Cranks

[davek]

Originally posted by drewski
In my experience, other fit characteristics like saddle height and position (fore-aft) as well as the choice of pedals ... impacted my knees more than my crank-length

Mmmm, there's a lot more to choosing the right bike than I've ever realised.

And I'm sure it can't help that my current frame is several sizes too big for me... still, reading all the excellent advice on this forum should set me on the right track to getting the right bike next time around, which I'm hoping will be within the next few months, budget allowing.

What's the general view on triple chainsets? I've always suspected they were pointless but I'm gradually revising that opinion.

 

[drewski]

Originally posted by davek

What's the general view on triple chainsets? I've always suspected they were pointless but I'm gradually revising that opinion.

uh, oh. that's another whole can'o'worms!!

here's a recent thread on the subject: http://www.cyclingforums.com/showthread.php?s=&threadid=57407&highlight=double+triple

bottom line, if you want smaller gearing than a double will allow (be-it for steep climbs, rest the knees, out of shape, etc) they will provide that for you. a compact double will too.

ignore the guys who say they're only for wimps, etc. if it works for you damn the elitists!

 

[davek]

Originally posted by drewski
uh, oh. that's another whole can'o'worms!!

Thought it might be... thanks for the link.

 

[skareb]

mines 175mm both bikes, not my choice but nothing else to choose here ...

 

[gingerviking]

ant! ...so how do u expect us to hold onto this disc to operate the jack? ...with a crankarm or handle? ....lol ...u seem to be forgetting that the legs/levers we use to connect to the bike are different lengths and therefore interact differently with the bike set-up and our training/experience and style.

A lever is merely the radius of the disc u mention, but levers dont do circles in engineering, they become cranks, and a complex integration of cranks, gears and levers is more than the sum of the separate parts. The loadings at these intesections are angle related and are critical to the design and useage. Now with a bike u also throw into the mix ...'how does that feel?' ....lmao ...no wonder no clear answer prevails.

The variety in human sizes far exceeds the range of standard parts ...ever heard of custom fitting a bike. Remember that for each different crankarm length ideally the bottom bracket of the frame would vary to maintain a standard ground clearance. For most people it isn't 'that' important ...it is the most efficient form of human machinary yet invented anyways. can u imagine how much more it would cost to cycle if only custom fitted bikes could be bought though, thank Henry (Ford) for mass production and limited choices which lowered costs and got us all to this point in history.

The lack of variety and promotion of custom crankarm lengths may be attributed to the ease with which gearing choice and use (and emotion) can be used to distract from the core of this discussion "ideal crankarm length". If it these sound like engineering terms well surprise, surprise!

Put 'crankarm-length" into google sometime and do some reading, I just wish I could find somewhere to try before I buy as 185 to 190mm cranks are hard to find ...I stand at 188cm with a 43cm femur.

 

[timmit]

I'm only 5' 7". Are you saying that I shouldn't ride 170mm cranks (which I have always done) and 165's on the track (because smaller cranks are slightly easier to spin faster). Surely putting on 180s would be hard to spin. Also - if your cranks go from 170 to 180 and you raise the saddle 10mm "to adjust for this" then surely at the bottom of your stroke your legs will be strecthed by an extra 20mm therefore I'd make sure the bottom of the stroke is correct i.e. lower the saddle 10mm and accept your knee will bend more than usual (being 20mm higher in relation to your saddle than usual).

Your thoughts?

 

[American_Lesion]

Originally posted by steve
Hi guys

What size cranks does everyone ride? Why do you like them?

Mine are 172.5mm campy chorus cranks, i'm happy to swap them for a set of any 175mm cranks that are in good condition.

I ride several different cranks.

The first being an authentic 1987 0r 88 Exage Trail M350 crankset in 175 mm. The chainrings have been replaced (the were nasty old Biopace 28-38-48) with a Syncros 46, a Sugino 36, and a Specialized Stainless 26).

next up is a 175mm Specialized "Son of a Strongarm" from 1995. The original steel rings have been replaced with a Deore LX outer, and the inners are Avitar 9non-pinned, non-ramped) aluminum. Chainring bolts are blue anodized alloy. 42-32-22


Next? A Truvativ 5D with a Syncros outer ring, Deore LX middle ring, and a stock Truvativ steel inner one. Crank arems are 175 mm. 44-32-22

Last? A 170 mm stock 2003 silver Deore Octalink model with stock 44, 32, 22 rings. Alloy-steel-steel.

