Just an observation, I have no dog in the fight but if these tires are wearing in the center I would think a lower air pressure would correct that. Low pressure wears the edges. High pressure wears the center.
There's
a LOT of discussion, shared experience, and knowledge here on the Forum about tires, tire pressures, and exactly this point you've raised (again), but if you want to delve into why this doesn't work with OEM Kendas &/or their clones, you really should do some searching and reading about it all.
But briefly, while what you've posted above
IS the case for most 'normal' car tires, it's simply
NOT the case for the very lightly constructed OEM Kendas & their clones - they
NEED about 28 psi of pressure in them to carry the (very light) weight of a Spyder, but because of the lighter construction methods & materials used in both the sidewalls and the tread layers, once the rear tire starts rotating at speeds anything much above about 30 mph, the width of the tread face that you'd hope remained in contact with the road surface gets thrown outwards by the rotational forces, making the middle/centre strip of the tread balloon outwards so that
ONLY the centre of the tread touches the road surface, wearing that little 2" wide strip rapidly and significantly compromising the tire's traction, even wear, and more!!
And if you run an OEM tire &/or any of their clones at anything much lower than about 2 psi less than their placard recommended pressure, the construction of the tire is such that you risk the catastrophic failure of those OEM tires, more so at speed than when travelling slowly - so please,
DON'T EVER RUN THE OEM TIRES AT LOWER PRESSURES, they aren't up to that, and you will not only be putting yourself at risk, but you'll also be putting all the road users around you at risk when your OEM Kenda fails!! And you probably won't get any significantly better tread life, either!
The better/stronger constructed a/mkt tires that many of us fit to our Spyders are made to carry weights/loads that are
UP TO a somewhat higher weight/load than that of a Spyder, which is not to say that they
cannot carry a lighter weight and still work effectively, because they can, they just don't need as much air pressure in them to do that! But even when running at those lower pressures which are more suited to the lighter weight of a Spyder, the stronger, better made sidewalls and tread layers of these 'normal' car tires that are capable of carrying loads up to maybe three times the weight of a Spyder, is such that it deforms less and keeps more of the tread surface in contact with the road surface most of the time, giving you, the Spyder Ryder, the better traction, wear, and performance etc from your tires, that those of us who have actually done this have discovered.
Oh, and don't kid yourself that without changing anything else, once the centre of the tread on the OEM tires wears out, you'll start running on the outer bits and can get more wear that way - there's a vast number of worn out OEM Kendas out there that go to show that this simply
isn't the case, and they've pretty much all worn thru to the canvas or to the rupturing stage
in the middle of the tread!! They don't wear out at the edges, cos that bit's not touching the road surface!! The centre of the tread on a OEM tire will
STILL throw out regardless of how worn the tire is in the middle, and that means it's
STILL going to be pretty much the only bit of the tire in contact with the road surface and therefore wearing!
That said, once the actual softer tread layer of the tire itself is worn away, the underlying carcass is a tougher and harder wearing material, so once you've worn the centre of the tread down into that harder layer, where it provides waaayyy less traction than the tread material proper did, even once that got worn, and that bald/harder strip has no real 'traction' &/or 'water dispersal properties' at all; but that harder layer of material does tend to wear a little slower than the tread did (until it fails, anyway) helping to fool some into thinking they've finally brought those outer edges of tread into play, when they really haven't, at least not to any appreciable level! Once the middle strip of tread has worn away, your OEM tire is nothing but a 'no longer legal to use' black round excuse for a thing that you
might think helps keep the metal bits of your Spyder off the road - but it doesn't!!
Just do the smart thing, and fit a 'normal' car tire and run it at a more suitable pressure for the lighter load of a Spyder vs that of the average car (18 psi has shown to be ideal for about 99% of the Spyder Ryding population so far, if they truly try/run it.
) ; choosing a tire that's not only better made and stronger than the OEM tires anyway, but is also a tire that's better suited to
YOUR riding needs, loads, ambient conditions, and wants, as well as better suited to the conditions and the surfaces that you generally ride in/on! I've run higher performance car tires and been very impressed with them, but due to my 'less than high performance' riding on a wide variety of surfaces and in a wider range of conditions that really weren't an ideal fit for any of those tires, I now run 'All Season M&S' tires, and they work waaaay better than the OEM black round excuses for things that barely managed to keep the metal bits of my Spyder off the road for less than 4000 miles before failing catastrophically!
) and it also causes all the rain that hits the windscreen to bead and run up off the screen and out to the sides (it makes a very interesting/attractive pattern when you're riding into the sun setting on the horizon thru a downpour that's dumping out of the clouds immediately above you, but which are high enough that they're not blocking the setting sun on the horizon! It's almost as good as the pattern seen when riding into the sunrise and the moisture beads formed by the morning mist on the screen all blow out and away from the centre of the screen! 
), and it creates an almost completely 'rain free' zone behind the screen so that both my pillion and I don't have any issues with too much rain on our visors either; even tho my head mostly sticks up above the top of the windscreen - even when the screen is in the fully raised position and my head is above it, it's still in the 'deflected air' zone. We basically just don't get wet unless we slow below 30 mph-ish &/or stop! And what little rain does hit our visors does the same as the rain that hits the windscreen; it's blown up and out, then off into the slipstream behind us! 
