Crank length (can of worms).

[Halfcab24]

So i just wanted to get peoples opinions,

During winter i ride a 1992 Dawes Impulse with 11 speed 105 crank length 170.

I recently purchased a Trek Emonda SL8 11 speed dura ace crank length 172.5. To ride in summer etc.

I seem to be able to climb better on the Dawes which strikes me as odd considering the Emonda is much much much lighter. I also seem to be more comfortable on the Dawes and get a lot of lower back pain on the Emonda.

The only difference in set up bar geometry etc is the crank length.

Could this be an issue stopping the Emonda perform? Or could it just be my fit on the Emonda. Or something else i have overlooked?

Thanks in advance,

Callum

 

[Specialeyes]

I'm pretty sure there'll be more differences between the bikes than simply crank length and post-1992 marketing!

That said, here's GCN's take on the thorny subject:


View: https://www.youtube.com/watch?v=eMAxH_Ud8YE

 

[Halfcab24]

Very interesting! Maybe bike fit has more todo with it... Will get a bike fit and see how it goes!

 

[ColinJ]

I have a friend who is convinced that he can feel a huge difference between 170 mm and 175 mm cranks. I don't think it makes a lot of difference. I'm sure that 140 mm would feel VERY short and 200 mm VERY long, but 5 mm difference ... nah! (2.5 mm, even less difference, obviously.)

I broke a 175 mm left crank on my Basso and replaced it with a 170 mm crank that I had spare. I have been riding the bike with unmatched cranks for years and don't have a problem with it!

 

[Gatters]

yep its not the crank length, its other stuff

 

[recumbentpanda]

You are worrying about a 2.5mm difference? You'll get that much variation just changing to a different pair of socks.

 

[Hacienda71]

There is probably a 2.5mm difference in most peoples legs....

 

[fossyant]

I have 170s on 3 bikes and 175s on the MTB. Can't tell the difference.

The 175s were because the cranks were in an end of line sale and super cheap.

 

[ColinJ]

There is probably a 2.5mm difference in most peoples legs....

There is over 1 cm difference in mine ... That is actually why I have stuck with the shorter crank on the left, which I think works well with the shorter leg. Having said that, my other bikes have matching 175 mm cranks!

Ah, except for my gym bike which has 150 mm BMX-style cranks. They DO feel short, but still usable. I get used to them after a few minutes. I'd prefer them to be longer but can't be bothered to change them.

 

[Prometheus]

Hi I had the same problem with a specialised road and a CX.

On the flat no difference in speed.

But I could clime 2 mph faster on the CX

over the same course with same gearing.

The answer for me was setback.

Got a new saddle with more adjustment backwards.

Now I have a road bike that loves hills.

 

[Halfcab24]

Interesting! I think i may get a fit somewhere in Yorkshire and see how I get on. I think it may just be a case of getting used to the Emondas position more than anything else!

 

[Elybazza61]

Mike Burrows ( Lotus bike and Giant defy deaigner and all-round clever bloke) has said that most people have too long cranks,think he reckons that a lot of bods would be better with cranks as short as 145.

Personally I've gone over to 170 from 175 and I see to be able to get a better position sorted on the bike also helped by going to narrower bars.

Article from Cyclist;

http://www.cyclist.co.uk/in-depth/360/is-there-a-correct-crank-length

 

[Deleted member 1258]

The only time I've noticed a difference in crank length was on my fixed, for some strange reason I could descend better on 165 cranks than I could on 170 cranks, apart from that all cranks feel the same.

 

[Prometheus]

Hi I had the same problem with a specialised road and a CX.

On the flat no difference in speed.

But I could clime 2 mph faster on the CX

over the same course with same gearing.

The answer for me was setback.

Got a new saddle with more adjustment backwards.

Now I have a road bike that loves hills.

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Hi I didn’t want to go all tecno on you.
So kept it short, simple no detail
I had gone down to a 165 crank the year before on the roady.
The first thing I did was to swap it back, still the same.

Now big puzzle in little China-town, 6 months later got new saddle with longer rails.
The most important measurement when climbing, is our sit bones in relation to the crank axle, sit back get more torque!
Time-trial far forward as possible, fastest speed but can't clime long hills.
Some trail saddles are designed for forward or back movement.

Different cranks give different knee displacement's, torque and possible top cadence.
Try this
https://www.google.co.uk/search?q=bicycle+crank+angle&biw=1427&bih=670&site=webhp&tbm=isch&imgil=RwzMelli50E0VM%253A%253BDmUtX_r9U0eLg

 

[400bhp]

There's absolutely no way that 2.5mm on the crank will make any difference to your climbing ability.

There's a school of thought (and I have no reason to disbelieve it, particularly because Boardman thinks it) that shorter cranks (150mm) make the rider more aero. I expect this to be utilised in the next couple of years, probably by track riders first.