Are you thinking of installing a tire with a
9" tread onto a 7" wheel?
Or one with a
9" profile?
Cuz, a 9" tread will have a profile about 1.5 inches wider, so say 10.5, which translates to about 267, which rounds up to a 275. But, a 275 on a 7" rim, at normal tire pressure, will pull the edges of the tread up off the road, and wear off the centers.
But
a 9" profile translates to a 225mm branded tire, which would be fine on a 7"rim.
Just remember, the rim width is determined by the measurement between the beads; and NOT from outside to outside which is always about ONE inch larger.
In other words, if you have a wheel that measures 7" from outside to outside, then it is actually a 6"wheel, and the ideal tire size for a 6" is about 218mm or less; so as already mentioned by others, rounds to 215.
To get a 215 up to 25.5 tall, on a 15, will require a branded tire of
215/65-15@26 tall or a
215/
[email protected] tall
On our A-bodies, when the front tires get too far from stock height, you will get wandering issues.
A 215 gets lost in the rear tubs of a Barracuda/Duster/Demon/DartSport..