DRW to SRW- pros and cons?

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pybyr

Minister of Fire
Hearth Supporter
Jun 3, 2008
2,300
Adamant, VT 05640
I recently lucked into the purchase of an incredibly well kept 1989 F-350 4x4 7.3 diesel dual rear wheel truck (12,700 miles on it) that's now become my daily driver (I gave it a thorough coat of bar & chain oil underneath to try to resist VT road salt).

I've never driven a DRW truck before- and find it great on dry pavement (M+S Michelins on back, Nokian Vativas on front as it came to me), but last night, with an icy layer + powedery snow top layer on the back unpaved roads, the truck's rear was ALL over the place.

I will rarely be carrying payloads that'd require the DRWs in back, and it looks to me as if I could set it up with just one set of wheels- pointed outwards- for temporary SRW except when DRWs are needed.

Can I expect better traction/stability with the SRW (more weight per tire = larger contact patch?) ?

Any other thoughts or suggestions?

Thanks
 
it's a lost cause, sell me your truck.
 
Realize that the dished wheel will put a twist on those rear bearings that isn't there when the oppositely dished wheel counters it.

What you need is ballast. Load a 1000 lbs of sand in the bed. Right now you've got that monster engine up front anchoring the front end and the drive wheels have nothing on them so they spin easily. Did you try engaging 4wd? This should limit rear wheel slippage to the same rate as the front end and should keep the back end on the road.
 
HB is right, I hear that those don't really see much impact from decent loads on mileage, so I'd throw some firewood in the back and maybe it will season quicker going down the highway, lol.
 
Just load up the bed, sand/gravel mix. Then you can sell your service to sand peoples driveways on the way home! No, honestly use caution when useing four wheel drive when loaded down, with diferent tires mixed on the vehicle. driving on higher traction surfaces can cause the drivetrain to load up and either jerk a little bit when that wind up is released or worse case senario when part of the drive train fails due to the extra strain.
 
Highbeam said:
Realize that the dished wheel will put a twist on those rear bearings that isn't there when the oppositely dished wheel counters it.

What you need is ballast. Load a 1000 lbs of sand in the bed. Right now you've got that monster engine up front anchoring the front end and the drive wheels have nothing on them so they spin easily. Did you try engaging 4wd? This should limit rear wheel slippage to the same rate as the front end and should keep the back end on the road.
Click to expand...

Thanks for the insights/ suggestions. I did put it in 4WD on some of the really squirrelley sections of road, but I don't like to drive around in 4WD with a part-time transfer case system (for obvious reasons).

I appreciate your raising the concern about the wheel dish and leverage-- but I guess that I'd have thought that this axle (Dana 60) probably has such herky bearings that such loads on the bearings (as long as the truck is not heavily loaded) would be inconsequential. Guess that I'll have to study up some more on that.

Studded snows would be appealing, but there's no way I can afford 4 of them for the back right now- not really even 2, although snow tires are cheaper than ending up off the road in a ditch.
 
Danno77 said:
it's a lost cause, sell me your truck.
Click to expand...

I won't sell the F350, though I am aiming to sell a 2009 Ram 1500 4wd- one adult driver (me) and only about 9,000 miles- that the F350 is replacing.
 
I have heard that DRW have traction issues for the very reason you stated, increased surface area. I am on a truck forum and there are guys out in the Montana part of the country that run SRW in the winter months. I wouldn't really worry about the bearings.

I have never tried this but it might work. Some people that live in cold regions where the temps stay below freezing for long periods of time buy cheap air mattress and fill them half with water. The bladder forms around the wheel wells and wont shift. Also there is a flat surface to place any load. When the warm weather comes back just drain it and go.

good luck
 
If you want to run SRW find a pair of SRW wheels. Then you won't have the offset issue. You can use Ford 8 lug wheels from '67-'97 trucks. Dodge wheels should work too. The Chevy wheels have the same bolt pattern, but the hub hole is too small for Ford axles. Incidentally, I have 4 of these wheels down in NY available for cheap.
Side note. F350s don't come from the factory with Dana 60 rears. Your truck should have a Sterling 10.25 rear which is stronger than a Dana 60.
 
Well, I have a '99 F250 7.3 Turbo-Diesel with SRW and I have to tell you, the truck is helpless on anything more slippery than wet grass. I bought it for interstate towing of my boat (8,000 plus pounds) for the 500 miles between here and where I fish. For everyday driving it actually is a lot nicer if I toss in firewood just enough to cover the bottom.

Other than that the truck has been good. Its had electrical issues but overall the thing has been pretty much trouble free. Mine's got 180,000 on it - averages 18.7 mpg.
 
My 2WD, DRW F350 has highway tread tires on it and traction is pretty lousy too. Some day I'll get some better tires for it. I have a 4x4 F250 for slippery stuff.
 
I don't think better tires are going to help much.

