Crank Length questions

[Len J]

I have 165MM length cranks on my Fixie & 172.5MM cranks on my Ottrott.

Yesterday, I rode 48 miles on the fixie, today about 30 on the Ottrott.....wind was from the same direction and I rode some of the same areas. Yesterday was a hard ride.......we really worked, plus riding the fixie added to the workout. Today, was designed as an easy cruise.

What I noticed waas hom much easier it was to ride at the same speed today as we rode yesterday on the same roads with the same wind. The only difference was fixed vs geared and the crank length. Even when I put it on the same gear as the fixie, it was noticibly easier on the longer cranked geared bike.

So my question is......If longer cranks give you more leverage and hence makes it easier, then How long is too long? why wouldn't I use the longest I could find?

Another question.......I have always fit the seat setback to the center of the BB......this allows for similar weight distribution. But it occured to me today that that puts me in a different position relative to the Pedal spindle on the shorter crank bike than the regular bike.....Is this the proper way to set up?

Thanks in advance, I really had too much time to think on the ride today.

Len

[Rink]

Len J.
Some quick answers are:
A crank can be too long because eventually you will reach a point that the angle between your sacurm and femur becomes too acute at the top of the pedal circle. This forces you to exceed your body's natural range. To set your saddle set back the fit tech will drop a plumb line from your tibial tuberosity and position the seat so the true vertical bisects the pedal spindal. You should see a fit tech for assistance on all of these issues and given that you ride an Ottrott, I am surprised that all of these concerns were not addressed the day you picked up your bike.

[Len J]

Len J.
Some quick answers are:
A crank can be too long because eventually you will reach a point that the angle between your sacurm and femur becomes too acute at the top of the pedal circle. This forces you to exceed your body's natural range. To set your saddle set back the fit tech will drop a plumb line from your tibial tuberosity and position the seat so the true vertical bisects the pedal spindal. You should see a fit tech for assistance on all of these issues and given that you ride an Ottrott, I am surprised that all of these concerns were not addressed the day you picked up your bike.

Fit is perfect on the Ottrott....I was really asking relative to the Fixie position.

Setting it up to KOP for both bikes does not make sense to me as My CG will be over 7/10 of a centimeter further back on the shorter crank bike.

Thanks

Len

[Smiley]

Len , The main reason people claim to need shorter cranks on fixee's is due to pedal clearance when turning corners . I am using 170 mm cranks on my Old Raleigh converted touring frame and have not had issues with pedal clearances , Again this bike is not being ridden on a TRACK with steep banked turns . Suggestion to you , go longers with the cranks . I'd say at least 170's . You probably spun way too many rpm's on those 165's . I like to spin but I also like to push a bigger gear when I can and your riding fairly flat terrain out there . To set you both bikes so the KOP is correct , drop a plumb from the nose of the saddle and measure the distance the pedal crank is to the BB , duplicate the same with the fixee and note that your Brooks Swallow will have a different nose position then your other saddle . What brand fixee did you buy , I hope its not a TRACK specific bike with a Steep STA .

[Len J]

Len , The main reason people claim to need shorter cranks on fixee's is due to pedal clearance when turning corners . I am using 170 mm cranks on my Old Raleigh converted touring frame and have not had issues with pedal clearances , Again this bike is not being ridden on a TRACK with steep banked turns . Suggestion to you , go longers with the cranks . I'd say at least 170's . You probably spun way too many rpm's on those 165's . I like to spin but I also like to push a bigger gear when I can and your riding fairly flat terrain out there . To set you both bikes so the KOP is correct , drop a plumb from the nose of the saddle and measure the distance the pedal crank is to the BB , duplicate the same with the fixee and note that your Brooks Swallow will have a different nose position then your other saddle . What brand fixee did you buy , I hope its not a TRACK specific bike with a Steep STA .

I've had a Gunner Street Dog for a year and a half. 73 STA.

Have a b17n on the fixie.

Len

[Smiley]

with a b17 n on the fixee it should be easy to duplicate the position , I'd ditch the shorter cranks . Too much spinning and the street dog with a 73 STA is more of a road geometry , I also bet its got a high bb anyway .

