For my 2019 Wide Body I looked at various tire combinations with the help of DGatzby a few years ago. He knows what works. This is what I wrote in my notes back then for Triumph rear custom 12" wide wheel possibilities. I wound up getting 345/30Z20 tires.
"For Michelin Super Sport tires in size 335/30ZR20...they have a diameter of 28", a width of 13.5”, mount on a 20" rim and have 744 revolutions per mile. It weighs 35 lbs, has a max load of 2,205 lbs, a maximum air pressure of 50 psi, a tread depth of 9/32" and should be used on a
rim width of 11.5-12.5”. (108Y) XL load index."
335/30ZR20 tires would have plenty of fender clearance in back (as would 345's), but unless I've forgotten something these would not fit up front even if you had the required wider wheel up front because of inside fender rub when you turn the wheels..
In case you're interested in a nice fat tire up front, I have up front on my custom 11" wide Triumph wheels 315/30ZR20 Michelin Pilot Sport 4S tires. I am not sure if my Triumph 11" wheels vary from stock Devils Rim 11" wheels regarding offset, etc. I doubt they would - maybe DGatzby knows? These tires have a diameter of 27.5", a width of 12.6", mount on a 20" rim and have 757 revolutions per mile. It weighs 30.5 lbs, has a max load of 1984 lbs, a maximum air pressure of 50 psi, a tread depth of 8.5/32" and should be used on a rim width of 10.5-11.5”. (104Y) load index. A note here - the max load of 1984 lbs is slightly below stock 107Y recommendations. That 1984 lbs. load factor is based on 32 psi (I'm pretty sure, not looking at them now). I inflate them to 34 psi for street and road course, which increases the load factor to close to stock. Plus when you drive them in most weather conditions they'll temporarily heat up to that and more. Just alway corner like a bandit and you'll even out the wear pattern *grin*.
If you get 12" wide rear wheels with proper offset (DGatzby?) you can run 335's or 345's on them - both would look good with 315's up front because of respective tire diameters. But, if you run stock 305's up front with either 335's or 345's in back your front tires will have greater diameter - I would not like that reverse rake/look. I have 345's in rear, 315's up front, and these respective tire diameters give my car a small bit more forward rake than stock. This photo was taken the day I had these tires installed.
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