Offsets and et numbers - help I'm confused

[richiep]

I'm trying to decide upon which wheels to fit to my bug and have found conflicting information on the 'net about how the offset or et of a wheel is derived. Some say that a positive offset moves the face of the wheel that attaches it to the hub out towards the outside rim of the wheel (larger offset thus tucking the wheel under the wheel arch more). Some say the it's the other way 'round. I understand that a beetle has a standard offset of 23mm. The dropped spindles and disk kit I am using increase the track by 10mm per side. To keep everything under the arches am I looking at an offset of approx 40mm if I intend to use a 5.5inch wide wheel. Tyre size I would like to use is 175 55 15 as found on the rear of a smart car. Anyone got any experience with these?

Any help given will be very greatfully received as my brain feels like it is going to melt soon!

Cheers
:doh: