Actually, that's not quite true. 225/40/18 is not an exact +1 size for 215/45/17, it's actually slightly larger. With the OEM redline, the maximum speed on the OEM tires (disregarding speed limiter) is 139.4 mph. With the 18" wheels and 225/40 tires, it is 142.1, almost 2 percent more. It's considered an acceptable error.
It's well within the +/- 3 percent allowable error for your speedometer, so you might actually get a more accurate speed indication. Most manufacturers including Toyco have their speedos indicate faster than you are actually going. Their tachs are also notorious for indicating higher than actual.
The only time this was not true was when the US Govt decided we didn't need a speed indication over 85 mph in the early 1980's. Those speedometers had to be +/- 1 percent, they were very accurate.