What the .......?????

[AC-T3]

How did this happen? What caused it? All 4 tyres (15" Toyo Open Country A/T) are treated with respect, inflated, rotated, re-aligned, balanced etc as needed. But this was found this morning, on the left rear inner. Photo doesn't really capture the damage which is limited to the inner extremity of tread and wall, perhaps 1.5 - 2.0 cm wide.    

[Oldman]

Too much negative camber ?

[AC-T3]

Too much negative camber ?

Yes, but why? How?

[Barry]

Can just be a shitty tyre. 
I was playing about with some different profiles and put some shitty no name on and they blew out like yours in about 5,000 kms. 

Replaced with Pirelli, same profile, same alignment. 
Reckon I have done 10,000km and still perfect. 

I know you have Toyo, but just saying, it’s probably the tyre and not the van.

[rstucke]

How did this happen? What caused it? All 4 tyres (15" Toyo Open Country A/T) are treated with respect, inflated, rotated, re-aligned, balanced etc as needed. But this was found this morning, on the left rear inner. Photo doesn't really capture the damage which is limited to the inner extremity of tread and wall, perhaps 1.5 - 2.0 cm wide.

donut on the left front rear torsion bar worn (oops, forgot you own a t3)
or maybe rear toe-out on that side
When you look at the rear wheels from a distance, is the left wheel tilted in at the top more than the right

Also is your ride height standard fully loaded (measured at the guard or roof gutter )

[luckyphil]

How did this happen? What caused it? All 4 tyres (15" Toyo Open Country A/T) are treated with respect, inflated, rotated, re-aligned, balanced etc as needed. But this was found this morning, on the left rear inner. Photo doesn't really capture the damage which is limited to the inner extremity of tread and wall, perhaps 1.5 - 2.0 cm wide.

Could be rear trailing arm out of alignment or perhaps rear wheel bearing

[AC-T3]

donut on the left front rear torsion bar worn
or maybe rear toe-out on that side
When you look at the rear wheels from a distance, is the left wheel tilted in at the top more than the right

Also is your ride height standard fully loaded (measured at the guard or roof gutter )

Left has an obvious tilt to the left. Right is perhaps taller. 10mm.

Oooops, yes left has an obvious tilt to the RIGHT

[AC-T3]

Thanks Mark, Barry, Phil and Rick, I really do appreciate your remote diagnostics.  After giving the the RHS and LHS a good inspection, fiddle and shove, it all checked out firm and OK.  So with much nervousness I booked bus in for a thorough inspection and 4 wheel alignment.  Turns out rear suspension and bearing bits are OK but the LHS camber and toe were way out. How and why?  Nuts and bolts losing a little tension over time?  Pot holes and gutters?  I avoid those like the plague coz bus has a perfect view from up on high.  So with no clear diagnosis it could be just age and wear and tear.  Bus drives, steers and turns like new, so who's happy now?

But, the speed with which the excessive and aggressive wear took place came as a complete shock.  Was fiddling down the back a couple of months ago and everything looked fine.

[Grantus]

Thanks Mark, Barry, Phil and Rick, I really do appreciate your remote diagnostics.  After giving the the RHS and LHS a good inspection, fiddle and shove, it all checked out firm and OK.  So with much nervousness I booked bus in for a thorough inspection and 4 wheel alignment.  Turns out rear suspension and bearing bits are OK but the LHS camber and toe were way out. How and why?  Nuts and bolts losing a little tension over time?  Pot holes and gutters?  I avoid those like the plague coz bus has a perfect view from up on high.  So with no clear diagnosis it could be just age and wear and tear.  Bus drives, steers and turns like new, so who's happy now?

But, the speed with which the excessive and aggressive wear took place came as a complete shock.  Was fiddling down the back a couple of months ago and everything looked fine.

Send the bill to your local council, for damage caused by their neglect to keep their roads, safe &  “roadworthy”.