Hi. Well, take friendly note that you're on the wrong forum -- this is for 140's and 164's; there is another one for the 240 series.
But aside from that, for summer tires I use 205/70-14's on the rear of my '80 245 -- I want more load carrying capacity for boat trailer towing and traction on boat ramps, and I don't care at all about the speedometer error. But I only use 195/70-14's on the fronts of that wagon, because I had a feeling that there may be clearance problems at full lock one way or another.
On my other 240's, all sedans (a '84 and a '93), I use 195/65-14's and they're all dead accurate (viz. the speedometer) as well as good handling.
I'm assuming that you put skinny tire sizes on for your winter snows, right? For snow, tall narrow tires work best.
Best regards,