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horizontal seat adjustment/placement(4 posts)

horizontal seat adjustment/placementshiner1132
Nov 29, 2001 11:54 AM
As a new rider, I was wondering how the different positioning of the seat affects riding. I've heard that triathletes tend to ride with the seat forward for a more vertical body to foot riding position, and some roadies ride with the seat back so that their feet are a little in front of their body.

I like to do medium ranged rides 30 to 50 miles a day, about two to three times a week, and was wondering what the best positions would be. I imagine that some of it is just personal preference, but the reasoning behind it would be helpful. Thanks.
re: horizontal seat adjustment/placementPsyDoc
Nov 29, 2001 2:34 PM
According to Kevin Lippert who is a cycling coach: Fore and Aft Position

With the crank arms still at 3 and 9, drop a plumb bob (a small weight attached to a string) from the inside of the leg at center of the knee joint. This is the point where the inside of the knee sticks out the most towards the other knee. In the past, it was always measured from the back of the kneecap. Well, I hate to disappoint you, but that is not where the knee is in the strongest position. It is the center of the knee where the Anterior Crucial Ligament and Posterior Crucial Ligament cross that should be measured from. This is roughly 1/2 inch or 12.7 mm behind the knee cap. Dangling from this position, the plumb bob line should pass in the middle of the pedal spindle. Not in ze front und not behind, but right in ze mittle!

After the saddle height and the fore and aft position is checked this way, there needs to be a degree angle of between 115 to 120 between the thigh bone (humorous) and the lower leg (fibula and tibia) when the crank is at the 3 o'clock position and the bottom of the foot is level. The 115 to 120 degree angle is measured from the center of the thigh, around the back of the leg to the center of the lower leg bones. There are four quadriceps muscles and three of them do not start to fire correctly until they reach that 120-degree angle, thus making them some what useless. The other leg should be checked this way next to insure consistency. Raising or lowering your heel during the fit process can affect the measurement of this angle. Having too long/too short of crank length, pedaling with your heels elevated, or incorrect cleat placement can affect this measurement as well.

You can see more at: http://www.kevinlippert.com/bike_fit_202.htm

After all of this, you should take a look at: http://www.bsn.com/Cycling/articles/kops.html
Simpler explanationNessism
Nov 29, 2001 5:53 PM
With your pedals at the 3 o'clock and 9 o'clock position, drop a plum bob off the small bony protrusion just under the knee cap. The plum bob should point at or be slightly behind the axle of the pedal. This of often refered to as the KOP or knee over pedal position. Of course this is only a rule of thumb. A little varation either way is acceptable. The real test of saddle position is whether the rider is balanced over the pedals while pedaling. It is important to be able to spin circles. Also, you should be able to balance on the saddle while pedaling without having to hold yourself up too much with your arms.
yeah.guido
Nov 30, 2001 1:26 PM
It seems if you raise the saddle to the highest point before the hips start to rock, and place the boney protrusion below the kneecap over the pedal spindle, your upper and lower leg will end up well within the angles mentioned.

Saddle tilt enables the rider to sit up, hands off the bars, and balance his weight on the sit-bones without falling forward. You've got it right when you can sit up, arms folded behind your back, and spin along a flat or up a moderate incline. By experimentation, trial and error, I've found a 2-3mm upward tilt, measured by a straight edge placed on top of the saddle, keeps me centered fore-aft, with holding onto the handlebars optional.