I'm not running Judys, but can tell you from experience that tyre sizes can be deceiving.
I recently put a set of 2.125" Duro tyres on a bike that wore 1.95" Schwalbes, and when I measured them I found out that the Duros were actually 1.89" as opposed to the Schwalbes' 2.01".
Also, rim width does play a role too, and you need to keep in mind that wheels and tyres can flex a bit too under sideways loads. Also keep in mind that mud etc need to be able to pass through the fork as well.
Keep a safe margin to avoid any clearance issues.