You did the math - I was scratching my head at the same thing and agree. The change from 225/65-17 to 215/70-17 basically keeps the same sidewall height for a skinnier tread patch. It might still be a ride improvement because of the longer, skinnier tread patch, but not from sidewall height. A possible detractor is the sidewall might also become more straight with less curve (“pooch?”) to flex, if that makes a difference. I’d think something like 225/70r16 might have better results… double check my guesswork with a specs chart or maths to make sure that’s right. In my opinion, 70 series starts riding like a softer vehicle with a more traditional, “average” steering response…