Having MPG issues, whats wrong?

Hahah the bumper is to stay unless you want to give me your factory and some money, then maybe we could talk pm me if serious! Lmao
I was just listing the scoop as something that could contribute to hurting as well as the skid plate since it's just an indent but doesn't circulate all the way to the engine to my knowledge, which would in turn just create an air pocket pushing towards the rear of the truck (just my thought, I'm only a 2nd semester mechanical engineer so I haven't gotten too deep in that stuff yet) even though tiny, it would contribute a little bit

 

Thanks I sure will! I will post in this thread since we're gathered and I'll also either make a thread about it or include it in my nonexistent build thread.

How much money?? Lol probably not since I like my MPGs as much as I like doing everything myself, I'm trying to fab my own front setup to imitate US offroad's "bumper".

And you're right that skid could very well be a culprit.

My first aeromod will be belly panels and then I might even try to duplicate the newer air dams. I like everything to look factory though. But if my undercarriage is made smooth I don't see the need for an air dam.

Are you in differential equations?

 

Unless the undercarriage plates are made super light they will negate the MPGs saved. Also, be careful when adding any weight when trying to increase MPGs as it doesn't do much

 

The bumper didn't hurt my mpg's at all! Surprisingly enough. Lol. And not yet. UT is weird. I'm in calc 2, physics for engineers 2, mechanical engineering statics, and chemistry 120 right now.

 

They're usually made of plastic, not steel. The weight of plastic panels will help your aerodynamics much more than it will hurt your weight. Not to mention at highway speeds, which is where us commuters spend all our time, like I said before weight is about 30% of your gas guzzling whereas aerodynamics make up about 70%.

Wow that's strange. Do you have a scangauge or ultragauge? And I took those last semester. Statics was fun, I am in the continuation of it, Mechanics of Solids. Remember your shear and bending moment diagrams as they are important and I am surprised by the amount of people who still have trouble with them. What's chemisty 120?

 

Imagine the benefits of carbon fiber instead of plastic...I didn't find much of a drop in mpg with my winch and winch bumper plus rock sliders on my truck strange eh?

 

Very strange but good for you! And how much lighter is carbon fiber than plastic?

 

I don't. But my tires should spin 1.07 times what the stocks did so I just calculate my mileage out that way and it didn't drop when I added the bumper. Chem 120 is our basics of chemistry class. Pretty much Chem 1

 

Good for you! How much does it weigh? And I took Chem 1 first semester, hated it. But I did a lot of my basics in high school like history math and english, so I took Cal 1 starting out. Could have taken Cal 2 but I knew HS calculus was not comparable to college calculus. How did your 33" KM2s affect MPG?

 

I think the bumper weighs ~75-80lbs. The KM2's destroyed my MPG though. I'm talking with the lift and KM2's I went from 18-19 to 14-15.

 

WOW. That is downright awful. Lol. How do they perform in sand and mud? I have one 285 KM2 as a spare (Bought it from a friend) I would like another one to put on when I go offroad.

 

Lol damn! And that is light for a bumper. Good for you. I might just do that one day... Having one to put your hands on, how hard do you think it would be to fab up your own? I think the hardest part would be the mounting locations.

 

The tires do great offroad, they suck in rain or any kind of slippery concrete situation. lol. Mine are getting pretty low on tread and I'll more than likely get another set. And the hardest part about building a bumper would probably be either cutting the pieces out straight if you don't have a jig or laser cutter etc.. or building the wings. The mounting locations is literally an L bracket steel plate with 3 holes drilled per side. Probably the easiest part of the bumper. Getting the angles all neat and lined up might be hard too, just because I'm a perfectionist and it would piss me off if they weren't perfect. We built a plate bumper and plate flatbed for a buddie's 88 yota but he owns a machine shop so we just built them in CAD, sent the files to the cutter about 20 feet away in the shop and welded the pieces together. lol

 

Even Toyota is wrong all the time. Their online payload numbers are way different from the door stickers on the trucks. They claim the TRD Pro has the exact same mileage as a TRD OR despite the fact the Pro as 2" more lift at the front and much heavier tires. Anyone who has put a bit of lift on their truck and put tires like the TRD Pro has on it knows from experience mileage is going down about 2 MPG for sure. But according to Toyota the Pro has some sort of magic pixie dust in it that keeps its mileage the same

Apologies, sloppy wording on my part. I meant the relatively small Cd differences from the Toyota specs would probably be very difficult to measure empirically on the road. If we have say 20.5 MPG at 70 MPH with a 0.394 Cd then changing the Cd to 0.419 results in 19.6 MPG at 70 MPH. Just a little shy of 1 MPG.

If you changed your cruising speed by just 2 MPH you would also get a 1 MPG difference just based on aero loads. Not to mention tire inflation, ethanol content of your gasoline, etc. etc. etc. So I suspect it would be really hard for two people with that small a difference of Cd to actually notice the difference if they compared their mileages.

On the other hand, if instead I'm a manufacturer trying to meet the CAFE standards then even 1 MPG can be a big deal and the testing is typically (at least in the US) closely controlled and so changing the Cd by a bit to eek out another 1 MPG in testing is worth it and noticeable. Hence the air dam on the 2016.

Your breakdown is spot on, at 70 mph aero is about 70% of the total resistance.

Sounds like a fun project! I'm always curious about the tapered devices you see on the rear of some truck trailers. Clearly they are meant to reduce drag from turbulence at the rear of the trailer and thus improve mileage. Wonder how good a job they do? Something to Google one day I guess...

At the risk of getting philosophical one of the nice things about engineering is that you will constantly be proven wrong no matter how many years you do it. In most cases hopefully it will be you who proves yourself wrong before anyone else notices. You get to be wrong and discover it multiple times a day. Every once in awhile you'll fool yourself long enough that physics will come along and prove you wrong in the view of others late in a project which is less fun. But the point is, you get used to being wrong and fixing it. Compare this to other fields not constantly tested against the laws of nature - politics, business, law and so forth. In those fields people can go whole careers believing they are always "right" building up insane levels of over confidence. You rarely run into over confident engineers.

 

FWIW, I would recommend getting CRC MAF Cleaner or an electrical cleaner. Some brake cleaners can be a little harsh and/or leave residues behind.

 

I could see the cleaner being harsh. I haven't noticed anything wrong yet and I just didn't wanna run to the auto parts store.

 

I'm wondering if the tire size difference is contributing. When I put bigger tires and lift on my old F150 it significantly changed the aeordynamics by lifting it higher and exposing more wheel surface area to drag.

I'm not well versed on the different trim packages but a sport suspension and bigger tires from the factory could mean different aero's enough to affect your MPG.

 

It's not the aerodynamics of the tires, its the rotational mass that hurts mpg.

 

In theory anything lifting the truck would probably increase the Cd - how much though I have no idea. And Toyota's numbers don't really jive with that theory since the OR and Sport have essentially the very same size tires and suspension height. So it is a little weird they call out the OR with a different Cd.

As to actual MPG as already mentioned usually the worst hit is in the higher rolling resistance of the larger tires rather than more aero drag. You can in theory separate the two effects by plotting how the truck rolls to a stop from speed on a flat stretch of road (with a curve fit you can separate the rolling resistance and aero drag coefficients). If you did that before and after the new tires you could figure out how much they affected rolling resistance and aero separately. Sounds like a lot of work to me though

 

The tires can affect aerodynamics if they're larger, they lift the truck up more and expose more of the tire to the wind.