Question on seat position and knee pain (long)



K

Keith Boone

Guest
I have a history of knee pain, but have my road bike set up perfectly to
avoid knee pain. I had a professional fitting for the bike to begin
with, then added speedplay X2 pedals which have a lot of float.
Finally, the seat position was tweaked endlessly until the ideal postion
for me was reached. I think the seat is a little forward of the
traditional point where the front of the knee is directly over the axle
of the pedal. In any case, I can now ride this bike for hours on end,
day after day without knee pain.

Earlier this week I purchased a new bike which I plan to use for
commuting, off road riding, riding in the rain etc. It's a Trek 7500
FX, which is sold as a flat handle road bike, but I've had it fitted
with wider tires, fenders, and a tall stem for an upright riding
position. I also added Speedplay Frog pedals to get that huge amount of
float. I was measured for the bike, and in theory it should be a
perfect fit. After 3 short rides of around 20 km each I find my knee
pain returning. I'm pretty sure this is because the seat is not in
exactly the same position as on the road bike. The road bike is in the
shop right now, but when it comes back, I'd like to make exact
measurements of the seat postion, and then set up the Trek the same way.

Now the questions (finally):
What exactly do I need to measure, and what's the best way to do it?
Obviously the seat height, but how do I measure the fore and aft
position? Is the plumb line from kneecap to pedal axle the only way to
measure? I'd really love check everything with a tape measure, but I'm
not exactly sure what to check. Does the different frame geometry of
the two bikes play any role? How about the upright riding position on
the Trek compared to the road bike? I'm about to leave for a week long
cycling vacation, and I want to take the new bike, but I'm getting
worried about knee problems. Any advice would be appreciated.
 
R

Rick Onanian

Guest
On Fri, 13 Aug 2004 02:41:13 GMT, Keith Boone
<[email protected]> wrote:
>What exactly do I need to measure, and what's the best way to do it?
>Obviously the seat height, but how do I measure the fore and aft
>position? Is the plumb line from kneecap to pedal axle the only way to


Considering your knee issues, I'd try to duplicate every contact
point as much as possible.

First, buy the exact same saddle as you use on your road bike.

Then, measure height from the ground at handlebar, saddle clamp, BB,
and pedal; and adjust the numbers for any difference in BB height
and crank length (I'd recommend using the same crank length).

I suspect a plumb line from the saddle clamp, measured to the BB,
would be better for you and easier than from the kneecap. Somebody
will speak up if I'm wrong, but I think an even easier method for
your purpose (duplicating the contact points regardless of geometry
differences) would be to back the bikes up to a wall, and measure
from the wall to each point.

>measure? I'd really love check everything with a tape measure, but I'm
>not exactly sure what to check. Does the different frame geometry of
>the two bikes play any role?


You should be able to overcome geometry differences with careful
attention to detail, but huge geometry differences might require
more adjustment than a given [seatpost|stem|whatever] has.

>How about the upright riding position on
>the Trek compared to the road bike?


If you want a more upright position, I'm not entirely sure how it
will affect your knees; as you sit more upright, your pelvis rotates
up and changes it's angle relative to your thighs (and knees).

>I'm about to leave for a week long
>cycling vacation, and I want to take the new bike, but I'm getting
>worried about knee problems. Any advice would be appreciated.


I'd be afraid to do that without spending a lot of time getting
comfortable on the new bike.
--
Rick Onanian
 
J

Jonathan

Guest
Rick gave good advice. I wish to emphasize the template route rather
than measurements. His suggestion of a wall space is good as it makes
the floor your "base line" if you are careful to keep the road bike
upright, wheels straight, mark the wheelbase onto the floor, and keep
the bike stationary while transfering the points to the wall. I
recommend a framing square to aid in accurate transfer (make sure you
choose a flat wall + floor sections). Pop a pedal off so you get
closer to the wall. After templating your road bike you'll be able to
compare the mountain rig's geometry pretty well.

I suffer knee pain as well and (not to overly discourage) have given
up off-road riding altogether. No matter how well the frame is fit
the irregular loading and constaint stand-sit changes in response to
terrain are much harder on the joints than spinning. Spinning has
*really* helped my knees by building muscle-mass around the joint, on
& off the bikes.

Remember, all pro-fittings will be biased towards performance not
joint well-being. It's how they are trained. Offroad frames in
particular are sold too small for healthy orbit of the joint. My ass
is quite a bit farther from the bottom bracket than the fitters would
ever put me. Crank length (orbit diameter) is something to watch too.
As to angle of torso (reach) while riding, the more upright you are
the more the bearing points on the saddle rotate back onto your pelvis
rather than on perineal area. When your pelvis is loaded it rocks
side-to-side more thus throwing your knee's orbit out of plane (knee
swings out at top of orbit as opposite hip drops). This is numero uno
no-no. Of course riding on the perineal area is #1 cause of erectile
disfunction, so take your pick. :)

(... or should that be "take your *****"?)

