[unruhjonny]

Some may not care, but my experience with 255/60R15 tires on 7" wide Rally II's is that they tend to balloon, and wear from the centre out;
My belief is that they are just too wide of a radial tire for a 7" wide wheel.
If you don't put many miles on, or plain old don't care, then I guess it doesn't matter.
I have found that the 245's wear much more evenly on a 15x7" Rally II.

I have gone down the rabbit hole of tire conversion sizing because I found myself a smidge frustrated that for pure stock type class tire rules, they only allow what is a generally accepted bias ply to radial equivalents, even though the radial equivalent has a significantly smaller tread width than the original bias ply tires - and for racing, tread width is kind of a big deal.

Goodyear F60/15
26.27" diameter & 8.25" tread width

An 'F' series bias ply tire is (as I've understood it) supposed to align with a 225(mm) width radial tire, but in the case of this size, a 225/60R15 would be the better part of an inch short, in addition to a smaller tread patch;
This radial tire diameter is listed as 25.6".
This is probably why the later 70's radial change over saw the tires change to a taller aspect ratio.
The accepted replacement for an F60/15 is a 235/60R15 which has a wider tread patch than a 225, but still comes in a tiny bit short at 26.1" diameter.

My true rabbit hole has to do with the tire size for my car...
(please bear with me for a second, because I'll bring this around)

Goodyear F70/14
26.45" diameter & 6.55" tread width
The accepted replacement is a 225/70R14, and the diameter is bang on at 26.4", but then there's the significant (for drag racing) tread deficiency;
stepping up to a 235/70R14 makes the tire too big at 26.95";
changing to a 235/60R14 makes the tire significantly too short at 25.1" tall
changing to a 245/60R14 makes the tread width about perfect, but it's still a bit too short, coming in at 25.57" diameter.

To bring this around full circle, the F7014 & F60/15 wheel/tire combinations used on our cars were interchangeable coming in at 26.45" & 26.27" diameters respectively;
If we look at a 225/70R14 & 245/60R15 their diameters are almost bang on matches for one another at 26.4" & 26.57" respectively.

Tire size comparison calculator

It seems to me that the difference in measuring a bias ply versus a radial tire leaves something to be desired and that a 245 width radial typically has the correct tread width for an "F" series tire on a 7" wide OE wheel, and if you were to see it in person, you just might agree with me.

[Norwood]

255 on the back, 245 on the front

[78w72]

255/60 are recommended for a 7" wheel... i have ran & am running them on 7" wheels & they dont balloon much at all IMO & ive never noticed uneven tread wear when inflated to the right psi.

the 225 width for later 2nd gens uses a 225/70 tire that is 27.4" tall. i realize the F series tires on earlier F bodies was shorter but for the most part the taller 225/70 or 255/60 (27") will fit on the earlier cars using factory rally 2 backspacing wheels.

whether a 255/60 or any similar size tire will rub is really based on the cars suspension/ride height, all of my cars are lowered at least 1-1.5" more than stock & 255/60s on the front dont rub & 275/60s on the rear dont rub.

[jhein]

245 front, 255 rear. 15x7 wheels.

[Bandit400]

I run 255/60R15 on all 4 corners of my 70, on 15x7 Rally IIs. I get a rub at full lock on the inner wheelhouse/frame rail. It is lowered 2" all around (PTFB Comp Springs).

[Transamric]

I've run 255's on my stock height '73 since 1990 on original 7" Honeycombs with little problem. Yes, they will rub on the inner side when turning near lock in either direction. Sounds knarly, but no damage to the tires. HOWEVER, because these tires are now 30 years old, I will be replacing the fronts with 245's, keeping the 255's on the rears.

[Formulabruce]

The 225 aspect ratio was used on later second gen cars
With 8 INCH wheels. This dropped the diameter when installed at correct pressure.
Fisher body built F body's to sit LOWER in the rear from 1/2 to 3/4 Inch for " Flush and dry" rocker/ vent system and for cornering/ handling.

[78w72]

Originally Posted by Formulabruce

The 225 aspect ratio was used on later second gen cars
With 8 INCH wheels. This dropped the diameter when installed at correct pressure.
Fisher body built F body's to sit LOWER in the rear from 1/2 to 3/4 Inch for " Flush and dry" rocker/ vent system and for cornering/ handling.

the later cars used the same 225/70 on the 7" wheel options too.

wasnt sure if you meant they ONLY used the 225 on 8" wheels since the way the post is written is kinda weird... no period after the first sentence, then a new paragraph for "with 8 INCH wheels" but no period until after the 8INCH wheels. but im sure you know they used the 225 tires on later 2nd gen for 7" wheels too.

[Formulabruce]

My point was rather related to over all diameter. 225 on a 8 inch rim has a smaller diameter...."mounted" and on car.
The charts really don't tell you the diameter on various width wheels, and not under load.

[78w72]

ok, apologies for reading it wrong.