[Sandy]

Where is the sacurm? How do you know that the angle has become too acute. I would really like to know as I am probably going to buy a 180 mm crankset, going from a 175 mm.

Thanks,

Sandy

[vaxn8r]

I would really like to know as I am probably going to buy a 180 mm crankset, going from a 175 mm.

Why?

[Too Tall]

Snandy that's not a good idea.

[Sandy]

Why?

Bambi

[dirtdigger88]

I know where this is going right now- so let me interject a question of my own- in reguards to crank length- why do (did I?) run crank lengths of 180 when I was in fifth grade racing BMX? Why do most BMXers use cranks much longer than rodies or MTBers? Is it due to the short distances traveled compared? I am not trying to be a 'short stemmer' here- I am just wondering- Too Tall- please continue, good man

Jason

[Matt Barkley]

Cranklength should be determined (among other things like HOW LONG you have been riding and HOW WELL you can turn over the pedals, ie pedal stroke) by how long 'yer legs are.... And "maybe" a little more specifically how long (proportionally) your femur is.

Shorter cranks for not hitting 'yer toes or running out of angle (torso to leg - or as serotta tech talks about sacrum) aren't really at all the main points regarding questions of crank length.

Learn how to turn over an appropriate crank length. For most of us non-Too-Talls that means a 170, a 172.5 or maybe if you are on the tall side with long legs or longer femurs (or have a good stroke and are pretty strong) a 175. :)

Now for specific applications like a fixie or, tt bike, or a lot of climbing, 'cross bike, MTB bike: I would suggest going just a tad shorter for a fixe, staying the same or a tad longer for TT,Climbing,cross, or MTB. But you still gotta learn that pedal stroke! Going from a 175 to a 180 if you are not already in access of 6'4" or whatever doesn't make sense. :beer: - Matt Barkley

[Too Tall]

Snambi, good advice given to me by someone who actually has some talent goes like this: as we get older and lose muscle mass and strength a faster cadence becomes even more important. That was the second reason that came to mind when you mentioned moving to a longer crank. The first reason is that a longer crank will change your bike position...change is bad!!! Esp. with us (cough) more mature athletes prone to soft tissue strains.

You will find some fairly convincing arguments in favor of really long cranks for tall riders. Infact using these formula's I'd ride a 203mm crank!

You are riding GREAT, nice spin and having fun on the bike...what's the problem?

Hey, just for grins do this: with your bike on a trainer and level...pedals horizontal and no shoes on try to lift either foot slowly off the pedal 1-2" and hold it there for a second. Can you do it? Well, with longer cranks this will become even harder and may require several position changes (the list goes on).

You'd gain more overall by working on forward flexibility. I'd LOVE to see you in my Pilates class...seriously.

[David Kirk]

I feel the crank length deal is one of the murkier things out there. I think crank length should be based on leg length, foot size, pedalling style, bike use, etc...........and I don't feel that there is one "correct" length for a rider.

The hard part about changing crank length is that muscle memory plays havoc with out perceptions. A longer or shorter crank might be better for us in the long run but it will feel like crap right at first and it can be hard to get past that.

I'm a long tall circus freak at 6'5" and I run 180's. They felt really short to me for a long time after my BMX racing days of running 190's. I now use 180's on all my bikes and they work well for me. I feel that is they were available I might like to try 182.5's but I don't lose sleep over it.

It's interesting to note that some of the preconcieved notions on crank length might be bunk. Greg Lemond rode 180's to his tour victories and he's about 5'9" - 5'10". David Phinney ( rode a 54cm frame) used 175's and was one the of the premier sprinters on the planet.

I'm not sure I have a firm point..............if there is one buried in here I'd say use what works for you and don't worry about what is "correct". If it works it's right.

Experiment, experience, learn.

