As I am seriously considering fitting a 170/60 rear tyre, I thought I would email Yamaha on the subject. Here is what they replied:
"Thank you for your email, in relation to your Yamaha MT-07.
We can advise, that we can only recommend the tyres sizes as stated in your Owner’s Manual, which...
See my Exhaust for sale removed off my 800 mile bike.
Any questions just email me. If you buy directly from me via this forum, its £400
Yamaha MT07 Exhaust Original | eBay