Crank length, gear ratios, and cadence

Hi Everyone,

I bought a new road bike this year and switched from 180mm cranks to
175mm. I did this because 180's are hard to find and the bike was
complete and I figured I was going to try to change my style from the
Ullrich school to the Armstrong school.

I had been using 177.5mm for years and had switched to the 180's sort
of recently. I was never in good enough shape when I was using 180's to
really be able to compare my performance to anything.

The other day I took the old bike (180's) out of mothballs and took it
out on a club ride because my new 175mm bike was broken. Besides the
downtube friction shifters and all that strangeness the bike felt
pretty good. But I noticed I was using much heavier gears than I
usually use. I was using the 53x13 and 14 a lot while I usually don't
go higher than 53x15 on the flat with the new 175 bike. I had no
problems keeping up and it felt pretty good.

So the question is, what size is optimal for me? In the old days I
calculated using the method in Greg LeMond's book that I need 177.5's.
I am interested in a discussion that takes into account various factors
such as foot length, shin length, body type, etc. I have long feet
(size 50 euro, 15 US), and longish shins. How does this affect things?

And how does crank length and chosen gear relate to cadence? When I'm
suffering up a hill, spinning a little faster that what feels normal
causes serious burn, while going with a bigger gear doesn't as much.
But with a bigger gear I can suddenly be in way over my head in a world
of hurt. Should I try to change my cadence preference to a set rate, or
should I try to find my body's optimal cadence? How do I do this?

Thanks!

Joseph

wrote:

I bought a new road bike this year and switched from 180mm cranks to
175mm...

I had been using 177.5mm for years and had switched to the 180's sort
of recently. I was never in good enough shape when I was using 180's to
really be able to compare my performance to anything.

The other day I took the old bike (180's) out of mothballs and took it
out on a club ride because my new 175mm bike was broken. Besides the
downtube friction shifters and all that strangeness the bike felt
pretty good. But I noticed I was using much heavier gears than I
usually use. I was using the 53x13 and 14 a lot while I usually don't
go higher than 53x15 on the flat with the new 175 bike. I had no
problems keeping up and it felt pretty good.

So the question is, what size is optimal for me?

It really isn't all that critical. Most cyclists can adapt to a fairly
wide range of crank lengths. The only limiting factor I've found is
that long cranks sometimes cause knee problems.

See: http://sheldonbrown.com/cranks for more.

And how does crank length and chosen gear relate to cadence?

See: http://sheldonbrown.com/gain

Sheldon "Long Legs, Short Cranks" Brown
+--------------------------------------------------------+
| As far as the laws of mathematics refer to reality, |
| they are not certain; and as far as they are certain, |
| they do not refer to reality. --Albert Einstein |
+--------------------------------------------------------+
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

Try Zinn's sight for a good discussion of crank lengths.
http://www.zinncycles.com/cranks.aspx

Personally I believe crank length can be very important but 5mm is a
pretty small change. I recently switched from 165 to 175 and really
didn't notice much of a dfference. I just continue to use the gear I
needed to maintain my normal cadence. I am 5'9" and didn't notice a
significant difference in my comfort or range of motion.

Wayne




wrote:
Hi Everyone,

I bought a new road bike this year and switched from 180mm cranks to
175mm. I did this because 180's are hard to find and the bike was
complete and I figured I was going to try to change my style from the
Ullrich school to the Armstrong school.

I had been using 177.5mm for years and had switched to the 180's sort
of recently. I was never in good enough shape when I was using 180's to
really be able to compare my performance to anything.

The other day I took the old bike (180's) out of mothballs and took it
out on a club ride because my new 175mm bike was broken. Besides the
downtube friction shifters and all that strangeness the bike felt
pretty good. But I noticed I was using much heavier gears than I
usually use. I was using the 53x13 and 14 a lot while I usually don't
go higher than 53x15 on the flat with the new 175 bike. I had no
problems keeping up and it felt pretty good.

So the question is, what size is optimal for me? In the old days I
calculated using the method in Greg LeMond's book that I need 177.5's.
I am interested in a discussion that takes into account various factors
such as foot length, shin length, body type, etc. I have long feet
(size 50 euro, 15 US), and longish shins. How does this affect things?

