You can have stock steel wheels widened by Weldcraft Wheel of Livonia, Michigan ... although I'd hate to pay what they charge for a measly half inch. You should also note that going from 235s to 255s will pretty much eliminate your gap between the rear tires with only a half inch increase in rim width -- especially if you have an aggressive tread pattern -- so under load you might get contact, rubbing, heating, and potentially early tire failure. You're going to need a spacer. If you have a little bit of gap left, you might get by with just a quarter inch spacer... in which case you might have enough stud length and bore pilot on your outer bearing housings to carry the outer wheels just fine. If you don't, then you're going to be faced with needing longer studs... or installing an adapter-spacer between the inner wheels. If you try to run a stud-through spacer any thicker than a quarter, you might run out of bore pilot, and then you'll get vibration. If you go with a bore-centric adapter-spacer instead, anything less than around 2.3" thick will require that you shorten your studs, which makes going back difficult... and which gives you a HUGE gap between the tires. And then you have to deal with the whole issue of 16 nuts for each rear tire stack. Also, anything thinner than around 1.9" in steel -- in my opinion -- doesn't offer a satisfactory factor of safety on total load capacity. There's just not enough metal to let the stress flow around the counterbores for the inner run of nuts. At least that's what my FEA runs told me. You might fix the gap issue by going to 17x7s, although you might start to get tight on the inside between tire and spring pack.
I should qualify those statements. The studs for the larger, later dually pattern might have a more convenient length, and a larger adapter-spacer is going to be inherently stronger than the smaller diameter unit required for earlier trucks with the smaller, older pattern. You might be able to run a thinner adapter-spacer, say, maybe an inch and a quarter or so, and have an indefinitely long service life for steel units. Might. No way I'd recommend trying that unless you can do the math for the loading to see what happens inside the steel. You'd still need to cut down your studs too. You might have more bore pilot surface on the bearing carrier, too.
I think since you're looking for a modest increase in width, wider custom steels -- the 17x7s -- might give you exactly what you need. It'll cost you about a grand and a half after shipping wheels around. You could start with some take-offs so your truck wouldn't be up on blocks for the weeks the widening might take. Unfortunately -- I'm not sure -- you might cause interference issues in front with 1" wider wheels on the concave side. Half-inch spacers would fix that... but just like in back, you'll run out of bore pilot and stud length for anything more than about a quarter to three-eighths.
Up-tiring a dually is never easy. It's going to cost time, money, performance, durability, or convenience.
There are four ways to do it:
(1) Squeeze wider tires down onto the stock skinny wheels and run an adapter-spacer between the wheels. Pros: Cheaper. Cons: damages load capacity or accelerates tire wear or both. Makes it hard to find a shop who will mount them up. Damages handling and stability. Operates outside of tire design limits. Comments: Pretty much demands steel hub- and bore-centric adapters in back to retain anything like stock load capacity. I would never put my family in a dually with tires mounted like that, or with aluminum spacers with any significant load on the back axle. Or at all in front with a CTD, let alone a CTD and a 9 ton winch. That's just me.
(2) Get a full set of custom plus size wheels from Monstir or Fuel. Pros: retains full load ratings with careful choice of wheels and tires. Safe. Any shop will mount them up. May actually enhance ride quality, mileage, or performance. Looks killer. Cons: $$$$... and you have three different kinds of wheels, so a spare is problematic. And you might STILL need spacers, depending on manufacturer and fitment.
(3) Get a 10-bolt true heavy duty conversion set -- hub adapters and HDT rims in a half-inch size. Pros: Components will last forever. Tires will last many tens if not hundreds of thousands of miles. Not the most costly option. Looks killer. All six rims and the spare are the same. Cons: Only truck stops can service your tires. Your truck will ride like poo. You will likely need a lift.
(4) Use custom widened wheels with modified hubs front and rear. Pros: Durable and tough and most like stock. Gives you tons of rubber for offroading. Uses inexpensive 17" tires. Cons: As costly as (2), and as heavy as (3). Looks almost stock, except for overall width. Or that might be a "Pro".
I run 295/70-17s on 17x8-1/2 modifed Ram steel wheels. In front, I have custom dually wheel offset adapters that are 2" wider than stock machined from cold rolled billet. I had them made before I knew about free-spinning hub and bearing upgrades.... and it's going to cost me another two grand to get a set made to go with the hub kit. In back, I run 2.35" adapter spacers fitted with Class 4 studs borrowed from a Kodiak. The hub extensions fit inside the tire pack and move both wheels outboard. They are each more than 50 pounds of steel. I know they'll last -- my wheels will fail before any of the studs or the extensions will -- because I ran full FEA sims under crazy loading conditions.
I wouldn't do it again. Next time I'll do (2), or (3), or start with a 4500/5500 and do a 4-tire conversion. Or simply not modify the truck that has to pull my trailers.
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