- drink glass of vino tinto
- carefully 'zero' and fix vernier gauge (i have an analogue version that measures to the 0.01mm)
- take multiple measurements from the steerers of the forks i have in use currently. detail: use flat sections of 'arms' of gauge rather than 'bladed' section in order to try and minimise lack of perpendicularity (my word, and its a good one) and use a 3 point contact on the steerer.
- take multiple measurements and average.
- Black Sheep ti fork 28.55mm
- Pace carbon 28.60mm
- custom steal Rick Hunter 28.60mm
- Project 2 28.60mm
You could be forgiven for think Ah ha! the black sheep is undersized, hence the thomson stem issue!
So i went the chris king website in order to try and find out a little more about tolerances etc.
This is a quote: " 8. The steerer tube may be undersize. Steerer tubes should be ±.025mm (.001") of the nominal size. We often see steerer tubes as much as .25mm (.010") undersize. Solution: Replace the steerer tube."
What is that nominal size? 1 1/8" or 28.575mm
So i have one steerer that is *just* undersize, and 3 which are significantly oversized, according to these criteria.
Of course, you have always known tolerances have always been in a range, and the bike industry is seldom a precision industry. I think what i have here is one of those unfortunate incompatibilities occurring as a result of the lack of high precision standards. No ones fault and thus nothing to moan, whine or complain about.
Interesting. Makes you realise why shimano rule he roost so often. They utilised a machine on the initial cartridge bb's to measure to the nth degree the size of the cup race and the bearing size and put together the most appropriate combo for each bb. Outstanding detail work from an industry giant, and well received. The UN-72/3 was always a special bb.
Ok, im done. This is prolly the reason i have 6, or maybe 7, unread magazines lying around the house...
(revised figures after re-reading and re-adding...)