Pro's and cons of shorter crank arms?

pinno

You van get shorter cranks but you might have a shorter 'sweet spot' and you can theoretically achieve a higher pedal cadence although you may get less leverage and you'll have to faff around with the seat post height.
On the other hand, if you got longer crank arms, you would have a longer 'sweet spot' and theoretically more leverage but a slower cadence and you may or may not put pressure on your knees and you'll have to faff around with the seat post height.

The transmission system on a bicycle is also known as a torque multiplication unit. This means that if you get shorter crank arms you'll simply find yourself in a slightly larger gear whereas if you get longer crank arms, you might find yourself in a slightly smaller gear on that same patch of false flat you did last week into a tail wind with your tyres pumped up 3 lbs psi less than they should have been after 1 hour more sleep the night before than you normally do but your breakfast did not quite contain the right carbohydrate to protein ratio and you ran out of High5 so you will have to suffer the effects of plain tap water in your drinking bottle.
If you had previously went to the gym for a period of 8 weeks interspersed with the odd cycle ride doing hill repeats (that's what I was told I should do instead), you could generate a lot more power theoretically but power won't do you any good unless you have the aerobic ability to sustain the power and the right crank arm length to suit your power to optimum VO2 intake taking into consideration your lactate threshold which was only tested at a pre-determined cadence and watts per kilo ratio written on the back of an empty Latex inner tube packet by an overweight lobotomy, err... sorry, Laboratory assistant called Nigel.

So you see, it's all very straightforward and you know you can always get some good advice on a cycling forum. Someone, somewhere even said that cycling was 'fun'? (The b4stards).

Most of all, make sure the padding in your bibs is thick enough to withstand the rigours of getting a kicking in the Bike Radar forum.

pblakeney

But how does all this apply when you are sat on the top tube for maximum aero effect?
Chris looked ungainly but there is no denying the result.

Anonymous

Pinno wrote:

You van get shorter cranks but you might have a shorter 'sweet spot' and you can theoretically achieve a higher pedal cadence although you may get less leverage and you'll have to faff around with the seat post height.
On the other hand, if you got longer crank arms, you would have a longer 'sweet spot' and theoretically more leverage but a slower cadence and you may or may not put pressure on your knees and you'll have to faff around with the seat post height.

The transmission system on a bicycle is also known as a torque multiplication unit. This means that if you get shorter crank arms you'll simply find yourself in a slightly larger gear whereas if you get longer crank arms, you might find yourself in a slightly smaller gear on that same patch of false flat you did last week into a tail wind with your tyres pumped up 3 lbs psi less than they should have been after 1 hour more sleep the night before than you normally do but your breakfast did not quite contain the right carbohydrate to protein ratio and you ran out of High5 so you will have to suffer the effects of plain tap water in your drinking bottle.
If you had previously went to the gym for a period of 8 weeks interspersed with the odd cycle ride doing hill repeats (that's what I was told I should do instead), you could generate a lot more power theoretically but power won't do you any good unless you have the aerobic ability to sustain the power and the right crank arm length to suit your power to optimum VO2 intake taking into consideration your lactate threshold which was only tested at a pre-determined cadence and watts per kilo ratio written on the back of an empty Latex inner tube packet by an overweight lobotomy, err... sorry, Laboratory assistant called Nigel.

So you see, it's all very straightforward and you know you can always get some good advice on a cycling forum. Someone, somewhere even said that cycling was 'fun'? (The b4stards).

Most of all, make sure the padding in your bibs is thick enough to withstand the rigours of getting a kicking in the Bike Radar forum.

That was almost word for word what I was going to say. I just ran out of F@*ks to give. :-)

pinno

PBlakeney wrote:

But how does all this apply when you are sat on the top tube for maximum aero effect?
Chris looked ungainly but there is no denying the result.

Surely that goes all the way back to the thickness of the padding in your bib shorts which were tested in a wind tunnel in deepest, darkest lab rat land away from the prying eyes of the French.

pblakeney

But sitting on the top tube is going against scientific proof.

pinno

It's scientific proof that the top tube of the Pinarello Dogma is strong enough to support the weight of a very fast, male super waif.
If you don't believe me, have you ever seen Greipel do that?

pblakeney

Fair point, well made.
Confirms my instinct that I shouldn't attempt it, and simply pootle to the cafe instead.

darkhairedlord

Short cranks are good for clown bikes in the circus, that's about it.

StillGoing

Maglia Rosa wrote:

I originally said I noticed zero performance change from 165mm to 170mm. That is 5mm. I also said becsuse of that the difference to 172.5 from 170 woild so so insignificant you would not notice. I am not just a guy who rides every sunday to the shops. I have raced plenty over the last decade or so. I am not new to this. Plenty dismiss is. I was taking the wee-wee out of the fact he was saying he can tell the difference in 2.5mm . That i doubt. And it would only be 2.5mm not 5mm as its the measurement from pedal to saddle.

So. Philthy. If you are going to jump into a thread to stirr up hatred and call people trolls you better et your facts straight.

You clearly don't get a circle do you. A 2.5mm shorter crank arm at the bottom of the pedal stroke (so at full leg extension) means the saddle will ride 2.5mm to cater for the reduced length. But, it is 5mm extra clearance at the top of the pedal stroke where the difference is noticeable. 5mm extra difference in unrestricted movement.

