Is having 20cm of Ti Seatpost inside an Al frame asking for trouble? Tips for surface prep?
The length isn't a problem per se, although it could become one if the two become one since the bond area will be large. Titanium is pretty bad news for your aluminium frame, but at least it will save itself while it kills your frame, so that's a plus if you like the post. If you must, assemble with Copaslip and keep it bone dry. Dismantle and recoat if you ever use the bike on a day when it is raining, has rained or looks like it might rain.
By far the best thing to do with titanium seat posts, and indeed most other titanium bike parts, is to find a greater fool to take them off your hands and use half the proceeds to buy aluminium or steel and the other half to buy a beer to celebrate dodging a bullet.
The length isn't a problem per se, although it could become one if the two become one since the bond area will be large. Titanium is pretty bad news for your aluminium frame, but at least it will save itself while it kills your frame, so that's a plus if you like the post. If you must, assemble with Copaslip and keep it bone dry. Dismantle and recoat if you ever use the bike on a day when it is raining, has rained or looks like it might rain.
By far the best thing to do with titanium seat posts, and indeed most other titanium bike parts, is to find a greater fool to take them off your hands and use half the proceeds to buy aluminium or steel and the other half to buy a beer to celebrate dodging a bullet.