THE Materials Oracle
Join Date: Feb 2006
Location: Finally... home :-)
Bikes: Univega Alpina 5.1 that became a 5.9, that became a road bike... DMR TrailStar custom build
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First, the difference in strength of 6/4 vs 3/2.5 is of the order of 3% as-rolled, drawn, heat treated and aged, in fact in any condition. Almost all of what you will hear from salesmen is B/S anyway, in all things, especially so with Ti alloys.
Right now it's almost certainly because of the market price of commodity titanium. It's unit price has shot up by a factor of at least three in recent years and aluminium and vanadium themselves (the two alloying elements added to both 6/4 and 3/2.5) do not decrease this value. A conscious decision has been made to reduce the content of both in the alloys produced to lower the total cost to manufacture...
If you look a round, you'll find some components that used to be manufactured from some of the more exotic titanium alloys - I'm thinking bottom bracket axles here especially - will also be being shifted to leaner alloys.