The bike will be around 170kg and I've been talking to the various manufacturers about running a 17x160 tyre on the rear and all have said its not a good idea as the load index on the 160 tyre is two small. In fact Pirelli started off their response with "Sei Pazzo"
Their recommendation is to run a 17x160 Street Tyre that typically have load indexes in the 60W + range or run something like Metzler's 18" RR race tyres that come in a 160 rear but are Bias ply and can take the weight. Bikes did come with a 17" front and 18" rear back in the day.
I guess my question is for the VRRA events can I run a 18" Bias Ply tyre rear and a 17" radial front, and then just swap the rear for a 180 radial for SOAR? The overall diameter between them is within a millimetre.
According to the internet you shouldn't mix bias and radial tyres but if you must do it the bias should go on the front. I don't know. Has anyone ever done the opposite? Will it pass tech? There is nothing that prohibits it in the rule book.
I should also mention that its for endurance so the tyre will have to last at least 2 hours.