blastrx

I just switched from the 17" to 19" and my average mpg went from 25 to 22. I know the bigger rims and tires weigh more, but is it really enough to lower my mpg by 3 miles?

does it have something to do with the bigger tire size = larger circumfrence = fewer rotations per minute, or something like that?

let me know what you all think and have you had similar experiences?

csmeance

what tire size did you get? also one factor is the weight of the rims, if they are heavyer, they bog down your car, rob performance and a few other things.

drdamian

yes... i noticed a significant difference in performace when i went from the stocks to 19's.. but i havent looked at the MPG..... i feel like i don't drive the car like i used to bc now im afraid of damaging my rims... i now drive much slower and cautiously... so, i would probably think that my MPG actually got better

xristos

I upgraded from 17" to 19" rims from VOLK. The rim itself is lightweight & hubcentric. I was getting 29 MPG on the freeway & now get about 26 MPG. I have a 245/35/19 tire on a 8.5" rim. I have the tires at 36 PSI all around.

I too noticed the drop of MPG right away. I had a dead battery, which got replaced by Acura, at the same time I switched rims & thought that had something to do with it. Since, I had to get jump started about 5 times & thought I might of messed up an electronic device in the engine. Acura checked out my electronics & fuel management to find everything was OK.

Seems like the drop of MPG is normal when upgrading to bigger rims.

csmeance

Speedometer Difference: 1.696% too slow
Diameter Difference: 1.67%

with 19's and 245/35 tires

ding069

heavier rotating mass plus larger/wider diameter width equals lower gas milage.

invincible569

Yes, with 20's, my car eats gas so much more

xristos

Would using a 235/35/19 tire size, instead of a 245/35/19 tire, raise my MPG average to notice a difference or no difference at all? Just curious.

leedogg

Do some manual mpg calculations. Use the trip meter between gas fillings and write down the gallons filled, and calculate the miles traveled per gallons used.

MrHeeltoe

iTrader: (1)

It is not just the diameter and overall weight you know. Even though your aftermarket wheels might be the same or less weight, and the tires may have the same overall diameter, there are a couple other factors.

1# Width. The wider wheels do offer a higher rolling resistance, and they also contribute to greater air resistance. And fyi, the wheels and tires are one of the biggest aerodynamic concerns on the car.

2# Moment of inertia. Consider a 16x7" wheel and a 19x7.5" wheel of the same weight. Even though the overall weight is the same, more of the weight on the 19" wheel is concentrated far from the center of the wheel. The farther from the center of the wheel the weight is, the more torque is required to turn it (same reason a figure skater spins faster with arms in than they do with arms straight out). Thus, the more foot pressure and gas required to accellerate the car. Low profile tires compound the issue. This is also why performance can drop as well. More power goes to turning the wheels than acutally motivating the car.

3# Slightly different overall diameters will effect the speedometer reading. A tire that is a little bigger than stock will cause the speedometer (and trip computer) to read a lower speed than the car is actually going. In turn, the car turns fewer miles in a given tank, and reports a lower mpg. This is a false reading though, as the car really IS getting more mpg, but the numbers lie to you. The only way to overcome this that I know of is to have the speedo run off a gps system.

I swapped out the stock wheels an tires on my Odyssey for some 18s and I lost about 2-3 mpg.

Marcus

djlehrmann53

The reason your acura seems to be getting fewer MPG is in essence what heeltoe was saying, but he did not elaborate fully. If your stock rims are 17" with a standard size tire let say your overall diameter for your wheel is 21"(this value is strictly hypothetical. i was to lazy to measure the stock set in my garage). This number gives your tire an overall circumference of 3.14X21"=65.94"

65.94" X 1FT/12"= 5.5FT

Now if you have a new set of performance tires and 18" rims, the tires have a lower profile, but your rims are bigger. Now lets say your new overall diameter is 22" for your wheel. The overall circumference of that wheel is 3.14X22"=69.08"

69.08" X 1FT/12"=5.76FT

So every revolution that your tire makes (every 5.5FT you travel with the 17" rims or every 5.76FT you travel with the 18" rims) your car will cover one of the above mentioned distances. If you have the bigger rims your car will travel an extra .25FT or one quarter of a foot! To put this in perspective if you travel 1 mile on your 17" rims you will have 960 revolutions on that wheel. If you swap out the 17" rim and put on the 18" rim and cover the same amount of revolutions you will travel 1.05 miles instead of 1 mile. After 300 miles or so this can start to have an effect on the gas mileage of your vehicle.

Your acura does not measure gas mileage at the ground it measures it at a location in your car (probably on the drive shaft and counts how many revolutions that shaft makes) to calc out your miles traveled. So by changing out the rims you will get a false reading on your MPG. One thing I am unsure of then is if the MPG's are calculated using the GPS systems in the newer acura's. If this is the case, then all the above stuff doesn't matter and your car is getting a worse MPG and I can't tell you why.

MrHeeltoe

iTrader: (1)

Yeah, I did not see the need to go that far into it...I am pretty sure the gps is not doing mileage calculations. Since not all the cars come with GPS capability, I don't think it would. Maybe when Nav becomes standard across all models it will.

For the best idea on what tire size to choose see this link.
http://www.miata.net/garage/tirecalc.html

This one's handy too:
http://www.1010tires.com/WheelOffsetCalculator.asp

ililillilillilil

thanks for the great expanation, Mr. Heeltoe
& good job elaborating on that, djlehrmann53


[QUOTE=djlehrmann53]So every revolution that your tire makes (every 5.5FT you travel with the 17" rims or every 5.76FT you travel with the 18" rims) your car will cover one of the above mentioned distances. If you have the bigger rims your car will travel an extra .25FT or one quarter of a foot! To put this in perspective if you travel 1 mile on your 17" rims you will have 960 revolutions on that wheel. If you swap out the 17" rim and put on the 18" rim and cover the same amount of revolutions you will travel 1.05 miles instead of 1 mile. After 300 miles or so this can start to have an effect on the gas mileage of your vehicle.[QUOTE]

donesn't rolling more help you not burn more gas?

jpeart0

I have gone to 18x8.5 rims with 245/40WR18's and it has done exactly as stated in #3. I know it is actually getting pretty much the same mileage but the MID is off because of the slightly larger circumference. I talked to the dealer and they cannot re-calibrate supposedly.

djlehrmann53

[QUOTE=ililillilillilil]thanks for the great expanation, Mr. Heeltoe
& good job elaborating on that, djlehrmann53


[QUOTE=djlehrmann53]So every revolution that your tire makes (every 5.5FT you travel with the 17" rims or every 5.76FT you travel with the 18" rims) your car will cover one of the above mentioned distances. If you have the bigger rims your car will travel an extra .25FT or one quarter of a foot! To put this in perspective if you travel 1 mile on your 17" rims you will have 960 revolutions on that wheel. If you swap out the 17" rim and put on the 18" rim and cover the same amount of revolutions you will travel 1.05 miles instead of 1 mile. After 300 miles or so this can start to have an effect on the gas mileage of your vehicle. Ummm, the point that I was trying make is that your TL measures gas mileage by the number of revolutions your drive shaft makes or some rotary component located in your transmision makes. It is ussually at the drive shaft though. By putting bigger rims and tires on your car, your car will cover a greater distance, but will only register that distance by drive shaft revolutions, not tire revolutions. With bigger tires you will go farther, but your car will be reporting distances of your stock tire configuration. Hence your reported gas mileage goes down, but you really are not getting a lesser MPG. Understand? If not I have no problem getting into more detail.