Mileage drop after mods?

hairtumor

hairtumor

New member
I did 3 things at the same time and trying to figure out which is the offender.

1 Went from stock 15" wheels and rims to stock 16" wheels and rims.
2 Put a wicked flow (magnaflow copy) muffler on.
3 Put a Yakima loadwarrior rack with extension on.

My mileage went from around 250 per tank to around 200 to 210 per tank. It also seems to downshift sooner on the hills than it used to. :mad:
 
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yep you've added weight to the tires and roof, changed the dynamic flow pattern of air over the truck , there is as much as a loss of 2mpg's and hour between a dirty and a clean car due to the change in aerodynamic flow.

just think about what the sail on the roof is doing for you.
 
also look as see if you got overdrive off,ect off, ect, playing with those setting can help increase gas mileage.

also change your trans fluid and see if that helps, that tends to be one of the most over looked fluids that needs to be changed regular.
 
do you think it would help a little to take the front fairing off the Yakima rack. The angle seems a little too straight up for smooth air flow
 
hairtumor said:
do you think it would help a little to take the front fairing off the Yakima rack. The angle seems a little too straight up for smooth air flow
Click to expand...

meh it's a 50/50 on that one as the air hits the fairing it's sent up and over the rack and comes back down behind it and that's where the drag is created, so it's a question of whether you get more drag by smaller wind breaks but alot of them (over the bars them selves) or more drag by one big wind break,

personally i think the guys at yakima have already done this in a wind tunnel
and figured it out, but then again maybe not maybe the soul purpose of the fairing it to reduce wind noise created by the chaotic numerous windbreaks by the bars.....


so that doesn't help at all man, try running a tank with and one without and record your mileage.
 
You need to regear to jump the milage back up. IIRC the 15's were 225/75/15's and that is like a 27" tire where as the 265/70/R16 is a 31" tire, that alone should have killed you milage, then adding the weight and drag to the roof also taking some miles off the tank. The muffler though will help your milage if you dont step on it, if you step on it you will see a drop.
 
Ummm... the answer is... yes! :lmao:

That rack is costing you at least 1 mpg, regardless of anything else. Air delfectors' primary purpose is to reduce vibrations and noise. The air deflector at the front of the rack is causing the rear spoiler to not channel air back down behind the truck, thus increasing drag. Either way, as mentioned above, you are dragging a sail down the road.

You said you went to different rim size, did the overall tire diameter change?

A slightly larger tire will skew you mpg readings. The overall diameter of the stock tire was different for models with 15" wheels than that of models with 16" wheels.

Downshifting faster is consistent with more drag or improper gearing.

The additional weight of the wheels and tires may be a smaller contributer as well, but should be less than 0.5 mpg difference.

The different bumper is supposed to be working in the other direction (better fuel economy), and it probably is...

EDIT: Didn't know the tire size difference was that big... you are no longer geared correctly, sir!
 
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Mr. Leary said:
Ummm... the answer is... yes! :lmao:

That rack is costing you at least 1 mpg, regardless of anything else. Air delfectors' primary purpose is to reduce vibrations and noise. The air deflector at the front of the rack is causing the rear spoiler to not channel air back down behind the truck, thus increasing drag. Either way, as mentioned above, you are dragging a sail down the road.

You said you went to different rim size, did the overall tire diameter change?

A slightly larger tire will skew you mpg readings. The overall diameter of the stock tire was different for models with 15" wheels than that of models with 16" wheels.

Downshifting faster is consistent with more drag or improper gearing.

The additional weight of the wheels and tires may be a smaller contributer as well, but should be less than 0.5 mpg difference.

The different bumper is supposed to be working in the other direction (better fuel economy), and it probably is...

EDIT: Didn't know the tire size difference was that big... you are no longer geared correctly, sir!
Click to expand...

Correct.

I went from the stock 15's to 18's 275/65R18. I just recently filled up and will see how that alone messes with the fuel mileage.
I was use to seeing between 330-350 in city 2.7L 5spd. I'd still be happy to get over 300 in a single tank of gas.
 
You'll probably never see close to 300 again because of the larger tires and because of that, your odometer is about 5-10% off. If you are getting 210, then you're really getting 231 if it's 10% off. And of course the rack isn't helping.
 
