I upgraded my wheels to a set of 17" OEM Volvo “Volans” a few months ago from the stock 16s. I bent the absolute [censored] out of the left rear wheel while offroading last week and today I switched back to my stock wheels until the Volan replacement comes in the mail. I immediately experienced something I had not seen in many moons…28mpg on the highway, 3mpg above normal. It makes no sense to me that it would be wheel related, as the footprint/height of the car is the same, with the -1 tire size, +1 wheel size. Would the added weight of that extra inch of steel all the way around be that significant? I am befuddled.
What size tires did you have???..and what’s the tire size NOW???
Have you changed your driving habits now that you have the “performance” tires???
The change could have been due to measurement error, driving style, rolling resistance differences, the width of the tread and many other factors.
Note: those fancy alloy wheels are usually heavier than steel and usually weaker than steel. While true racing wheels then to be stronger, lighter and much more expensive, the consumer versions are often just the opposite, except for the price part, although they are considerably cheaper than their true racing rich cousins.
There was a thread last month that this reminded me of…
http://community.cartalk.com/posts/list/450809.page
JEM posted a reply I agree with. To summarize, if the outside diameter of the tires on the 17" wheels is larger than the tires on the 16" wheels, you might have seen a drop in your gas mileage when you switched away from the stock wheels. With a larger diameter, you’ll get fewer miles on the odometer over the actual distance. Put the 16" wheels back on (with a theoretically smaller diameter tire), and you’ll jump back up to your original mpgs.
While they are heavier/larger wheels than stock, they are not aftermarket, and are genuine OEM Volvo, and were even offered as an optional upgrade during that year. I would think that the 3mpg(9.33%) negative hit would be significant enough that the EPA would require Volvo to place a separate EPA window sticker for its cars sold with each differing wheel. Actually, they probably just put the smallest wheels on the EPA tester and used the highest numbers across the board.
I would bet that the diameter of the 17" wheel with the tire is larger than the diameter of the 16" wheel with the tire. This has probably thrown off the odometer reading. You could measure the diameter with a measuring tape, or, go on the interstate and check the odometer against the mile markers.
I had a similar experience many years ago. I bought a used AMC Javelin with really worn tires. I found a set of 14" tires that were barely used, but two sizes bigger than what was on the car. The service station where I traded said they would work. I also bought two new tires from the service station that were also two sizes bigger than what came on the car. All was well until we took a long road trip. I was driving the speed limit, but passing everything on the highway. When we stopped for gas, we were barely getting 16 mpg with a 232 cubic inch 6 cylinder engine. The car also needed a quart of oil and we had never had it use oil up to that point. My wife complained about how noisy the engine sounded at highway speed. When she calculated our average speed against the distance on the map, we had averaged 87 mph. It then dawned on me what had happened: the larger tires had made the odometer and speedometer fewer miles and a slower speed. Your problem is the opposite–you lowered the diameter which would allow the odometer to record more miles for the rpm that the wheel turns. At any rate, start by measuring the diameter of the different wheels with the tires.
From your posts, I gather that the sticker matched the car, including the wheels, you purchased so I don’t really see the problem. IIRC, EPA has mileage estimates for models that vary significantly (different engines and/or transmissions)…asking them to rate each possible variation would be ridiculous. If you spring for winter floor mats and splashguards, should they recalculate the mileage because of the extra weight? EPA also states quite clearly that mileage will vary based on a variety of factors, including vehicle condition and maintenance.
I’d say your 3 mpg difference is probably a combination of different tire diameters (if they do actually differ) and the other factors that JEM mentioned.
The profile of the car remains identical to the stock 16’s. I added 1" to the wheel, and -1" from the tire, so everything, theoretically should be the same. I know that metal weighs more than rubber, and I should expect to sacrifice a modicum of fuel efficiency with the added weight, but a whole 9.33%? This is extreme. This equates to $80 per month in added fuel costs. That’s one helluva “Vanity Tax”. Now is the 2nd day on the old stock 16s and I am amazed at how much smoother my ride is. Anyone want a set of almost new Volan’s + Conti’s?
http://memimage.cardomain.net/member_images/11/web/587000-587999/587838_59.jpg
All you’ve said so far is they’re the same…Myself and others can’t determine that unless you give us the numbers.
What size tires were on there??? And what is the new size???
I’m betting they are NOT the same???
i have learned that the tire and rims are all variable.
find a measured mile, or even an interstate with mile markers.
do a test to ensure that your change in mileage is real. i surmise that you actually have NO change (or negligible) in mileage. BUT i bet the difference in wheel sizes is skewing the math, making you think the mileage is off.
i bet the different tires and rims are NOT actually adding up to the same true height.
so you went from a 16" rim to a 17" rim. by changing the tires down a size height, of course the ride is going to be “harder” you got rid of a 1/2" cushion, and probably got a higher speed rating too (im assuming)
just goes to show you, you dont get anything for free. (smooth ride, or higher ground clearance) by the way, how much extra ground clearance were you looking for when you changed to the larger rims?
It could even be that the tires have different rolling resistance. What’s holding you back could be a complete surprise.
Did you have a tail wind?
It’s just one tank of gas. I’ve noticed some variability in my mileage due to traffic and how I drive during that particular tankful. See if it continues for the next week or two.
The +1/-1 does not mean that the diameters are exactly the same. List both tire sizes. If they were the exact same diameter, you wouldn’t have needed to change all four wheels when you bent one rim.
It may also be the tires themselves have different rolling resistance. Just by keeping the same rims you can sometimes have a swing of up to 3MPG by changing tire models/makes.