I rocked a welded diff with 37s for about five trips broke four teeth of the ring gear before the birf broke... but I have seen samurais with toy axles break on 33s so it just depends on the driver if you like the skinny pedal and hop at all it will break them on 35s and up if your nice and crawl you probably can run up to a 37 on a good day thats just my opinion. Also I think some birfs are stronger then others depending on what they came out of or who has wheeled them before because i have seen a truck break one in really simple spots and throw a diff one in and not break one when in harder stuff so it all just depends, with that said just buy longs or anything stronger...
