Measuring rim - where is the "internal" width?
 

My bike has some cheap generic rims and I've no idea what they are, so I had to measure them. I will then use the table on Sheldon Brown to pick a tire width.

However, I'm not entirely sure what "internal" width to measure, because my rims have a lip on the circumference. Should I use the smaller width on the lip, or the larger width below the lip?

Attached is a quick diagram to show what I mean. The current tires are 41C by the way. (Huge, I know.)

Cheers,
Ben

Use the 20 because the walls below the lip are not parallel and you get a different reading depending on whether you measure at the the top or bottom.

So looking at Sheldon's table I could use something between 35 and 44. Is that correct?

I would say maybe 32-47? you'll notice all the others in that area get 15-16mm of play...

OK, I just ordered some Continental City Contact 32s. Maybe a bit dangerous, but hey, inner tubes are cheap. :p

Thanks for your help. Much appreciated.