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Old 02-12-2014, 06:06 AM   #1
jwindbigler
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My MPG lowered. Want help to fix

I track my MPG on a websit called fuelly.com. Specifically:

http://www.fuelly.com/driver/jwindbigler/focus

I have recently done some upgrades, and have seen about a 4mpg decrease in fuel efficiency.

Recent upgrades:
STEEDA CAI
Strut bar
17" wheels with 215/45R17

Now Im certain that its because Im running wider snow tires on a bigger wheel. The wheels are about an inch taller (with tire) than my stock 16s. But I dont want to go with a smaller sidewall (due to detroit potholes, and already cracking one of the wheels). I would return to stock however, the added stability with the tires is something I dont want to give up.

The wheels dont seem to be throwing my speedometer off, but since they are an inch taller, would this make a difference in what im seeing in my mpg tracking?

If anyone knows how to get my mpgs back up into the 30s with the mods I have, I would greatly appreciate it.


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Old 02-12-2014, 08:25 AM   #2
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Are the 17's you bought heavier than your 16s? Usually going bigger moves more of the unsprung weight to the outside of the wheel/tire and that will cause an mpg decrease. I noticed a couple mpg loss when going from oem 15"s to SVT 17's.

Have your driving habbits changed at since installing the Steeda short ram? As in, are you enjoying the new sound and getting on the gas more often? That would cause some of a drop too.

Also, 215.45/17 is an oem Focus size..,they shouldnt be an inch taller than 205/55-16's
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Old 02-12-2014, 09:08 AM   #3
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Quote:
Originally Posted by rambleon84 View Post
Are the 17's you bought heavier than your 16s? Usually going bigger moves more of the unsprung weight to the outside of the wheel/tire and that will cause an mpg decrease. I noticed a couple mpg loss when going from oem 15"s to SVT 17's.

Have your driving habbits changed at since installing the Steeda short ram? As in, are you enjoying the new sound and getting on the gas more often? That would cause some of a drop too.

Also, 215.45/17 is an oem Focus size..,they shouldnt be an inch taller than 205/55-16's
This is exactly what I was going to type lol
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Old 02-12-2014, 11:23 AM   #4
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Even though I do like the new sound of the intake, I have kept my foot out of it. I recently did a freeway trip to Grand Rapids. About a 300 mile round trip, and normally I would get about 30-32mpg, and this last time I got 26.

The wheels I got seem to be of similar weight to that of my OEM wheel tire combo. Yet, I feel that the engine is working too hard to push the 215s, and thats what is causing my mpg decrease.

I have another set of 17" wheels for the summer time, and was considering running a 205/45R17. Would that help with my mpg a little bit?
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Old 02-12-2014, 11:48 AM   #5
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Weight of the wheels will decrease mileage in a hurry. Intakes are exactly a mileage increaser either.
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Old 02-12-2014, 02:20 PM   #6
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Weight of the wheels will decrease mileage in a hurry. Intakes are exactly a mileage increaser either.
An intake will increase your mpg if you maintain the same driving habits as before. increased efficiency = more mpgs
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Old 02-12-2014, 02:24 PM   #7
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Which wheels did you have on it before the 17"? I honestly believe the decrease your seeing is because the increased weight in wheels. Someone with a second gen went from the oem 15" wheels to the ses 17" wheels a couple of years ago and saw a 4-5mpg decrease. Where increase wheel weight really knocks the mpgs is in town or stop and go driving. It now takes additional force to get them rolling than before.
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Old 02-12-2014, 02:48 PM   #8
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When I went from the stock 15" wheels to the 17" eaps on my zx3, I noticed an immediate 3mpg drop from 30 to 27. Part of the price to play the game. It's now worse since I'm boosted and have issues with right foot control lol.
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Old 02-12-2014, 02:59 PM   #9
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There are simply too many variables, all of which are likely contributing factors to at least some degree or another:

Stock sizes in 2007 were 195/60-15 (~24.2" OD) and 205/50-16 (~24.1" OD). This is what the cars odometer is calibrated around. A 215/45-17 has a ~24.6" OD. This will reduce the accuracy of your odometer, and thus your calculations. It can also affect driving style due to the effect of taller gearing on acceleration. Granted, in this case it's not a huge difference either though at ~2%.

Driving style changes due to effective gearing change and modifications.

Winter weather.

Higher rolling resistance tires.

Wider tires.

Potentially, but not necessarily, heavier wheel/tire package.

In my experience, unless it's drastically different from stock, the weight and width play a relatively minor role...Especially on the highway, where you specifically note the problem to exist. Snow tires do have a rather high rolling resistance though, a sacrifice you make in exchange for having a car on the road rather than in a ditch. You may also think you're staying out of it, but even minor increases driving enthusiasm can have surprisingly detrimental fuel economy effects. It's far easier to decrease your fuel economy, than it is to increase it.

But in looking at your fuelly data, I would be inclined to believe that the biggest culprit is simply the winter weather. Your 1 year fuel economy graph looks suspiciously like it's following the temperature trends. Over the years I've noticed that all of my fuel efficient daily drivers have averaged 3-5mpg worse in the winter than the summer.
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Last edited by Driven5; 02-12-2014 at 05:07 PM.
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Old 02-12-2014, 03:22 PM   #10
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Quote:
Originally Posted by Driven5 View Post
There are simply too many variables, all of which are likely contributing factors to at least some degree or another:

Stock sizes in 2007 were 195/60-15 (~24.2" OD) and 205/50-16 (~24.1" OD). This is what the cars odometer is calibrated around. A 215/45-17 has a ~24.6" OD. This will reduce the accuracy of your odometer, and thus your calculations. It can also affect driving style due to the effect of taller gearing on acceleration. Granted, in this case it's not a huge difference either though.

Driving style changes due to effective gearing change and modifications.

Winter weather.

Higher rolling resistance tires.

Wider tires.

Potentially, but not necessarily, heavier wheel/tire package.

In my experience, unless it's drastically different from stock, the weight and width play a relatively minor role...Especially on the highway, where you specifically note the problem to exist. Snow tires do have a rather high rolling resistance though, a sacrifice you make in exchange for having a car on the road rather than in a ditch. You may also think you're staying out of it, but even minor increases driving enthusiasm can have surprisingly detrimental fuel economy effects. It's far easier to decrease your fuel economy, than it is to increase it.

But in looking at your fuelly data, I would be inclined to believe that the biggest culprit is simply the winter weather. Your 1 year fuel economy graph looks suspiciously like it's following the temperature trends. Over the years I've noticed that all of my fuel efficient daily drivers have averaged 3-5mpg worse in the winter than the summer.
Good Info Here^
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