Dave

[jerk]

long cranks for steady hard efforts....short cranks for rapid accelerations and changes in tempo...modify for personal preference and size....the crazy swiss once did a study with a bunch of olympic caliber cyclists to see the effects of crank arm length on cycling performance. they used everything from 120mm-200mm cranks....what they found was that crank arm length has no effect on anything....remember this was with pro cyclists...what does this tell you and the jerk? probably nothing....jerk likes 170s on his track bike and 177.5s on his race bike, 180s on his tt bike and 175s on his fat, slow and lazy and out of shape but still wants to ride bike....the coni manual says you should base your crank length on leg length....but then again it also says you should never build a bike with a top tube longer than 59cm.....so what the heck do those italians know? that would mean the jerk would need like a 140mm stem!!! oh the shame :rolleyes:

[Too Tall]

I used to run 170's on my track bike and BOY was that a torquey SOB (is that a real word?). Ultimately the switch from 170's in the winter to 180's in-season was a PITA. I'm running 175's on my current track bike and quite frankly my dear correcting my position was a HUGE PITA and I'll prolly go back to 180's. Change is bad.
For what it is worth there is a local d##D racer who is one of the winningest category racers EVER. He is nearly my height and one of the best sprinters too....he rides 175's. I asked him why and it's because he was "told" to.

Pick something and stick with it.

[93legendti]

I used to run 170's on my track bike and BOY was that a torquey SOB (is that a real word?). Ultimately the switch from 170's in the winter to 180's in-season was a PITA. I'm running 175's on my current track bike and quite frankly my dear correcting my position was a HUGE PITA and I'll prolly go back to 180's. Change is bad.
For what it is worth there is a local d##D racer who is one of the winningest category racers EVER. He is nearly my height and one of the best sprinters too....he rides 175's. I asked him why and it's because he was "told" to.

Pick something and stick with it.

This is sage advice: "Change is bad...Pick something and stick with it."

Unless you are a 25 year old pro with access to daily massage and a chiropractor, different crank lengths (on bikes used more than just occassionally) are tough on the joints, muscles, tendons, etc.

[Ti Designs]

the crazy swiss once did a study with a bunch of olympic caliber cyclists to see the effects of crank arm length on cycling performance. they used everything from 120mm-200mm cranks....what they found was that crank arm length has no effect on anything....

I've done my homework on this subject, both from a perspective of picking a crank length for racers as well as changing single crank lengths for leg length discrepencies. I have yet to see a documented study which involves enough time for the test subjects to adapt to the changes in crank length - and I've probably read a good two dozen studies and conclusions on the subject. None of the studies I've seen address the issue of the bodie's adaptation to range of motion or muscle memory. I have a theory that it's hard to find 50 bike racers who are willing to sacrifice the better part of a season to take part in a controlled crank length study...

So anyway, here's my take on the subject: The body will adapt to just about any crank length you use, but there is an optimal range (which could be plus or minus 5mm - I did say "range"). In finding that range, one would need to use a set of cranks for many hours, let the body adapt to the pedal circle, and see what the results are. Most people change crank lengths and expect to see positive results in one ride - not gonna happen. I found it amusing that the stance on crank arm length at Serotta fit school was that what they were on was probably correct. What they meant was that they have a Coputrainer on a Size Cycle with adjustable cranks and they tested a few people out on different crank lengths and they found that what they were on (and had put hundreds of hours on) were the best.

I base crank length on femur length, then take a look at how the rider rides, what kind of flexability they have, where they ride... If you think about the dynamics of it, the femur is the crank stroke, anything below the knee is a connecting rod. I also do a whole lot of pedal stroke work with my riders - one foot clipped in on the trainer, low RPMs, teaching the rider the sequence of muscle groups that must fire to produce a round pedal stroke. Most people find that when they start doing this there is a thunking noise between 11:00 and 1:00 (that's pedal position, not time of day). What they have just learned is that they are pushing one leg over the top with the other leg. This tends to be worse with longer cranks because the hip flexors need to work that much longer. My reason for working on pedal stroke first is simple, there's more to gain in efficiantcy within the pedal stroke than there is with power gains later on. You may gain 5% in torque output with longer cranks, but if you're fighting yourself for 15 degrees of the pedal stroke you're throwing that all away.

