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Old 01-07-2013, 02:29 PM   #1
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MPGs plummeting?

So after upgrading to 20s from factory 15s, I noticed that my MPGs on my car were horribly low. With the 15s my car averaged 21.8 (22 in the city is factory rating), and now with the 20s my car is getting roughly 18.0-18.2 MPG. The thing that throws me off is I called ford and they said that it was about 100 more pounds on your car so it would affect your gas mileage by 2%. So if we take 22 x .02 = .44 decrease, which should give me 21.56. How is it that I am getting 18 MPG. Any suggestions?
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Old 01-07-2013, 02:32 PM   #2
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Different driving since you put the wheels on?
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Old 01-07-2013, 02:33 PM   #3
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Different driving since you put the wheels on?
Ride is a little rougher, but thats common. other than that no not really
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Old 01-07-2013, 02:35 PM   #4
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But 3mpg is not bad for upgrading from 15' to 20' and ford might o just thrown that 2% number at you
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Old 01-07-2013, 02:48 PM   #5
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But 3mpg is not bad for upgrading from 15' to 20' and ford might o just thrown that 2% number at you
I dont think so. 4 MPGs for just 100 pounds? that just doesnt seem right at all...
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Old 01-07-2013, 02:57 PM   #6
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More tire to rotate heavier rim. But maybe you've been driving with a heavier foot??
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Old 01-07-2013, 02:59 PM   #7
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More tire to rotate heavier rim. But maybe you've been driving with a heavier foot??
I dont think ive gotten on it enough to make a 4 mpg difference but idk about the tire. it could be a possibility but again a 4mpg difference?
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Old 01-07-2013, 03:04 PM   #8
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Is your overall tire height different. If so you may have changed your wheel RPMs. Is your speedo off, or did you retune?
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Old 01-07-2013, 03:06 PM   #9
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My God! You are now down to 18mpg!!!!

You better sell that Gas Robbing monster before you go broke!

Check you tire pressure.
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Old 01-07-2013, 03:27 PM   #10
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You will lose some mpg because of the larger wheels but it shouldn't be THAT much.

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Is your overall tire height different. If so you may have changed your wheel RPMs. Is your speedo off, or did you retune?
I was just thinking that. If the revolutions per mile have changed, your speedometer and odometer may not be accurate anymore.

Do you know the new and old tire sizes?
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Old 01-07-2013, 03:36 PM   #11
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Is your overall tire height different. If so you may have changed your wheel RPMs. Is your speedo off, or did you retune?
I'm sure speedo is off and no I havent calibrated it yet

---------- Post added at 03:36 PM ---------- Previous post was at 03:35 PM ----------

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My God! You are now down to 18mpg!!!!

You better sell that Gas Robbing monster before you go broke!

Check you tire pressure.
Bad joke...and tires are a week old and all are at required tire pressure
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Old 01-07-2013, 06:28 PM   #12
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Yeah I've got the GT/CS 18X8.5" wheels stock compared to my buddy's stock 16" base wheels and he gets like 2mpg better city
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Old 01-07-2013, 07:35 PM   #13
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Yeah I've got the GT/CS 18X8.5" wheels stock compared to my buddy's stock 16" base wheels and he gets like 2mpg better city
Yeah same here I have 18" gt rims but I still average 22.3 mpg an it's mostly city
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Old 01-07-2013, 08:07 PM   #14
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Yeah same here I have 18" gt rims but I still average 22.3 mpg an it's mostly city
Maybe I've just got a lead foot then lol
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Old 01-07-2013, 10:18 PM   #15
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Yeah same here I have 18" gt rims but I still average 22.3 mpg an it's mostly city
How do you get that much city MPG?! Lol do you drive 20? I don't accel very fast and I only get 18-20
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Old 01-07-2013, 10:36 PM   #16
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How do you get that much city MPG?! Lol do you drive 20? I don't accel very fast and I only get 18-20
I change the tune to 89 oct
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Old 01-07-2013, 11:21 PM   #17
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Welp, talked to AM and I'm just going to send them back, but on the bright side I can start saving for a turbo lol
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Old 01-08-2013, 08:35 AM   #18
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Welp, talked to AM and I'm just going to send them back, but on the bright side I can start saving for a turbo lol
Buy some clean take offs from someone an save the money for the turbo !
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Old 01-08-2013, 09:32 AM   #19
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Buy some clean take offs from someone an save the money for the turbo !
Ding ding ding! Your right! Saving up for a turbo. Project pshhhhh
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Old 01-08-2013, 11:17 AM   #20
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I wish I got 18mpg I average 14-16mpg. :/
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Old 01-08-2013, 03:03 PM   #21
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I wish I got 18mpg I average 14-16mpg. :/
Wtf ? How do u manage to get that lol
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Old 01-08-2013, 03:05 PM   #22
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I wish I got 18mpg I average 14-16mpg. :/
Same here!!
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Old 01-08-2013, 08:33 PM   #23
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Wtf ? How do u manage to get that lol
Honestly I have no idea. It sucks so bad, I feel like I am filling it up every couple days and I don't even drive a lot considering I am in a small town.
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Old 01-08-2013, 08:40 PM   #24
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Honestly I have no idea. It sucks so bad, I feel like I am filling it up every couple days and I don't even drive a lot considering I am in a small town.
I don't fill up that much. I fill up bout every week and a half with driving around town every day...if I drive like everybody else does!! Haha
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Old 01-08-2013, 09:10 PM   #25
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Honestly I have no idea. It sucks so bad, I feel like I am filling it up every couple days and I don't even drive a lot considering I am in a small town.
U would be better off buying a gt lol
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Old 01-08-2013, 09:16 PM   #26
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U would be better off buying a gt lol
Yeah for real
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Old 01-08-2013, 09:21 PM   #27
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That is all city, right? Highway mpg should improve, but because you have to turn your wheels so much more, it takes more work off the line- more torque isnrequired.
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Old 01-08-2013, 09:38 PM   #28
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Yeah, all city driving. On the highway I get about 22-24mpg. That's a bug reason why I am going to trade it in this summer for either a 11 GT, 370z or range rover if I decide SUV. I figured since I already get bad gas mileage why not get something that I would enjoy more.
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Old 01-08-2013, 11:03 PM   #29
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That is all city, right? Highway mpg should improve, but because you have to turn your wheels so much more, it takes more work off the line- more torque isnrequired.
Refer to first comment about fuel % being affected
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Old 01-09-2013, 05:39 AM   #30
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Quote:
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Refer to first comment about fuel % being affected
I did. Adding weight lowers efficiency, but all thing being equal, increasing tire diameter has a positive influence on cruising mpgs.

