Horrible mpg. Help!

IMO there is no need to warm up a modern day vehicle for more than 2minutes in frigid temps (-30-40 C ). I idle my Tacoma in frigid temps for 2 minutes and then drive slowly 30 mph until engine is warmed up. It takes much longer to warm up an engine sitting at idle than driving it slowly. Just use some common sense and dont drive it at highway speeds until engine is fully warmed.

 

I am not in the winter but after adding my suspension setup I am getting 9-12mpg. Its horrible. I did bump it up to 285's but did not expect that big of a drop.

 

If my research and math is correct larger tires will make it appear you are getting less mpg. Due to the fact that you are going faster than you really are, so your odometer says you went 250 miles but you really went 260 approx. So, it may only be 1 to .5 mpg of a difference but it could account for some of the loss. I'm running 265/75r16's that are 1 inch bigger and weight about 44 pounds. I average 15.5 mpg, but could really be 16.5.

 

One thing to keep in mind about changing the wheel size, is that your odometer won't be accurate. If you are calculating MPG based on the odometer reading and not adjusting for the difference in tire circumference, then you will calculate lower MPG than what you are actually getting.

For instance, a 285/75R16 has a diameter of 32.8 inches, circumference of 103.04 inches.
A 245/75R16 (stock size) has a diameter of 30.5 inches, circumference of 95.82 inches.
The difference is 7.22 inches, or 7.54% (bigger than stock).

So if your odometer reads, lets say 350 miles, then your real mileage will be 350*1.0754 = 376.4 miles.

If you burned 20 gallons of fuel, then you got 17.5 MPG using the odometer reading, or 18.82 MPG after compensating for the difference in wheel size.
Note that you can also apply the correction to the MPG value rather than the distance value, to arrive at the same "corrected" MPG.

True that it still doesn't get you all the way back to factory MPG, since with the bigger wheels you also have a higher profile, and less efficient gear ratio, but at least it gives you a more true value that isn't quite as ugly.

 

Totally, I know my direct numbers are not exactly correct but even without converting its down near 10mpg so it dropped a lot. Thanks for the note, ill give the conversion a check to see. I will be changing up my gearing soon as well.

 

Thanks, good info!