Here is a formula for figuring the checking rim width that I think all tire manufacturers use. ............ Section width/25.4 x .7 = checking rim width.so with 245s it looks like this
245/25.4 x .7 =6.75. That means the section width was determined using probably a 7 inch rim. On an 8 inch rim, the section width will be wider(perhaps 255), cuz the beads are spread an additional inch.At the bottom of the catalog page is a note that indicates that you can usually mount any tire on a rim that is within 1 inch of it's checking width;so in this case the 245 can be mounted on a rim between 6 and 8 inches.The tire pressure may need to be adjusted to get the tread to sit flat to the ground, and thus provide optimum tire wear.
But you can work the formula backwards as well. Say you have an 8 inch rim and want to know what the optimum tire size would be to fit on there.
...............section width/25.4 x .7 = checking rim.........rearranging ,we get
..........section with = checking rim x 25.4/.7 = 290.
So, the tire manufacturer would build a tire, slam it on an 8 inch rim, and check the sidewall section and find it to measure 290mm, and he would then publish that in the catalog. And down on the bottom of the page it would allow a plus/minus of 1 inch.
Now most guys will tell you that an 7 inch rim is just way wrong for a 290, and I would agree. It will corner horribly.But at 9 inches it would be fine. I would not install it on an 8 inch either.But this is how the tire manufacturers determine the section widths.
Personally, I have had excellent results with 275s on 8inchers. Long tread life, with good manners at reasonable tire pressures.The checking rim for 275s is 7.6 inches.
The checking rim for 225s is 6.2 inches.So they would normally be mounted on rims between 5 and 7 inches, with 6 being the sweetspot. If you can actually get them mounted on 8 inchers,they will not do well. It will take a lot of tire pressure to get them flat to the road, and if one goes flat and pops off the bead, you will have to visit the tire shop to have it re-seated.If they are not inflated to run flat to the road, then the outside edges will be taking all the load. the carcass will overheat from flexing and kill tire life. And with any alignment error it will steer like chit.
I urge you to reconsider.
FWIW. It's a pretty safe bet that, whatever rim width you are using, you can mount a tire on it that has a similar tread width. So on an 8 inch rim, you can mount a tire that has a tread width of 8 inches. Unfortunately tire manufacturers do not normally supply tread widths on P-type tires. So bring a tape-measure,when you go shopping.
