What size 10 ply tires should I get ordered to slap onto these 15 inch rims I bought for my 1990 ranger?

 

Why in the world would you want 10 ply/load range E tires?

You can't even come close to maxing out 6 ply/load range C tires on a ranger

 

It's not about the loads it's about the roads.

 

The little truck is going to ride like a buck board wagon.

 

Yep. So what would you recommend then?

 

Review Tires, find out what tires have a higher ply in the sidewalls.
There are a few companies out there that have heat duty sidewalls, and should stand up to rocky roads.

Most HD sidewalled tire for off-road use usually have a heavier tread designs so pick and choose.

BUT... as I always say, it is your truck, build it the way YOU want.

p.s. How important is the tread design, can you live with an aggressive tread and see noise on the road ?