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Discussion Starter · #1 ·
This may be an odd question but here goes : I like to ride Mountain bikes. The problem I have is a bad knee that will not bend past 90 degrees. So this makes riding just about impossible. Could I remedy this by adjusting the seat high and perhaps replacing the original handlebar stem with a longer one so that my riding position is more upright ? I think that would take some of the bending out of my knee. Anyone else ever had or heard of a problem like this ?
Thanks in advance
 

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Discussion Starter · #6 ·
Shorter cranks cause you to raise the saddle, and not have as much leg bend (because you go to the same extension).
Shorter cranks cause you to raise the saddle, and not have as much leg bend (because you go to the same extension).
can this be accomplished by just raising the saddle ? bear with me I know nothing about mechanics of a bike
 

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Bar position in and of itself (which is what messing with stems affects) has almost no bearing on how much you bend your knees. Saddle height and crank length is what determines that.

Saddle height is based on what gives you proper leg extension at the bottom of the pedal stroke. Don’t go messing with that.

So, for a given amount of extension from the saddle to the pedals at the bottom of their rotation (6 o’clock) the pedals on a shorter crankset will be lower (relative to the saddle) at 12 o’clock than a longer crankset would be. Thus your knee will be less deeply bent.

Of course, to get that same extension from saddle to the 6 o’clock position, you will need to raise the saddle slightly for the shorter cranks, since the pedal is a little higher off the ground.
 

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can this be accomplished by just raising the saddle ? bear with me I know nothing about mechanics of a bike
Sounds like maybe you need to insure your starting point with saddle height is in the proper range for efficiency.

A good (basic) starting point - with your heel over the pedal spindle and your hips square, you should be near complete extension at the bottom of pedal stroke. When you place your foot with more towards midfoot/ball as you would to put power down, you should now have a slight bend in the leg.
 

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Discussion Starter · #9 ·
Bar position in and of itself (which is what messing with stems affects) has almost no bearing on how much you bend your knees. Saddle height and crank length is what determines that.

Saddle height is based on what gives you proper leg extension at the bottom of the pedal stroke. Don’t go messing with that.

So, for a given amount of extension from the saddle to the pedals at the bottom of their rotation (6 o’clock) the pedals on a shorter crankset will be lower (relative to the saddle) at 12 o’clock than a longer crankset would be. Thus your knee will be less deeply bent.

Of course, to get that same extension from saddle to the 6 o’clock position, you will need to raise the saddle slightly for the shorter cranks, since the pedal is a little higher off the ground.
My problem is that I cannot bend my left knee past the 90degree mark. thats as far as it will go. so by getting shorter cranks this would fix my knee bend problem, correct ? and could you recommend a brand for say a Trek 27.5 or 29 inch ?
 

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Sounds like you need a proper bike fitting.

I don’t think a normal seated pedaling position ever has anyone with their knee going past 90 degrees.


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My problem is that I cannot bend my left knee past the 90degree mark. thats as far as it will go. so by getting shorter cranks this would fix my knee bend problem, correct ? and could you recommend a brand for say a Trek 27.5 or 29 inch ?
stand on the floor, lift one leg about 14" (175mmx2), then lift your leg to about 13" (165mmx2)
compare the difference in knee bend (maybe enough less degrees of knee bend with the 165 mm cranks to help)
 

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Sounds like you need a proper bike fitting.

I don’t think a normal seated pedaling position ever has anyone with their knee going past 90 degrees.


Sent from my iPhone using Tapatalk
I think it is actually not uncommon to see a bend a little past 90 when the pedals are around the 10-11 o’clock position on the upstroke.

I had an extensive professional fitting and I’ve got a bend past 90 with 165mm cranks.

A quick search of images from bike fitting and professional races yields plenty of examples of this.
 

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Discussion Starter · #13 ·
I think it is actually not uncommon to see a bend a little past 90 when the pedals are around the 10-11 o’clock position on the upstroke.

I had an extensive professional fitting and I’ve got a bend past 90 with 165mm cranks.

A quick search of images from bike fitting and professional races yields plenty of examples of this.
after 3 surgeries and tons of scar tissue and calcium deposits 90 degrees or maybe even 85 degrees is all I can bend out of it.
 

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Canefield makes super short cranks.
By using the shortest crank possible
You will bend your knee less.

i would look at something with slcker seat tube angle (sta).

74 degrees sta is a more traditional angle. I did some angle measurements myself when switching bikes and slacker sta will help with total knee angle

you are right that a higher seat will limit your knee bend. Pedal w the front of the foot rather than the middle. But this is a very minor adjustment.

A good shop will help you test fit.

Cranks are an extra that most shops wont have in stock.

Good luck
 

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Discussion Starter · #17 ·
Canefield makes super short cranks.
By using the shortest crank possible
You will bend your knee less.

i would look at something with slcker seat tube angle (sta).

74 degrees sta is a more traditional angle. I did some angle measurements myself when switching bikes and slacker sta will help with total knee angle

you are right that a higher seat will limit your knee bend. Pedal w the front of the foot rather than the middle. But this is a very minor adjustment.

A good shop will help you test fit.

Cranks are an extra that most shops wont have in stock.

Good luck
what is a slacker seat tube ?
 

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stand up

bring your foot up 350mm directly underneath you.

bring your foot up 350mm in front of you.

which one places less bend in the knees!
Stand up, lay down, or be at a 45 degree incline. Do the same thing. Same result.

All slackeing the seat tube does is move where in the crank rotation the deepest knee bend occurs.
 
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