I was thinking of trading my cosmetically poor 15" 15 hole wheels with 3 good and 1 worn Toyo tires plus $200

for

4 good (not ultra smooth, perfect show quality, but good) chrome 15" 15 holes with Michelin Energy MVX 4 plus tires with even wear.

My questions are:

1.) How do I measure the amount of tread left?
2.) If there is say 40% tread left would this be a good deal.

I'm very sorry, I meant to post this in Wheels and Tires forum