1 (a) - Has anyone ever fitted super singles to their rear axle? (I'm a single/no tag fella)
Yes, it's been done.
1 (b) - What if any are the pro's & cons (apart from the wider single track being more likely to rip up ashphalt etc when turning!)?
- Slightly better fuel mileage (I doubt you could even measure it, though)
- Less unsprung weight on that axle
- Fewer wheels to buy, if you are changing wheels anyway
- Looks cool; all heads will turn at bus rallies
- Can't rotate steers to drive to square them off and vice-versa
- Can't carry a single spare that fits all wheels
- Can't "limp home" if a drive tire goes, or swap drive to steer if a steer goes and no spare
- A blown drive will sideline you far longer than with normal duallys, as the supers are not widely stocked
- Supers are generally pricier than a pair of duals
FWIW, you don't see supers on owner-operator rigs or buses for all the "con" reasons above. Generally, only large fleet operators benefit from the supers. The get the benefit of volume pricing and having their nationwide maintenance outlets stock the tires and wheels for them, and their buying power means they can get the trucks equipped that way from the factory. With hundreds of trucks on the road running millions of miles, the tiny bump in fuel economy adds up. For most of us, the investment will never pay off, and one tire failure on the road can completely negate any benefit in a hurry.
1 (c) - Are there any structural and/or stress issues to be concerned about?
To change standard dual drop-center offset rims to a super-single? No. To increase wheel circumference by 7%? Maybe. You'd need to measure clearance in the wheel well and to the other running gear, and you'd need to calculate the increase in torque required to turn the bigger wheel, and make sure your powertrain is up to the task.
2 (a) - The tyres I have access to are currently on steel spider rims, but I have a couple of spare 10 stud rims. Has anyone converted spider rims to 10 stud or done the reverse?
I am assuming you are talking about mountable rims or what many would call "Dayton" rims here. Dayton wheels use a completely different hub than disc wheels; you'd need to change out the hubs. By contrast, there are "adapters" to mount Dayton-style wheels onto stud-pilot hubs.
If you are going to change hubs anyway, I would recommend changing to the more modern hub-pilot design rather than stud-piloted (also called Budd wheels).
I think I mis-read this the first time through. If I understand correctly, your bus has 10-bolt hubs, which I assume are stud-pilot. You have some tires available that are mounted to split rims or Dayton rims. Apparently, you also have some stud-pilot rims (which I assume fit your hubs). I can only guess this question has to do with the tires you have on the other rims being the wrong size for the correct wheels.
The simple answer to this is to ditch the incorrect tires and get the proper size ones for your wheels.
2 (b) - For example, could I laser cut the centres out of the spares and weld them onto the spider rims?
Not sure why you would want to do this. You'd have a major challenge aligning things before welding, and it will never be as strong as a forged wheel. Welding on the forged rims will likely weaken them. Steel wheels are cheap, and take-offs are even cheaper from folks upgrading to aluminum. Buy the drop-center wheels
if you fit that type of hub
2 (c) - Alternatively, I wondered if anyone has seen or heard of a conversion plate to fit spider rims to 10 stud stub axles?
Yes, but they are rare.
Again, not sure why you'd want to save the rims.
If you change to 10-bolt hubs,
just buy the wheels and be done with it.
If you really want to get use from those rims, keep the clamp-style hubs you have now.
If you do go to the supers, the clamp-on rims are of no use anyway,
and you need to go to the 10-bolt hub