Tire size
 

Right now I got 235/75r15 with atock ride height, I'm thinking about going up to a 31/10.5r15, I did do some searching online and I believe they should fit without any adjustments is this correct, will I lose a bunch of power, my truck is mainly used for highway driving, just want a bigger more aggressive tire if I ever need it. The truck is a 1984 pickup

Fit yes, allow stock turn radius and up travel probably not.

Jack up the wheel under the control arm untill the bump stops touch and measure. Clearance of the tire centerline and the pinch seam, then crank the steering fully to each side and measure clearence at the side to the frame and along the pinch.

Further verify your current tire size isn't already oversized, my badge says 225 not 235 if my memory serves me right. You might already be a half inch over if so.

I don't know the width off hand but going from 225(28.5) to 265(31.5) looks like it fits without any modifications other than adjusting the stops. Based on the clearance I see on my 4runner, but this is an assumption since my previous owners installed spacers and flattened the pinch aswell as clearenced the firewall corners for larger tires than I have now. I estimate it will accept tires over 33" now.

Appears these should fit after the measurements you gave me, but they might rub around sharp corners.

The next question is: will I lose a bunch of power by increasing the tire to a 31x10.5

31's were one of the first things I put on my '89. You won't discern any difference in power and the turn radius is fine. If you were to move up another inch, to 32's, you might have some rubbing but at that size most people are able to hammer the fender a little. IMO 31's are a no brainer. There are more tire choices among AT and MT rated tires than the size you now have. My '89 has Firestone Destination because they were cheap. They look good IMO but they don't have a warranty. I have Cooper Destination AT's on my 2000 4Runner and they are supposed to last 50,000 miles. I'll probably stay with Coopers in the future and they're made in the USA. Here's a not so great pic of the '89. My photobucket is disorganized. I forgot to tell the dealer to turn the white letters in and I'm too cheap to remount them. My son likes the white letters anyway.

Attachment 111023

Because you have a 84-85 your turning and everything should be unaffected. There is a slight power difference but usually only on certain long shallow hills where you may need to down shift at freeway speeds. If you go wider than a 10.5 tire you could end up with rubbing and such but that can also be solved with different back spacing on your new wheels. You should get new wheels if you go wider than a 10.5 tire.

I run 31/10.5/15 BFG A/T on my stock 85 4Runner and have zero issues.

Good luck hope this helps.

Thank you everyone for your help, I'm going to get the 31's for sure. Thanks again