 

[gnmano]

I currently ride 170 on the road and 175 on the mtn.bike. I have a 31" inseam. I used to ride 172.5s on the road, but my new bike (slightly used Gerciotti with Record 9spd) came with these 170s. I was all concerned about them being too short. After a season of riding and racing, they didn't feel too bad. However, I wonder how much power I am losing. I have though about going up to 175s but I can't justify the cost.

Here is the question of all questions: How much power will be gained by increasing the lever 5mm or even 10mm? It is hard to believe the actual gain is significant with such a small increase.

My personal belief is that the power gained is minimal at best, but what is truly achieved by playing with crank length is the size of the circle the feet are traveling in, and how comfortable you are with that circle. Ten milimeters increase in crank length equals 20 mm increase in circle diameter. That could make a difference in range of motion and how it suits that individual.

Engineers or physics people: calculate how much force is required to push down on a lever 170mm long to lift a given weight. If that lever is lengthened by 10mm, how much less force is needed to lift the same weight?

Regards,
GMAN

 

[soneca2]

I use Dura Ace Ex 1.70 cranks.

For whom has doubts about cranks, there is an interesting site
http://www.cranklength.info/, where you can find out more about your eventual needs.

Best regards to everybody.

 

[Whitney]

You are talking about measuring torque; or rotational force, which is usually foot/pounds here, or newton/meters in Europe.

you can do a quick and simple calc. to get an idea of the change by multiplying the lever arm by the force.

So if you were doing say, 100 pounds of force on a 170mm crank (.5577 feet) it would be

55.77 foot/pounds

if you went to 175mm (.5741feet), you would have

57.41 foot/pounds - so almost 2 foot/pounds of force.

This is all but a 3% increase in force, which makes it a little more comprehensible.

You can see that it actually does make an appreciable difference.

Whit

 

[drewjc]

I believe that the term power is used incorrectly by gnmano. My current knowledge leads me to believe that the increase he is talking about is actually the torque around the bottom bracket for a given force on the pedals. To achieve a power figure u must factor in time (cadence) which is going to change depending on crank length. What Whitney has said is correct in that the force required is somewhat reduced.......... But to produce this force for a longer effort (for the same crank length increase of 5mm the pedal rotation increases by 3% thus increasing time/decreasing cadence by the same.......3%). Therefore u get no direct increase in power from riding on longer cranks. You may find that your body produces peak torque better at lower cadence so longer cranks are easier to use, but as far as relationships with power go, it is impossible to increase power merely by changing cranks length. Imagine what Sean Eadie would do if u put him on 180mm cranks if he can produce ~2000W on 165mm!

 

[murky]

Hi Timmit,

I agree with you that if you increase crank length, you should LOWER your seat by the corresponding amount. This will lead to your knees and hips and possibly ankles, moving through GREATER angles of motion. Some have observed that this puts MORE stress on the joints.

This sort of change (from 170 to 180 mm) usually requires a gradual buildup to readapt. ie never in mid-season. I understand that like any changes in position, it is best done in the off season.

Having said that, I do know it is possible to reap the immediate benefits of the increased leverage of a longer crank, in mid-season. I train up a particular steep climb and do my intervals (10 times).

The year before, I used a 172.5 mm crank. During peak fitness, I swapped to a 175mm and did the same session, and actually achieved a personal best.

I then switched back to the 172.5's. I had a feeling that if I'd continued to use the 175's for the rest of the season, I'd be inviting some sort of joint injury.

In the off-season, I put the 175's back on and tried to adapt to them for the new year.

I must say that I had a hard time repeating my training regimen. Muscular endurance seemed to be the issue, or the lack of it. Meaning I didn't seem to able to attain the same strength endurance to spin the big gear.

I'm switching back to the 172.5's this year and see how it goes.

I guess it's pretty subjective with different riders responding differently.

This has just been my experience.

