Knee pain from one bike, but not the other

[Benjamin Slade]

I have two bikes, one is a high end road bike (Airbourne - Valkyrie),
the other is a cheap bang around mountain bike (Gary Fisher - Tarpon)
that I use for around town stuff.

On the road bike, my knee is fine. On the mountain bike, my right knee
hurts. I'm trying to figure out what the difference is. I see two..

The mountain bike has a lower seat angle. Ie. the seat post is more
tilted back, effectively moving the seat farther behind the pedals.

Also, the mountain bike has 3 gears on the front ring. This combined
with the geometry of the pedal crank arms means that the pedals are
farther apart (farther left and right).

With regards to the seat post being tilted back, I've always felt like
this causes the rider to put more pressure on the knee higher in the
stroke. Exactly where my knee has problems.

I'm debating selling the cheap mountain bike, and trying to find a
hybrid bike that's closer to the geometry of my road bike (pedals closer
together, seat post less tilted back so the seat is more over the pedals).

Any experiences to share or opinions on the subject?

Thanks
Ben Slade
Washington DC
(if sending me email, append 030516 to the subj to bypass my spam filters)

 

[rdclark]

Benjamin Slade wrote:

> Any experiences to share or opinions on the subject?

As you've discovered, saddle position relative to the pedal spindles
can be critical. You should start by quantifying the differences to see
if they're significant.

Sitting on the bike with your butt where it usually is, put one crank
exactly parallel with the ground, forward.

Drop a plumb line (a weight on a string) from the kneecap on that side,
from the spot just under the pointy protrusion on the kneecap, and see
where the weight falls relative to the pedal spindle.

Do this for each bike. Then see if you can adjust the position of the
MTB saddle so that it yields the same relationship between knee and
pedal spindle that you have on the Airborne. You'll have to adjust
height as well as fore-and-aft position, and you want the same amount
of knee extension on both bikes, as well as the same knee/pedal spindle
relationship.

As for q-factor - the distance between the pedals - the obvious step is
to measure the bikes and see if there really is a difference. If there
is, the amount and direction you need to change the MTB will determine
your strategy. Save that for later, when you know what's required.

RichC

 

[Bill H.]

Just a thought, but could it be that you're pushing too high of a gear
on the mountain bike and spinning a lower gear on the road bike?

 

[John_Kane]

Benjamin Slade wrote:
> I have two bikes, one is a high end road bike (Airbourne - Valkyrie),
> the other is a cheap bang around mountain bike (Gary Fisher - Tarpon)
> that I use for around town stuff.
>
> On the road bike, my knee is fine. On the mountain bike, my right knee
> hurts. I'm trying to figure out what the difference is. I see two..
>
> The mountain bike has a lower seat angle. Ie. the seat post is more
> tilted back, effectively moving the seat farther behind the pedals.
>
> Also, the mountain bike has 3 gears on the front ring. This combined
> with the geometry of the pedal crank arms means that the pedals are
> farther apart (farther left and right).
>
> With regards to the seat post being tilted back, I've always felt like
> this causes the rider to put more pressure on the knee higher in the
> stroke. Exactly where my knee has problems.
>
> I'm debating selling the cheap mountain bike, and trying to find a
> hybrid bike that's closer to the geometry of my road bike (pedals closer
> together, seat post less tilted back so the seat is more over the pedals).
>
> Any experiences to share or opinions on the subject?
>
> Thanks
> Ben Slade
> Washington DC
> (if sending me email, append 030516 to the subj to bypass my spam filters)

If you're using clips or clipless pedals make sure the ??? what is that
term?? anyway make sure your toes are pointing at the same angle. Also
check things like saddle height etc. You may need to play around with
them a bit or get a couple of opinions from the local bike club or
LBSs.
John Kane
Kingston ON