it probably has more to do with cost than anything physiologically based.

That's correct. It's expensive for manufacturers to make a large number of options so they just
cater for the masses with about-average legs. Nevertheless, just as it's worth getting riding
position right to within milimeters, I am sure there are physiological advantages in optimising
crank length within 2.5 or 5mm despite there not being any clear test evidence to prove it /yet/.
Human comfort and general fatigue is very difficult to measure. Quite frankly, I trust my own
judgement more than any machine with such things.

~PB

Tony Raven <[email hidden]> wrote:

: Come off it. Tim Moore just jumped on a bike with no training and rode most of the stages straight
: off with panniers on. Your not telling me that he could do what hundreds of experienced cyclists
: couldn't surely ;-^)

Bet he didn't try it on 39/26 with panniers though!

Low enough gears make an enormous difference in the mountains - they mean that you can just keep
riding along. If you can keep going long enough you get there in the end.

If your legs are totally seized from riding big gears however, you won't

--
Arthur Clune clune.orgclune.orgOpen ↗ "Technolibertarians make a philosophy out of a personality defect"
- Paulina Borsook