Hi All!
There seems to be A LOT of consternation the past few weeks regarding 12mm hexes and width so for more clarity I went and measured the stock XB4 12mm hex wheels vs standard 12mm hex wheels (Associated, Losi, Hot Bodies).
If you recall we were the first to release 12mm hexes for the original XB4 and so established our hex width for the available wheels of the time (Associated/ Kyosho). Later, more front wheel options came out via the D413 and 22-4. The Associated/Losi/Hot Bodies/Kyosho seem to have industry standard off set in the rear (makes it easy for handout rear tires for Reedy Race etc!) so we have based our newer hex widths for these wheels.
The confusion comes from the fact that the Xray wheel is a
different off set than the other brands listed. The Xray wheels makes the width 1mm wider at
each wheel. So if you go by that then please use this list to give you a measurement.
1456 makes the rear wheel width about 243mm wide with AE/HB/KYO style wheels. XRAY 12mm wheel width is about
245mm wide.
1408 makes the rear wheel width about 247mm wide with AE/HB/KYO style wheels.
1409 makes the front wheel width about 247mm wide with Kysosho 4wd front wheels.
1409 makes the rear wheel width about 243mm wide with AE/HB/KYO style wheels. XRAY 12mm wheel width is about
245mm wide
1410 makes the front wheel width about 243mm wide with B44.2 4wd front wheels.
So if you want 245mm width then you simply need Exotek 1456 rear hex set and 1409 front hex set along with Xray wheels.
I'm happy to use Associated style wheels though- makes life easy when you are at the track and wish to borrow a set of tires from a friend and it will be much easier on the wallet.
And please remember- the difference between 243mm and 245mm is ONLY 0.08%!. Really not worth stressing over. 
Hope that helps!
Best