Crank length selection and seat position. Not just knee over pedal. Is this correct?
thirty-six
rider is that which sets the pedal axle not behind the sit spots made
upon the saddle by the ischial projections but as near to it. The
knee should also not pass forward of the pedal axle in the forward
position so limiting the smallest size and saddle position.
The crank length when at the maximum then sets the seat to bottom
bracket position very closely. 170mm cranks give me no leeway in
position and my seat position is set at 74deg. This limitation of
position causes discomfort in my back after about 5 hours (or less).
A 5mm shorter crank permits a 5mm position change on the saddle,
necessary to get on the rivet and also useful when climbing. My other
bike allows this mobility and I may ride 8 hours without incident.
The position changes are not necessarily concious efforts.
With accurate measurements of pelvis to knee and knee to pedal spindle
then accurate suggestions of crank lengths may be made using
trigonometry.
Have I overlooked something which also would have a bearing on crank
length choice not covered by the method I present?
Chalo
>
> I hypothesise that the correct maximum crank length for any distance
> rider is that which sets the pedal axle not behind the sit spots made
> upon the saddle by the ischial projections but as near to it.
Since the rising leg isn't doing much work (negative work most of the
time), I don't see how it makes much difference how far back the
rising pedal is.
> The
> knee should also not pass forward of the pedal axle in the forward
> position so limiting the smallest size and saddle position.
I don't know that this matters either, except inasmuch as a crank can
be too short by other measures and might also exhibit this trait.
Chalo
thirty-six
> thirty-six wrote:
>
> > I hypothesise that the correct maximum crank length for any distance
> > rider is that which sets the pedal axle not behind the sit spots made
> > upon the saddle by the ischial projections but as near to it.
>
> Since the rising leg isn't doing much work (negative work most of the
> time), I don't see how it makes much difference how far back the
> rising pedal is.
The little difference it does make should improve efficiency because
the limbs are not being contorted through unnatural angles, with
associated ligament and tendon strain nor has the rider a need to
supply energy to counter this strain (when clipped in) or keep his
feet placed securely on the pedals.
>
> > The
> > knee should also not pass forward of the pedal axle in the forward
> > position so limiting the smallest size and saddle position.
>
> I don't know that this matters either, except inasmuch as a crank can
> be too short by other measures and might also exhibit this trait.
To keep the joint mobilty within normal ranges and a knee forward of
the pedal axle in it's forward postion requires the rider to supply
additional energy to stop himself rocking forward on the seat when
pressing on. With the knee above or behind he stays firmly planted in
the seat without the wasteful rocking to and fro.
I thank you for your response, could you please elaborate on what
measures a bicycle crank can be too short?
landotter
With proper saddle height and cleat position--everything else usually
falls right into place. A long femur might want the saddle back a cm
or two, and a short torso might beg for a compact stem. I'm not a
professional fitter, but there's really no substitute for putting a
body on a trainer and listening to it.
thirty-six
I've realised that what I have said could be simplified to use cranks
less than half the length of the upper leg and the position will
follow. I've given you the reasons why.
If the cranks are short it gets pretty hard to get sufficiently out
of position to cause a problem but position may need refinement with
crank lengthening. As others have found, handlebar position is not
quite so critical and 10 or 15mm in stem length or height increments
will satisfy all but The Great Eddy. Long cranks however will make
handlebar position more critical (for a distance cyclist) as the
naturally economic leg position is restricted in the saddle.
How do typical Tour riders get on with 172mm cranks steaming up the
Alps? Why, they soak their feet in phosphates each night to grow
their legs longer.
Steve Freides
Yes, you've overlooked the obvious - ride your bike a lot, try a lot of
different crank lengths, perhaps even under the guidance of an
experienced coach, and settle on what works best for you. Any formula
should be taken as a starting point and nothing more. The same goes for
cleat position relative to pedal spindle, and saddle fore/aft position -
start with a formula, then ride, ride, ride, make small adjustments and
live with them each for a while.
I'm reasonably sure that if you look through, e.g., the riders at the
recently completed Tour de France, you'd find all sorts of variations
from what's supposed to be.
Every formula I've seen has recommended cranks that are shorter than
those I actually ride. I'm a short-legged 5' 7" and the usual
recommendation is 167.5 (which no one makes, anyway). I ride 172.5
merrily, including on my fixed gear where I spin down hills like a
freakin' sewing machine. I rode, for a minimum of three months and
often longer, cranks in 160, 165, 170, 172.5 and 175 mm, and nothing
ever felt as right as the 172.5's.
