I have used Toyo T1R'S on the rear in the past, and have found the rear of the car tends to float a bit until they have a few K's on them, so maybe take it easy when you first get them on.
Some people think the sidewalls are a bit soft on these, however I believe it is more likely to be tread flex because the rear end float goes away when the tread wears down a bit and the rubber hardens up.
Yeah they feel horrible for the first xx amount of k's. I rang Toyo and spoke to one of their technical department about it a few years ago. The dude said he'd read our comments and said we had no idea of what we were talking about!
At that point I wished that there was more choice for our tyres
On other news I spoke to Toyo's development dept about the rumours of the T1R being discontinued, Toyo confirmed those rumours were true.
But don't panic, they also said that they were bringing out a new design of our rear size. It is due for release towards the end of 2018. No idea what its going to be named.