Lower pressure will result in slightly lower mpg as the rolling resistance increases.
I've got some experience with tire pressure changes, and instead of even wear, you will likely see the outside of the front tires begin to wear more rapidly than the center. This is more noticeable in heavier vehicles.
The bulk of my experience is from 2000 and 2004 Jeep Grand Cherokees of around 4000 pounds. I bought one with 72k and the other with 18k; both had badly worn outer edges on the front tires, and were inflated to the factory specified 30psi. I immediately went to max rated pressure (35) and kept those tires awhile, until they started washing out in the wet. Upon replacement my new tires were rated for 44psi max; after some experimentation I found that 40-42psi was a pressure that gave even wear as well as noticeably crisper handling.
The ride was not a cushy as it had been before, but for me it was worth it to have tires that kept their wet handling capabilities their entire life and lasted 60k rather than 35k.
You're going to get a lot of opinions on this one, many of which will preach to use the placarded pressure.....so
Ultimately test different pressures and decide for yourself.
Originally Posted By: JohnnyJohnson
Well the tire shop is just helping you to your next shopping experience in their store. I always check my tire pressure right after I leave from having my tires rotated.
Agreed!