They CYA the speedos for speeding liability. I was intending what I wrote to imply they are set to keep the driver 3-5% slow. Everything sounds about as expected. My thumb rule has been 5%ish nominal losses for a nominal tire size increase.With the factory tires, the odometer was ridiculously accurate. Like, under 1 mile of a difference over a thousand-mile trip. The speedometer was reading under 4% high, so with 3% larger tires the speedo is almost dead on, but the odometer is (also very accurately) 3% off. The gas mileage went down by ~6% with odo change taken into account.
"Trip computer," or whatever algo Ineos uses to estimate gas mileage, was badly wrong before, it is wrong-er now.