My limitations on crank length are based on flexability. If I see a rider who can't pedal with one leg clipped in without compensating with their lower back as the pedal goes over the top, they need shorter cranks. How and where they ride is also a factor. Quick changes in tempo are easier to handle with leg speed rather than torque, so the tendency is to go shorter. Hills require sustained torque, thus the push to longer cranks. I leave the final decision up to the individual with a lot of guidence and some testing.

In my own experiance I have spent my whole racing career trying to convince myself that 172.5mm cranks were right. I'm back on 170mm cranks on all of my bikes now and very happy about it. In testing it's taken me a month to adapt to a change in crank length. It wasn't that noticable with only 2.5mm changes, but going from the 165mm cranks on my track bike to the 175mm crank arms on my mountain bike was killing me. Then I tried something stupid, I switched all of my bikes to 170mm, and I haven't wanted to go back. In the fall I set up fixed gears for many of my riders, I use the same crank length they use on their road bikes (training a specific pedal stroke), as well as the same saddle to pedal relationship.

[Len J]

It sounds like everyone's best advice is to put 172.5's on the fixie.

I bought the 165's because that's what harris cyclery recommended trying to avoid hitting a pedal on the inside of a turn while pedaling with the fixed gear. It sounds like that was a mistake.

Since the BB drop is only 7 and i use speedplays, I probably have more pedal clearance than I think.........especially since I don't usually bomb thru turns on the chip n seal around here.....there is way too much loose gravel on the inside of turns.

Guess I'll bite the bullet and replace the crank......anyone need a 165 Dura ace set of cranks?

As to the other question I asked.....I still don't get the logic of setting up the shorter cranks based on relative KOP (+ or _ normal KOP setback).....it seems to me that this method changes the weight distribution on the bike with the shorter cranks relative to the one with the longer cranks. What am I missing?

Thanks again.

Len

[Too Tall]

I just happen to keep a log of all sorts of athletic calculations and crank lenghts is one of my favorites. I didn't want to post this (see links below) before a few others chimed in as it contains the results of what happens when an engineer get's involved!!! Kidding, I LOVE engineers but don't ask one to tap a keg OK? Matt, TiD and Senor' be a shining light for our beloved Bambi :)

(When Engineers have gone bad)

Leg length calculations:
http://www.nettally.com/palmk/crref.html
http://www.nettally.com/palmk/crankset.html
L(mm) = 2.16 x I(cm)
or
L(mm) = 5.48 x I(in)


(Traditional sizing...whatever the heck that is)
60 to 65cm 150mm
66 to 70cm 155mm
72 to 75cm 160mm
75 to 78cm 162.5mm
79 to 81cm 165mm
82 to 83cm 167.5mm
83 to 86cm 170mm to 172.5mm
87 to 90cm 175mm to 177.5mm
91 to 94cm 180mm
94cm plus 185mm

( Below is what I recall Zinn uses...I might be wrong)
the rule of thumb is: 20.8% of inseam, +5mm for long femurs, -5mm for short femurs. also considered is ankling and toes pointing down while pedaling

[flydhest]

as a largely useless extra observation, I give the following:

I have 170s on my track bike, 175s on my 'cross bike (cranks that were on my road bike) and 180s on my road bike. Soon, I'll have 175s on my other road bike. (sidebar: hee, hee. I have four bikes. I just got the parts for my new-to-me CSi that I got from dbrk. Three Serottas (Serottae?) and a Vanilla)

I suspect that each person's adaptability matters a lot, but one can switch among cranks and not get hurt. I do notice, however, I need to make sure I pay attention to my positioning on my road bike with the 180s so that I can notice if I'm developing any extra strain. That said, for me, switching back and forth is not the huge deal others may make it out to be.

Then again, Len, you know me and how I ride. I ride for fun and enjoyment, I'm pretty slow, and haven't been doing any serious "hammer away for hours at the edge of my ability" kind of riding.

[zap]

I've been riding 175 on everything for over a decade.

