Originally Posted by
tigrrrtamer
The bike was measured with the wheels off actually.
I re-mearured everything today. Wheels on this time. But my inclinometer is [+/-] 1 degree, not the most precise device, but it's better than nothing (digital ones were too expensive for the little use they'd get) - so any fractions are guesstimates. Head tube angle appears to be actually a fraction over 76 degrees, seat tube angle a fraction over 77 degrees. Sorry for the mistake.
Co-planar. All 3 string segments were co-planar. You can sight that out quite well. Why don't you give it some thought as to how you'd do that accurately? Hint: the string goes through the front dropouts, and from each dropout, drapes over the stem/extention.
BTW, the handling on this track bike appears less than ideal. It appears not to be conform to conventionally accepted geometry standards. I merely answered a question here, but there is nothing mission critical about this. So according to your expertise we have 2 inches of trail... I think that with a little more trail, the bike would handle much better (on the road). But then again this is a real track bike, not some commercial knockoff destined for bike messengers riding on pavement with their singlespeeds. And on Montreal's velodrome, this thing was agile as hell. Accelerations with the stiff tubing was better than anything else I'd ever tried. We had 49degree banks, and I used to plunge down from their summit, be able to pass someone on the inside at the bottom at full speed, which made for a very sharp turn, on an incline (and leaning the wrong way to make the turn), and this bike always handled beautifully. Not to say that I didn't get a scare sometimes while doing that - but it never let me down in even the toughest of situations.
Frame angles with wheels off or on shouldn't matter. The extra 1/4 degree comes from your stated differential radius of 4 mm, front smaller than rear, and the claimed (average) wheelbase 38 inches.
I notice that now your measurements are different from before. This is not bad or unusual, I just note it. But it does indicate why one often should repeat a measurement process a number of times, at least three, and report the average value of each measurement.
Regarding your strings, if you have an explicit method for making sure the strings are parallel to the head tube, please explain it. I'm not going to guess using hints. The problem I see is sensing or seeing the actual steer axis and extending it long enough (and accurately) that you can easily see if the strings are parallel to it.
The only accurate method I know for fork rake is to remove the fork, fixture it so the steer tube is parallel to a reference plane, and perform precise measurements from there with machinists' tools. The only accurate method I know for head tube is to read teh angle of the head tube with a digital angle meter with the head tube badge removed, or made irrelevent to the measurement, with the frame in a known orientation. If you can't do these things, I think my on-bike method done with digital tools is reasonably good. I don't get how yours shows the direction of the steer axis.