Crank arm length

drlodge

A longer crank gives you more leverage, its like having a lower gear. But its all quite marginal.

lesfirth

philthy3 wrote:

lesfirth wrote:

Still laughing but now I can't work out who is serious and who is taking the p1ss. I think there are some who I think really must be taking the p1ss but in fact are serious!

Or maybe you're simply being a jerk and don't understand simple gearing? A larger wheel will take longer to rotate than a small wheel, which is effectively what you have with shorter crank arms. to turn the larger wheel at the same rpm, you'd need to put a hell of a lot more effort in to achieve it.

https://pptcrafter.wordpress.com/2013/0 ... owerpoint/

Instead of calling me names your time would be better spent reading the post by lostboysaint and thinking about your post.
Chill out and enjoy the rest of your day.

Alex99

philthy3 wrote:

lesfirth wrote:

Still laughing but now I can't work out who is serious and who is taking the p1ss. I think there are some who I think really must be taking the p1ss but in fact are serious!

Or maybe you're simply being a jerk and don't understand simple gearing? A larger wheel will take longer to rotate than a small wheel, which is effectively what you have with shorter crank arms. to turn the larger wheel at the same rpm, you'd need to put a hell of a lot more effort in to achieve it.

https://pptcrafter.wordpress.com/2013/0 ... owerpoint/

For a given power at the same cadence, longer cranks require less force to be applied. Alternatively, at a fixed pedal force at a given power, cadence would be slightly lower for the longer crank. I think this is what you're getting at with this talk about turning wheels and effort to turn wheels. But this is still nothing like proof that longer cranks makes for a lower cadence.

rick_chasey

Alex99 wrote:

. But this is still nothing like proof that longer cranks makes for a lower cadence.

take

My experience of riders is they tend to apply the same force, regardless of crank length.

So for a given power and a given force, the time taken for the revolution needs to be bigger in order to for the equation to work if the crank is longer (d).

imposter2.0

I think the point which people are trying (and evidently failing) to make others understand is that 90rpm is still 90rpm, regardless of crank length.

rick_chasey

Imposter wrote:

I think the point which people are trying (and evidently failing) to make others understand is that 90rpm is still 90rpm, regardless of crank length.

Or that people like to bring up mistakes by others repeatedly to make themselves feel better.

Alex99

Rick Chasey wrote:

Alex99 wrote:

. But this is still nothing like proof that longer cranks makes for a lower cadence.

take

My experience of riders is they tend to apply the same force, regardless of crank length.

So for a given power and a given force, the time taken for the revolution needs to be bigger in order to for the equation to work if the crank is longer (d).

Agreed, given the assumptions. There are only three variables to play with.

rick_chasey

Alex99 wrote:

Rick Chasey wrote:

Alex99 wrote:

. But this is still nothing like proof that longer cranks makes for a lower cadence.

take

My experience of riders is they tend to apply the same force, regardless of crank length.

So for a given power and a given force, the time taken for the revolution needs to be bigger in order to for the equation to work if the crank is longer (d).

Agreed, given the assumptions. There are only three variables to play with.

Rings true to my own experience. Spinning at larger lengths is quite uncomfortable - for me anyway.

I find the exercise bikes have particularly long cranks - feels like i'm striding.

I just put on 165mms on my road bike and I spin them out much more. It's mainly a comfort thing, rather than seeking performance. Hurts my hip flexors less.

Alex99

Rick Chasey wrote:

Alex99 wrote:

Rick Chasey wrote:

Alex99 wrote:

. But this is still nothing like proof that longer cranks makes for a lower cadence.

take

My experience of riders is they tend to apply the same force, regardless of crank length.

So for a given power and a given force, the time taken for the revolution needs to be bigger in order to for the equation to work if the crank is longer (d).

Agreed, given the assumptions. There are only three variables to play with.

Rings true to my own experience. Spinning at larger lengths is quite uncomfortable - for me anyway.

I find the exercise bikes have particularly long cranks - feels like i'm striding.

I just put on 165mms on my road bike and I spin them out much more. It's mainly a comfort thing, rather than seeking performance. Hurts my hip flexors less.

