19.5 measurement question

[Detroit Dan]

I have a 1982 cab & chassis crewcab 1 ton. I put a fleetside bed over the narrow rear axle for the tucked under dually look. A friend has direct bolt 8 lug steel wheels with 245/70/19.5 tires on his 87 dually. Another guy I know has some on his 95 cab & chassis, with 225/70/19.5s, and he might be willing to part with them. I measured his some time ago and figured they would easily fit under my fenders, which is important because I dont want to put on fender flares if I dont have too. But, the 225/70s are pretty small, and would look weenie under my lifted truck. So, eventually I would want to upsize to a 245/70 traction tire. It seems to me that when I measured the other truck, the rears were about 2 feet wide, from outer tread edge to inner. Which would put it way outside my fender. Why would this be? I did some math on paper and if the wheels are the same the 245 tire should only stick out about half an inch or less, more than the 225. I mean, 20mm wider means 10mm on each side of the tire, so 10mm sticking out (or .37 inch). I'm not getting into aspect ratios here, I'm only worrying about section width. (Before some tire guy decides to write a discourse trying to prove 245mm isnt 20mm wider than 225mm.) Just wondering if I'm missing something, because it doesn't seem like the 245s should be a heck of a lot wider than the 225s.

I really need to get some bigger meat under this truck, the lift makes the 235/85/16s look weenie. BTW, 235mm tread section width is right in the middle, rim width notwithstanding. But I dont know if I want to buy the rims with the 225s if I'll never be able to upsize to 245s.

This is probably my last shot at keeping it a dually and going to bigger rubber. I'm about to swap it to SRW just so I can put 35s on it.

 

[deejaaa]

i am running 8R19.5 on the back, single and 225 on the front. i was wanting as skinny as i could get so the 8R's are perfect. i mounted them on a set of railroad rims. i can't stand to hydroplane anytime, empty or loaded. we get a lot of rain down here at certain parts of the year. i spent less than 400.00 in them, including tires. they get a lot of questions, especially "is that an old railroad truck?" they aren't for everyone but i like them and they will last many miles. have 30,000 so far and they still new.
the best info i could find was on the rickson site, if you can get get over the high prices and hype. the readers section also has a few pics of rides with wheels so it will give you a pretty good idea what they look like. http://www.ricksontruckwheels.com/ i know the rears need spacing due to heat/rubbing. the guidelines on the site will give you an idea of what to get without wasting your money.