Quantifying Fit
 

I have an old bike that i really love. The power stroke is in exactly the right position and handle bar reach is good too. I'm trying to replicate the fit on another bike. In order to take the measurement, i thinking about putting a board from the seat to the handlebar, with a plumb line attached to the center. With the pedal in the 3oclock position, measure the height of the plumb line, and the length of the board from the plumb line to the seat and to the handlebar. I guess i need the length from the seat to the pedal and from the handle bar to the pedal as well to get seat and handlebar heights. I'll use the front of the pedal to measure from but I'm unsure where to measure the seat from since they are different shapes. Is there any systematic way to do any of this?

Stuff you need to know:

Crank arm length, should be stamped near the pedal end of the arm on the inside.

Saddle height, measure from the center of the BB/crank arms straight up the seat tube. This should put you at around the center of the saddle from front to back.

Saddle set back. Drop a plumb line from the nose of the saddle and mark where it hits the chain stay. Measure from that mark to the center of the BB.

I use the same or similar model of saddle on all my bikes, so these will be pretty consistent. If you are changing saddle model, you may need to account for the overall length being different or your sit bones being in a slightly different spot.

Replicating the above 3 items gets you very close to the same fit when copying bike.

Now you can set up the front end.

If you are using the same bars and levers, then just measure from the nose of the saddle to the center of the bars. Adjust stem length as needed. If you're using different bars, measure to a repeatable spot like the center of the brake hood.

Measure nose to ground and then bars to ground to get the HB drop on old bike then adjust spacers as necessary.

Some adjustments slightly affect others, so be iterative until you get it dialed in just right.

Tape measure and an Angle finder are Useful.. Quantifying is Numbers .

You can get both at a Builder's supply.

Lenard Zinn suggests propping a bike against a wall, then measuring from the wall to the various points of interest. Then, some arithmetic will yield distances between those points. Heights can be measured from the floor, again with some subtraction or points of interest. All those dimensions will need to be recorded systematically. I use this chart. Road Positioning Chart - Park Tool I continually tweak my fit so that about once a year I measure everything again. I now have 4-5 years of those measurements and find it very interesting to see how my fit has changed in that time with changes in cycling fitness.

I've been experimenting with some measuring. in the original post i mentioned i have an old bike that i love the position, especially the power stroke, going uphill is almost effortless(at least for a while). I'd like to setup an exercise bike the same way. I have a 1x2 board about 3ft long (yardstick would work ok too). I cut off an old ruler from a tape measure(from the dollar store) and attached it. on the end where the 0 mark is I put a plumb line. and i taped a little torpedo level to the top. the crank set is rotated so one pedal is in the 3oclock position. I put the device on the seat with the plumb line at the center of the pedal (where the crank attaches). The tricky part is determining where to measure on the seat. I taped a short piece of thick rope across the seat, and moved it around until i found the spot where my ischium (on my pelvis) rests on the seat. The measure for this point is my horizontal seat position. I hold the plumb line where it touches the crank and fold it back along the tape measure to get the seat height. As for handle bar adjustment, thats a separate issue depending on ergonomics and aerodynamics. for the exercise bike the more upright the better, for riding the lower the better ( although i need a more upright position because of some back issues).

Innovative! Does it feel like a match?

Yes, its working very well. The seat on the exercise bike is radically different than my bike seat, its wider and more padded so the feel is different, but the trick with finding the ischium spot is working. My knees are much happier. The exercise bike had no ability to adjust horizontal, so i had to spend a couple hours coming up with a new bracket. Its a bit of a hack job for now, I might make it nicer later.

You might replace the exercise bike saddle with one more like the road bike saddle.