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Rider anatomy - legs

Hi Brent,

With regard to measurements L1, L2, and L3, is L1 is from the bump on the outside of the knee to, where -- an anatomical landmark on the hip or something more visual?  How about L2: knee bump to bone that sticks out on the ankle (base of fibula?). L3: base of fibula to bottom of shoe heel?


Legs in rider anatomy

First thing I should make clear is that the representation of the rider that is dependant on these dimensions is of no consequence to the frame geometry recommendations made by the Fit advisor. This is discussed at: bikecad.ca/rider_anatomy_tabs. The representation of the rider is only there as a tool for you to visualize the rider on the bike and apply your own judgments about how such a rider might fit on the bicycle in question. As such, L1, L2 and L3 can be used by different fitters in different ways. If you choose to measure between anatomical landmarks, your processes will likely be more repeatable. On the other hand, you may also want to measure to a spot that may seem to better represent the center of the hip or knee joint. Of course, hips and knees are not in reality pin joints as they are idealized to be here. Therefore, when measuring to what you deem to be the center of the joint, just be aware of the small margin of error due to human joints being more complex than simple pin joints.

Thanks, Brent -- that helps.

Thanks, Brent -- that helps.

Hips in rider anatomy

I do not understand this reply.
When I ask BikeCAD to show me HipAngle etc, then there is a hypothetical centre of the hips.
Maybe it is a simple representation of the real body, but it makes things clear to me.

I use these hypothetical centre of the joints to calculate the gravity centre of the body.
An indication of the hypothetical centre of the joints of the left leg would be very welcome

But my question for today is: Why is the X value of the hypothetical centre of the hips different from the X=0 reference point of the saddle?
Now I have to change the value of Saddle reference X so it matches the hypothetical centre of the hips.
Most of the time this value is around 47 mm
I am able to change every dimension of the saddle in the Saddle dimension dialogue box, without affecting the sitting position (X value) of the rider.

I would like to understand your thoughts.
Thank you.

Hips in rider anatomy

It might be helpful to check out this video about saddle dimensions.

The hip joint by default does line up with the point on the saddle defined by dimension A in conjunction with dimensions P and Q. You claim that you can change every dimension of the saddle without affecting the sitting position of the rider. That may seem to be the case as you can see in the example below where I only change dimension A.

However, if I were to change P and Q as well, I would get a different result. A simpler option is to define the rail position by P2 and Q2. In that case, when I change dimension A, I get the following result:

Changing the saddle reference point won't have a significant effect on the hip position. The purpose of these dimensions as discussed here is to change the point on the saddle from which saddle height and other dimensions such as rider compartment are taken from.

What will have a more significant effect on hip position is the Sitting position dimensions shown here lifting the body right off the saddle.

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