I was sitting here trying to remember my history on tires for this truck but its all a blur. When I got it the thing had whatever the stock tires were on it. When they wore out I went wide and found out very quickly that was a bad idea. I believe I went up to 285's and with them it was everything I could do to keep the truck in its own lane on the road. It just wondered all over the place. So I immediately took it down to 265's (All Terrain TA's) which were much better on the road but just like the stock and wide tires, they were helpless on any marginally slick surface - seriously, I have got the truck stuck on damp grass on dead flat land and had to use 4WD to get it moving again, its that bad.

The tires that are on it now are the best I've had, they are 265's and 8-ply or something like that, if it wasn't so cold out I'd go look and see. One of the things that makes a very big difference with the SRW trucks is air pressure. It effects both traction and hadeling more than you might immagine. I run the fronts 10 pounds below the maximum and the rears 5 pounds less for general highway use and bring them back up to full for heavy loads or towing.

I suspect the problem comes from an inballance in weight distribution of the trucks. I don't know what the thing would be with a standard gas engin but lets say its something on the order of 55% front and 45% read. That would be with a typical gas engine weighing 500 pounds. Take that out and put a 1,000 pound Diesel engine in there and I'd guess it changes to something closer to 60/40. Just a guess on the numbers but you get the idea, with the heavier diesel engine in the front the already bad weight distribution of a pickup truck gets even worse.

One lesson learned years ago - get rid of automatic hubs in favor of after market manual replacements. You can run them locked in year round.
 
There are only a few possible reasons I can think of why you're all over the road.

- Poor weight distribution. Guaranteed you have to deal with this.
- Too much torque and you're spinning the wheels. Possible given you have a big deisel, but I expect you know how to drive in slippry conditions and you're not flooring the throttle all the time.
- Lousy tread for the conditions. Possible, but unlikely given that you're indicating you have decent tires all teh way around.

I doubt running with duals is causing too small of a contact patch. Even though you're not squashing your tires down, you still have twice as many...probably smaller that SRW, but not significantly so.

From your post, it sounds like its the rear end, not the front, right? Its gotta be weight distribution. Toss a half ton of weight int he badk and go for a drive. I'm a member of Plowsite.com (you can guess the content from the name), lots of guys seek out DRW trucks becaue they can plow driveways in 2wd in all but the worst of conditions...its all about loading up on the ballast. Since you're not plowing you want to get as much of your ballast centered over your rear axle so you don't compromise the front end traction.

I used to drive my Fasther's old 77 V-6 powered Pinto in the snow...you wanna talk about a vehicle with really poor weight distribution, that was about as bad as it can possibly get. Most of the cast iron motor was mounted in front of the front axle and there is about a foot of car behind the rear axle...I used to put 300lb of sand in the truck just to keep from doing donuts all the time...in the summer it would smoke the back tires at every stoplight.
 
Actually I meant that it was all over the road when I was driving down a paved highway at normal speeds on a bright sunny day without a curve in sight. Those trucks really do not respond well to wide tires.

As for the Dually question, without a load there is no difference what so dever between the contact area of one of them and a single rear wheel truck when there is no load present. Its sort of like the myth that wider tires put more rubber on the ground than skinny ones. I didn't believe it at first either but they don't. The contact area is a function of wheel diameter, the flexibility of the rubber, and the weight of the truck - not tire width. As you put on wider tires the contact patch just gets shorter, but the number of square inches of rubber on the ground remains the same. Two tires have the same contact area as one tire, its just split between the two tires. The beauty of duallies doesn't come from having more rubber on the ground, not in that sense, it comes from other gains to be had by 4 tires aft instead of two.

The real gain comes in lateral stability. Simply put those 4 rear tires have 8 sidewalls to resist the flexing that makes a tall truck wonder around rather than two. That's why Duallies are so great for towing - steady as a rock heading down the highway. The next thing is what happens when you get stuck in a soft medium, like mud or sand. While the static contact area isn't effected by having 4 rear tires the same can't be said once the tires start sinking into the muck - the deeper it sinks the greater the advantage of the Duallie but of course because of what the tractor people call "flotation" the tires don't sink as bad as a SRW truck would. So basically the Duallie isn't going to do you any good on hard slick surfaces but if you are in soft stuff frequently it will be less likely to get stuck, and it will be way better for towing.

Two things about the truck I can say with certainty, it has to have weight in the back of it during the winter and it also has to be plugged in if the temperature is even going to turn chilly. If it gets good and cold where you live be ready to replace glow plug relays about once a year and fuel filters more often than any man should have to immagine.

On Edit: One more touchy subject. I know every guy is the best driver that ever lived but its awfully easy to knock those rear wheel flares off the truck, particularly in the woods but also in parking lots. You up to it?
 
