What happened MPG?

[Denise Hayes 2]

Just curious if someone has the answer. Was getting 19.5 mpg on highway, now 17.5 mpg. After putting new tires on it is when the fuel mileage dropped. I was thinking it was because they had put only 32 psi in the tires was the problem, so I bumped the air pressure up to 40psi, as I had in the Michelins that were factory, but still no increase in mileage. The oil has been changed and I have put a new air filter in it also. Do you think it could be the tires ? They are the Firestone- Destinations. I am frustrated.

 

[Jimmy Lavoie]

Did you change gas? Something with Ethanol? The 2mpg drop is the usual effect of using that crap. :angry:



Mine did the same thing. Unfortunately, there are no gas stations in my area that don't use 10% Ethanol.



I also changed my tires recently with the same OEM brand/size and there was no effect on the mileage. The 10% Ethanol made a huge difference.

 

[Tom Schindler]

Tire size change? Tire tread pattern more agressive? Tire compound more sticky? tire pressure lower on the new tire?



Tires play a big role in fuel mileage.





Tom

 

[Ray McIntireJr]

Mine dropped about the same when I put different tires on too. Went from more of a street tire(General Ameri-star) to Firestone Destination AT(which imo is more of an all-terrain tire).

 

[FlipTrac_511]

My mpg dropped some too after getting new tires. I switched from original GY Wrangler RT/S to GY Fortera Silent Armors. Same tire and wheel size.

 

[Denise Hayes 2]

Don't think it had Ethanol added. Bought gas in Shreveport and in Dallas. Same results. Same tire size and tire pressure. It's a Firestone Destination S/T. A standard street tire tread. This is frustrating.

 

[Richard L]

Gas mileage can be very elusive, and fluctuate due to seemingly minor changes. I assume your driving habits have not changed, so here are a few suggestions. Probably no single item is causing your reduction in fuel mileage, but a combination of several factors.



Different tire models and manufacturer can have a different diameter even if they are they same size. This can induce a small amount of speedometer/odometer error that may account for some of your mileage loss.



Also, different tread patterns and tire design can increase the roll resistance and make the tire use a little more gas.



Different gas from a different pump may account for some of the variances as well as where you buy your gas. Most 87 octane gas contains some Ethynol (alcohol) which gets about 25% less mileage. Different brands blend different amounts of Ethynol to their gas. Check the amount of ethynol in the gas you are using and look around for an 87 octane that contains less ethynol. Your gas station may have changed how they blend their gas?



The other big variable in gas mileage is the traffic. Now that school is starting, traffic is getting heavier and the more stops/starts or slow-down-speed-up cycles in your daily commute, the more gas you will burn and that can be significant in the Sport Trac due to the heavier weight. Also, consider that many people may be on the roads in your area who are on vacation and that may contribute to a slight increase in traffic. Just catching a few more traffic lights can burn more gas, and you may not even notice the extra traffic, or that you have caught a few more lights, or the lights stay red longer, etc.



Also, the weather can play a big role in mileage. Cooler temperatures may require a little more gas for the engine a little to warm up, while really hot weather lowers the engines power.



Rain and snow will increase tire slippage and reduce mileage.



Way too many causes than can be listed, but it could also be an engine sensor has gotten a little out of tollerance but not enough to trigger a CEL, but coupled with the other factors listed above may be eating a little more gas than it did before?



...Rich

 

[EddieS'04]

I have found. Not all tires of the same size are exact same diameter and rolling resistance.