I hear you. The other thing is, we're not engines. We don't apply an even force all around the pedal stroke. We assume that force will be applied for a greater distance on each revolution with longer cranks, but, perhaps not. The pedals will of course move in a larger circle, but how much of that is 'useful' to the rider may vary a lot.

N0bodyOfTheGoat

Is the ease to attain ~5nM torque on a bike bolt, between a short hex key and a long handled torque wrench, not a decent analogy (albeit cranks typically vary in length by ~10mm, not ~10cm like between my hex keys and Sealey wrench)?

milemuncher1

Knee joints are a crap design, anything that aids keeping them alingned for longer during an exertion is going to get a big thumbs up from me.

dstev55

I've got weird proportions, 89cm inseam with a total body length of 181cm, so very long legs. The only pain I suffer with when cycling is lower back and neck paid. I'm a spinner rather than a grinder and usually like to keep my cadence around the 85-90rpm mark. I current run 172.5cm cranks but I'm thinking 175cm cranks woukd actually help my back and neck as I'd be 2.5cm lower and therefore less of a drop to the handlebars.

Any thoughts on my theory?.

milemuncher1

dstev55 wrote:

Any thoughts on my theory?.

It goes horribly wrong when you take the design of the levers doing the work on the cranks into account.

dstev55

Milemuncher1 wrote:

dstev55 wrote:

Any thoughts on my theory?.

It goes horribly wrong when you take the design of the levers doing the work on the cranks into account.

Please explain?

rick_chasey

dstev55 wrote:

I've got weird proportions, 89cm inseam with a total body length of 181cm, so very long legs. The only pain I suffer with when cycling is lower back and neck paid. I'm a spinner rather than a grinder and usually like to keep my cadence around the 85-90rpm mark. I current run 172.5cm cranks but I'm thinking 175cm cranks woukd actually help my back and neck as I'd be 2.5cm lower and therefore less of a drop to the handlebars.

Any thoughts on my theory?.

Raise your handlebars by 2.5cm...

shortfall

Dstev the cranks are 172.5mm and 175mm. ie: mm not cm. In other words you're not going to be able to drop your saddle by any meaningful amount that might help with your neck pain. Probably easier to flip your stem or add spacers if you haven't cut your steerer.

dstev55

Yeah, getting a bit confused with my lengths here

I'm looking to replace my Rotor crankset with a Campag Super Record crankset. I want the older 5 arm design and there's loads of 175mm ones on eBay but not many 172.5mm ones, I guess I'm just looking for justification to buy 175mm but in all honesty I'd be better sticking to what works well for me I think.

shortfall

Get the 175mm. I've tried 172.5 and 175 and can barely tell the difference. I'm well over 6 foot and by rights my correct crank arm length should be over 180mm but I seem to get by ok on 172.5 ok.

Thick Mike

My advice is to get a ruler and draw a 175mm line, then draw a 172.5mm line. Look at the lines, and then stop obsessing over the length of your cranks.

I spend some time on HiFi forums, and have come to the conclusion that, just because you can measure a difference, doesn't mean it makes a difference.

StillGoing

Thick Mike wrote:

My advice is to get a ruler and draw a 175mm line, then draw a 172.5mm line. Look at the lines, and then stop obsessing over the length of your cranks.

I spend some time on HiFi forums, and have come to the conclusion that, just because you can measure a difference, doesn't mean it makes a difference.

Not for you, but then, some people are more attuned/sensitive to minute changes. And in any case, it is double the difference in length not the single difference.

Thick Mike

philthy3 wrote:

Thick Mike wrote:

My advice is to get a ruler and draw a 175mm line, then draw a 172.5mm line. Look at the lines, and then stop obsessing over the length of your cranks.

I spend some time on HiFi forums, and have come to the conclusion that, just because you can measure a difference, doesn't mean it makes a difference.

Not for you, but then, some people are more attuned/sensitive to minute changes. And in any case, it is double the difference in length not the single difference.

Trouble with drawing a 350mm line is that it falls off the end of my ruler...maybe I need a 355mm ruler...or a 360mm?

fat daddy

start smaller then ... draw a 25mm line and a 28mm line. ..... see the difference, and we all know there is no difference between 25mm and 28mm tyres

Thick Mike

fat daddy wrote:

start smaller then ... draw a 25mm line and a 28mm line. ..... see the difference, and we all know there is no difference between 25mm and 28mm tyres

Just a 12% difference in width, which is quite small.