Thanks for all the input, all-

Re: rear wheel extended fenders, I don't have those, as it has a Reading work-box on the back. I'd have thought that that (plus a truly immense 5/16 diamondplate platform bumper) would've given it some weight back there-- but I guess I need more.

I do know that less is always more when it comes to stepping on the pedal in any sort of slippery conditions. And this engine is very adequately powered, but is not tuned for total max power the way the more recent diesels are.

I had a truck a few years ago that had an Eaton TrueTrac helical-geared torque proportioning differential in the back, and it was truly amazing in its ability to walk right out of situations like wet grass without even a hint of wheelspin. I wish it weren't a big project to swap a diff (at least in terms of setting up the gears properly) or else I would really like to put a TrueTrac in this rig.

Anyone know if there is anything on the rear axle ) apparently a Sterling, per Flatbedford) that'd give me a sign of axle ratio or whether it's got any form of enhanced traction diff in it?

Thanks for all the input
 
I thought that the Ford fleet VIN decoder at (broken link removed) would give you at least the axle ratio, but I punched mine in and no such luck.

Kong,
What axle ratio are you running to get that kind of mileage? My '99 7.3L has a 4.10 and the best I can get it to do is around 14 but it does have a heavy flat bed on the back that adds to the total weight of the truck too. I haven't ever really experienced anything like the OP's issues but I rarely ever even see snowflakes in this climate. I'm running 265s that look to be a Chinese knockoff of a Goodyear tire that were on there when I bought the truck. I think the name on them is Treva.
 
You might be able to get that info from Ford. Ask your dealer if they can decode your VIN for you. GM products have RPO codes on a sticker in the glovebox that tells you each and every single feature that truck had when it rolled off the assembly line (rear and front axle ratios, sprcific motor, tranny, interior and exterior color, type of seating, load ranges front and rear..everything you could want to know). I don't know for sure, but I'd be surprised if Ford didn't do something similar.

Or go floor it on a dirt road...if you leave two (well, 4 really) marks then you have a locking rear end, otherwise its open.

For the ratio,
 
There should be a tag under one of the cover bolts on the rear axle that will have the gear ratio on it. If it ends with an "L" then it is limited slip. Also, you can get the axle code from the sticker on the drivers door jamb and look it up here:

(broken link removed)
 
Yep, read the axle tag. Mine has an L on it and I can tell you that Ford's limited slip is pretty much garbage. My last chevy had the eaton locker and that was a wonderful feature. The rear end would lock solid and both wheels would spin at the same time. That's great in slow motion but when you were on the pavement and both rear wheels started to spin that rear end would slide right out from under you.

Throwing 1000 lbs of ballast in there is cheap and easy. Nothing to lose by trying.

Very cool to think of a dually as having the same contact patch as a SRW. It makes perfect sense that if the tires have the same psi in them that the same amount of square inches will be touching the ground whether DRW or SRW. Otherwise the dually would float away.
 
Thanks for the continuing suggestions. The DRW is definitely more stable side to side (on washboards on curves, etc) than any SRW I've driven.

I also realize I should check the air pressure in the tires-- the prior owner (fire dept) may have had them towards top pressure and they'd probably have a better contact patch with more modest pressure.

Any thoughts on whether putting the weight in the most rearward toolbox on each side would be best? I've heard people say "straight over the axle" but I'd think that far-rear would do the most to balance out the front/rear weight proportioning.
 
I believe mine has 3.55 gears in it but to be quite honest I do not know why I believe that, they could be 3.70's. I believe there may be a paper tag on the passenger side axle that gives a code that can be decoded to tell you the ratio - but I might be thinking about an old Blazer we had to put a new rear end in one time.

That overall fuel milage is pretty good but its not at all unheard of with the single rear wheel trucks. Also keep in mind that a lot of my miles are interstate miles on the cruise controll and following my habit of not speeding. It makes all the difference in the world to slow down to 60~65 with these trucks. Actually the very best milage I ever got out of it was just under 25 mpg but that was during the dead heat of August on a road that was absolutly flat at near sea-level and traveling non-stop for just 200 miles on the cruise control. There wasn't a thing in the truck but me and I was wearing shorts; needless to say I was working at getting the best milage I could for that particular run. Having done it once I returned to reality. Towing the boat, and particularly through the eastern mountains of northern Virginia, western Maryland, and of course eastern West Virginia, the milage was - as you will certainly expect - considerably less, something in the 11~14 range is more like it.
 
The ballast has the most effect if placed as far to the rear as possible. So yes, throw it way in the back. This actually transfers weight off of the front axle to the rear axle to get more bang for your ballast buck.
 
If you want to transfer weight off the front axle, put the ballast as far back as you can. If you want to weigh down the rear tires you want the load over the rear axle.

Normally I'd say without a plow you want the load over your axle so you don't unload the front axle enough to cause you to have less steering control... but you've got that big cast iron deisel there. Try both and see which one works better for you.
 
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