I'm wondering what tire pressures people generally run on vintage Vespas. I've got a 1978 Super 150 (Mk II Eurospec) that has 8" tires (with tubes, obviously). The original manual says to run 15.5 PSI front, 18.5 PSI rear with one rider, or 32.7 - 35.5 PSI with two.
Those single rider figures seem way too low to me. We've recently had some quite cold temps here (below freezing at night) so naturally tire pressures have dropped; on a short test drive they felt quite squirmy so I knew a refill was a must. After pumping them up, I thought even 20 PSI front and 25 or so rear seemed somehwhat low compared to what I had run comfortably on in the summer (I've got Michelin S83s 3.5x8).
I know tire compounds have changes drastically since the 70s when the manual was produced, might innertubes have also changes and different pressures are suitable now? What do others use -- I'm particularly interested in responses by those with 8" tires as well.
On another note, it's been more than usually difficult to fill up the rear tire: the valve stem end is so close to the hub (it bends over the split rim half) that I can't even fit a pump onto it without removing the wheel entirely off the hub first. I might switch front and rear over the winter and see if it makes access easier.