minimum clearance to springs?

3/8". Absolute minimum. But as long as you keep your tire pressure right it should be okay. Make sure you're measuring the smallest clearance. 1/2" would be better, you'd be safe at a 1/2".

My Duster actually has a very questionable 3/8" to the springs, it's marginal, more like a fat 5/16" :p. I've never had the springs and tires rub even cornering hard. But the 295/35/18's I've got have shorter sidewalls.