Cranck length decision

[Azonic]

I'm 1.89m tall. Use 175mm on my road bikes, and 180mm on my MTBs.

[Canaris]

I'm 1.89m tall. Use 175mm on my road bikes' date=' and 180mm on my MTBs.[/quote']

 

and your inseam length, foot size and femur length are?

What is your muscle flexibility, do you have tight hamstrings?

[THE BODY CENTRE]

When you do a trackstand' date=' you exert torque on the crank but generate no power.

 

 

[/quote']

 

Correct, but will you be able to generate power without torque (in the above example)?

 

 

Just for this explanation, consider torque just a force that goes "round the bend" and lets just simplify it to linear force for a moment.  Your question would then be can you generate power without applying a force to a body?

 

No.

 

 

 

 

Exactly. So they are two entities. But they are related - in the sense that the one cannot be generated without the presence of the other one. (again in this example)

 

JohanB - i agree with you - and you are respected for being an 'exact man'. I just thought your choice of wording (p2 of this thread) was open for misinterpretation ..

[Azonic]

I'm 1.89m tall. Use 175mm on my road bikes' date=' and 180mm on my MTBs.[/quote']

 

and your inseam length, foot size and femur length are?

What is your muscle flexibility, do you have tight hamstrings?

 

Foot: 10.5 (Size 45)

Muscles are quite flexible, not sure how you want to verify that.

I very rarely get sore muscles, just slight tightness after rides over 140km, but nothing a nice stretch session can't fix.

 

I'll check my inseam and femur lengths tonight.

[Canaris]

I'm 1.89m tall. Use 175mm on my road bikes' date=' and 180mm on my MTBs.[/quote']

 

and your inseam length, foot size and femur length are?

What is your muscle flexibility, do you have tight hamstrings?

 

Foot: 10.5 (Size 45)

Muscles are quite flexible, not sure how you want to verify that.

I very rarely get sore muscles, just slight tightness after rides over 140km, but nothing a nice stretch session can't fix.

 

I'll check my inseam and femur lengths tonight.

 

even though you have very long cranks, you don't see to show any symptoms of a bad fit.  BUt if you are willing to shove a tap measure in various places, take some photo's I am sure there are some sicko's here who would enjoy them.

[Azonic]

My fiance says my inseam is long enough so that's all that matters

 

I started using 180mm cranks on the MTB by chance. The MTB I bought years back had 180mm on, and I've continued that tradition. If I ride a MTB today with 175's I feel very limited and restricted, almost clostrofobic.

[Johan Bornman]

 

JohanB - i agree with you - and you are respected for being an 'exact man'. I just thought your choice of wording (p2 of this thread) was open for misinterpretation ..

 

You are right, it was sloppy wording. Thanks for pointing it out.

Johan Bornman2008-04-21 07:57:47

[bruce]

Another way to understand the issue here is that the muscles in the cyclists legs are the "engines" i.e. they convert stored energy (in the form of glygogen, fat, and even a little protein) into various forms of energy such as potential energy (lifting the mass of the rider and bike up a gradient), kinetic energy (forward motion) and heat etc.

Everything after the muscles in the legs of the rider can be viewed as a "linkage" to transfer the force applied to the pedal, to the force applied by the tyre to the road.  This includes the joints/bones in the riders legs, ankle, feet, then the cranks, through the spider, through the chain, rear cassette, hub body, spokes, rim, tyre, then finally the road.  Linkages cannot contribute energy (and therefore perform work) to the system, all they can hope to do is transfer that energy as efficiently (i.e. with as little loss) as possible.

 

So, changing the crank length cannot make you produce more power, just like changing the shape of the chainring cannot make you produce more power.

 

But, does changing the length of the crank make the linkages more efficient, i.e. does more of the energy converted in the muscles end up pushing the bike forward?  I'm not a mechanical engineer, so I wouldn't want to argue too much about this subject, but I'd assume that there are optimum lengths for the various levers that are providing the linkage in the system.  There are certainly optimal contraction velocities and joint angles for the muscles in our legs (based on lengths of femur, fibia, tibia etc as well as muscle fibre composition).  So, the rationale behind altering crank length is not about producing more power, it's about losing less power along the way.

 

The force applied by wind resistance is not linear, but improving a 60min TT by 30sec equates to 0.8% faster.  30sec is a significant margin when looking at the performances of pros in major TT's.  Can changing the crank length make the power transfer on a bicycle more effiecient by a similar order of magnitude?  Possibly, which is why people are prepared to put some research into this issue.

 

I think the issue that needs to be taken into account, is that the difference between say the top 5 TT riders, or the top climbers, is tiny.  Any change to equipment that yeilds improvements in small amounts can be beneficial.

 

But that is for top level pro's - which most of us mere mortals aren't

 

 

[Johan Bornman]

Another way to understand the issue here is that the muscles in the cyclists legs are the "engines" i.e. they convert stored energy (in the form of glygogen' date=' fat, and even a little protein) into various forms of energy such as potential energy (lifting the mass of the rider and bike up a gradient), kinetic energy (forward motion) and heat etc.

Cut cut cut cut cut.......

 

But that is for top level pro's - which most of us mere mortals aren't

 

 

[/quote']

 

Bruce, this is an excellent explanation that puts a lot of questions arising on this forum in perspective. I just wish we had a FAQ section where gems like this can be catalogued.

 

With regards to the linkages, I always smile when I see these expensive cycling shoes that claim more efficient power transfer than other brands. Somehow they suggest that the harder and thinner the sole, the better the energy transfer. Howerver, after a certain hardness (hard rubber upwards), making the soles harder or thinner doesn't create a more efficient linkage.

 

It's just an excuse to build more carbon fibre into stuff and getting suckers to pay more for it.

 

We used to see the same argument applied to chainstays - making them sorter makes for a better link....or so they claimed. Today the stays are as short as the wheel allows and this is now no longer a marketing line they can use.

[bruce]

If you think cycling is bad, just take a look at the world of high-definition audio!  There they talk about all sorts of interesting things that you would only be able to hear if your ears were capable of significant sonic bandwidth, and which the original artist never put in there in the first place, and wouldn't have been able to be captured by the recording equipment used, or stored on a medium that records samples at a rate of 44.1kHz IIRC (but let's not worry about the violation of Nyquist's Law)

[Johan Bornman]

If you think cycling is bad' date=' just take a look at the world of high-definition audio!  There they talk about all sorts of interesting things that you would only be able to hear if your ears were capable of significant sonic bandwidth, and which the original artist never put in there in the first place, and wouldn't have been able to be captured by the recording equipment used, or stored on a medium that records samples at a rate of 44.1kHz IIRC (but let's not worry about the violation of Nyquist's Law)[/quote']

 

Yup, been there, made enemies there too. Here's my favourite retort when someone starts justifying (through pseudo-science of course) why they paid a zillion rand per meter for oxygen-free monster cable.

 

http://gizmodo.com/363154/audiophile-deathmatch-monster-cables-vs-a-coat-hanger

 

For those of you who don't feel like a click-through, it is an experiement connecting two identical hi-fi systems and letting experts attempt to hear a difference. There was no difference, they said,  but the one hi-fi was connected using soldered coat hangers, the other one using fancy Monster cable. Go figure.