Originally Posted by
tkamd73
Don’t know if this helps, but Trek went back to True Temper, for the 400 frame in 88. I have one, and just measured the seatpost, it is 27.2.
Tim
I noticed references to that and other year Treks using True Temper tubing after my last comment, so I edited it to correct the error.
I also found what appears to be a 1987 True Temper catalog online:
The Bicycle Info Project :: True Temper Bicycle Tubing Catalog circa 1987
Based on that catalog, if I've done the math correctly it looks like a True Temper frame could take either a 27.2mm seatpost (RCX tube kit, with less than 0.1mm finishing reaming), 26.8mm seatpost (RC tube kit, with 0.02mm finishing reaming necessary), or a 26.6mm seatpost (RCR tube kit, no finishing reaming required).
Or True Temper could have done a special production run for Trek, in which case all bets are off. Dunno.
Unfortunately, my frame sticker doesn't say which True Temper tube set was used. Bummer.