Terry Butterfly vs Thomson seatpost

[laura*]

(reply part 1)

If you are smaller, like me, one thing that happens in an effort to shorten the top tube in smaller bikes, the STA gets steeper.

I'm taller. The old stand over test might have a salesperson rolling out their biggest bike - a bike where I wouldn't be able to reach the handle bars. Back in 1990 I bought a new MTB which made my shoulders hurt. At the time I didn't know enough to know that it was too big. In 1994 that bike was stolen. The replacement was a tiny bit smaller and fit a lot better.

Look at the bike specs (if not with your booklet when bought, google manufacturer on line for a chart) to see how steep it is.

I actually didn't get any literature at all with the frame! But that's OK. I'm assembling this new MTB from a bare frame, choosing every component. Thus, I have data downloaded for every component. One reason I'm building this bike from scratch is to get a bike that's tall enough yet short enough.

PLUS--what's the geo/STA on your old mtb? Compare the two (old mtb & new mtb) geos. Did everything feel ok? If so, try to match that???

Hey, I have the tool available for measuring angles. So why hadn't I? ...scurries out to the garage and back... The old (non-suspenion) MTB measured at 72.5 STA. The new one (hardtail) is speced at 73, but with a suspension fork of course that's true only at the designed for fork length.

I was trying to compare the old and the new but with suspension in the mix, it was hard to compare seat fore/aft position. A change in assumed fork length would cause seat position to measure different. Plus of course 15 years of evolution in bike fit theories.

One comparison I can be fairly certain of is BB to saddle distance. I have an even older Schwinn road bike that I last road 20 years ago. Its saddle was only 8mm taller than my old MTB's saddle. And come to think of it, every spring I've had to raise the MTB's saddle because it seems to sink during the winter. Thus the two might agree "exactly".

So I think 6cm sounds about right (5.6cm=4cm+1.6cm)... 4cm in the Terry saddle fore/after rail, plus 1.6cm w/the lay back of the Thomson seat post angle.

Not 6cm, but 6mm. Thats 47mm - 41mm to keep the Thomson clamp entirely within the STOP> <STOP range. The back of that range really does seem like a "don't cross this line" limit. The saddle rail starts curving there.