MPG Calculation...

[MrSeth]

So, I have a feeling that after going from the stock size tires to large ones, my MPG's have changed big time and my "Miles Until Empty" reading on my digital display may be incorrect. My MPG reads 9, and my miles until E on a full tank only reads 225mi... my speedo is off by 5mph (the car is actually traveling faster than what the speedo says) and I think that its messing the computers up.

So I did a little math and am wondering, is this crap even correct?
--------
So my old MPG was about 15.5 when on the stock wheels.

Bridgestone 265/65R17: 680 Revolutions per mile.

Cooper MTP 315/70R17: 587 Revolutions per mile.
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So, we calculate the difference between the revolutions per mile, then multiply the original MPG by the number.

15.5(680/587)= 17.95 mpg... right?


I read that the larger tire weight would negate the added mpg... but the truck has been stripped down, and has lost 265lbs (4 corner scales) so would I really be getting 17.95mpg?


Any input is appreciated, and any re-calibration solutions are welcomed!


:toilet:

 

[AuSeeker]

Bigger tires also have more friction on the road, they also take more power..i.e. gas to rotate which is the biggest MPG killer IMHO, I'm pretty sure you're not getting anywhere near 17.95 MPG, I willing to bet you're getting less MPG than before the tire swap.

If you truly want to know your actual MPG I would suggest, take a short road trip that you know the actual distance/miles, you can use a GPS to know how far you travel or use a map app to get the distance, etc., etc., fill up and then at the end of the trip fill up again, then hand calculate your mileage from distance traveled and gallons used, this of course is only accurate for the type of driving done while on the road trip.

 

[LarsBars]

Using Google Maps and driving to and from a specific location, you can compare the real world mileage vs what your odometer says. It helps if you fill your gas right before you go and then again at your destination. I found out mine's very close to 6% greater, so whenever I fill up, I take my trip reading, multiply by 1.06, then divide that by the gallons used.

 

[RonJR]

The ratio of diameter of the 315/70/17's to the 265/65/17's is 1.12, which is a little less than the 680/587 = 1.16 factor that you were using. But, your formula is basically correct. Take the ratio of the tire sizes and that will give you the change in the odometer reading.

However, the better way to do it is as suggested, calibrate your odometer against a GPS. Drive exactly 10 miles (according your odometer) on a relatively straight road, and see what your GPS reads. Divide your resultant GPS reading by 10 and that becomes your new odometer calibration factor.

Note that your speedometer error may be different from your odometer error by a couple of percent either way.

Any odometer errors will cause the mpg meter in the dash to be in error as well.

Once you have a good odometer calibration factor, compute mpg over multiple tanks of fuel to get an average you can have some confidence in.

 

[fourwd1]

Moving to General Discussion.

 

[Skywriter]

I check my odometer against the mile marker signs on the road, then calculate from there.

 

[Number_6]

In addition to tire size and distance, I'll add this. Fill the truck at a gas station until it stops. After you drive around, go back to that same pump and fill until it stops again. Not all pumps stop at the same point.

 

[Christian90]

Good info thanks

 

[Spanky4R]

Get gas buddy & log your fuel. Fill up & I mean top it off to the top a couple times & they'll calculate it for you.

 

[4Runner fun]

So, I have a feeling that after going from the stock size tires to large ones, my MPG's have changed big time and my "Miles Until Empty" reading on my digital display may be incorrect. My MPG reads 9, and my miles until E on a full tank only reads 225mi... my speedo is off by 5mph (the car is actually traveling faster than what the speedo says) and I think that its messing the computers up.

So I did a little math and am wondering, is this crap even correct?
--------
So my old MPG was about 15.5 when on the stock wheels.

Bridgestone 265/65R17: 680 Revolutions per mile.

Cooper MTP 315/70R17: 587 Revolutions per mile.
---------
So, we calculate the difference between the revolutions per mile, then multiply the original MPG by the number.

15.5(680/587)= 17.95 mpg... right?


I read that the larger tire weight would negate the added mpg... but the truck has been stripped down, and has lost 265lbs (4 corner scales) so would I really be getting 17.95mpg?


