My truck is a 4x4 and I'm wondering if I have to lift it to clear 285/75/16s. Also, is it hard to change the speedometer to read correctly with the new tire size?

 

No need to lift it to clear those tires. Might just need to shim the bumper out a touch if they happen to rub. I cleared 33's on my 4x4 F-150 with no lift at all.

 

No. You can clear those no problem.

The speedo is easy to set but can only be set a few times. There is a procedure on how to do it but i don't know it. You may be able to search and find it here.
I run that size tire and never set the speedo. It is just about 2 miles off at 65 - 70 mph I believe.

 

I run 285's on my 2wd and don't have problems with rubbing except with turning really sharp. They rub on the radius arms a tiny bit at full lock.

 

Friends truck on 285', f-250 ext cab, stock...he could clip his leaf springs on the front, just touch them.



My f-350 on 285's that it came with...front wheels are turned..it's nowhere close to hitting.