Hi Al, I have a r3 tourer. standard tyre is 180/70R16. the only tyre for my bike i could fit to keep the rolling diameter the same was 195/65R16c.
I think with the 240 rear end the guys were going to a 245 tyre. Here is a link
Tire Size Calculator to help you find the perfect match.
You will need to measure the distance in your swing arm (i have to fit my tyre deflated). It is best to keep the revs/miles box as close to possible with your original tyre. I wouldn't fit the tyre till you have the chair fitted! A car tyre fitted to your bike is very hard to corner because of the profile (great for an outfit). I have to run my tyre at 28 psi so I have roll in the sidewalls and hence the 16c; c stands for commercial tyre with 6 ply side walls. You wont have this problem with a chair. Hope this makes some sense? Who is doing your chair for you???