Legal width is 102" or 8.5', not counting safety devices,
Federal Size Regulations for Commercial Motor Vehicles - FHWA. This also applies to things like the ladder and awning on the side of 102" wide RV's.
As others have said there is no RZR that is legal to flat carry sideways. There are some people that have angled ramps they carry machines on that makes them short enough.
The RZR 900 trail models with the square body style are 105" wide, the new round body are 110" but that includes the roll cage that goes behind the machine.
I carry a 2018 RZR trail cross ways with almost 10,000 miles so far in less than a year. Yes it is illegal, yes I am willing to risk it, yes machine is well inside the width of my mirrors. At some point we will buy the newer style and I will be removing the rear portion of the roll cage to keep the length down.
I am attaching 2 images. First is one with the RV and how we normally haul. The second image is of a trip we took from WA to AZ and I agreed to haul several of the machines. When the other guy said trail, I thought it was an RZR, it was not and it was 110". I found out the morning we left so I did not have a lot of choice, but I would not do it again in the future.
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