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Will 205/40/17 wheels that weigh 38pds (tire/rim) make your gas mileage worse by 115 miles per tank? I ask because i never realized the crappy gas mileage til i put the wheels on a month ago and just realized i was getting crappy gas mileage. Any ideas?(i just cleaned my air filter too and still same problem)...thanks?

 
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Stock Tires
Sidewall: 5.12 in
Radius:12.23in
Diameter:24.25in

New tires
Sidewall:3.23in
Radius:11.73in
Diameter:23.46in

Speedometer reading with new tire is 3.25% too fast.

 
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Yes, what Civicvtec1ps said. Your wheels are turning to fast and making your engine run at a higher RPM than it should be, therefore you are burning more gas than you need to. With a 215/45-17 tire you will be closer to stock diameter and that should get you back to normal.

 
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Wow, thats awesome. Thanks for the help, yea i noticed that today driving by one of those Speed radar things that show how fast you are going, and it said 37 while the speedometer said close to 40. Is there a way to reset the ECU so that it will change due to the tire change, or do i have to wait until my tires wear down to get 215/45?

 
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Will it really affect the gas milage THAT much though? Just wondering because i am about to buy a new set of rims. Thanks

 
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so he's running 3.25% too fast and getting poor gas mileage ...theoretically what would happen if he was running 3.25% too SLOW????

 
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I believe the weight has to do with poor gas mileage, considering I have 215/40/18s that weigh about 30lbs each, my old gas mileage was 360-400, now it's 290 and I drive the same, so if the wheels are heavier, it forces you to put more gas in to move the car, thus wasting more gas...so I guess both RPM and weight can be a factor.

 
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Correct the weight is also a major issue too, less weight the engine has to turn the faster it will accelerate. But combine a heavy weigt wheel with a smaller diameter wheel and yes it will have an effect on the milage of the car, maybe not a huge effect but noticable.

 
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only way to fix speedo is have it recalibrated... so no.. no real way to fix without good money,,, get corect sizer tire or deal with it... LOL

 
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I believe the weight has to do with poor gas mileage, considering I have 215/40/18s that weigh about 30lbs each, my old gas mileage was 360-400, now it's 290 and I drive the same, so if the wheels are heavier, it forces you to put more gas in to move the car, thus wasting more gas...so I guess both RPM and weight can be a factor.


civicmorph: like said above, your wheels have to spin more to make it like the oem milage.. the computer caounts more revolutions of the wheel to go a mile because of overall diameter being smaller

 
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It also could be that it's getting colder outside which gives you worse gas mileage.

 
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diameter and weight will cause gas mileage issues for sure

 
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Also keep in mind that your new tires are probably stickier. Thats the problem with my summer tires... great for grip...but it adds resistance ...resistance kills gas milage. Cold weather decreases gas milage as well. The wieght is also a factor. Last but not least maybe you drive faster with your new wheels cause they feel "sportier" seems funny but that has an effect. I always seem to drive faster when my car is shiny. All things to keep in mind.

 
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good points, i figured the weight had something to do with it, but now when i go to work and back i can see the needle dropping about 1 1/2 lines, i never noticed that...also whenever i start the car the needle is usually lower down...its retarded, maybe i should reset the ECU too

 
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as i understand it, the ecu doesnt control the speedo... this could be outdated info, but my last car was a cherokee that had oversized tires on it... to correct the speedo theres a little plastic gear on the tranny that needs to be replaced to acurately measure the speed... dunno if its the same on the new civics or not, but worth findin out about at the dealer or someplace as the gear is about $3 and about 10 minutes to fix...