Good luck! -Jonathan
 
M

Mike Jacoubowsky

Guest
> Earlier this week I purchased a new bike which I plan to use for
> commuting, off road riding, riding in the rain etc. It's a Trek 7500
> FX, which is sold as a flat handle road bike, but I've had it fitted
> with wider tires, fenders, and a tall stem for an upright riding
> position. I also added Speedplay Frog pedals to get that huge amount of
> float. I was measured for the bike, and in theory it should be a
> perfect fit. After 3 short rides of around 20 km each I find my knee
> pain returning.


Don't underestimate the issue of different shoes/pedals between the two
bikes. In particular, check to see that the cleat position on the new shoes
isn't further forward than your older ones. Even slight differences there
can make huge differences in knee pain; I *always* err on the side of
caution, moving cleats back slightly from under the ball of the foot.

The easiest experiment would be to simply swap pedals/shoes between the two
bikes and see what happens. I'd suggest this before trying to get
everything else worked out.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com


"Keith Boone" <[email protected]> wrote in message
news:[email protected]
> I have a history of knee pain, but have my road bike set up perfectly to
> avoid knee pain. I had a professional fitting for the bike to begin
> with, then added speedplay X2 pedals which have a lot of float.
> Finally, the seat position was tweaked endlessly until the ideal postion
> for me was reached. I think the seat is a little forward of the
> traditional point where the front of the knee is directly over the axle
> of the pedal. In any case, I can now ride this bike for hours on end,
> day after day without knee pain.
>
> Earlier this week I purchased a new bike which I plan to use for
> commuting, off road riding, riding in the rain etc. It's a Trek 7500
> FX, which is sold as a flat handle road bike, but I've had it fitted
> with wider tires, fenders, and a tall stem for an upright riding
> position. I also added Speedplay Frog pedals to get that huge amount of
> float. I was measured for the bike, and in theory it should be a
> perfect fit. After 3 short rides of around 20 km each I find my knee
> pain returning. I'm pretty sure this is because the seat is not in
> exactly the same position as on the road bike. The road bike is in the
> shop right now, but when it comes back, I'd like to make exact
> measurements of the seat postion, and then set up the Trek the same way.
>
> Now the questions (finally):
> What exactly do I need to measure, and what's the best way to do it?
> Obviously the seat height, but how do I measure the fore and aft
> position? Is the plumb line from kneecap to pedal axle the only way to
> measure? I'd really love check everything with a tape measure, but I'm
> not exactly sure what to check. Does the different frame geometry of
> the two bikes play any role? How about the upright riding position on
> the Trek compared to the road bike? I'm about to leave for a week long
> cycling vacation, and I want to take the new bike, but I'm getting
> worried about knee problems. Any advice would be appreciated.
>
>
>
 
T

Tim McNamara

Guest
I'd check the Q factors between the two bikes. Q factor is how far
apart the outer faces of the cranks are at the pedal holes. I find
this is an issue for me in knee pain- a Q factor of 140 to 142 mm is
about ideal, narrower is acceptable but wider is not.
 
F

Frank Senkel

Guest
> > Now the questions (finally):
> > What exactly do I need to measure, and what's the best way to do it?
> > Obviously the seat height, but how do I measure the fore and aft
> > position? Is the plumb line from kneecap to pedal axle the only way to
> > measure? I'd really love check everything with a tape measure, but I'm
> > not exactly sure what to check. Does the different frame geometry of
> > the two bikes play any role? How about the upright riding position on
> > the Trek compared to the road bike? I'm about to leave for a week long
> > cycling vacation, and I want to take the new bike, but I'm getting
> > worried about knee problems. Any advice would be appreciated.
> >
> >
> >


I have the same problem, I need an exact set-up to avoid knee pain and
have multiple bikes. The route I've gone is to have the same pedal
system, crank length, and saddle on all bikes. I have one bike
tweaked, and transfer measurements in the following way:

1. Using a plumb bob, make a mark on the top tube that lines up with
the bottom bracket centerline on each bike.
2. Hang the plumb bob off the nose each saddle and mark the top tube.
3. Measure the distance between marks on the good bike and adjust the
others as required.

I'd also try to keep roughly the same body position on each bike if
possible.

As an aside, my knee pain was on the medial side of the cap,
tendonitis I think; I've had some luck with using a single Lemond
wedge on the medial side of that shoe. I also went for look pedals,
wide, stable platform, and adjustable float, good for over-pronators.

Regards,

Frank