ECU reset needed after wheel change?

[FLAteam]

I just changed out my wheels about a month ago, from 13 inch steel wheels to 15 inch alloys. Since then, I've noticed that my fuel economy has dipped dramatically (from 32mpg to 25mpg). Is it possible that I need to reset my ECU for a change in wheel/tires? What else could be the cause of this? From my research, the wheels should only weigh about 5 lbs more than each steel wheel, a total of 20 lbs extra.

thanks.

 

[defvayne]

I doubt it. What size tires are you using?

 

[FLAteam]

I was using 175/75R13, then on the 15's i'm using 195/65R15.

 

[defvayne]

I was using 175/75R13, then on the 15's i'm using 195/65R15.

you should of used 195-55-15 tires..seems that your speedometer is going to read 4-5 mph faster. So if your going 50 your actually going 55-56.

 

[Genuine Rolla]

that would explain your gas mileage because you are traveling faster than you usually would.

 

[TheWingMang]

^ Actually wouldn't it explain that his gas mileage isn't necessarily changing much, but the trip meter is now reading slow? That would mess up his calculation.

 

[bmoua]

the reason why your buring more gas is 1. LIke everybody said, your speedo is off by 5mph (im in the same boat, i doubht its the problem though) and 2. you upgraded to 15inch rims. Any time you upgrade to a bigger rim size/ tire, you will lose your rated mpg. Bigger rims/tires means more weight added weight, more added weight means the motor has to work a little harder, the motor working harder = more buring of gas.

 

[TheWingMang]

2. you upgraded to 15inch rims. Any time you upgrade to a bigger rim size/ tire, you will lose your rated mpg. Bigger rims/tires means more weight added weight, more added weight means the motor has to work a little harder, the motor working harder = more buring of gas.

Not necessarily. When I got my 16" Rotas I weighed them versus my stock wheels (both with tires on obviously). The 14" steelies were 35lbs, the rotas were 34lbs. So a bigger wheel doesn't always mean more weight.

Maybe I'm wrong, but heres what I'm thinking. If his tire diameter is now bigger, and his speedometer is now reading slower, then wouldn't the trip meter also be reading slower? So when he goes to fill the tank and check the mileage, the trip meter says he didn't go as far as he actually did, so the calculation says hes using more gas, but he actually isn't. Does that sound right?

 

[RIP Formula]

Not necessarily. When I got my 16" Rotas I weighed them versus my stock wheels (both with tires on obviously). The 14" steelies were 35lbs, the rotas were 34lbs. So a bigger wheel doesn't always mean more weight.

Maybe I'm wrong, but heres what I'm thinking. If his tire diameter is now bigger, and his speedometer is now reading slower, then wouldn't the trip meter also be reading slower? So when he goes to fill the tank and check the mileage, the trip meter says he didn't go as far as he actually did, so the calculation says hes using more gas, but he actually isn't. Does that sound right?

you are right about the calculation, however, you left out the facts of rotating mass. given 2 sets of wheels/tires with the similar dead weight, the set with the Center of Mass (of a cross section of tire/wheel) closer to the axis of rotation will require less energy to spin/stop. this is known as the figure skater effect or coriolis force. the larger diameter wheel, even with a smaller dead weight, will have most of its mass farther from the center of the wheel, thus a larger rotating moment. since weight and arm (distance from center) are multiplied to find the rotating moment (the number your engine cares about when turning those wheels) a change in either weight or wheel diameter can effect it either positively or negatively.

in this case, bigger rims can yeild better mileage if they are light enough (assuming same final tire outer diameter)

i hope i didn't just make everyones heads explode

 

[rover4x4]

Is it possible to recalibrate the speedometer?

 

[pikachu25]

i believe you are losing MPG's because you are not using the recommended tire size.
the tire size is recommended for a reason and im sure most people who changed their rims
have also noticed a decline in fuel economy.