Any input is appreciated, and any re-calibration solutions are welcomed!


:toilet:

There are a # of Speedometer Apps. download one to your phone and do the flat level road deal, 10 miles is a good number but with some math you can figure it out with any distance. doing the speed might be easier. The faster you go the more out of sinc. you will be.
Also your speedo and odometer will be exactly the same off. how do you think they work, Miles per hr and miles traveled are directly connected.

and as far as loss of MPG, you will defiantly see a loss, you've changed what Toyota thought was optimal. In my case My single tire and wheel combo is 100 lbs each, the truck sees that as added load. thus loss of MPG, to the tune of around 12MPG.

Good luck.

Also your computer bases everything off of STOCK, so throw the computer reads out the window until you know what your multiplier is.

 

[bsa70]

I hear that the 4 runner calculator is very accurate when everything is stock, has anyone found this to be true.

I went thru the big tire phase with my wrangler. Big will absolutely kill your mpg. no need to worry about it.

Just get a pencil and paper and figure out old school...

 

[thennen]

I hear that the 4 runner calculator is very accurate when everything is stock, has anyone found this to be true.

I went thru the big tire phase with my wrangler. Big will absolutely kill your mpg. no need to worry about it.

Just get a pencil and paper and figure out old school...

My stock 2019 TRDOR with a little under 3k miles says 20.9 mpg average, and that matches what I've been calculating all along, averaged out. So it seems accurate.

What I don't know is whether the computer continues averaging across ALL miles driven, or if it works off a pool - say, the most recent 1000 miles driven, for example. If it's across all miles, then I think you would eventually reach a point where it would never change anymore.

 

[Sifrk]

I hear that the 4 runner calculator is very accurate when everything is stock, has anyone found this to be true.

I went thru the big tire phase with my wrangler. Big will absolutely kill your mpg. no need to worry about it.

Just get a pencil and paper and figure out old school...

I certainly have not experienced this. In my 4th Gen, the speedo was accurate compared against multiple "your speed is..." signs as well as multiple mobile apps (e.g., Waze). My 5th Gen TRDP is consistently 2 miles above the same speed signs and mobile apps. I assume, and I could certainly be wrong, the MPG is calculated using the registered speed. I don't know if the Nitto Grapplers on the TRDP would explain the difference, I wouldn't think so, but I heard from other TRDP owners on this forum that claim their speedo is accurate. I assume then their MPG is more accurate than mine.

 

[Rhinle]

I have been slightly concerned about my MPG in my 2018 ORP. My city driving is pretty consistent at 15/16 MPG on a stock 4Runner. I am not an aggressive driver either. I was able to get 21MPG on a recent 100 mile round trip using a freeway. However, within a quarter tank of gas of city driving immediately after I am back down to 16.5.

 

[mteolus]

I have been slightly concerned about my MPG in my 2018 ORP. My city driving is pretty consistent at 15/16 MPG on a stock 4Runner. I am not an aggressive driver either. I was able to get 21MPG on a recent 100 mile round trip using a freeway. However, within a quarter tank of gas of city driving immediately after I am back down to 16.5.

That's pretty close to what I get, although I have a 3" lift. Stock tires though. In order to get better in city mileage you have to baby it big time, keep the ECO green light on as much as possible, but you will be pissing people off with your slow acceleration.

 

[bsa70]

That's pretty close to what I get, although I have a 3" lift. Stock tires though. In order to get better in city mileage you have to baby it big time, keep the ECO green light on as much as possible, but you will be pissing people off with your slow acceleration.

Do you think the 2wd version would get better mpg in the city?

 

[mteolus]

Do you think the 2wd version would get better mpg in the city?

It should get better gas mileage highway and city. Not sure how much, but a transfer case is quite heavy. That plus the axles and CV Joints and other things that add weight. Weight loss means more MPG.

Driving habits also make a difference. If you approach a red light and then slam on the brakes or you accelerate fast from a stop that will significantly lower your MPGs.

And as people have said before, you don't buy a 4Runner for the gas mileage. If you want a similar sized vehicle that gets better gas mileage, a Highland is a good option.