Tires: 1994 Chevy C3500 tire change, rear wheels, c3500

Question
I have scoured the vast reaches of the net to no avail. I have purchased a '94 Chevy c3500 "dually" that I am considering switching from the called for 225/75-16's to a 235/85-16. I know the speedo will change, as I have found the calculators online, but what I can't find is this. Will I have to put a spacer in between the 2 rear wheels so they will not touch? This of course being that I do have a regular factory truck bed, wheels, and factory 1-ton suspension. My second question is that I am running 8ply load "d" tires right now that call for 45lbs of pressure. The new ones I am looking at are 8ply load "e" that call for 83lbs of pressure (i believe). Can I run them with less pressure while not "hauling" and still be okay width (see initial question), and wear wise?

Answer
Vic,

There are certain parts of your questions that I can answer - and certain parts I can't.  That's because my expertise is in the rubber parts, and not the metal parts such as wheels.

Dual spacing:  An LT225/75R16 requires a minimum of 10.2", while an LT235/85r16 requires a minimum of 10.75".  Now I don't know what GM may have supplied to your vehicle, but I'm guessing is would be closer to 10.2" than 10.8".

But you can measure this yourself.  Dual spacing is just the distance from the centerline of one tire to the centerline of the other one - and to make it even easier, you don't have to use the centerline of the tire - just the same points, so pick an edge of a groove.


Tire pressure:  On the sidewalls of tires is a maximum pressure - which is to say, you shouldn't exceed that value (with a couple of exceptions) - but using a lower pressure is just fine provided you have enough load carrying capacity.  So you can use a tire with a higher rating and use the lower pressure.