When your dualie needs new booties it's not as simple as slipping on a pair of new shoes. Ever notice how different makes of footwear vary slightly in fit, even if they're both exactly the same size? That's even more true with tires.
When it came time to replace the aging rubber on a '96 Dodge dualie, we found that we couldn't just use the same code on the sidewall of the existing tires (LT235/85R16) that were from a different manufacturer and were larger than the factory-recommended size (LT215/85R16). That's because the spacing between the pairs of rear tires was not the same for the two different companies (especially around the sidewall bulges at the bottom, where clearance is critical, particularly when you add a heavy load). On the old tires, the spacing was about half an inch, but new Bridgestones with the identical size code would have overlapped by about an inch. (And there's no shoe stretcher available to make these booties fit better, either.)
Getting down to the nitty-gritty numbers, if we had used the old tires' sizing, the Bridgestone Dueler A/T Revo would be 4.9 percent larger in overall diameter than the recommended OE tire size, and the company engineers indicated that we needed to stay within +/- 3 percent. At one point we even considered going to a LT245/75R16 size, but that would have required 2-inch wheel spacers. Sure, we could have added the spacers to make sure there's sufficient daylight shining between the sidewalls, but we decided to start with a simple stock setup on this go around, partly because this work truck is used for hauling heavy loads (on boat docks), and we were more interested in durability and reliability than appearance.
Are we disappointed by going to a slightly smaller tire than what was already on the vehicle? Not at all. We noticed an immediate improvement in handling. A wider and taller tire can create more rolling and turning resistance, and while the truck used to track like a freight train, it was anything but agile when changing lanes.
 We ordered seven tires in...  We ordered seven tires in all (don't forget the spare). The blue tint easily washes off the white letters. |  Time to retire these tires!...  Time to retire these tires! Note all the warning signs of wear: rounded shoulders, thin tread (if the head on a quarter shows, the tread is too thin), and cracks in the sidewalls. |  Here's the critical measurement...  Here's the critical measurement on tires for a dualie. While there's plenty of room in the wheelwell, it's the space between them that matters. Going to a different brand of tire may have a different sidewall bulge at the base, so measure carefully. Spacers may be needed if you change manufacturers, even with the same size code. |