Phil Brown wrote:
>>Drop a plumb line from the top tube which intersects the centre of the BB shell. Measure two of
>>the three sides of the triangle you have created (the long lengths are better for this as any
>>inaccuracies have less effect on the result). The top tube to plumb line angle is 90 degrees, so a
>>little trigonometry will then give you the seat tube angle.
>
>
> Sorry, the top tube/plumb line intersection is not necessarily a right angle. In fact I would be
> surprised if it was. A degree or two slope in the surface the bike is resting on will throw all
> your calculations into a cocked hat. And how are you going to measure the lengths? Intersection of
> the tube. Very hard to get that accurate. Why not just use a protractor? And if you can't get a
> protractor in the space make up an angle and use the protractor to measure that. Phil Brown
Have you attempted this? If you did, you would see that it is relatively easy to do. The length of
the tubes can be measured centre to centre to within a couple of mm by eye with a tape measure. In
my case, 2/620 is an error which is <0.5% - small enough to be unimportant. Even for a small frame,
this only grows to around 0.5%.
I have compared my technique to the specs of frames from, I think, three different manufacturers and
come close enough for my needs in all cases (within ~0.2° of the spec).
--
R.
<> Richard Brockie "Categorical statements <> The tall blond one. always cause trouble." <>
[email protected]