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you should get one of these and a nuespeed sticker, that's sure to help! (sic)



41ijddey2mL.jpg
 
future reference, and not sure if your rim size change has caused your ecu to
throw things off that badly alone.....but possibly i haven't ran the number as i get bored doing this at work all day, lol


the math equation for this is
A = 3.14159 / 4 * (d^2 - di^2)

I = 3.14159 / 64 * (d^4 - di^4)

Z = 3.14159 / (32 * d) * (d^4 - di^4)

J = 3.14159 / 32 * (d^4 - di^4)

k = sqrt((d^2 + di^2) / 16)

y = d / 2

more moment of inertia calc's for cross sections

Properties of Sections
 
theizzardking said:
future reference, and not sure if your rim size change has caused your ecu to
throw things off that badly alone.....but possibly i haven't ran the number as i get bored doing this at work all day, lol


the math equation for this is
A = 3.14159 / 4 * (d^2 - di^2)

I = 3.14159 / 64 * (d^4 - di^4)

Z = 3.14159 / (32 * d) * (d^4 - di^4)

J = 3.14159 / 32 * (d^4 - di^4)

k = sqrt((d^2 + di^2) / 16)

y = d / 2

more moment of inertia calc's for cross sections

Properties of Sections
Click to expand...

I've got a headache just looking at those calculations
 
If the bigger wheels/tires mean a bigger circumference, and you haven't adjusted your spedometer/odometer to compensate, then maybe you're actually travelling further per tank than you think.

Which means, youre not losing that much mpg.
b
 
kingwilliam said:
If the bigger wheels/tires mean a bigger circumference, and you haven't adjusted your spedometer/odometer to compensate, then maybe you're actually travelling further per tank than you think.

Which means, youre not losing that much mpg.
b
Click to expand...

that would be nice :zoom:
 
man it's easy you just have to know what your loking at


i=inertia
d=diameter

soooo

I = 3.14159 / 64 * (d^4 - di^4)

inertia = pie divided by 64 times greater diameter cubed subtracted from inner diameter cubed.

and that's what i was kind of saying is that the over all diameter of your wheel hasn't changed just the size of the cross section or inner diameter, of course when changing the greater diameter i.e. the overall size of the tire
your messing with the axis of rotation quite a bit and that's why you need to flash your ecu to compensate, but when the over all diameter of teh tire remains the same and the inner diameter of the wheel it's self changes changes the moment of inertia is impacted but no where near as much as when changing the major diameter.


at least that's the way i'm seeing it, and hey don't let my drivel change anything, you obviously have a problem somewhere and like others are saying i'd look at some of the stuff you changed, this is more of a thought experiment and just general information on how crap works.

ssooo yeah i'd check your mileage via iphone,gps or good 'ol paper and pen to confirm actual mileage or you can get one of those sweet scan gauges that people are talking about lol
 
theizzardking said:
man it's easy you just have to know what your loking at


i=inertia
d=diameter

soooo

I = 3.14159 / 64 * (d^4 - di^4)

inertia = pie divided by 64 times greater diameter cubed subtracted from inner diameter cubed.

and that's what i was kind of saying is that the over all diameter of your wheel hasn't changed just the size of the cross section or inner diameter, of course when changing the greater diameter i.e. the overall size of the tire
your messing with the axis of rotation quite a bit and that's why you need to flash your ecu to compensate, but when the over all diameter of teh tire remains the same and the inner diameter of the wheel it's self changes changes the moment of inertia is impacted but no where near as much as when changing the major diameter.


at least that's the way i'm seeing it, and hey don't let my drivel change anything, you obviously have a problem somewhere and like others are saying i'd look at some of the stuff you changed, this is more of a thought experiment and just general information on how crap works.

ssooo yeah i'd check your mileage via iphone,gps or good 'ol paper and pen to confirm actual mileage or you can get one of those sweet scan gauges that people are talking about lol
Click to expand...

LOL bah! You're talking to a guy who had to retake almost all of his math classes over agian to get thru high school. Still not doing so hot in college although I'm doing better lol.

But I see I see and I understand. Thanks for the clarification.

hopefully we'll get a gb going on!
 
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