why offroad mpg is listed 17/20 vs 18/23 for limited

With same engine and automatic tran, why there is difference in MPG ?

 

Different wheels and tires.

 

It's not the wheels but the tires and the valance too. Maybe the tonneau cover on some of those models? Heard something about adding it to a certain percentage to add mpg across the board.

Tyler

 

17/20 is for the manual transmission. 18/23 is for autos. Manual is geared lower so spins faster at highway speeds. That is why the manual feels like it actually has some nuts whereas the auto feels neutered.

 

Yeah, what TacoJohn said.

An Auto Off road will get similar (maybe only slightly lower) mpg as a Limited (which doesn't come in Manual I believe)

 

Bed covers actually reduce mpg.

 

Per the brochure:
OR runs standard 16-in. machined contrast alloy wheels with P265/70R16 tires
Limited runs 18-in. polished alloy wheels with P265/60R18 tires

The Limited's tires have less rolling resistance, improving MPG.

 

I could have sworn that I saw a wind tunnel video that showed that soft bed covers increase MPGs. Do you have a source by any chance?

 

Limited has the air dam too, right?

 

Bed covers (or tailgates down) disrupt the air pocket that naturally occurs in the bed, reducing drag.

When you cover that space up or remove it altogether, you lose the air pocket - increasing drag and lowering MPGs.

It's science, not a video. Mythbuster show tested the tailgate down concept and proved it was less fuel efficient, and then explained why - the same theory applies to anything that prevents the bed from developing that pocket.

 

While tailgate down does disrupt the air pocket and create drag, I don't believe that's true for bed covers. It seems to be that the air pocket is not as sufficient as an actual hard surface to flow over. Here is a chart describing results of various configurations.


Source: A Practical Guide to Pickup Truck Aero-mods

 

So it's 60% +/- more efficient with a tonneau cover?

Cool graph, good info - if accurate.

 

17/20 is definitely the M/T OR 4x4 rating, not the automatic. Automatic is 18/23 for the OR 4x4, just like the Limited.

 

Not really, do you mean 60% on that graph? It may be a little misleading, the "Drag Reduction" axis actually ranges from -5% to 20% and is in reference to an open bed. Tailgate Down is a few negative percent, whereas the bed cover (Not sure if soft or hard) reduces drag by about 5%. A wing and cover combination or the oh-so-rare aeroshell is listed as 10% to 20%.

This means that a bed cover probably won't noticeably increase your fuel mileage, but perhaps by 1 MPG highway, which translates to less than 1 MPG combined. An aero-shell should increase highway MPG by 2-4 MPG, and however than translates to combine MPG.

As for the accuracy - that I wasn't able to verify. I first found it in a Masters thesis research paper, but Google pulled up that article when I searched. There is no telling where either source took the picture from, but it makes sense.

 

Devin. <3

 

Hey buddy. <3

 

Nope...

Did you not science? Plenty of studies showing tonneau's help. That is why GM added them to the high MPG trucks and like I stated before Toyota (just verified by searching) Toyota added them so they could post a higher MPG on the Tacoma if they sold 30% with it.

Not sure how bringing in the tailgate argument is relative here as everyone knows it is worse, but a tonneau is a different animal. So a tonneau does the opposite you are vouching for, it helps mpg.

This, all day. A soft tonneau from what I have read is the best, but a hard helps as well. Nice post.

Tyler

 

Aight. I don't know what to believe anymore.

 

I will settle this. The Sport manual gets 21 mph highway, the DCSB Off road gets 20 highway. Don't pay attention to the images in these on this EPA site. They use one stock image for all configs.

 

You need to work on your comprehension skills and Internet ability. They are the same.