Join Date: Jan 2015
Location: Injun Territory, 'Merica!
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Not sure who complied that chart, 05 GTO. Herb Adams specced 255/60R15 on his VSE (American Racing) 15x8 Zero offset wheels on his late 2nd Gen Bird VSE FireAm builds. That was also the specced size for all of us who ran his VSE suspension parts on our late 2nd Gen T/A's. The result, easily the best handling prepped 2nd Gen T/As of the era.By your chart, we should have been running 235's or 245/60's. Uhhh, no. Neither of which size even have the section width to protect a 15x8 wheel. 35 years ago, my lightly modded 80 T/A pulled .88G CCW on a skidpad marked off by local SCCA club, also ran 0-60's in the high 5's & topped out @ 136, all on 255/60/R15 Eagle NCT's. In late '84 I picked up a pair of 265/60R15 NCT's which were nearly an 1" taller. Picked the 265's up and mounted them on the rear as I was blowing the 255's away on the street, the T/A slowed a little, but i found those taller rear tires lasted twice as long.
Today in 255/60R15's, BFG Radial T/A's and Cooper Cobra GT's are the most common styles, & from spec sheets, both have near identical section width & tread width. Pricing, looking at $150-160 a tire, always smart to watch for rebates! Without measuring what suspension height is under the front of a '72 GTO I'd prob error on 245's up front.
Kelsey Tire, a few years ago, had the GT Radial & Eagle GT reproduced in 255/60R15 size. Both are very expensive restoration use tires (Eagle GT's were oem on '80-82 Vettes). Have a few 255 Eagles that are NOS, been in an air conditioned closet for the last 25 years. Both the original Wingfoot & NCT in the 255/60R15 size were 1/2" narrower section width wise along with having softer tread compound (stickier) than same size tread design Eagle GT counterparts. So much for generic MM sized tire charts. Back in the 80's ran through many pairs and sets of Goodyear Wingfoots, NCT's, as well as a set of even softer BFG Comp T/A's. Also bought 255/60 Eagle GT's through same wholesale deal, which used many times for local buddies who typically gave me their Eagle GT takeoffs with 1/4 tread. Keeping tires on my first TransAm was a lot of expense for the way it was driven on the street/occasional autocrossing. Tire expense was one of the things that eventually pushed me out of the "balls to the walls" performance driver, & into collecting & restoring earlier '70 Pontiac roundport cars, as well as hardcore restorations. Just, passing this on, as many of us learned to never trust generic tire sizing charts.