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Do you guys think you get better gas mileage with alloys? I don't know the weight difference between the 17" alloys and the 17" style steel wheels, but it is additional rotational mass. Or do you think it doesn't make a lick of difference for the 269hp of the V6?

Thanks in advance!
 
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I think the difference may be too small to measure or at least too small to care about.

Rotational mass is important to cyclist (bicyclists). They will fret over a few grams such as the weight of tires and rims but they are only putting out a few hundred watts of power under the hardest of efforts.

I think this might be something that we could calculate or estimate but it is the Friday before a long weekend. Wrong day to procrastinate at work :wink:
 
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There are two other issues involving wheel weight. One is that the less unsprung weight the less bumpy the ride. Second, the less overall weight per given horsepower the better the mileage, however slight, and I believe the weight difference between the Base model standard wheel/tire size of 16" steel and the optional 17" alloy is about 10 lbs per wheel/tire or 40 lbs over all.
 

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There is a difference.
Less obvious in the V6, but it is there.
I noticed a big diff in another car that went from 15's to 16's.
 

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the difference you saw was the difference in tire diameter which threw off your odometer which threw off your gas mileage calculations

thinkingman said:
There is a difference.
Less obvious in the V6, but it is there.
I noticed a big diff in another car that went from 15's to 16's.
 

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That's a possibility, but generally people just "plus size" thier wheels. Meaning that although you're going from a 15" to a 16" rim, the tire has less sidewall, and therefore the same overall diameter. The stock 215/70R16 wheel has a diameter of 27.9", the 225/65R17 has a diameter of 28.5", and the 235/55R18 on the sport has a diameter of 28.2". Click this http://www.miata.net/garage/tirecalcold.html to use the tire size calculator. So you see in this case, the Sport actually has smaller tires than any of the 17" wheels. There is different unsprung weights for each wheel and tire combination, so that is a factor also. Just hop on tirerack.com and look at some of the different weights for the wheels alone and you'll see what I mean.

flyingn said:
the difference you saw was the difference in tire diameter which threw off your odometer which threw off your gas mileage calculations

thinkingman said:
There is a difference.
Less obvious in the V6, but it is there.
I noticed a big diff in another car that went from 15's to 16's.
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flyingn said:
the difference you saw was the difference in tire diameter which threw off your odometer which threw off your gas mileage calculations

thinkingman said:
There is a difference.
Less obvious in the V6, but it is there.
I noticed a big diff in another car that went from 15's to 16's.
No...
The +1 upgrade was from 195/65/15 to 205/55/16.
Less than 1% diff in circumference.
The difference was felt...as in seat-of-the-pants accel and braking.
Throttle response was a little slower.
It costs alot to get a +1 or +2 wheel/tire package that doesn't increase rotational mass or unsprung weight.
 

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thinkingman said:
No...
The +1 upgrade was from 195/65/15 to 205/55/16.
Less than 1% diff in circumference.
The difference was felt...as in seat-of-the-pants accel and braking.
Throttle response was a little slower.
It costs alot to get a +1 or +2 wheel/tire package that doesn't increase rotational mass or unsprung weight.
^^^^ I agree! You have to be very careful to watch the overall wheel & tire weights, even with "lightweight" wheels in a larger size, you're most likely adding unsprung weight when going up even just one size. If you go to any high-level autocross or track day, you'll see that most people run the smallest rim that will clear their brakes. Adding unsprung weight definitely hurts performance.

DJ
 
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