Yes, I get that, but you linked the rear tire size directly to the 120 front when you said, "I'm limiting him to a 150 since the front will be a 120", I'd love to know why you think that's important...?
What size rims are you using on the young fella's bike again Cal..?
That wasn't so much a "linking" as it was poor grammar. Front is a 3.5 and rear is a 4.25. Both are Sun rims.
He just wants the fat, modern Superbike kind of look, or modern Hooligan rubber aesthetic. Its good to still have the power to say "No" to some things 
150 is the maximum i'd use on a 4.25x17, I wouldn't run a 160 on a 4.25x17, its a bit tight.... not trying to niggle but, I wouldn't have gone with a 3.5 up front, the bike will steer better with a 100/110 on an 18 inch rim in 2,5/2.75 inch widths, even a 2.15 front rim would have done, even with the offset adjusted to suit, the rake on these bikes is better suited to 18 inch front rims and slightly less wide tires, thats why you don't see many of these bikes racing with 17 inch rims, even in Australia where lots of older bikes race now with 17's {1100 katana's, GS1000/1100, boldor {dohc} Honda's and the Z900/1000 variants..

.. And yes, I do know what young fella's are like, sometimes its easier to bang your head against a wall than to try and give rounded advice...
