I own an 83 280zxt 5spd with stock gears and I'm trying to put a wider tire on my car. From what I've learned through the archives what I'm looking for is a 225 55 15. Sounds great except I don't want to pay $194 per tire on my car...I'm just not that rich. Anyways, I've got an R200 diff with 3.9 gears siting in my garage that I'd been planning on putting in my car. My question is this, is there any way to set up a configuration between a speedo cog, 3.9 diff and a certain size tire to keep my speedo right...without paying a fortune for tires? I don't care if my tire is lets say a 60 or 65 or 70, just as long as I can get atleast a 225 width and still have my speedometer fairly accurate. Anyone been in this situation before?