Originally posted by Visian
Rob -- first, there are two sizes of top boxes, 45- and 65-liters. I personally do not think that the weight is a significant issue, but here are a few caveats:
Actually there are 3-sizes; small (holds 1 full face helmet and typically is used on the F650 GS, medium (holds 1 full face helmet plus) & large will hold 2 full face helmets.
1) my wife is a featherweight... wish I could say the same about me!
When she is on the bike with the box, and I have adjusted the hydraulic preload on the rear shock properly, I can hardly tell the difference compared to an unladen bike. Of course, I don't ride agressively with my wife on the back (although she says she just closes her eyes sometimes during "interesting" maneuvers...)
2) Al Jesse says that he avoids selling the big box to people because they tend to over-pack it. This is not only dangerous to have a lot of weight hanging way out back, it can also fracture the cast aluminum rack on the 1150/1100 GS, and can aggravate the transmission boss breakage problem on the 1100s. I have not looked closely at the Adventure model rack, so don't know if this is an issue with this model.
The best thing to do is to talk with Al Jesse.
He owns an Adventure and will be 100% candid with you about what will and will not work.
Regarding comfort as a backrest, my wife says that it works for her just fine. I have experimented with a pad from, of all things, a Harley TourGlide top box. This actually fits the shape of the big Jesse box perfectly, although there needs to be a bit of bracketry designed to attach it correctly. My wife said that it wasn't worth the trouble, so the project has languished. If you're interested, I can ship this pad to you. It looks practically like it came from the factory.
One thing I can tell you not
to do... a few years ago I took my wife on an extended tour on the back of a rented Goldwing. Whatever you do, don't
make that misake... the back of your GS will never be good enough.