And how does crank length and chosen gear relate to cadence? When I'm
suffering up a hill, spinning a little faster that what feels normal
causes serious burn, while going with a bigger gear doesn't as much.
But with a bigger gear I can suddenly be in way over my head in a world
of hurt. Should I try to change my cadence preference to a set rate, or
should I try to find my body's optimal cadence? How do I do this?

Thanks!

Joseph

Try Zinn's sight for a good discussion of crank lengths.
http://www.zinncycles.com/cranks.aspx

Personally I believe crank length can be very important but 5mm is a
pretty small change. I recently switched from 165 to 175 and really
didn't notice much of a dfference. I just continue to use the gear I
needed to maintain my normal cadence. I am 5'9" and didn't notice a
significant difference in my comfort or range of motion.

Wayne




wrote:
Hi Everyone,

I bought a new road bike this year and switched from 180mm cranks to
175mm. I did this because 180's are hard to find and the bike was
complete and I figured I was going to try to change my style from the
Ullrich school to the Armstrong school.

I had been using 177.5mm for years and had switched to the 180's sort
of recently. I was never in good enough shape when I was using 180's to
really be able to compare my performance to anything.

The other day I took the old bike (180's) out of mothballs and took it
out on a club ride because my new 175mm bike was broken. Besides the
downtube friction shifters and all that strangeness the bike felt
pretty good. But I noticed I was using much heavier gears than I
usually use. I was using the 53x13 and 14 a lot while I usually don't
go higher than 53x15 on the flat with the new 175 bike. I had no
problems keeping up and it felt pretty good.

So the question is, what size is optimal for me? In the old days I
calculated using the method in Greg LeMond's book that I need 177.5's.
I am interested in a discussion that takes into account various factors
such as foot length, shin length, body type, etc. I have long feet
(size 50 euro, 15 US), and longish shins. How does this affect things?

And how does crank length and chosen gear relate to cadence? When I'm
suffering up a hill, spinning a little faster that what feels normal
causes serious burn, while going with a bigger gear doesn't as much.
But with a bigger gear I can suddenly be in way over my head in a world
of hurt. Should I try to change my cadence preference to a set rate, or
should I try to find my body's optimal cadence? How do I do this?

Thanks!

Joseph

wrote:

So the question is, what size is optimal for me? In the old days I
calculated using the method in Greg LeMond's book that I need 177.5's.
I am interested in a discussion that takes into account various factors
such as foot length, shin length, body type, etc. I have long feet
(size 50 euro, 15 US), and longish shins. How does this affect things?

Studies have shown that the crank length has no significant effect on
power output... even over a wide range (145mm - 220mm).

http://www.ncbi.nlm.nih.gov/entrez/q...&dopt=Abstract


AFAIK there are no studies that show otherwise, although there are
plenty of testimonials from people who love their long or short cranks.
I'd wager that crank length is really not important, and you won't
compromise your performance by choosing something in the normal range.

It makes sense that you would select bigger gears with the longer
cranks, but even a 1 gear change (from 15 -14 tooth cog = 7%) is much
greater than your change in crank length (175-180 = 3%).


Should I try to change my cadence preference to a set rate, or
should I try to find my body's optimal cadence? How do I do this?

I think there might be something to Lance's fast cadence on hills, but
I also suspect that it is something you'd have to specifically train
for. In theory, a higher cadence might help save fast twitch muscle
fibers, resulting in less fatigue on long efforts.

I did a little study myself to see if varying cadence on a hill made
much of a difference. The only way to do this is to compare all-out
efforts... so it was an "interval day" with plenty of recovery time in
between each run. The hill I selected had a pretty steady 6% grade for
almost a mile, so I could put the bike in one gear and leave it there
for the duration of the climb. The results we

Gear Speed Cadence

39/19 12.96 81
39/21 12.66 87
39/23 12.46 94
39/21 12.66 87
39/19 12.61 79

I concluded from this that my power output was not very sensitive to
small changes in gearing and cadence... at least not for a short
effort, even though it certainly *felt* different. The first trip up in
the 39/19 felt like the gear was too big, yet that was my fastest (it
isn't unusual for my first interval to be the fastest one). The last
time up with the 39/19 felt much better, but I was slower. The 39/23
felt way too small, but I was only a little slower in that gear. 39/21
felt about right. In all cases I was completely fried at the top.

