I Gottcha!....I always wonder why some people put traction tires on the back, and that is what I thought you were referieing to.
Ah I see say the blind man! LOL! Naw we run same tread all the way around, just we replace per axle if 1 drive gets tore up or what ever we buy 4 and use 2 as tags and 1 as a spare or what ever some times they sit around til I need a new spare or what ever! But with keeping new ones on the steers down to about 50% then transfering them to the tags, and regroving them we do pretty good. Up til this 45'er we just bought I'd never put a BRAND new tire on the tags, and then we wore one out in 3 trips (less than 3,000 miles!). But it was outta round and our tire guy is fight'n with his distributor about it for us! BK