Bike Fit: How critical is KOPS

Dear All,

Due to medical reasons I want to install a crankset with shorter crankarms (from 170 to 127). The reach on this bicycle is already a bit on the long side so even though I will raise the saddle to maintain the appropriate amount of bend at the bottom of the stroke, I cannot move the saddle backwards to bring my knee over the pedal spindle.

My question: How critical is the KOPS (Knee Over Pedal Spindle) rule? Are there any risks pedaling with my knee in front of the pedal? How will the performance be?

Many thanks in advance

Dimitris

On Monday, July 10, 2017 at 5:14:12 AM UTC-7, dstamat wrote:
Dear All,

Due to medical reasons I want to install a crankset with shorter crankarms (from 170 to 127). The reach on this bicycle is already a bit on the long side so even though I will raise the saddle to maintain the appropriate amount of bend at the bottom of the stroke, I cannot move the saddle backwards to bring my knee over the pedal spindle.

My question: How critical is the KOPS (Knee Over Pedal Spindle) rule? Are there any risks pedaling with my knee in front of the pedal? How will the performance be?

Many thanks in advance

Dimitris - I have never found it to be a problem as long as you don't go to extremes. After all, you are sliding back and forth on the extremes of the saddle with variations of terrain.

On Monday, July 10, 2017 at 5:14:12 AM UTC-7, dstamat wrote:
Dear All,

Due to medical reasons I want to install a crankset with shorter crankarms (from 170 to 127). The reach on this bicycle is already a bit on the long side so even though I will raise the saddle to maintain the appropriate amount of bend at the bottom of the stroke, I cannot move the saddle backwards to bring my knee over the pedal spindle.

My question: How critical is the KOPS (Knee Over Pedal Spindle) rule? Are there any risks pedaling with my knee in front of the pedal? How will the performance be?

Many thanks in advance

Dimitris


Sounds like a large change. 170 to 127? I would have thought 170 to 160 would be significant.

On Monday, July 10, 2017 at 8:14:12 AM UTC-4, dstamat wrote:
Dear All,

Due to medical reasons I want to install a crankset with shorter crankarms (from 170 to 127). The reach on this bicycle is already a bit on the long side so even though I will raise the saddle to maintain the appropriate amount of bend at the bottom of the stroke, I cannot move the saddle backwards to bring my knee over the pedal spindle.

My question: How critical is the KOPS (Knee Over Pedal Spindle) rule? Are there any risks pedaling with my knee in front of the pedal? How will the performance be?

Many thanks in advance

Dimitris

KOPS has pretty much fallen by the wayside along with a few other bicycle fit guidelines such as the handlebar hiding the front axle when viewd fromthe rider position and touring bikes needing a lower bttom bracket for stability. I think the latter was so you didn't have to lean the loaded bike when stopping.

See https://sheldonbrown.com/kops.html

The Myth of K.O.P.S.

An Alternative Method of Bike Fit:
by Keith Bontrager

originally edited by Doug Roosa
HTML and additional editing by Sheldon Brown
Minor edits and a few comments by John Allen

Cheers

On Monday, July 10, 2017 at 10:23:02 AM UTC-7, Sir Ridesalot wrote:
On Monday, July 10, 2017 at 8:14:12 AM UTC-4, dstamat wrote:
Dear All,

Due to medical reasons I want to install a crankset with shorter crankarms (from 170 to 127). The reach on this bicycle is already a bit on the long side so even though I will raise the saddle to maintain the appropriate amount of bend at the bottom of the stroke, I cannot move the saddle backwards to bring my knee over the pedal spindle.

My question: How critical is the KOPS (Knee Over Pedal Spindle) rule? Are there any risks pedaling with my knee in front of the pedal? How will the performance be?

Many thanks in advance

Dimitris

KOPS has pretty much fallen by the wayside along with a few other bicycle fit guidelines such as the handlebar hiding the front axle when viewd fromthe rider position and touring bikes needing a lower bttom bracket for stability. I think the latter was so you didn't have to lean the loaded bike when stopping.

See https://sheldonbrown.com/kops.html

The Myth of K.O.P.S.

An Alternative Method of Bike Fit:
by Keith Bontrager

originally edited by Doug Roosa
HTML and additional editing by Sheldon Brown
Minor edits and a few comments by John Allen

Nevertheless the Fit Kit gave a fit almost identical to KOPS except for the extreme MTB's that had a radical seat tube angle. I have a vague recollection of being friends with Keith since I was friends with his chief machinist.

On Mon, 10 Jul 2017 05:14:08 -0700 (PDT), dstamat
wrote:

Dear All,

Due to medical reasons I want to install a crankset with shorter crankarms (from 170 to 127). The reach on this bicycle is already a bit on the long side so even though I will raise the saddle to maintain the appropriate amount of bend at the bottom of the stroke, I cannot move the saddle backwards to bring my knee over the pedal spindle.

My question: How critical is the KOPS (Knee Over Pedal Spindle) rule? Are there any risks pedaling with my knee in front of the pedal? How will the performance be?

Many thanks in advance

Dimitris

Over the years I've found that KOPS is a good starting place in
adjusting fit. But once one gets a basic saddle height and reach
established that moving the seat back and forth and maybe raising or
lowering the handle bars doesn't cause a problem.

While a 40mm change in crank length seems sort of radical I think I'd
try a few short rides and see how it feels. After all a time trial or
tri bike has a relatively forward seat position and those guys don't
seem to have a problem with their knees.

I might also comment that, while it isn't the extreme that you seem to
be planning, I change between bikes with 170 and 175 crank arms and
don't even notice the difference.
--
Cheers,

John B.

On Monday, July 10, 2017 at 8:24:54 PM UTC-7, John B. wrote:
On Mon, 10 Jul 2017 05:14:08 -0700 (PDT), dstamat
wrote:

Dear All,

Due to medical reasons I want to install a crankset with shorter crankarms (from 170 to 127). The reach on this bicycle is already a bit on the long side so even though I will raise the saddle to maintain the appropriate amount of bend at the bottom of the stroke, I cannot move the saddle backwards to bring my knee over the pedal spindle.

My question: How critical is the KOPS (Knee Over Pedal Spindle) rule? Are there any risks pedaling with my knee in front of the pedal? How will the performance be?

Many thanks in advance

Dimitris

Over the years I've found that KOPS is a good starting place in
adjusting fit. But once one gets a basic saddle height and reach
established that moving the seat back and forth and maybe raising or
lowering the handle bars doesn't cause a problem.

While a 40mm change in crank length seems sort of radical I think I'd
try a few short rides and see how it feels. After all a time trial or
tri bike has a relatively forward seat position and those guys don't
seem to have a problem with their knees.

I might also comment that, while it isn't the extreme that you seem to
be planning, I change between bikes with 170 and 175 crank arms and
don't even notice the difference.

I agree. The only thing I've found I cannot change is the length of the cranks.