While this is neither here nor there about the emissions fix, I suppose it does have some relevance because tire sizes are part of the overall emissions. EVERY site I have looked at online says (essentially, not word for word) that smaller diameter WHEELS are better for both mileage and, with the correct tire, ride comfort. The smaller (17" wheel used on the Rebel, specifically) and the Toyo LT285/70R17 Open Country A/T II tires are so slightly smaller overall (even though Ram advertised the Toyo tires as being 33" tires) than the stock to the Laramie standard (20" wheels with P275/60R20 tires) that no noticable difference in the speedometer has occurred. (In fact, the 20" wheels and tires were EXACTLY 33" in height, while the 17" wheels and tires are 32.7" (NOT the 33" Ram advertises.)
I did extensive research to insure that putting the Rebel wheels and tires on the Laramie would work and not cause any trouble. The Rebel suspension was tweeked so it would ride NORMALLY 1" higher than the other Rams, but nothing was done to change the tire clearance in the wheel wells!
The difference between the 20" and 17" wheels and the matching tires is that I am actually doing 64.4 MPH when my speedometer reads 65. DUH! I don't know about you, but I can't tell a difference of 0.6 MPH on MY speedometer!
Also, the extra 3" of sidewall on the tires made the ride in my 2015 Laramie w/4 corner air (YES, the air DOES make a difference) smoother and "softer" than the ride in my wife's Lexus RX350. (NOTE: the Lexus has 19" wheels and appropriate tires on it.)
One more tidbit for you to ponder -- by adding ONE inch of tire diameter, you add slightly less than one HALF inch to the ground clearance. Half of the added height goes above the hub of the wheel and half goes below -- plain and simple. For every inch of ground clearance you want to gain, you have to add TWO inches of wheel/tire diameter.
YES, wheel and tire size DOES have to do with emissions. Changing the size of the wheel/tire changes the amount of work our wonderful little Diesel engines have to do. If the weight goes down (smaller wheels), the work the engine does is less and the more fuel mileage we get. (Okay, I won't mention that my instantaneous mileage at 70 MPH is 22 MPG. Nor will even say that I get 22 MPG at 80 MPH. (If you ask, I will point out that the speed limit in SD is 85 on the I29 - so there!))