Put 165's on your bike (assuming I read your message correctly - 170's
bother your back, 165's work well and don't hurt) and be done with it.
Or do some more math - these things are interrelated, which means you
could keep 170's and try different cleat position and/or different
saddle offset rather than changing crank length right away.
-S-
thirty-six
> thirty-six wrote:
> > I hypothesise that the correct maximum crank length for any distance
> > rider is that which sets the pedal axle not behind the sit spots made
> > upon the saddle by the ischial projections but as near to it. The
> > knee should also not pass forward of the pedal axle in the forward
> > position so limiting the smallest size and saddle position.
>
> > The crank length when at the maximum then sets the seat to bottom
> > bracket position very closely. 170mm cranks give me no leeway in
> > position and my seat position is set at 74deg. This limitation of
> > position causes discomfort in my back after about 5 hours (or less).
> > A 5mm shorter crank permits a 5mm position change on the saddle,
> > necessary to get on the rivet and also useful when climbing. My other
> > bike allows this mobility and I may ride 8 hours without incident.
> > The position changes are not necessarily concious efforts.
>
> > With accurate measurements of pelvis to knee and knee to pedal spindle
> > then accurate suggestions of crank lengths may be made using
> > trigonometry.
>
> > Have I overlooked something which also would have a bearing on crank
> > length choice not covered by the method I present?
>
> Yes, you've overlooked the obvious - ride your bike a lot, try a lot of
> different crank lengths, perhaps even under the guidance of an
> experienced coach, and settle on what works best for you. Any formula
I tried that route and wasted racing time. I wasn't fit to race in
the hills. The restriction caused by the cranks meant it was
difficult for me to find a good out of the saddle position.
> should be taken as a starting point and nothing more. The same goes for
> cleat position relative to pedal spindle, and saddle fore/aft position -
> start with a formula, then ride, ride, ride, make small adjustments and
> live with them each for a while.
I'm trying to sort out that formula to help others. The second set of
racing cranks I used, I trusted my coach and my framebuilder. There
was a fair amount of money invested in them and they should have
allowed me some room to move. I hadn't the knowledge or sufficient
experience at the time to realise that the standard length was not
entirely suited to me.
>
> I'm reasonably sure that if you look through, e.g., the riders at the
> recently completed Tour de France, you'd find all sorts of variations
> from what's supposed to be.
>
> Every formula I've seen has recommended cranks that are shorter than
> those I actually ride. I'm a short-legged 5' 7" and the usual
> recommendation is 167.5 (which no one makes, anyway). I ride 172.5
> merrily, including on my fixed gear where I spin down hills like a
> freakin' sewing machine.
I can spin at over 200rpm with 170s, in only one precise position. It
took me s long time to find I could spin like that because I was
always trying to find a better position with cleats, handlebars and
saddle. I didn't think of just spinning in the saddle and see what
comes from there until long after I had abandoned racing.
> I rode, for a minimum of three months and
> often longer, cranks in 160, 165, 170, 172.5 and 175 mm, and nothing
> ever felt as right as the 172.5's.
You see, to many it doesn't make sense that I have a 33" inside leg
and much prefer 165 over 170mm. The 170s are good enough for short
(up to 3 hours) social rides but probably never served me well when
racing, forcing me to overgear to get power. Bad for hills, bad for
sprinting. I don't appear to have anything different in my available
leg movement, but perhaps it was due to a more active childhood with
climbing and running has set me for a greater restriction than those
who took up competetive cycling at an earlier age to the exclusion of
other sports.
>
> Put 165's on your bike (assuming I read your message correctly - 170's
> bother your back, 165's work well and don't hurt) and be done with it.
I'm thinking though that even when I wasn't experiencing any pain that
I was down on riding efficiency so leading to early exhaustion. This
is apart from the fact that any steep gradient would see me going
backward throught he pack. I did much better in pacelines, only
having trouble due to bike changes before finalising position.
> Or do some more math - these things are interrelated, which means you
> could keep 170's and try different cleat position and/or different
> saddle offset rather than changing crank length right away.
There is perhaps a 2mm variation in saddle position I can use, no
more. It's centred in the area causing least discomfort. I played
about with cleat position and found it benefitting to bring the right
cleat back to compensate for a longer leg. Hours, days, weeks,
months, years have passed and I still cannot accept any variation in
position with 170mm cranks.
Preparatory hamstring stretching is essential if I'm going to get down
in the drops and put in a burst of speed.