Next time I'll try starting in the 39/23 and move up to bigger gears,
and then back down to see if that gives a different result.

Anyway, you could try something like this yourself if you are
interested in getting a feel for the effect of varying cadence... it's
a great workout, too!

-Ron

It makes sense that you would select bigger gears with the longer
cranks, but even a 1 gear change (from 15 -14 tooth cog = 7%) is much
greater than your change in crank length (175-180 = 3%).

The length change is only 3% but isn't the leverage change greater,
since it's 5mm that is on one end, that is "past" the fulcrum in a way?
The radius of the 53 is about 110mm, so the effective difference
between 175's and 180's is about 7%. So I guess it makes sense that I
would go up one tooth based on feel. (Did that make any sense to anyone
besides me?)


I did a little study myself to see if varying cadence on a hill made
much of a difference. The only way to do this is to compare all-out
efforts... so it was an "interval day" with plenty of recovery time in
between each run. The hill I selected had a pretty steady 6% grade for
almost a mile, so I could put the bike in one gear and leave it there
for the duration of the climb. The results we

Gear Speed Cadence

39/19 12.96 81
39/21 12.66 87
39/23 12.46 94
39/21 12.66 87
39/19 12.61 79

I concluded from this that my power output was not very sensitive to
small changes in gearing and cadence... at least not for a short
effort, even though it certainly *felt* different. The first trip up in
the 39/19 felt like the gear was too big, yet that was my fastest (it
isn't unusual for my first interval to be the fastest one). The last
time up with the 39/19 felt much better, but I was slower. The 39/23
felt way too small, but I was only a little slower in that gear. 39/21
felt about right. In all cases I was completely fried at the top.

That is very interesting. Since power is more or less constant, I guess
the question becomes which style leaves you less fried 100km down the
road. Care to report back test findings on that one? ;-)


Next time I'll try starting in the 39/23 and move up to bigger gears,
and then back down to see if that gives a different result.

Anyway, you could try something like this yourself if you are
interested in getting a feel for the effect of varying cadence... it's
a great workout, too!

I think I will. Almost sounds like fun!

Joseph

wrote:

The length change is only 3% but isn't the leverage change greater,
since it's 5mm that is on one end, that is "past" the fulcrum in a way?
The radius of the 53 is about 110mm, so the effective difference
between 175's and 180's is about 7%. So I guess it makes sense that I
would go up one tooth based on feel. (Did that make any sense to anyone
besides me?)

I don't think it does to me. You are adding the length to your
crankarm, so that is the place to compare the two values. If your power
output (speed) is the same in both cases, then pedal force x crank
length x cadence will also be the same. The point I was making is that
you increased the crank length only 3%, but reduced cadence by 7% with
the higher gear, which would mean about a 4% *increase* in pedal force
to compensate.

I understand that it was not a controlled test, and power output, wind
conditions, etc could have varied also. But normally I wouldn't expect
someone to change their gearing more than the change in crank length.
Studies have shown that the optimum cadence variation is less than the
crank length variation, as the optimal pedal force seems to increase
with shorter cranks and decrease with longer ones.

That is very interesting. Since power is more or less constant, I guess
the question becomes which style leaves you less fried 100km down the
road. Care to report back test findings on that one? ;-)

I was trying to keep my level of perceived exertion pretty constant
(maxed out for 4 minutes), but my power *output* varied a bit as
evidenced by the different speeds. At least where I am now, I seem to
be faster with gears that seem too big, than I am with gears that feel
too small... for this short distance at least.

I've heard a couple of different coaches claim that doing intervals
like this... using both higher and lower gears than we'd normally
select... is a good way to train. At the very least I think it will
make me more "cadence tolerant".

You're right, it *would* be nice to do a longer test... something on
the order of a 30 minute uphill time trial maybe, but the hill I used
is the longest one I can ride to. Maybe a benefit with higher cadences
would show up on the longer distances.

-Ron