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Pedal Spindle to Saddle Measurement & Saddle Height (again)(3 posts)

Pedal Spindle to Saddle Measurement & Saddle Height (again)serbski
Oct 28, 2003 6:15 PM
If one is measuring from the center of the pedal spindle to the top o' the saddle it makes sense that the pedal should be in the six o'clock position, right? Am I correct here or should the pedal be in a position more parallel to the seat tube (is *that* the position of greatest leg extension?) ? I am just curious to check the 108-110% of inseam formula as I seem to be able to ride comfortably with (what I consider) a fairly wide ranging saddle height. I bring this up because, and this seems quite odd to me, I just began riding on a trainer (as all of L.A. seems to be in flames) and I feel more comfortable with a lower saddle height while on the trainer yet this feels too low while riding "in the real world" especially when climbing for extended periods. I have an 86cm inseam and run the saddle around 76cm BB-saddle on the "low" side and up to around 77cm on the higher side but can deal with variances on either side of those measurements. I do have an orthotic in my cycling shoes which is about 5mm thick to factor into any equation. Point is, I thought I liked a lower saddle height as it made for a more comfortable butt until the front of my knees began to hurt for the first time and I began, a couple of mm's at a time, raising the saddle back up into the 77+ cm. from BB. Well, now I am more prone to saddle sores and I feel a bit high while on the trainer. I am very aware of C-40 and others' suggestion regarding a 2-3cm drop below horizontal while locked-out at bottom of stroke and am curious as to how that jives with such theories as the LeMond .883 of cycling inseam et al. Is a full cm. an acceptable amount by which to vary from the above methods of calculating saddle height? Should C-40 read this, the top of my saddle is currently 18.5cm from the TT of my 56c-c LOOK and I have LOOK pedals on Pearl Izumi shoes (rather thick carbon sole). Any and all comments welcomed!
Oct 29, 2003 7:40 AM
The saddle height values that you are posting can't be from the center of the pedal spindle or they would be much larger. I assume that you are posting values from the center of the crank arms to the top of the saddle.

As for your question about the maximum leg extension, it would technically be a straight line from the center of your hip joint to the center of the pedal spindle. The exact angle would not likely be with the pedals at the 6 o'clock position or with the cranks in line with seat tube. The good news is that there is very little difference in the length of a line at any position in this vicinity. You are worrying too much about 2-3mm.

As for comparing your saddle height to some formula, that's a worthless endeavor. The formulas do not take into account the "stack height" of the many combinations of shoes and pedals on the market. The stack height variation is easily as much as 10mm. The formulas only provide a rough ballpark measurment, just as the other common advice to maintain a 15 degree angle of the leg at the bottom of the stroke, or my adivce to drop your heel well below horizontal.

You mention adjusting your saddle height, but not the fore/aft position of the saddle. When changing from a bike or trainer with a different saddle, the fore/aft position could be substantially different, creating a substantial error in the length of the maximum leg extension.

After getting the saddle height in the ballpark, the only thing that you can do is experiment to find a height that allows a fast and smooth cadence with ample ability to apply torque. If your cadence is slow or choppy you may have problem with height or saddle fore/aft position.

I've been experimenting with saddle fore/aft position in a effort to improve my climbing. My experiments definitely support the idea that moving the saddle further back enhances the ability to apply torque to the cranks. When the saddle is moved back, it must also be moved down to maintain the same maximum leg extension. I've moved my saddle back a full 2cm and down about .6cm. At 2cm further back, I think I've reached the point where a I may be experiencing a reduction in cadence, so I'm quitting there.

Also keep in mind that you don't have to sit in the same place on the saddle at all times. During the toughest climbing, I move back as far as possible on the saddle and try to maintain a 70-100rpm cadence. On a 45mph descent, I move forward and pedal at 130rpm.
2nd the opinions on the formula and fore-aft suggestion.dzrider
Oct 29, 2003 8:34 AM
I checked my inseam vs distance from pedal spindle to top of saddle and found it to be close to the formula you cite. That being said, it would seem to me that how much riders point their toes at the bottom of the stroke would have a profound effect on this measurement for an indivicual rider. When I use this dimension to set up a bike I put the crank arms parallel to the seat tube which looks to be the longest distance from the pedal axle to the top of the seat.

I'm not sure there is a correlation between saddle sores and saddle height. On the other hand I can't say there isn't. The experience with a low saddle and knee pain is similar to my experience.

If you have a stand, put the bike in it and fiddle around til you find a good spot. There is no right answer other than the one that makes you feel comfortable on the bike.