Steve Freides
You've answered this one already by yourself - you know what works for
you, so use it.
-S-
--D-y
What can I say, when I tell people I ride 165's on the road, I get all
kinds of reactions from "THOSE ARE TOO SHORT!!!" to being accused of
thinking I'm "special".
I don't remember anyone ever saying "Good, you figured out what works
for you!". 165's work, longer ones don't. All else follows.
--D-y
thirty-six
> thirty-six wrote:
> > I'm trying to sort out that formula to help others.
>
> You've answered this one already by yourself - you know what works for
> you, so use it.
First of all, I don't know what works best or with least effort per
mile. It could well be that a 5" or 6" long crank be best. Does the
way I've assessed for correct length stand up to scrutiny and so used
for others or is there a damning reason to go shorter still? I do
understand the claim for an aerodynamic pursuiters position being
benefitted by shorter cranks to assist in breathing and reduce
aerodynamic drag. That's not a particular requirement for me. A 5"
crank would also require a frame change, so the evidence would have to
be strong to get me to that size. I suspect that I should be able to
use 100mm in saddle length which would indicate that the cranks need
to be around 50mm shorter than they are (just because I'm so
restricted with them). But this would suggest 120mm cranks. Even a
5" (127mm) crank sounds too small, but I've been conditioned to 165 to
175 as the norm.
Steve Freides
There is no "perfect" to be had here. As engineers say, everything is a
compromise. You have to pick you priorities.
As but one example, I'm sure a lot of pro's hate their TT position but,
as long as it doesn't get them injured, that's just tough luck for them
because performance comes before everything else when you're getting
paid for your performance.
Don't forget, either, that track bikes (your example of pursuiters) are
fixed gears and, as such, crank length has at least a somewhat different
meaning. I can tell you from personal experience that when I was
recovering from a serious back injury about 15 years ago, I could ride a
fixed gear but I couldn't ride a normal bike - mind you, I have no idea
if this is significant in the grand scheme of things but I can tell you
that things are different when you're on a track, and even when you're
on track-style equipment like a fixed gear on the road.
If I could sum up my advice to you in a word, it would be "relax" - your
quest to improve has to start with being able to perform safely and,
especially since, I assume, you're not doing this for a living, anything
that causes you back pain after a ride is simply an unacceptable
compromise, even if it helped you be faster. OTOH, if you find you
prefer to race criteriums with a different size of crank than you use
for long road races because it makes you go faster at those shorter
distances, well, that would be an example of an OK compromise in my
book. Just don't forget that there are tradeoffs in any choice of
equipment and it is not - I repeat _not_ - an exact science.
-S-
mtb Dad
the riders current flexibility and strength than actual anatomical
limitations. Its a compromise of comfort and power, often in a single
session, so there's little incentive to prescribe strength and
flexibility exercises and evolve a position that is more aero, or uses
a longer crank for hills, for example.
I do like a local physio who is a former high performance rider and
does fittings. She looks more at strength and flexibility of the
individual than the knee over pedal type rules of thumb. Still, it's
kinda one shot deal, vs a plan to work towards an ideal.
thirty-six
This is all very interesting but I am not competetively active nor am
I likely to be. Yes, I'd prefer to go out for six hours on the bike
and get home and not have to worry about having to have a soak,
massage and bed rest to help recouperate. If I think objectively it
means I should look for the shortest available cranks off the shelf
with 9/16" pedal fitting, at a low price... and see what happens.
Supposedly I'll need smaller gears. Hmm, my ex-racing bike is
slightly undergeared as it is, but I doubt that a135mm BCD crankset
exists in the sort of length I am looking for (closer to 120mm than
170mm).
I'm too tired now to think much further at the minute but have been
considering how the rotation of position as a rider moves into the
hooks should move him forward on the saddle. It seems I could have
used bars with a greater reach and drop than I did. I favoured the
tight bends because my hands were secure over rough tracks, and race
circuits are not necessarily on the best roads.
dusto...@mac.com
Go for the comfort and ergonomics ("protection from injury/
discomfort"). Try the 165's on a bike that otherwise suits you and see
what happens. Worked for me.
--D-y
Steve Freides
> Go for the comfort and ergonomics ("protection from injury/
> discomfort"). Try the 165's on a bike that otherwise suits you and see
> what happens. Worked for me.
> --D-y
+1 - based on everything you've said, it sounds like you'll be happy
with 165's.