If he did more highway driving, a bigger tire diameter would lower engine speed. So, inthe city with stop and go, there is a negative affect. I wanted to clarify he is doing almost all city.

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I did. Adding weight lowers efficiency, but all thing being equal, increasing tire diameter has a positive influence on cruising mpgs.

If he did more highway driving, a bigger tire diameter would lower engine speed. So, inthe city with stop and go, there is a negative affect. I wanted to clarify he is doing almost all city.
Ford is talking about weight increase. Not tire diameter,if it changed at all, which I imagine it did.
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Old 01-09-2013, 03:17 PM   #31
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Quote:
Originally Posted by UltArc

I did. Adding weight lowers efficiency, but all thing being equal, increasing tire diameter has a positive influence on cruising mpgs.

If he did more highway driving, a bigger tire diameter would lower engine speed. So, inthe city with stop and go, there is a negative affect. I wanted to clarify he is doing almost all city.

---------- Post added at 06:39 AM ---------- Previous post was at 06:38 AM ----------



Ford is talking about weight increase. Not tire diameter,if it changed at all, which I imagine it did.
Still don't see how it is a 4 MPG decrease. I could see 1, maybe 2...but 4? Idk =[
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Old 01-09-2013, 03:29 PM   #32
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Still don't see how it is a 4 MPG decrease. I could see 1, maybe 2...but 4? Idk =[
Its not just weight, it's rotational mass, which effectively multiplies that weight by a factor somewhere between 5 and 10, if my research is any good. Thus, if wheel X was 10# heavier than wheel Z, you could see an effective weight difference of 200-400#. Those are rough numbers obviously, but you get the idea. Would that equate to 4mpg difference? Dunno, but it would definitely contribute. I have one of the lowest mpgs reported that Ive seen despite few mods and Im leaning heavily towards heavy wheels being the issue.
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Old 01-09-2013, 03:31 PM   #33
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Its not just weight, it's rotational mass, which effectively multiplies that weight by a factor somewhere between 5 and 10, if my research is any good. Thus, if wheel X was 10# heavier than wheel Z, you could see an effective weight difference of 200-400#. Those are rough numbers obviously, but you get the idea. Would that equate to 4mpg difference? Dunno, but it would definitely contribute. I have one of the lowest mpgs reported that Ive seen despite few mods and Im leaning heavily towards heavy wheels being the issue.
Well what's weird is the stock wheels I had (with the tires on them) were about 1/2 less in diameter compared to these
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Old 01-09-2013, 07:32 PM   #34
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Well what's weird is the stock wheels I had (with the tires on them) were about 1/2 less in diameter compared to these
The other forum I use is rather positive it is four times for rotational mass. One pound that needs to spin equals four pounds sittin in the trunk.

And tire diameter, td, can make a huge difference. Increasing td equals dropping your gear ratio. So a 2.7 gearing with 15s will have, in theory, better torque/less hp than the same vehicle with 22s. It takes more force for the engine to spin the axle once with a bigger td. When it gets started, it is fine and efficient-usually, but getting started to a constant rate of speed with 22s would take more force than 15s from a stop.
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Old 01-09-2013, 07:49 PM   #35
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Op I thought the same thing when I put 37" tires on my truck. Turned out , nothing had changed due to revs per mile difference. Your actually driving more miles than the speedo is recording. The site tacomaworld.com will give you the formula to figure the difference with. It will also show different tire sizes side by side for comparison. It's a tire sz calculator site, the best I've found.
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