Cheers
Mark

Originally posted by timmit
I'm only 5' 7". Are you saying that I shouldn't ride 170mm cranks (which I have always done) and 165's on the track (because smaller cranks are slightly easier to spin faster). Surely putting on 180s would be hard to spin. Also - if your cranks go from 170 to 180 and you raise the saddle 10mm "to adjust for this" then surely at the bottom of your stroke your legs will be strecthed by an extra 20mm therefore I'd make sure the bottom of the stroke is correct i.e. lower the saddle 10mm and accept your knee will bend more than usual (being 20mm higher in relation to your saddle than usual).

Your thoughts?

 

[gclariosa]

used to be 172.5 but shifted to 170 which i feel is more comfortable and efficient during climbs

 

[jjones41]

I was reading all this talk about crankarms and how long they should be??? I'm 6'3'' inseam 34.5" and have alway's used 175mm. When I climb (out of the saddle) I've alway's felt like my legs are turning too small of circles. Like the crankarm comes down too fast, too soon.

I have ordered a set of Dura-Ace 180mm's and will give them a go. I have also been doing some reading on the www.zinncycles.com website, he has some great info on how long crankarms sould be. According to the formula (your inseam in mm x .216) my cranks would need to be 189mm!!!

This brings to to my last point. About 3 years ago I was doing a crit and afterwords my wife said to me "yeah, while you we racing it looks like your legs don't move or rotate as much as the other riders". I told here it was just because my height....not thinking much about it until the last couple of months.

-Anyway, check the Zinn site out.

 

[Claes]

I ride Record 180 on two roadbikes, old shimano 600 on winter hack, 175 mm.

 

[cydewaze]

172.5 for me.

I'm a bit surprised at the longer = better discussion that happened when this thread was first started. Crank sizes must, of course, be chosen based on the rider's physical proportions (leg length, thigh length, calf length, foot size, etc) so that the rider's knee isn't at an impossibly tight angle at the top of the pedal stroke.

Remember that for every increase in crankarm length, the seat has to be lowered the corresponding amount (to avoid over-extension of the legs). This means that you get 100% of your crank length increase at 3:00 and 9:00, and 200% at 12:00 (top center).

Eventually, if you keep going longer and longer on crank arm length, your knees are going to be jammed up into your chest and you're not going to be able to pedal. The experts at Campy and Shimano (cough) have had decades and decades to arrive at an ideal size range, and whichever length is chosen should be based on the physical proportions of the rider who will be using those cranks.

 

[TheDL]

175mm ISIS splined TruVativ Elita Triple; 'cause that's the length I needed and I got a great deal on 'em.

 

[Claes]

I was reading all this talk about crankarms and how long they should be??? I'm 6'3'' inseam 34.5" and have alway's used 175mm. When I climb (out of the saddle) I've alway's felt like my legs are turning too small of circles. Like the crankarm comes down too fast, too soon.

I have ordered a set of Dura-Ace 180mm's and will give them a go. I have also been doing some reading on the www.zinncycles.com website, he has some great info on how long crankarms sould be. According to the formula (your inseam in mm x .216) my cranks would need to be 189mm!!!

This brings to to my last point. About 3 years ago I was doing a crit and afterwords my wife said to me "yeah, while you we racing it looks like your legs don't move or rotate as much as the other riders". I told here it was just because my height....not thinking much about it until the last couple of months.

-Anyway, check the Zinn site out.

I am 6'2 and my inseam, measured, is 88 cm or roughly the same as yours.
I have tried 170, 175 and currently ride 180 on two bikes. I have the same feeling as you, when out of the saddle it feels too small, particularly with the 170s. I have seen advice from 18 % up the figure you mention. I really like my 180 Records. I still have a cadence over 90 on flat road. So, try it and see what you think, I like it.

People react when you ride 180 and say "boy you must be 100 ft tall or something". Funny that, frame sizes go from say 50 cm to 63 cm. The smaller figure is 79 % of the bigger. 170 is 95% of 180. To me it seems like most people run with a cranklength that is wrong. If you are short, they are too long, if you are tall they are too short.

 

[cavedave]

165 Dura ace on my cannondale raod bike. With 53 39 works great.The bike is only 47cm for me it is perfect

 

[jbieryjr]

http://www.myra-simon.com/bike/cranks.html

Thanks for the info. Always had an idea that I was not efficient in my pedaling and was wondering how to adjust. Again thanks.