72' with 15X7 Rally II's-need tires - Pontiac GTO Forum
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post #1 of 6 (permalink) Old 04-04-2018, 03:03 PM Thread Starter
 
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72' with 15X7 Rally II's-need tires

I've got 15X7 Honeycombs w/BF Goods P245/60R15's all around. I have a new set of 15X7 Rally II's and really want a taller and wider tire. Any suggestions w/o having problems with the wheel wells?
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post #2 of 6 (permalink) Old 04-04-2018, 05:55 PM
 
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15" tires

I've used P225-15s on a couple of that vintage car and they look and work good. I used 60s but the profile just didn't look right to me. However, it's still a mater of preference.
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post #3 of 6 (permalink) Old 04-04-2018, 07:20 PM
 
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245/60-15's closely approximate the size & height of G60x15's. G60x15's were used on 15x7 wheels as part of several optional pkgs for mid '71 GTO's as well as '72 performance Pontiac A-body's. 255/60R15's typically mount near an 1" taller, and replaced the letter size H60-15's.

255/60R15's typically have enough tread width that when they are mounted on 15x7 rims, the tread rolls over into the section width area of the tire. Not all lines of 255 60's have the same section width & same tread width. Though far from optimal, some have no problem with the rolled over tread style of a 255/60 on a 15x7. Over the years, I've purchased & installed well over 3 dozen sets of 255/60x15's. Nearly always have mounted them on 15x8 zero offset wheels for late 2nd Gen T/A use. Have also had several such tire/wheel combo's on '71 & 72 Pontiac GTO's. One important thing to consider if your original '72 springs are tired, wheel/tire clearance is lost. Original '71's & 72's with factory mounted 15x7's and G60-15's were factory equipped with the firm ride springs (& shocks) and thus the car set up an 1" taller at rhe rocker panel than standard suspension (non firm ride) equipped '71 & 72 performance A-body's. 245/60's on the front & 255/60's on the rear on 15x7's is something I've had in here several times, 255's on 7" rims, up front, typically rub.
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Pinion head,
Thank you very much for the detailed response. The taller tire height you mention with the 255/60R15's is what I'm most interested in....The car has been restored and has a very beefy suspension so i'm not too worried about wheel rub on height....but a little worried on the width in front. Should I be? Also, in terms of tire brands, knowing I've got 15X7's and not 15X8's as you have used in the past with the 255's have you had better success with one brand over another? Also, because tire height is of primary concern would you recommend a 70's series over a 60's series?
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post #5 of 6 (permalink) Old 04-05-2018, 05:41 PM
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Originally Posted by lucashadley View Post
Pinion head,
Thank you very much for the detailed response. The taller tire height you mention with the 255/60R15's is what I'm most interested in....The car has been restored and has a very beefy suspension so i'm not too worried about wheel rub on height....but a little worried on the width in front. Should I be? Also, in terms of tire brands, knowing I've got 15X7's and not 15X8's as you have used in the past with the 255's have you had better success with one brand over another? Also, because tire height is of primary concern would you recommend a 70's series over a 60's series?
lucashadley,

Here is a wheel width chart with suggested tire sizes, I would never mount a 10" wide tire (255) on a 7 inch wheel, according to this chart a 225mm tire is the max width you should mount on a 7" wheel, If you want a taller tire look at the 225/70r-15 which is 8.8" wide. has a 6.2" sidewall height and is 27.4" tall.
A 255/60-15 is 10" wide, has a 6" sidewall height and is also 27" tall. Just my humble opinion,


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post #6 of 6 (permalink) Old 04-05-2018, 07:13 PM
 
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Unhappy

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.
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