MPG with 33s accurate on dash display?

[GMC207]

I added 33s to my 2015 sierra and am wondering how accurate the dash display of MPG is. If its reading 17 and i have 33s is it less or more than 17?

[werked]

MPG will be slightly higher than the DIC reads AFAIK.

 

Sent from my Note 4

[GMC207]

I thought that but wasnt sure. Any idea how much its off? Not that it matters just curious what im getting compared to my ecoboost I had before.

[TxTruckMan]

3.4% higher is what it was for me. I previous went from stock 275/55R20 (32") to 275/60R20 (33"). So you're going 3.4% faster than speedometer says, and you're getting 3.4% more mileage than the DIC says. Add about 0.6 mpg if you're around 17 mpg.

[Rawyzf]

My $.02.

 

With factory size tires, I always found the DIC to read about .5 MPG too high. So, if it said 17 and I hand calculated the MPG it was closer to 16.5.

 

Since I've switched to 33" tires, I have found the DIC to be almost directly on as far as MPG. However, the way it is calculating that is not really accurate.

 

Best way to calculate your MPG to see how close the DIC is: Reset Trip, fill tank. Drive until you feel the need to gas up again, and fill the tank. Check Trip miles and multiply them by 1.045. (33" tires are 4.5% larger than OEM 265/65/18 tires). Then take that number and divide by how many gallons it took to fill back up.

 

Ex.

300 miles on trip. X 1.045 = 313.5

313.5 / Gallons to fill up (ex 17.55 gallons) = 17.86mpg.

[smrr1]

My $.02.

 

With factory size tires, I always found the DIC to read about .5 MPG too high. So, if it said 17 and I hand calculated the MPG it was closer to 16.5.

 

Since I've switched to 33" tires, I have found the DIC to be almost directly on as far as MPG. However, the way it is calculating that is not really accurate.

 

Best way to calculate your MPG to see how close the DIC is: Reset Trip, fill tank. Drive until you feel the need to gas up again, and fill the tank. Check Trip miles and multiply them by 1.045. (33" tires are 4.5% larger than OEM 265/65/18 tires). Then take that number and divide by how many gallons it took to fill back up.

 

Ex.

300 miles on trip. X 1.045 = 313.5

313.5 / Gallons to fill up (ex 17.55 gallons) = 17.86mpg.

X2 exactly what i would have typed. Exactly what i do.

[GMC207]

Mint. I will try that. I didn't think of the x1.045 idea, but it makes perfect sense.

[Rawyzf]

Mint. I will try that. I didn't think of the x1.045 idea, but it makes perfect sense.

 

I haven't heard mint for some time. Is it making a comeback? (I'm old and out of the lingo loop) Thank you for that, gonna use it tonight while having a beer with some buddies for the game. Want to see how it plays out.

[GMC207]

 

I haven't heard mint for some time. Is it making a comeback? (I'm old and out of the lingo loop) Thank you for that, gonna use it tonight while having a beer with some buddies for the game. Want to see how it plays out.

Haha. I'm bringing it back!

[Rawyzf]

Oh, and make sure your calculation is correct.

 

1.034 if your truck came with 275/55/20s

1.045 if your truck came with 265/65/18s

[SgtShiv]

Have to agree, mine read lower mpg than actual after getting new tires and before getting odometer/speedometer corrected. Now back to reading higher than actual.