> My recollection is that the 1100s were the worst bouncers in the tunnel. Felt like they'd come off the track at any moment. The early 10s (the converted double-enders; everything was single-end in the 1960s) were better, and the newer 10s (the last streetcars Muni bought) were quite smooth. So the track certainly contributed, but the car design (probably the truck design) had a lot to do with it.

All the 1000s had B-3 trucks, all the 1100s had B-2s. While neither were really designed for open track, which is track not in pavement but open like on the outer M line near SF State and in the two tunnels, the B-3s generally rode better. Both had provisions for the addition of shock absorbers, but the Muni never used them on any of the PCCs of that era. B-3s have friction snubbing for the truck bolsters, and when this wears beyond a certain amount, the car will bounce around all over the place. B-2s don't have this feature.