After putting on after market rims and tires my gas mileage went from 28 to 20?

[Kaotic Lazagna]

Originally Posted by VeganGirl

I did not get an alignment after putting these rims on, I did get an alignment maybe like a few months before I put them on when I got lowering springs, but that was stock rims and tires. I thought if the car still drove fine I didn't need an alignment. It doesn't veer of to one side or anything.

I will check the direction when I get out of work

Nope. The car can track straight, but your toe specs could be all wrong. That means you'll be scrubbing speed, so that in turns means you'll have to apply more gas to drive the same speed you would otherwise. That also means you'll go through those tires a lot quicker.

[tyler_win_photo]

Originally Posted by VeganGirl

I don't know the exact specs on my wheel. I know they are 18 inches by 9.5 back and 18 inch by 8.5 front and they are rays gram light 57xtremes. My love drives his car with 11inch tires in the back and kraftwerks c30 and his mileage is 19-20. I hope when I out my edelbrock kit it doesn't drop down to like 15 or something. I live in Florida and I haven't changed my driving habits. Me and bf both drive automatics and daily our cars. I don't really know if anything else that would have caused my mpg to drop so bad cause I only noticed it after putting the rims, but to me they feel almost the same weight as stock or lighter, they don't feel heavier but I could be wrong . I am not mechanically inclined at all soo...

The wheels are definitely heavier. But something most people forget to consider is that the tire you're using for a wider diameter + width wheel is going to be considerably heavier than stock. My guess is that your rolling circumference is larger than stock making it seem like you're getting less mpg - which you should be able to notice easily if your speedo is off. And my other guess is that now that you've got some actual grip you're just driving more aggressively without noticing.

[Jajanken86]

Originally Posted by tyler_win_photo

The wheels are definitely heavier. But something most people forget to consider is that the tire you're using for a wider diameter + width wheel is going to be considerably heavier than stock. My guess is that your rolling circumference is larger than stock making it seem like you're getting less mpg - which you should be able to notice easily if your speedo is off. And my other guess is that now that you've got some actual grip you're just driving more aggressively without noticing.

What change negatively affects mpg? Smaller or larger rolling circumference?

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[tyler_win_photo]

Originally Posted by Jajanken86

What change negatively affects mpg? Smaller or larger rolling circumference?

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Larger rolling circumference. Your wheels take less rotations to travel a set distance.

[churchx]

Larger rolling circumference or in other words bigger wheels imho won't affect mpg THAT much for mpg drop to be of mentioned extent. After all, it's just overall gearing change. People installing FDs for lower gearing didn't had mpg change by 41% even while had gearing changed often more so then if with different wheel size.

[Yardjass]

Originally Posted by df.dima

I was getting close to 27-28 stock as well and with wider/stickier tire I get 24.5 (245 MPSS on x9 light weight wheel). Dipping beyond 20 seems pretty excessive, but depends on the way you drive I guess is possible, or you have some other factor. I can't imagine you drove aggressively and got 28mpg on stock, similarly, I expect you don't drive much different with wider tires now.

This sounds like a more realistic reduction for doing nothing but switching to wider wheels/tires. Something else is going on here.

Originally Posted by churchx

Larger rolling circumference or in other words bigger wheels imho won't affect mpg THAT much for mpg drop to be of mentioned extent. After all, it's just overall gearing change. People installing FDs for lower gearing didn't had mpg change by 41% even while had gearing changed often more so then if with different wheel size.

I guess it depends on how much bigger the wheels are. I assume the odometer counts rotations but I'm not 100% sure on this car. If your wheel/tire diameter is larger than stock, the computer may perceive that you are traveling a shorter distance per rotation of the wheel than you actually are. In other words, it will calculate a stock wheel diameter for each rotation instead of what you have. This could result in erroneous MPG but it would have to be a fairly large difference in wheel size to be that noticeable. For example, if your wheel/tire combo goes from a 20 inch diameter to 21, you're only talking like a 7 inch difference in perceived distance, which is roughly a 5% change.

[tomaszjanczak]

The major factor affecting MPG is the low rolling resistance of the stock tires.