I wouldn't change your gearing at all - you can always do that later if
you need, but the difference isn't that dramatic that you have to run
out and buy a new drivetrain.
-S-
Steve Freides
Yes, I agree - the better the fitter can look at the person getting
fitted in all their aspects, the better the results will be, e.g., if
someone comes in who's obviously athletic, looks like they're open to
advice, and has tight hamstrings, then the best thing might be to
suggest working on the hamstrings for a while before having a fit kit
done.
I'm showing my exercise prejudice here, but the kettlebell swing and
barbell deadlift both have potential to solve tight hamstrings and
improve strength as well. I used to always have to lower my saddle
every Spring because I'd lost some of my cycle-specific flexibility over
the winter, but once I started doing kettlebell swings regularly, that
problem went away and has never come back.
Disclaimer: I'm an instructor (actually, an instructor's instructor) in
the RKC program, see here
http://www.dragondoor.com/steve-freides/?apid=1022
The picture should let you know I don't have hamstring flexibility
problems. :)
-S-
"\"T°m Sherm@n >
> [...]
> I thank you for your response, could you please elaborate on what
> measures a bicycle crank can be too short?
"The cranks on a bicycle should be long enough to reach from the bottom
bracket spindle to the pedal axle." - Abraham Lincoln
--
Tºm Shermªn - 42.435731°N, 83.985007°W
I am a vehicular cyclist.
"\"T°m Sherm@n >
Shorter cranks provide more clearance between the knees and the fairing
shell while pedaling. I know people riding cranks that have been
shortened to 110-mm length.
"\"T°m Sherm@n >
> [...]
> Supposedly I'll need smaller gears. Hmm, my ex-racing bike is
> slightly undergeared as it is, but I doubt that a135mm BCD crankset
> exists in the sort of length I am looking for (closer to 120mm than
>
If you want cranks that short, here is the place:
<http://bikesmithdesign.com/Short_Cranks/index.html>.
Sheldon Brown's Gain Ratio calculator can assist in helping you decide
what size chainwheels you want with different crank lengths:
<http://sheldonbrown.com/gears/>.
thirty-six
On my second bike (same size, softer stays) I have 165s, I'm thinking
that with smaller crank again I will resort to a wind-cheating
position more frequently without fear of incurring hamstring strain
leading to back pain. From what I can make out there is little I can
lose out on. It's a little further to get up and down from but the
payoff is greater lean angles (at least in the dry) and more capable
off-road use.
I fully understand the requirement to do hamstring stretches for a
racing position with the typical length cranks, but I usually want to
just jump on the bike and go, exactly like when I was 16.
thirty-six
Get yourself a long-board tricycle with forward cranks, disc wheels
and a luggage box. The aero benefit of a leg fairing is negligible.
Obviously you need to padlock the rear box in high-crime areas or it
disappears, just like in this photo. You should appreciate that the
weight is negligible and the drive efficiency is remarkable, at an
unobtainable level from any other means. The reduction in wheel size
has not only a weight and aerodynamic advantage but also contributes
to the powertrain efficiency. A truly remarkable machine at any
price.
Steve Freides
"... exactly like when I was 16." Well, that's a conversation starter,
for sure. There are a lot of things that you just can't do exactly like
when you were 16. According to my wife, some of those changes are for
the better. :) But you must realize that as you get older, retaining
the _functionality_ you had when you were younger requires _work_. If
you aren't willing to do the work, you will have to accept the reduced
functionality.
No one is telling you to do a half-hour yoga routine every time before
you ride, but if 30 seconds of toe touches help, then that seems to me
to be a more than worthwhile tradeoff. And here's another good thing to
think about - if you do the stretching _most_ of the time, you can get
away with missing it once in a while. Our bodies remember what we're
able to do and not do very well, and you'll still have the hamstring
flexibility, or at least most of it, on those times you skip the
stretches.
Me, I'd be happy to ride fast enough that cheating the wind made a lot
of difference. :)
-S-
andre...@aol.com
Don't know if this has been talked about, but this is the great
discovery of triathletes. By having 78 degree angles on their bikes,
they can get really low and the angle between their lower backs and
the hamstring is not as steep.
I used to get back pain after riding about 40 miles and would have to
get off my bike and stretch. I had a custom built ti frame made in
china for peanuts with a 76 degree angle. Now, I can ride aero non-
stop for miles on end without getting a tight lower back. I usually
ride around 50 miles, non-stop every sat and sunday. No back problems
to report. It was a huge difference for my short femurs to get a 170
crankset and a 76 degree angle. I do have a 73.5 angle bike. But, but,
but....I have the longest saddle possible, fairly forward, and I tend
to sit up front. Also, no problems with my lower back.
