I took a 250mi round trip yesterday and avg. 20.5 mpg carrying 8 people in my Suburban.
A Prius gets about 2x that mileage but carries 1/2 as many people right?
All 8 people enjoyed a smooth ride while watching a DVD and having a good time.
The X factor is that there is no way to look cool in a Prius .

 

How fast were you going? I can't get that kind of mpg unless I keep it below 60.

Was that actual calculated mpg or was it off the DIC?

 

I set the cruise on 67mph. The trip was on relatively flat ground. I used the DIC for the mileage estimate. I even have heavy wheels and tires (22" w/305 tires) so I was surprised by the mileage.
Must be the chrome mirror caps I recently installed!!

 

Cruise control really keeps those RPMs down. Recently, I've been throttling more than usual. I get around 17.6 on the bad days. Close to 19-20 when I don't start quick off the line, set cruise, and don't brake or throttle un-necessarily.. etc. My suburban carries 7 people. I set the cruise on my way to CA from AZ, and my MPG sky-rockets.

 

hmmm, i got 22'' and also mirror covers but can get near that. D u have also door handles covers ?

 

I replaced the painted door handles with GM chrome handles so that probably accounts for the mileage increase!

 

I get 18-20 mph hwy on my 08 Sub 1500 LT with the 5.3 motor. I went down to 17's, debadged completely and took off the chin spoiler (for weight reduction) :-).

 

A Tahoe can drag 4 Prius sideways to boot!

 

larger wheels can keep rpms down because of the effort required to keep the car at speed is reduced.

for example, using hypothetical numbers if you were driving 60mph and had 15" tires, your engine would be at 2400 rpm in 4th. But using an 18" wheel has increased your rolling radius by 3 inches your rpm should decrease by 20%. Because with every rotation of the wheel you cover an extra 3" of ground. And once you get to your set speed(maintained by cruise) your tach should put itself in the 1800 rpm range. It doesnt, because a disadvantage is that a larger wheel weighs more than a 15" AND the tire fitted to the wheel usually isnt the most conducive to long range travel(well up to 20" but 22", 24" and 26" are awful on the highway because the rubber is so thin). But you could see a drop of few hundred RPMs on the tach with a larger tire. And higher MPGs granted you use cruise and are in a flatland area like Central Texas or Florida.

 

That makes sense at constant highway speeds as my trip was. I would guess that city, stop/go driving would reduce MPG with larger wheel/tires because it takes more energy to get the extra mass rolling.