How do I work out which fork to use? 700 or 27"

[jools]

I picked up a bike frame recently that has no markings and no fork. How do I work out if it is a 700C or 27" frame? I'm assuming if I get the wrong fork it will alter the angle of the bike?

[bigfriendlyvegan]

What's the spacing on the back dropouts? 126mm points to an older bike and 27" is more likely (though not definite), while 130mm is more modern and 700c is more likely. The difference between a 700c and 27" fork may not be very much at all, given that the difference in the wheels is between 622mm and 630mm. This means that, for a given brake reach, the difference in the fork lengths will only be 4mm.

Pics might help, if you have them.

[jools]

The dropout spacing is more like 130mm - I'll measure again tomorrow and get some photos as well. I tried measuring the distance between the dropout and the brake mounting and comparing this with a couple of my other bikes - a 700C and a couple of 27's but that didn't really help much either as they were all a bit different.

I'm planning on running 700C wheels on it, so if it ends up being a 27" frame with a 700C fork and 700C wheels the 4mm drop at the front probably won't be that noticable, I hope