I noticed that most of my buddies ride on the brake hoods. I ride on
the drops all the time. I believe that most people would be much more
comfortable on 76 to 78 degree angled bikes. But, since 23 year old,
ultra fit, pros, who ride a million miles a day ride 73 degree angles,
all bikes are designed like that. When you buy a bike from a local
bike shop, they fit you as if you were Lance Armstrong.
Steve Freides
I have a 74 degree angle on my custom bike (and a very long top tube) -
I had a long discussion with the builder (Stephen Bilenky in
Philadelphia, http://www.bilenky.com ) about seat tube angles and
triathletes because, even though I've never been a triathlete, I used to
regularly run in addition to bicycling, just because I enjoyed it.
His explanation agreed with yours to a point - he said that because
triathletes also run, their build/strength/tightness/what-you-have tend
to make them more comfortable with a steep seat tube angle. Apparently
people who just bicycle still tend to do best with a 73 degree (or so)
angle rather than steeper.
I don't recall more than that.
-S-
thirty-six
$southslope.net"> wrote:
> On 7/25/2011 6:19 AM, thirty-six wrote:
>
> > [...]
> > I thank you for your response, could you please elaborate on what
> > measures a bicycle crank can be too short?
>
> "The cranks on a bicycle should be long enough to reach from the bottom
> bracket spindle to the pedal axle." - Abraham Lincoln
I'm coming around to this.
thirty-six
This would put me too far forward, I like to spin two or three times
an hour and this can only be done economically with the knee behind
the pedal axle. IME KOPS is the absolute maximum forward position
after which high power spinning is hampered due to reduced
gravitational pressure on the forward leg. This is probably not the
complete picture, but I believe is significant.
>
> I used to get back pain after riding about 40 miles and would have to
> get off my bike and stretch.
If I'm on the 170mm I go through a few on the bike stretches after 1/2
hour of upright riding to prevent problems later in the ride.
Sometimes though I'm out for longer than anticipated. If I stretch
every 1.1/2 hours and don't get in the low position for long I'm still
good after I get home. I forget, and it's only as I cool down do I
stiffen up with a painful back.
thirty-six
> triathletes because, even though I've never been a triathlete, I used to
> regularly run in addition to bicycling, just because I enjoyed it.
>
> His explanation agreed with yours to a point - he said that because
> triathletes also run, their build/strength/tightness/what-you-have tend
> to make them more comfortable with a steep seat tube angle. Apparently
> people who just bicycle still tend to do best with a 73 degree (or so)
> angle rather than steeper.
>
> I don't recall more than that.
>
> -S-
It is possible to have souplesse in both cycling and running, but I
imagine that most competitors will be so developed in running that
they fail to develop the necessary cycling skill required for
efficiency.
Nick-L-Plate
I'll go a bit further on crank length selection and assume the correct
length to be the same as the distance between the centre of the ankle
and the centre of the large ball of the foot. My thoughts are that the
feet have developed appropriately for the natural gait (or determine
such) in walking and running and crank length should be directly related
to this measurement if not actually the same. At 150mm for me, it
certainly is on the right side of what I've used before (170 & 165mm).
I wonder how this measurement relates ito other distance rider's
preferred crank lengths.
thirty-six;2215674 Wrote:
> I hypothesise that the correct maximum crank length for any distance
> rider is that which sets the pedal axle not behind the sit spots made
> upon the saddle by the ischial projections but as near to it. The
> knee should also not pass forward of the pedal axle in the forward
> position so limiting the smallest size and saddle position.
>
> The crank length when at the maximum then sets the seat to bottom
> bracket position very closely. 170mm cranks give me no leeway in
> position and my seat position is set at 74deg. This limitation of
> position causes discomfort in my back after about 5 hours (or less).
> A 5mm shorter crank permits a 5mm position change on the saddle,
> necessary to get on the rivet and also useful when climbing. My other
> bike allows this mobility and I may ride 8 hours without incident.
> The position changes are not necessarily concious efforts.
>
> With accurate measurements of pelvis to knee and knee to pedal spindle
> then accurate suggestions of crank lengths may be made using
> trigonometry.
>
> Have I overlooked something which also would have a bearing on crank
> length choice not covered by the method I present?
--
Nick-L-Plate (36)