F-450 SRW Conversion

#1
I'm just starting a project converting a 2007 Ford F-450 Super Duty to an offroad camper used for ski mountaineering and rock climbing. One of the first things I'm looking at is converting the DRW to SRW since I drive on dirt roads and snow a lot.

At the moment the truck has DRW 19.5" wheels with 245mm F rated tires. I was considering going with the Rickson 8.25x19.5" SRW conversion wheels with something like the Toyo M608Z in 285/70R19.5. Does any experience with these? I'm looking for something that can take a lot of weight, drive reasonably fast (maybe 75mph) and perform on unimproved jeep roads in dirt and snow. I don't plan to go rock crawling in moab or anything like that, but I don't want to get stuck either.

Currently the truck rides a little rough on the 245 19.5" dually wheels. Should I expect it to ride pretty much the same on SRW 285s or might it improve a little since the 285s are a bit taller and wider? I'm not running with the weight of the camper on it just yet so that should weight it down by another 3500lbs or so. Maybe more once I put gear and water in it.

thoughts? comments? Thanks in advance!
 
#7
The higher the rating the stronger the sidewall. Stronger sidewall typically is a result of more plys or thicker plys which translate into stiffness. Stiffer sidewalls = harsher ride. I would figure out what your total weight/load is going to be then select a tire with a load rating that will support it. You are going from the load being carried by four tires in the rear to two.
 

doug720

Expedition Leader
#8
We have 19.5's on our class A motorhome and we use DRW's still, so this is more anecdotal, than specific information.

I have a buddy who is a Bridgestone tire engineer who I asked about options to help with the rough ride with the short 19.5 tires sidewalls. He recommended we go from F rated tires to G's, and run a little lower pressure. He gave me a formula to follow once we had the motorhome weighed while loaded.

Now, we are running about 10% lower tire pressure with the higher rated tires than the F's, and the ride is noticeably better. We have had these tires for several years and thousands of miles and have been very happy with the improved ride. The tire engineer stated the reason why higher rated tires are not installed as OEM, is twofold.

Costs, the higher rated tires cost more. Save a buck...

The big reason is liability. He said most motorhomes and many other other vehicles are driven close their GVWR. Manufacturers are concerned that owners will see the tire ratings and overload the chassis. So they spec lower rated tires with higher running pressures.

For us this worked.
 

Mundo4x4Casa

West slope, N. Ser. Nev.
#9
The most important issue is how much eventual weight is going to be put on each axle, and how far off road you plan to go. I drive an off road truck camper and had to do a lot of improvements/upgrades to the suspension and running gear to carry my measly 2700 pounds of loaded camper (1842 pounds wet). Once you have a ballpark number you can work backwards to find the best wheel/tire combination for your specs. I run super singles with custom made Stockton Wheels, so called, 'Power Wagon' wheels with a stupid high load rating. But this was with a SRW 2500 Dodge Dana 80/35 spline axle. You have the very deeply backspaced 450 wheels, I think 7.5 inch, which are more difficult to replace with a single, but they are out there. Just remember that it's the tire diameter that make the most difference in selecting 2 widths of wheels. Just keep the diameters less than 3% difference. This was the approximate setup with last set of tires: 375x65R16 tires on 12 inch wide rims:


And this is my current setup with 315x75R16's at 35 inches in diameter on Stockton Wheels:


As has been discussed above, 19.5 tires don't do well on sand since they cannot be deflated. If you never plan to reduce the pressure for dune running or across the Gobi, this won't matter.
Another issue with different size wheels is what do you do about a spare? I use the narrower spare tire with the same diameter that will fit up underneath in case I need a spare on the road. But, my experience over the last 25 years is that tires are better than they were 50 years ago when I first started 4WD-ing. Almost no flats the last 20 years, and any that did appear were easily patched up on the road with the tire and wheel still on the truck with a supply of Safety Seal puncture repair plugs and either an air compressor or a CO2 tank on board.
jefe
 
#10
Ask Gary Wescott. The last couple Turtle expedition rigs he's built run SRW's. He's a guy that has a wealth of F450 info and very nice people too. He shouldn't be that hard to contact.
 
