All I ran the last 5 years prior to retirement and ours was 108" wide with the slide tarp mounted on the rub rails. I pulled a Reitnauer 8 axle spread on air. 10-2 between the front axle 6 tight on air and the rear axle was 36 on center. Trailer was 53 foot long. We were never bothered in Ohio, Michigan or Indiana. In fact, I was never pulled over for a DOT inspection, our equipment was always top shelf, 2 year old or newer Western Star conventionals with big motors and 13 or 18 speed Roadrangers.
I could legally roll 104 thousand every day in Michigan and Ohio and Indiana on over weight permits. Trucks were kicker plated for 161 thousand GVW.
The regs say 102. Have a copy here. Various states can alter the max width requirement but on an interstate highway, the 102 applies.
Why I called Hay Dude on his comment. I know what it says. No way anyone is legal on any road (without permits) hauling round bales side by side if they are 5 footers. You might get away with it for a while but sooner or later you will get pinched. Not legal and never will be but then it's up to the officers discretion.
The farm equipment exemption is everywhere I know of. I'm regularly pulling implements over 10 feet wide on secondary roads and of course all the required SMV placards in place and amber flashing lights plus a amber beacon on the roof of the tractor. One time I got done after dark and was coming home (all lit up of course) and picked up a State Highway Patrol car and he followed me hone and went on his way. Guess he didn't have anything pressing to do.