I dabbled with 177.5 on one bike two years ago for a year and everything was fine until I got out of the saddle. It was strange going 2.5mm lower at the bottom of the stroke and 2.5mm higher at the top. Don't ask me why it was more noticeable out of the saddle. I wouldn't have thought 2.5mm would feel different, but it did and now someone else is riding those cranks.

[flydhest]

Zap,

That's very interesting. I find the difference most noticeable when I'm sitting and out of the saddle, the difference really fades for me.

Go figure . . .

[vaxn8r]

It's interesting to note that some of the preconcieved notions on crank length might be bunk. Greg Lemond rode 180's to his tour victories and he's about 5'9" - 5'10". David Phinney ( rode a 54cm frame) used 175's and was one the of the premier sprinters on the planet.
Dave

The thing about Lemond and a lot of pros back in his day was a lot of them were mashers. Watch video of Lemond climbing anything. He had a cadence of about 60-70.

It seems to me the thing you'll get with longer cranks is more leverage. So if you like to peddle the lower RPMs and stomp on 'em then I'd think (maybe)you'd want a longer crank. I may be full of it but that's my take.

Sandy, I think it would be a bad idea but if you have the money to burn and want to try it who's to say no?

[Ken Robb]

I'm, unfortunately, not much of a spinner. 100rpm is really fast for me and my natural go-fast cadence seems to be around 80rpm. On flats with nobody pushing me I'm happy at 65rpm. The Legend I bought recently came with 10spd Dura Ace 10spd and 53-39 dbl. with 11-23 cogs. I didn't think I could even ride up the hill to my home with that gearing but-------it had 180mm cranks and the extra leverage and power was amazing to me. After all 25mm is only about 1/4" for goodness sake.
Well we have lots of hills in San Diego so I swapped the cassette for 12-27 and things got better. 4 of our road bike are triples so I'm used to pretty low gears to help me climb. Our CSi has 10 spd Chorus with 53-39 and 13-29 gears which is almost enough help.
Anyway, I just placed the DA 53-39 with FSA 50-34 and that's about as low as I need to go. If I could have got the compact in 180mm I would have but 175 is as long as FSA makes carbon compacts. I miss the leverage of the longer arms and I need lower gears for any given hill now that I have short(er) cranks again.

[vaxn8r]

So Ken's experience gives credence to my point, that longer crank arms might be more useful for power riders who prefer a low cadence.

I've tried to become less of a masher over the years. I can generate a lot of power and I used to climb seated and slow cadence, like Lemond used to do it, but I find that I pay for those efforts in terms of recovery time between rides. Faster cadences seem to correlate with quicker recovery times. For me anyway. Maybe I ought to try 180's. Sounds like they may suit me.

[csb]

you having them lg. size cranks makes me axe,
should i go longer?
(i dont want a certain horse jockey pushing
the pace tooo much this spring)

[Ken Robb]

Since some of you asked: See my ad to sell the DA 10spd cranks in the classifieds.

[vaxn8r]

That's more than a fair price Ken...but way too steep for such an experiment. Now if someone is selling 172.5 DA 10's for $275 I'll be all over it....awesome crank that it is.

[Rink]

Sandy
Sorry for the late reply. The sacrum is located at the base of the spine and consists of five fused vertebrate. Your flexibility is assessed during the fitting process and I could not offer a quick at home self assessment. I can offer some advice though: stick with the crank length that you have been riding. Your body has adapted to this spin over the thousands of miles that you have ridden. There is something called the S.A.I.D. principle: Specific Adaptation to Imposed Demand. This means that your body adapts to a highly repetitive motion and resists change. No doubt you could get use to a new crank length but why?

[flydhest]

you having them lg. size cranks makes me axe,
should i go longer?
(i dont want a certain horse jockey pushing
the pace tooo much this spring)

at 63, he's not pushing the pace, usually pushing the stool.

[keno]

First, I ain't no horse jockey, I'm a hors duver. Second, that's not stool, that's s'tool. Third, I'm getting a bit cranky.

Meth, formerly keno and before that not much of anything soon to be again

[flydhest]

sorry about that, lxiii

[csb]

are those his real teeth?