Lbxpdx

I’m curious what the tube thickness is on my 1991 trek 990. It is OX II ultra. I do know the seatpost is 29.8 and the seat tube is 1 1/4”. 29.8 is 1.173. Can I assume that if the difference between the seat post and the seat tube is .8, that the tubing is 8/5/8?

guy153

The difference between that seat post and seat tube is nearly 2mm, much more than 0.8. Seat tubes are always reinforced in some way at the top for the seatpost, either with some kind of a lug, or they're often "externally butted"-- the metal is thicker on the outside as well as on the inside.

I don't know the best way to measure the gauge of the tubing on a built frame with regular tools. You could try a depth gauge between one of the bottle holes maybe? Measure the distance from the top of the boss to the inside back of the tube. Then measure the height of the boss and subtract it.

unterhausen

You can't assume anything from the seat tube. Seat tubes are different because they have to fit the seat post.

There is a way to do this with ultrasonics, but the standard thickness checkers don't go down that thin.

Nessism

.8/.5 or .9/.6 would be my guess