Hi Mike.....All the best for the New Year.
SRW conversions are a huge part of our business so obviously there is a little sales pitch in what I'm saying here but we've been involved in this since day one of the FG's here in Australia. We live at what's considered to be the gateway to Fraser Island which is a busy international eco-tourism destination. In the early days, the eco-tour operators ran whatever they could get there hands on....plenty of old WWII ex-US Army Studebaker trucks, Landrovers and even a few VW micro buses. Once the FG's came on the market, there was an immediate need to make them perform in soft sand or pay the price....namely loosing a loosing a vehicle to the tide....and that resulted in SRW conversions.
I know the original poster asked if duals were that bad, well no they're not bad as long as you don't want to get into any soft stuff and for plenty of general running , the duals are perfectly acceptable but SRW will transform an FG and if for some reason the minister of finance said I could only do one modification to that truck , I would put it above everything else.....have always said that a properly sorted SRW conversion is the single best mod on an FG by far. So here goes ......
Apart from the obvious sidewall damage that can be caused from rocks caught between duals, there are quite a few benefits.
With SRW's , the rear wheels follow in a compacted track caused by the front. With duals in the soft stuff, the rears are always ploughing fresh ground so whether it's sand or mud they create plenty of drag and on a vehicle that doesn't exactly oooze power this can be a killer.
Standard dual setups always run really narrow tyres and at the front axle, they seem to knife straight down in soft ground. When you change to singles all round, the larger tyres don't just allow a greater load safety margin on the front axle, they have far more floatation as well.
Next , what I call the "tri-cycle effect".......a standard dual set up always has an exaggerated difference between the outer edge of the front tyre and the outer edge of the outside rear tyre. This is quite noticeable when driving an FG.......go to a properly setup SRW conversion where the front wheels are wider and the track greater and the rear has been brought into line astern, then the vehicle will always feel more stable underneath you, particulary on medium speed country roads.......think cornering on a tri-cycle when you were a kid.
Next, would come all the benefits associated with larger rolling diameter tyres on a vehicle that is very much under geared to begin with. Gearing with a SRW truck will normally come up by around 10% . Depending on which model FG, speed on the highway is far more pleasurable as the engine rpm range at highway cruising speed falls more into line with the power curve of the engine......in other words, you can put your foot down to overtake and not be on the down side of the torque curve with nothing in reserve. Of course average lower engine rpm also brings with it, improved fuel consumption (although this depends on the operator more than anything), increased engine and bearing life, etc.
Larger rolling diameter tyres also means greater ability to traverse uneven ground and corrugations which also adds to more comfortable ride, larger footprint in sand and mud, and they simply last longer ...... bigger circumference means more rubber around the tyre which means less wear overall.
The tyres used on a proper SRW conversion also need to be load rated much higher too, maybe without realizing it, this greatly improves punture resistance and the chance of sidewall damage. By comparison to OEM, the tyres we tend to use are total overkill and almost indestructable. This has been proven time and time again. One of our customers ran over 50,000k's overland through Africa with one blow out when he hit a washout at 100kph and deflated the tyre....that was it after some of the worst terrain on the planet. Have plenty of other testimonies of how tough these tyres are by comparison to OEM too.
Probably more to add later.....
Really hard to spot an under inflated tyre on the rear with duals too......I always used to whack the rears with a wheel brace bar when fuelling up at the servo. A bit crude but a dull thud is a sure giveaway. With SRW, you can spot it at a glance. Now we have TPMS systems , I suppose.
Regards John.