Go with the stiff sidewall, M/T told me the soft (regular) sidewall tires are for light cars with no rear suspension . I like the Mickey Thompson. They are real consistant and I get a bunch of passes out of them. The 31x14x15 will be the M/T part number 3074S and that's a stiff sidewall L8 compound. Follow M/T's instructions for checking/correcting rollout BEFORE you do the 1st burnout with them. With the weight of your car you'll probably start with around 6 lbs of air.