Spare dosen't have a TPMS sensor so you will likely have the light on in your dash when using the spare. I would definatley put the spare on the front. I'm not 100% certain, but don't think the abls works on the front when in 2wd. Although when you step on the brakes the ABS system will cause the truck to act funny, cause some brake wear, etc. I'd say you should be ok using if on the front for a day or so even though you do drive quite a bit, but take it easy; try to avoid using 4x4 unless absoplutely necessary and avoid sudden, hard stops. If you have the locker and used it with different size tires at each end(rear end), you could severly damage your rear axle(if that would happen I'd put the same size tires on, take it to the dealer and play stupid).