How to get 20 MPG out of a R50

[Mike W.]

I can't really say I was surprised by the MPG, or lack thereof in my 03 QX4, but I am disappointed. I really hoped I'd be able to get 20 on the highway at least. Not that the seller told me that, he said 16-17, but I thought surely I could do better. Uh, not much, but I have put some thought into it.

• Biggest thing seems to be the lack of locking/unlocking hubs. Not an option on my Q, but it is on at least some of the Pathys. People suggest it's worth 2MPG, but even if it's just 1, it's significant.
  
  Something else that would probably bring a full 1 MPG is tires, as in a nice smooth highway tire, inflated close to max pressure or at least up into the 40s, not the 30 PSI that the door says. Again, not an option for me since I specifically bought it for it's 4WD capabilities and why minimize that with highway tires. Probably passenger car tires, not truck.
  
  Next is the tupperware that the Q has. Again, not much of an option for me since it all ties into the F and R bumper covers (how can it be a bumper cover if there is no bumper to cover. But that's another issue) But the bulbous door and fender appendages add to frontal area and aren't smooth.
  
  Up top, that roof rack. Definitely lose the crossbars, they do the wind resistance no good at all. I haven't tried it, but I suspect if I removed the channels the bars mount to, they would be even dirtier aerodynamically.
  
  And running boards? Really? I thought they went out with the 40's cars. Now with my long 29" inseam legs entry isn't a problem, except from having to step over the damned things to get in. That extra 6 inches I have to step over doesn't help any. But I know, not everyone is as long legged as I am.
  
  That airfoil to keep the rear window clear? It's nothing but drag.
  
  Premium gas. Now that's kind of a wash. My vacation mileage, which I track pretty closely, says I get 3.3% better MPG with premium over mid grade. That comes out to a 13 cent differential at 4 buck a gallon. If it's a dime a gallon difference, it to your advantage to buy premium. If it's 20 cents, no, it's not.
  
  Speed. I've been surprised on this one. Generally from a 60 to 75 MPH speed limit, and generally doing close to that, it doesn't seem to make much difference. But with an 80 speed limit, and accordingly a bit faster, it is a noticeable drop. Even modest stop and go knocks it down 1 or 2 MPG. CC also likely helps some.

So, what's my history, being able to do little about most of the important things. I'm seeing 18.7 on long trips with a modest/moderate amount of dirt/4WD offroading and premium. I'm usually good for 1 or 2, 20MPG tanks per ~3.5K vacation. And one tank I saw 22.3. Yes it was real, I had 343 miles on the tank when I filled up and the light wasn't even on. Soft highway, but not that soft.

So after mentally whining about it for several years I gave it some thought and with all of the above, 4300 pounds empty, let alone the way ours gets loaded for vacation, a coefficent of drag of .58 and the frontal area of a billboard, I guess the 18+ trip MPG I get isn't bad. As always, YMMV.

[VStar650CL]

So after mentally whining about it for several years I gave it some thought and with all of the above, 4300 pounds empty, let alone the way ours gets loaded for vacation, a coefficent of drag of .58 and the frontal area of a billboard, I guess the 18+ trip MPG I get isn't bad. As always, YMMV.

Excellent evaluation, very well thought-out.

For the uninitiated, curb weight is by far the biggest determiner of MPG, regardless of engine size and other factors. There's only so much improvement you can make with a 2-1/4 ton GVW.

Aerodynamic drag increases as the square of the speed, so as Mike found out at 80+ mph, you reach a point where the energy needed to push past the wind becomes a real factor. With a vehicle whose best aerodynamic analog is a brick, at 100 the air is like pushing through soup. Again, there's only so much you can do aside from keeping it below 70.

[QX4ME]

Absolutely true that curb weight is the #1 factor of MPG.

When I had a 96 Maxima I read someone posted in Maxima forum, who wanted to improve 0-60 time. He started taking out seats, inner door panels, floor mats, etc., almost everything that does not affect the drivability. I don't remember what 0-60 and MPG he got in the end. He did one step at a time, took out one item and measured the performance then next step.

I enjoyed reading that post.

[VStar650CL]

Absolutely true that curb weight is the #1 factor of MPG.

In the words of my hero, Isaac: F=M*A.
Leave out relative efficiencies, mass M takes power F to accelerate at rate A. Ya can't get around it.

[Mike W.]

Yes and no. Acceleration, absolutely yes, mass vs power is the most important factor by far. But on mileage, not so much. Once you're up to speed, it's aerodynamic drag, tire friction, bearing friction and accessory drive. You know, alternator, A/C, etc. Added weight does increase tire and bearing friction, but not enormously. More like some. Weight getting up to speed is a factor, think city driving, but on the highway not so much. Yeah, weight costs going uphill, but in my experience, contrary to popular belief, you get more than you lose going downhill. I've always gotten better mileage in mountain/hilly terrain.

The following is something I saved from Cummins, the diesel engine manufacturer some time ago, and the most important MPG factors. Yeah, it's oriented towards heavy trucks, but mostly it applies.

• Aerodynamic Drag

• Grade Resistance

• Tire Rolling Resistance

• Engine Accessory/Drivetrain losses

[VStar650CL]

Aerodynamic drag increases as the square of the speed, so it's generally negligible at under 40mph but goes up like a rocket after that. Drag at 85mph is 13% higher than at 80mph, for a 6% increase in speed. In most vehicles 60mph is the line where aerodynamic effects exceed tire and other rolling losses.