27 inch wheels and 700 wheels, what's the story?

a bit of a hijack, but is there a similar story with 26" and 650? Are they the same? I've heard conflicting info.

650 are diffrent to 26" mbt wheels google sheldon tyre sizes for more info

Sheldon says this:

26 x 1 (650 C) 571 mm Triathlon, time trial, small road bikes

I've inherited a 26" zipp 400, which has come from a TT frame, so from this I can assume it's the same as a 650 then?

The ERTO of a 650 wheel is 571 but a 26" is 559. There were some quite trick 26" road wheels in the mid 90's so the size is not limited to offroad wheels but I'm afraid they're more obscure when it comes to tyres. It was pretty common to have quite a bit of clearance on the front forks on a TT bike so you can often fit either 26" or 650c if you have a frame and are on the look out for a wheel. Tyres though, it would seem, are not interchangeable. A 1" road tyre comes up more like a 23c than a 25c in width though, go figure.