Effect of crankarm length on saddle height?

[Luigi de Guzman]

A stupid question for you guys:

All else being equal--frame, rider, etc--would mounting shorter (say by
5mm? 10mm?) cranks mean a corresponding decrease in saddle height to get
the same amount of total leg extension?

I'm riding 175mm cranks now; my old bike was a bit big, but ran with
170mm cranks. I'm debating whether or not I should go to shorter cranks.

-Luigi

--
Luigi de Guzman
http://ouij.livejournal.com

[sally]

Luigi de Guzman <luigi12081@cox.net> wrote in news:GPGgi.652324$2Q1.241147
@newsfe16.lga:
> All else being equal--frame, rider, etc--would mounting shorter (say by
> 5mm? 10mm?) cranks mean a corresponding decrease in saddle height to get
> the same amount of total leg extension?

You would need to raise your seat if you got shorter crankarms, right?

[sally]

Luigi de Guzman <luigi12081@cox.net> wrote in news:GPGgi.652324$2Q1.241147
@newsfe16.lga:
> All else being equal--frame, rider, etc--would mounting shorter (say by
> 5mm? 10mm?) cranks mean a corresponding decrease in saddle height to get
> the same amount of total leg extension?

You would need to raise your seat if you got shorter crankarms, right?

[Bill Sornson]

Luigi de Guzman wrote:
> A stupid question for you guys:
>
> All else being equal--frame, rider, etc--would mounting shorter (say
> by 5mm? 10mm?) cranks mean a corresponding decrease in saddle height
> to get the same amount of total leg extension?

Actually, you'd /increase/ the seatpost height to keep the same
pedal-to-saddle distance.

> I'm riding 175mm cranks now; my old bike was a bit big, but ran with
> 170mm cranks. I'm debating whether or not I should go to shorter
> cranks.

No real reason to if current set-up is comfortable. You likely wouldn't be
able to tell the difference once saddle height is adjusted (slightly).

[Bill Sornson]

Luigi de Guzman wrote:
> A stupid question for you guys:
>
> All else being equal--frame, rider, etc--would mounting shorter (say
> by 5mm? 10mm?) cranks mean a corresponding decrease in saddle height
> to get the same amount of total leg extension?

Actually, you'd /increase/ the seatpost height to keep the same
pedal-to-saddle distance.

> I'm riding 175mm cranks now; my old bike was a bit big, but ran with
> 170mm cranks. I'm debating whether or not I should go to shorter
> cranks.

No real reason to if current set-up is comfortable. You likely wouldn't be
able to tell the difference once saddle height is adjusted (slightly).

[Luigi de Guzman]

On Wed, 27 Jun 2007 21:46:07 -0700, Bill Sornson wrote:

> Luigi de Guzman wrote:
>> A stupid question for you guys:
>>
>> All else being equal--frame, rider, etc--would mounting shorter (say
>> by 5mm? 10mm?) cranks mean a corresponding decrease in saddle height
>> to get the same amount of total leg extension?
>
> Actually, you'd /increase/ the seatpost height to keep the same
> pedal-to-saddle distance.
>
>> I'm riding 175mm cranks now; my old bike was a bit big, but ran with
>> 170mm cranks. I'm debating whether or not I should go to shorter
>> cranks.
>
> No real reason to if current set-up is comfortable. You likely wouldn't be
> able to tell the difference once saddle height is adjusted (slightly).

This is all good news. Yay!

When this summer is out, I'm thinking about going to shorter cranks on my
main bike--mainly to try and solve an annoying toeclip/fender overlap.

-Luigi

--
Luigi de Guzman
http://ouij.livejournal.com

[joseph.santaniello@gmail.com]

On Jun 28, 6:46 am, "Bill Sornson" <a...@ask.me> wrote:
> Luigi de Guzman wrote:
> > A stupid question for you guys:
>
> > All else being equal--frame, rider, etc--would mounting shorter (say
> > by 5mm? 10mm?) cranks mean a corresponding decrease in saddle height
> > to get the same amount of total leg extension?
>
> Actually, you'd /increase/ the seatpost height to keep the same
> pedal-to-saddle distance.

One formula in use for determining seat height is to use inseam x 1.09
to get the seat height from the bottom bracket + the crank length.
This means that longer crank arms would result in a lower seat
relative to the bb. In other words as you say if you swap to shorter
crank arms, you would raise the seat.


> > I'm riding 175mm cranks now; my old bike was a bit big, but ran with
> > 170mm cranks. I'm debating whether or not I should go to shorter
> > cranks.
>
> No real reason to if current set-up is comfortable. You likely wouldn't be
> able to tell the difference once saddle height is adjusted (slightly).

I ride 165's, 170's, 175's, 180's and 195's. And occasionally 172.5's
and 177.5's. Each of these bikes has the seat adjusted to compensate
more or less for the different lengths. I can hardly tell the
difference between 165 and 175, and the jump to 195 is only really
noticable in that it encourages a much lower cadence and has more
aerobelly interference.

OP, In other words go for shorter cranks if you want, and maybe bump
the seat up a corresponding amount.

Joseph

[Luigi de Guzman]

On Wed, 27 Jun 2007 21:46:07 -0700, Bill Sornson wrote:

> Luigi de Guzman wrote:
>> A stupid question for you guys:
>>
>> All else being equal--frame, rider, etc--would mounting shorter (say
>> by 5mm? 10mm?) cranks mean a corresponding decrease in saddle height
>> to get the same amount of total leg extension?
>
> Actually, you'd /increase/ the seatpost height to keep the same
> pedal-to-saddle distance.
>
>> I'm riding 175mm cranks now; my old bike was a bit big, but ran with
>> 170mm cranks. I'm debating whether or not I should go to shorter
>> cranks.
>
> No real reason to if current set-up is comfortable. You likely wouldn't be
> able to tell the difference once saddle height is adjusted (slightly).

This is all good news. Yay!

When this summer is out, I'm thinking about going to shorter cranks on my
main bike--mainly to try and solve an annoying toeclip/fender overlap.

-Luigi

--
Luigi de Guzman
http://ouij.livejournal.com

[joseph.santaniello@gmail.com]

On Jun 28, 6:46 am, "Bill Sornson" <a...@ask.me> wrote:
> Luigi de Guzman wrote:
> > A stupid question for you guys:
>
> > All else being equal--frame, rider, etc--would mounting shorter (say
> > by 5mm? 10mm?) cranks mean a corresponding decrease in saddle height
> > to get the same amount of total leg extension?
>
> Actually, you'd /increase/ the seatpost height to keep the same
> pedal-to-saddle distance.

One formula in use for determining seat height is to use inseam x 1.09
to get the seat height from the bottom bracket + the crank length.
This means that longer crank arms would result in a lower seat
relative to the bb. In other words as you say if you swap to shorter
crank arms, you would raise the seat.


> > I'm riding 175mm cranks now; my old bike was a bit big, but ran with
> > 170mm cranks. I'm debating whether or not I should go to shorter
> > cranks.
>
> No real reason to if current set-up is comfortable. You likely wouldn't be
> able to tell the difference once saddle height is adjusted (slightly).

I ride 165's, 170's, 175's, 180's and 195's. And occasionally 172.5's
and 177.5's. Each of these bikes has the seat adjusted to compensate
more or less for the different lengths. I can hardly tell the
difference between 165 and 175, and the jump to 195 is only really
noticable in that it encourages a much lower cadence and has more
aerobelly interference.

OP, In other words go for shorter cranks if you want, and maybe bump
the seat up a corresponding amount.

Joseph