#11
I would just keep the duals. I don't see the point in going with 19.5's single. The dually will drive better, and be more stable and safe. You can't really air down 19.5 anyways so I fail to see the need to go singles. You also lose capacity.

What kind of camper is it? Those things loaded up always seems to be way heavier than people first realize.

I don't have any experience with Rickson but there have been a few reported wheel failures on here, and I have also heard that their customer service is poor, like people waiting almost a year for their wheels to arrive.
 
#12
The most important issue is how much eventual weight is going to be put on each axle, and how far off road you plan to go. I drive an off road truck camper and had to do a lot of improvements/upgrades to the suspension and running gear to carry my measly 2700 pounds of loaded camper (1842 pounds wet). Once you have a ballpark number you can work backwards to find the best wheel/tire combination for your specs. I run super singles with custom made Stockton Wheels, so called, 'Power Wagon' wheels with a stupid high load rating. But this was with a SRW 2500 Dodge Dana 80/35 spline axle. You have the very deeply backspaced 450 wheels, I think 7.5 inch, which are more difficult to replace with a single, but they are out there. Just remember that it's the tire diameter that make the most difference in selecting 2 widths of wheels. Just keep the diameters less than 3% difference. This was the approximate setup with last set of tires: 375x65R16 tires on 12 inch wide rims:

Dang Dodge put a Dana 80 under a 3/4 ton truck? Thats some heavy duty parts.
 

Mundo4x4Casa

West slope, N. Ser. Nev.
#14
If I were to do it again, I would get (4) 18x10 inch wheels with the stock back spacing (6.25 inches) as they would fit over the disc brakes with more clearance and you would not loose the scrub radius on the front axle. Plus, they are deflatable since they have enough sidewall and are not a ".5" tire. Take a look at a demounted .5 tire/wheel (16.5, 19.5) and look for the safety bead hump that keeps the tire on the rim. None found. Plus, the 18's come in the highest load rating (of the 16, 17, and 18 inch size) around 4K pounds or more on some tires. My 35 inch, 315x75R16's tires are rated at 3860, which for my purposes (maximum sidewall) is plenty enough to haul my loaded Lance around. Here is a short vid of me climbing the Diablo Drop Off in the Anza Borrego Desert, a 300 foot blow sand hill. The spectators thought we were crazy. specs: 4th gear low range; tire pressure 20 pounds all around; downshifted to 2nd low range for the mogols near the top; True Tracs worked great. My bro tried the hill in his mostly stock '99 F-250 diesel/6 speed/pop up camper @ 30 pounds of air, in 3rd gear and sank to the frame about 1/2 way up the hill. Too much power/not enough floatation. I have a vid, but you don't want to watch the 3 minutes it took him to back down the hill with out turning. He then reported to me to lower the pressure and start in 4th gear. Check. Motored right up as you shall see, as he did on the 2nd try. jefe
https://www.dropbox.com/s/bfj5y93wsd7vfkw/jefe does sand hill at dry wash of the devil Anza.m4v?dl=0
 
#15
Thanks for all the feedback everyone!
I think I've about decided to stick with the 19.5s (22.5 just seems too big and I wouldn't feel comfortable maxing out E rated tires on 18s or 20s) and run the minimum pressure but I'm not sure if I want to go with Rickson Wheels considering they quoted me a ridiculous lead time before I can even put an order in.

I'm sort of wondering if I even need custom wheels for this. Is it possible to just use an off the shelf ACCURIDE 19.5x8.25 steer wheel with 6.63" offset? I really want to make sure the tracking is the same on the front and the rear wheels I"m not sure if a 6.63" offset would work, or what size offset I would need.

Maybe this isn't safe and I really do need custom wheels for this from buckstop or 1st attach? Admittedly I don't know that much about wheels.
 
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