Cap

Will running a tire that's 1 inch taller on the rear than front cause a problem mechanically or warranty wise? Putting a heavier duty tire on rear for towing.
Thanks

65mechanic

Definitely not advised. Mismatched tires and 4wd DO NOT MIX. It can create binding on the axles, transmission, transfer case, etc and the weakest link breaks. Unless you want to never put it in 4wd or if you'd only use your 4wd in low low traction situations. Still I wouldn't do it. I could see it voiding a warranty as well

Throwitup518

Even not in 4x4 the front driveshaft, ring and pinion and cv's are freely spinning (no load from the tire since 4x4 isnt engaged), and if you change the tire size in the rear it is going to spin at a different speed than the front tires. So you have the rear driveshaft connecting to the tranny to the transfer case then to the front driveshaft to the front pumpkin, and if your rear driveshaft and front driveshaft arent spinning at the same speed that is a huge issue. Things will bind up and break most likely the first time you drive it.

Watt-maker

I would recommend upgrading all 4 tires to the same size and load rating. They don't have to be the same tread pattern, (hi-way tires on front, mud tires on the rear) although not sure why anyone would want to do that especially being 4x4 but some old timers like to run them this way around here. Running different sizes can cause some drivability and mechanical issues especially if used in 4x4 on a high-traction surface. The ABS and traction control systems may have an issue with it as well. As far as warranty, Ford would definitely have a problem with different sizes front to rear but if they were all the same size there would likely be less of an issue. Really it would come down to how the service writer, tech, and service manager were feeling that day. I've seen trucks running 37" tall tires get warrantied and I've seen folks get denied for just going from a "P" series to a "LT" series tire. If you go up in tire size, don't forget about the spare.