Now if you couldn't tell the difference with 10mm extra movement at the top of the pedal stroke, I don't think there is any hope for you. Read through and you'll find I was on this thread from early on and haven't just jumped on. So, are you simply trying to back pedal (no pun intended) by claiming you are on a wind up, or are you trolling. You can't have it both ways. DO yourself a favour and simply admit you're out of your depth on being able to offer anything constructive re shorter crank arms. :roll:

StillGoing

Clearly a lot of dickheads on BIke Radar who would be best suited on the Cake Stop board with the tree huggers and left wing liberals.

fat daddy

darkhairedlord wrote:

Short cranks are good for clown bikes in the circus, that's about it.

Dura ace sizes go from 165mm-180mm ... at what point is it considered short.

Or is it a typical case of, if its shoprter than mione, its short and you are doing it all wrong and if its longer than me, its too long and you are clearly doing it wrong.

oh and I decided the reference point, not through experimenting, but what came on my bike when I b ought it ?

pblakeney

This is Road Beginners. Anyone thinking that 2.5mm (or even 5mm top stroke) will make any difference to a beginner other than a slight saddle adjustment is taking things too seriously.

sloppyschleckonds

is that the summary of the first 4 pages?

HTH

darkhairedlord

fat daddy wrote:

darkhairedlord wrote:

Short cranks are good for clown bikes in the circus, that's about it.

Dura ace sizes go from 165mm-180mm ... at what point is it considered short.

Or is it a typical case of, if its shoprter than mione, its short and you are doing it all wrong and if its longer than me, its too long and you are clearly doing it wrong.

oh and I decided the reference point, not through experimenting, but what came on my bike when I b ought it ?

If clown bikes come with short cranks? Then yes!

fat daddy

darkhairedlord wrote:

If clown bikes come with short cranks? Then yes!

They come with a standard clown length crank .... Some clowns are shorter and have back problems so think they might benefit from shorter cranks ... Some clowns prefer longer cranks.

I think it depends on the clown

darkhairedlord

fat daddy wrote:

darkhairedlord wrote:

If clown bikes come with short cranks? Then yes!

They come with a standard clown length crank .... Some clowns are shorter and have back problems so think they might benefit from shorter cranks ... Some clowns prefer longer cranks.

I think it depends on the clown

Don't forget toe overlap, a real problem with clown shoes.

bernithebiker

Important points;

a) longer cranks do NOT give you a 'magical' mechanical advantage. To gain extra torque on short cranks, simply change up a gear.
b) BUT your body MIGHT be able to produce more torque easier on longer cranks depending on your morphology*.
c) within reason, it will be easier and more economical to maintain high cadence on shorter cranks.
d) shorter cranks allow lower torso = more aero
e) it may be easier to 'get on the power' quicker with shorter cranks, and have a smoother, longer power stroke, due to less leg extension.

The trend seems to be towards shorter cranks. I benefitted hugely by dropping from 175 to 172.5 to 170, and would now like to try 167.5 (I'm 1.74m with shortish legs).

So many riders just accept the 172.5mm cranks they're given when buying a bike without questioning if they are optimal for them. Common sense tells us that this cannot be right for riders from 1.70 to 1.85m

*leg length and proportions

pinno

Unless you are doing silly miles, none of that matters unless you're cranks are way to short or way too long.

Think about it - ' more aero' ?! Marginal gains amongst the general (amateur) populace fed on a diet of marketing hype.

bernithebiker

Pinno wrote:

Unless you are doing silly miles, none of that matters unless you're cranks are way to short or way too long.

Think about it - ' more aero' ?! Marginal gains amongst the general (amateur) populace fed on a diet of marketing hype.

Well it worked for me. I'm lower and faster now and spin better.

But sure, it all depends on what you want out of cycling. If it's just happily cycling around with your mates enjoying the view, then more power to you. Personally I want to see how fast I can go before old age hobbles me, but I accept that not everyone is the same.

pinno

bernithebiker wrote:

Pinno wrote:

Unless you are doing silly miles, none of that matters unless you're cranks are way to short or way too long.

Think about it - ' more aero' ?! Marginal gains amongst the general (amateur) populace fed on a diet of marketing hype.

...Personally I want to see how fast I can go before old age hobbles me...

...and when you get to that point (or at least increasing effort becomes totally disproportionate to diminishing returns), you say "WTF, let's just go out and pedal. When I were a lad...".

fat daddy wrote:

darkhairedlord wrote:

Short cranks are good for clown bikes in the circus, that's about it.

...oh and I decided the reference point, not through experimenting, but what came on my bike when I b ought it ?

What?! You didn't analyse it to the nth degree and seek some advice on a cycling forum first? What's the matter with you?

fat daddy

Pinno wrote:

What?! You didn't analyse it to the nth degree and seek some advice on a cycling forum first? What's the matter with you?

newbie mistake ..... I honestly didn't know they came in different lengths until I discovered this forum :oops:

pinno

fat daddy wrote:

Pinno wrote:

What?! You didn't analyse it to the nth degree and seek some advice on a cycling forum first? What's the matter with you?

newbie mistake ..... I honestly didn't know they came in different lengths until I discovered this forum :oops:

Now you're going to tell me that you suddenly have knee and lower back problems or you've noticed you're legs are flapping around at 150rpm since discovering the length of your crank arms. If you see what I mean.

bernithebiker

Nothing wrong with taking an interest in the technical aspects of your bike and cycling. I quite enjoy the engineering / equipment side of it, others don't, horses for courses.......

pinno

bernithebiker wrote:

Nothing wrong with taking an interest in the technical aspects of your bike and cycling. I quite enjoy the engineering / equipment side of it, others don't, horses for courses.......

We all love shiny bits. That's why once you get bitten, you'll be in a forever cycle of more bits, upgrades and N+1.