SO, I see threads everywhere with people running 28"+ tires with their cars, but not a lot of them(if any) are auto...I'm working with a 98 obs 4eat, and looking to put 28"(215/75r15) or the wider 29(235)" tires on it. I've been looking at some open country AT/destination AT options, but if having the 3.5" larger tires is going to destroy the transmission, I'd rather get some more aggressive MTs(hankook dynapro mt) and only put them on when I go offroad, as I rack up 60+ miles of highway travel a day and am offroad only 3-4 weekends a month. Switching them out wouldn't be a huge/time consuming issue as cordless impact is bae, but if the 215s wont hurt the transmission any less, I wouldn't mind leaving them on full time. Car does have a aftermarket trans cooler, and the trans is a 140k takeoff trans that was just put in 10k ago. I'm also not a very aggressive/fast driver so the acceleration isn't a concern for me.

 

 

The 4eat transmission is tough. You won't have any issues running big tires.

issue will be loss power and torque to wheels. bigger they are weaker car will become.