The difference between 175mm and 172.5mm cranks is 1.4%.

Anyway, feels like we're getting into physics here. I'm sure some people can tell the difference, but I'm glad I can't. Makes life easier as I can choose the cheaper option. I am a crap cyclist too though.

drlodge

I have an 18" rule if you'd like to borrow it?

I seriously doubt 2.5mm radius difference (which is 5mm diameter) on the crank is going to make a great deal of difference. I think I could feel the difference when I changed from 170mm to 172.5mm, but it was marginal and only on the hills when cadence dropped - I felt a bit more leverage. And probably a shorter person would feel more of a difference with that change that an averaged sized person...but as thicko says, its much like changing speaker cables. You might be able to hear a difference, but is it better or worse, or just different?

svetty

The bike I have permanently mounted on the turbo has a 172.5mm NDS crank and a 170mm DS crank. All my road bikes are 172.5mm. I can't tell any difference riding the turbo bike with unequal crank lengths....

StillGoing

Svetty wrote:

The bike I have permanently mounted on the turbo has a 172.5mm NDS crank and a 170mm DS crank. All my road bikes are 172.5mm. I can't tell any difference riding the turbo bike with unequal crank lengths....

Is that not more a case of your lack of ability to notice rather than it not making a difference.

They will always be two camps re crank arm length. Those that say it works for them and those that say it is absolute rubbish and makes no difference. If you don't have the ability to sense any difference, you will fall into the latter camp. If you do have ability, you'll fall into the former. Counter arguments either way make absolutely no difference to the individual.

svetty

philthy3 wrote:

Svetty wrote:

The bike I have permanently mounted on the turbo has a 172.5mm NDS crank and a 170mm DS crank. All my road bikes are 172.5mm. I can't tell any difference riding the turbo bike with unequal crank lengths....

Is that not more a case of your lack of ability to notice rather than it not making a difference.

They will always be two camps re crank arm length. Those that say it works for them and those that say it is absolute rubbish and makes no difference. If you don't have the ability to sense any difference, you will fall into the latter camp. If you do have ability, you'll fall into the former. Counter arguments either way make absolutely no difference to the individual.

If we accept your premise for a moment, what is the 'difference' I am not appreciating? Pain? Fatigue? See the problem : if there is no perceptible difference I struggle to see what difference there is - unless you still maintain that the shorter crank must rotate faster than the longer one?

StillGoing

Svetty wrote:

philthy3 wrote:

Svetty wrote:

The bike I have permanently mounted on the turbo has a 172.5mm NDS crank and a 170mm DS crank. All my road bikes are 172.5mm. I can't tell any difference riding the turbo bike with unequal crank lengths....

Is that not more a case of your lack of ability to notice rather than it not making a difference.

They will always be two camps re crank arm length. Those that say it works for them and those that say it is absolute rubbish and makes no difference. If you don't have the ability to sense any difference, you will fall into the latter camp. If you do have ability, you'll fall into the former. Counter arguments either way make absolutely no difference to the individual.

If we accept your premise for a moment, what is the 'difference' I am not appreciating? Pain? Fatigue? See the problem : if there is no perceptible difference I struggle to see what difference there is - unless you still maintain that the shorter crank must rotate faster than the longer one?

The point being made, is that the shorter crank arm has less distance to travel the full circumference enabling those that like to have a high cadence to make the desired rpm far easier. I accept that I incorrectly described that and touche to you for noting it. But to disparage the notion that it does make a difference to riders that can tell, is folly.

rick_chasey

The difference is less to do with the physics of the crank itself and more around the hip angle.

Your knees don't come up quite as high and so put less stress on your hip flexors.

If you're tall, you'll not really notice all that much - if you're quite short, you might.

As for cadence - I feel it's easier to pedal a higher cadence with shorter cranks, and I think that's because we usually feel our effort in terms of force through the pedals, so for a given force & power, you're pedalling faster.

e999sam

I've used everything from 165 to 175 and I can't tell the difference.