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Saddle Fore - Aft Position + Stem Length(7 posts)

Saddle Fore - Aft Position + Stem LengthNik
Mar 22, 2001 6:11 PM
With regard to the fore aft position on the bike, I'm finding it hard to understand where exactly does the plumb line falls from. Kevin lee Lippert's article reads at the center of the inside knee at the point nearest to the other knee. Hmm.... you know what? I don't know where it is.

I used to take it just at the front of the knee. (like what colorado cyclist website shows). I've just bought a Giant TCR 2001 small size (44cm) - Seat tube angle 74 degrees and top tube length 53.5cm (Horizontal distance).

Inseam 79cm

With the cranks at 3 & 9 o'clock position, the plumb line, if it's according to Kevin at the center of the inside knee point closest to the other knee, the line drops way back (~1 inch or more) from the pedal spindle. If it's measured at the center of the knee in front (patella), then it bisects the spindle. My Seat is already in the further most up position towards the stem.

Can anyone help me with the correct positioning?

Another thing, the stem length. Just long long/short should it be? I'm using a 120mm which effectively makes my edge of handlebar/stem to center of seat tube (horizontal distance) to be 65cm. With the seat at the furtherst up position, The Front hub is ~10mm in front of of the bars/stem mounting point.

besides having the back flat/bunched up, is there anything else that will make bike fit improper. Meaning - does stem length really matter so much?(perhaps this is a stupid question??)

Anyway, thanks for any and all help in advance.
re: Saddle Fore - Aft Position + Stem LengthEd2
Mar 23, 2001 6:37 AM
Hmm,
Some sizing tips in order of importance...

1AAA - Be comfortable on your bike! A flat back is no good if it is not a comfortable position for you...

1. Your seat height is correct
2. You should place your seat fore and aft for the most efficient pedalling motion, i.e. don't shift your seat to fit your stem, the stem can be changed. Front of knee over pedal spindle at 3 and 9 should be a good starting point.
3. Why is your seat pushed so far forward? Is it because the stem is too long?
4. Your seat height should not be more than 2-3 inches above your stem...having them closer to level increases comfort.

Hope that helps a bit,
Ed
that is a teeny bike...44cm ??john de
Mar 23, 2001 4:49 PM
i think the knee bisecting the pedal spindle is a good thing because it makes sense biomicanically ( you exert force similarly to when you run)...i used to have my seat back to compensate for a short bike but the stem is deffinatey a better place to make the adjustment..good luck..
I'm beginning to think...TNC
Mar 23, 2001 5:02 PM
that all of these formulas and traditionally accepted standards should only be starting points. Seems to me that none of these standards take into consideration the age, flexibility, injury history, body size/shape, or goals of the rider. Aren't most of these standards taken from the racing ranks? Aren't those ranks mostly made up of younger, fitter, "cream-of-the-crop" riders who have a performance-at-all-cost attitude and capability? Obviously this is no slam to riders in that arena, but I've been finding more and more fit issues on my bike that have improved by slowly deviating from some of these normal settings. Now I'm not advocating tossing out those normally accepted principles. It just seems that we should experiment alot more for the perfect setup for each rider personally.
I'm beginning to think...Sonia Alvarez
Mar 23, 2001 8:08 PM
Inseam 79cm and a 44cm bike...I'm 78.74 and my bike fit (x .65) is a 51.2, or simply a 51....isn't it a bit toooooooo small?
I'm beginning to think...Nik
Mar 24, 2001 3:46 AM
Hi guys,

Thanks for the input. It's true that the methods are a bit old and also perhaps they're more suited to those pro Racers. But I suppose it's a good starting point before you fine tune things right?

This frame is a Giant TCR Team ONCE which is a compact frame. They only come in 3 sizes - s,m,l (44,50,55cm). It's darn light. Frame only 2.6lbs. (size s)

Here's What Kevin Lee Lippert(CTS coach - Lance Armstrong) said when I posed this question : -(this is taken word for word from www.ridefast.com)

------
I will make sure that I am more clear on my article, I can go in a add to it. What you are looking for is where the ACL and PCL bisect. This is roughly 1/2 of an inch or 1.2 cm behind the petella (knee cap), this is a rough measurement. Not a full inch. The size of the bone at your knee joint will determine the placement of the plumb bob. Look for the most medial part of the Medial Condyle. What you have been dropping the plumb bob from is the Tibial tuberosity. The Tibial tuberosity is at the front of the Tibia or larger lower leg bone. Where this measurement came from is 25 year old information. It doesn't jive with physics. You want the strongest part of the joint to accept the large part of load, right?

The problem you are having is, you are trying to drop the plumb bob from the center of your total knee mass. This is not what I intended to convey, guess pictures would help huh? Also, if you are droping your heel when you don't ride that way or if you are raising your heel when you ride with heel down, that can make your plumb bob be off. Other things that can make your fit difficult are, too long of cranks, set back seat posts, ill fitting shoes, improperly placed cleats.

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I'm moving the seat so far forward not because of the stem but because of the fore - aft position to get my Knee/plumb Bob to bisect my pedal spindle.

I'm still in a bind but thanks for all the help. The wonders of the internet.. The whole world is helping out another person.

Cheers,
Nkik
i think its i good idea to go for the knee over the spindlejohn de
Mar 24, 2001 4:03 PM
i had a really annoying knee injury which i chalked up to having the seat too high and also being too far back, i think your efforts are warranted..i now ride at 83.3 of my inseam and with the knee over the spindle (the seat is far forward) and my knee is almost as good as it was and still improving...good luck, maybe you have a freak body and need a custom frame but i doubt it..if you moved the seat all the way up i dont know what more you could do though....get the shoe cleat on the ball of your foot thats all i can think of that could possibly be the problem...seat height as i said before could also be a factor...