Crank length change

[Buff]

Okay, so I've upgraded to Campy... finally... but now I'm riding 175 cranks as apposed to 172.5's.

Here's the question: Do I drop my saddle by exactly 2.5mm?

 

Ta

[Gumpole]

No, otherwise the distance from top of pedal to saddle will reduce by 5mm!

[linnega]

...so you may want to raise your saddle 2.5mm.  Frankly, I wouldn't bother - 2.5mm is no big deal in terms of saddle height.

[Buff]

2.5mm makes a difference when you're been sitting in that position for 7yrs

Maybe I'll just change it a mill at a time and see how it goes.

[Barend de Arend]

2.5mm makes a difference when you're been sitting in that position for 7yrs

 

I changed from 170.0mm to 172.5mm after four years.  It felt exactly the same, so I checked the writing on the crank.  Yep, it was longer.

 

I feel a much bigger difference when getting off my powercranks and on the normal cranks:  it feels like the normal cranks are 20 mm shorter, even though they are the same size.

 

[SwissVan]

 

If you are worried about the change of 2.5mm then drop the saddle height by half 2.5mm (hmmm = 1.25mm) which is a fraction more than a BH.

 

Or you could leave it as it is and see how you feel after a few rides and if any new niggles creaks and groans appear adjust the saddle height accordingly. (Might have to move it up or down, depends on how hi / low it was set pre new cranks).

 

 

 

[Sir Fed]

since your cranks go round in circles, you may want to consider moving it back, or forward, by 2,5mm ...

 

Crank length is not a factor when determining saddle height, leave it where it is and avoid the tendency to crunch monster gears with your new found power. At least until your body is used to the changes.

[Hype]

No' date=' otherwise the distance from top of pedal to saddle will reduce by 5mm![/quote']

 

Please forgive my ignorance but if the cranks are 2.5mm longer then how does lowering saddle height by 2.5mm result in an increase in distance from pedal to saddle of 5mm ?

[Barend de Arend]

No' date=' otherwise the distance from top of pedal to saddle will reduce by 5mm!

[/quote']

Please forgive my ignorance but if the cranks are 2.5mm longer then how

does lowering saddle height by 2.5mm result in an increase in distance

from pedal to saddle of 5mm ?

 

reduce == decrease.

 

At the top of the pedal stroke, your knee will be 5mm closer to your chest, and that could be a problem in the drops.

 

[Hype]

No' date=' otherwise the distance from top of pedal to saddle will reduce by 5mm![/quote']Please forgive my ignorance but if the cranks are 2.5mm longer then how

 

does lowering saddle height by 2.5mm result in an increase in distance

 

from pedal to saddle of 5mm ?

reduce == decrease.At the top of the pedal stroke, your knee will be 5mm closer to your chest, and that could be a problem in the drops.

 

 

Still not getting it. You lower the saddle by 2.5mm and you get a reduction of 5mm between saddle and pedals.

 

How does that come about when the cranks are only 2.5mm longer ?

[Buff]

If I leave it as is, the crank is 2.5mm longer at the bottom of the stroke but 2.5mm shorter (closer to my bum) at top of the stroke.

Therefore, if I lower the saddle 2.5mm, the bottom of the stroke is sorted but the top of the stroke is 5mm closer to my ass... which is actually not a problem as you always set your saddle height according to inseam measurement i.e. you shouldn't have a straight or excessively bent knee at bottom.

[Barend de Arend]

The saddle is 2.5 mm lower. (permanently)

The pedal is 2.5 mm higher. (at the top of the stroke)

 

2.5 + 2.5 = 5.0.

 

[Hype]

The saddle is 2.5 mm lower. (permanently)The pedal is 2.5 mm higher. (at the top of the stroke)2.5 + 2.5 = 5.0.

 

 

Thanks guys. Had a bit of brain fade there.

[Barend de Arend]

which is actually not a problem as you always set your saddle height

according to inseam measurement i.e. you shouldn't have a straight or

excessively bent knee at bottom.

 

Unfortunately it is a problem.  Crank size is almost never used in bike measurements.  And it should be.  You can normally get road bikes from 48cm to 63cm (ignoring compact measurements) from manufacturers.  Or a 31 % change.  Cranks are normally 170 mm to 180 mm, or a 6 % change.  Doh!

 

So using something like .883 times your inseam to measure your saddle height completely ignores crank lengths: if you are very short or very tall, those calculations are just plain wrong.

 

It doesn't help, though: the bottom bracket clearance doesn't change, so if you plug a 200 mm crank on, the pedals would hit the floor.