average mpg using scangauge ii and oversize tires

[northguest47]

Today I got 40.8 mpg on the drive home it is hilly with 2000ft overall drop for the 31 mile drive into town. This is the third fill-up I have done with the unit so it should be calibrating pretty well. Of course I need to do the run the other way to see what the uphill mileage is which I will do... but my question is about the oversize tires... 185/70/14 so the miata net calculator says they are 6.4% too slow so am I correct in saying that the mileage for the run was closer to 43.5 if its assumed the stock odometer is precise?

[petrified.rabbit]

that sounds about right, mathematically.

I would verify the difference using a GPS for your actual speeds, and check the distance difference on your odometer to a "measured" standard.

[northguest47]

Posting some numbers for today, same run, 31 or so miles, 2000 or so vertical feet, this time both ways, with a distance factor of 1.05 for the larger tires:

uphill : 32.3 mpg
downhill: 47.9 mpg

average: 40.1 mpg

This is impressive, as it is coast mountain driving, not relatively flat freeway or hwy. Still have to get the gps set up to calibrate the odometer (hoping it is within 5%), and do a couple more tank fills to make sure the unit is calibrated and not over-reporting trip mileage which admittedly can be happening. Nonetheless....

The coasting method of driving was used, using as little acceleration as possible. Top speed was maintained at 50 mph occasionally peaking to 55. The cold air intake helps out for sure as all the shifting was targeted at 1750-1800 rpms, for example, up long hills too steep to hold 5th gear, downshifting to 4th gear was done around 1750 rpms.

Wowzers

[northguest47]

Just wanted to add that above calculations were using US gallons (1USGal=3.78L), not imperial gallons (1Imp Gal=4.55L). Just realized never mentioned in my original post, and that is important as industry is quoting some car stats using imperial gallons here in Canada for the Sonic. For reference my measurement of 40.1 miles per US gallon would be 48.3 miles/imperial gallon. Hence the wowzers. Will have to duplicate this test for accuracy and maybe even measure the front tire circumference and the stock hankook along with gps data for improved precision.

[Tardis]

Have you calculated your mileage by dividing your mileage by gallons put in for a whole tank? The reason I'm asking is that I had purchased the Ultra Gauge and it was stating that I was getting over 38 MPG, but when I started to keep track per tank full the actual number was more in the 33 MPG range. After some major recalibration, The Ultra-gauge and the manual method are much closer.

[NYChevoo]

I've always clocked only 30 to 32mpg with 195/70/14's and mines an automatic. I typically am always running 70mph on my commute to work which is roughly 145 miles roundtrip. By the way "WOO-HOO! 1500TH POST"

[northguest47]

Have you calculated your mileage by dividing your mileage by gallons put in for a whole tank? The reason I'm asking is that I had purchased the Ultra Gauge and it was stating that I was getting over 38 MPG, but when I started to keep track per tank full the actual number was more in the 33 MPG range. After some major recalibration, The Ultra-gauge and the manual method are much closer.

Tardis: Many times for one or two tanks in a row I have monitored the mileage and have got 36 in summer, and mid to high twenties in the winter, but that was all before any changes to the car. If I could get 330 to 360 miles on my useable tank (about 9.3 gallons on average) that would be great, but seeing that your unit was out by 15% I see what you mean.. its all about good data. If my initial numbers were out by 15% that would put the car at 35mpg which we all know is doable, so I'm hoping for better. And keep in mind this was trying to get really good mileage which for a whole tank, takes a lot of patience, and mostly hwy cruising to achieve a good result. I have had neither recently

[northguest47]

NYChevoo 30-32 seems realistic for that speed I was trying to get best mileage by keeping below 55 which I understand would be hard to do on most daily commutes. 145 miles!! Whoa! Guess you've logged some miles.

[Tardis]

I've had my car for a couple of months now, and I do keep track for every tank full. I've ranged between 31mpg to 35mpg. Depending on how much high way, and top roads. The sweet spot for this car is 41mph, but I find that it is not to bad up to 64mph. Once I get above that MPG really start to dip. You mentioned some up grades to your car, are these to get better MPG or for Power? What were they?

[NYChevoo]

NYChevoo 30-32 seems realistic for that speed I was trying to get best mileage by keeping below 55 which I understand would be hard to do on most daily commutes. 145 miles!! Whoa! Guess you've logged some miles.

Mileage is absolutely right northguest47. Aveo now has 149628 miles on it currently. Owned the car since new in 2004. Car has never seemed to waiver from those miles per gallon its whole life.