Toyota 4A-F and 7A-FE engines
According to this chart, my engines torque output is pretty much flat after 2500 rpms.
Since I don't travel really less than 60 on the highway I'm guessing this means that I should aim for a tire size that gives me 2500 rpms at 60 mph? And then any speed beyond that is good as far as torque is concerned.
The one issue I have is that the torque output is at full load... We're hardly ever driving there. However, I guess this makes sure that all the parts can handle the increased torque load from bigger tires.
Anyways my car has no tachometer on it, so I looked up my gear ratio for the three gear A131 Auto Tranny to deduce my rpms.
1993-1997 Toyota Corolla transmissions and axles
Right now I'm going 3330 RPMS at 60 mph with my worn tires at 21 3/8 OD and with new tires at 22.5" OD that are the same it would be 3180 RPMS. Still high.
So if I were going to go 2500 rpms at 60 mph, that would be a 28.22 OD on the tire.
I think I'll go for 2800 rpms just to be on the safe side, so that yields a 25" OD.
That doesn't sound too drastic. A 10% change from stock conditions, 15% change from my current worn tire conditions.