MPG change after getting new tires
I'd been running on Bridgestone 960AS tires (stock size) and decided to swap them out and put 4 new Pilot AS's on since they were on sale/clearout everywhere with the new Plus model that was just brought out. I sometimes take trips to Houston from Dallas and back. On the 960's I would average between 30-33 mpg on these trips, even hitting 34 mpg on one trip. I noticed with the new Pilots, I only got around 27-28 mpg on a recent trip.
I'm going to check the cold pressure on the tires - I usually have the tires at 32 psi all around. The size of the tires on both sets were the same (235/45/17). Have you guys seen this much of a mpg change swapping tires out? Is this common? If not, any ideas? The Pilots are great, btw. Great roadfeel and handling. |
hm...i haven't had any personal experience with the pilot a/s series but i'd imagine it could be weather related? isn't it snowing practically everywhere? lol well...then again you mentioned Houston, right? the tires could maybe be bit heavier with more tread life, etc? on the contrary, low tire pressure could be the culprit :shrug:
i haven't seen such drastic changes in mpg going from tire to tire here... but then again, i tend to stay within the bridgestone family... |
What you're describing isn't uncommon in my experience.
Firstly, are you getting your mileage from a real calculation (miles/gallons used) or from the on board computer? The computer on my 2008 TL isn't very good at displaying accurate MPG. It is usually off by 2-3 MPG when I compare it to the calculation. Fill your tank until the gas pump stops. I can squeeze an additional 0.3 gal or so before it's full. Reset a trip odometer. Drive the car until your near empty, then refill to the approx. same level (i.e. until it stops, then add the same amount you did, 0.3 in my case). Now divide the miles as per the trip odometer by the gallons. If you're calculating your mileage that way, next verify that your new tires aren't affecting your speedo/odometer. See this post for several methods of doing this. Beyond that, your Pilot A/S tires might have a higher rolling resistance than your Bridgestones and thus negatively affect your mileage. I can tell you that my stock tires got 2-3 MPG better than the Bridgestone 960 AS tires I replaced them with. Here are a few factors that will affect mileage, there are probably more: -Errors due to incorrect tire size (i.e. now your odometer is counting too fast) -Outside temp (colder being worse) -Winter/summer gas formulations (winter being worse) -Weather (rain, snow, etc.) -Driving style (fast starts, high speeds, etc.) -Cruising speed (you'll get better mileage at 65 than you will at 80) -Traffic density (frequent slow down/acceleration) -Head/tail winds -Tire rolling resistance (performance tires are worse in general since they are made to be 'sticky' and provide you with traction. A/S tires can also hurt mileage, but hey, you bought them for their saftey and grip didn't you? -Inflation (under inflated = worse) |
Just as an aside -- and this doesn't apply to you since your case was going from an aftermarket tire to another aftermarket tire -- stock tires are usually selected by the manufacturer not for their safety factory or inclement weather performance, but for their ability to boost the vehicle's mileage thus raising their fleet's overall mileage.
I'd post a link if I had one, but a given auto maker has to hit a fleet (i.e. all their consumer autos) MPG target as dictated by CAFE standards as per EPA guidelines. For example, in order for GM to sell a gas guzzling SUV, they have to sell so many efficient little cars to offset the one inefficient SUV's poor mileage such that the sum of all cars sold/produced = that fleet CAFE standard. Anyway, if they can raise the mileage even by 1-2 MPG by using an 'efficient' tire (one with a lower rolling resistance), so much the better. Acura/Honda is also bound by these CAFE fleet standards. Just wanted to share that. |
dont use the factory air pressure numbers
Look at the max cold at max weight listed on sidewall of the tire You are probably about 80% of max weight- so use 80% of pressure and maybe drop a few psi down from that Example max cold- 50psi - 20% =10 psi = 40 cold set for you You may find that a bit rough ride so drop a few Many of us, on whatever size tires, have found 36-38 to be good for mileage and and handling |
cafe standards is why gen3 uses 5/20 oil instead of the better for the engine 5/30
A slight increase in the `testing mileage number` for the TL, and each model they make, adds up for the fleet average...iirc is currently required 24mpg- to help detroit cars, in 2012 its 27, big whoop. Not each car has to get that- a 40mpg car balances out a 20mpg car in the companys fleet SUVs and trucks are exempt from the cafe testing- thats how they are able to sell them at all. or were able to sell them.... only the passenger cars and light trucks are included |
Originally Posted by erick3
(Post 10318138)
hm...i haven't had any personal experience with the pilot a/s series but i'd imagine it could be weather related? isn't it snowing practically everywhere? lol well...then again you mentioned Houston, right?
the tires could maybe be bit heavier with more tread life, etc? on the contrary, low tire pressure could be the culprit :shrug: i haven't seen such drastic changes in mpg going from tire to tire here... but then again, i tend to stay within the bridgestone family... |
Originally Posted by darksky
(Post 10318148)
What you're describing isn't uncommon in my experience.
Firstly, are you getting your mileage from a real calculation (miles/gallons used) or from the on board computer? -Outside temp (colder being worse) -Winter/summer gas formulations (winter being worse) -Weather (rain, snow, etc.) -Driving style (fast starts, high speeds, etc.) -Cruising speed (you'll get better mileage at 65 than you will at 80) -Traffic density (frequent slow down/acceleration) -Head/tail winds -Tire rolling resistance (performance tires are worse in general since they are made to be 'sticky' and provide you with traction. A/S tires can also hurt mileage, but hey, you bought them for their saftey and grip didn't you? -Inflation (under inflated = worse) Thanks guys. I'm hoping it's just the air pressure - I assumed (like a moron) that it would be correct after they installed the tires. We'll see how much difference those couple of PSI make (assuming that correction will give me better mileage). |
@rocketsfan - the problem is that making comparisons between two trips is only 'ballpark' since there are so many factors that you either can't control, or can't accurately directly measure/factor into the calculation. All these little things introduce differences that are cumulative and contribute to your experimental error. Bottom-line: you need a pretty large dataset to help control for these factors, i.e. many miles (large data sets) on each set of tires.
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put the tires at 36 psi- tire shops rarely set them correctly
fill the gas tank with 91 to the first click, reset the trip meter and write down the current mileage Drive normal till the low fuel light comes on, fill to first shutoff- write down miles and amount of gas purchased. do the math on miles traveled to verify against the mid- then divide gallons just purchased into miles driven for a real number- example 300 miles/ 15 gallons= 20mpg |
you can also do a quick fuel injector/induction cleaning with 1 can of seafoam or redline SI-1 fuel cleaner --6 bucks
Add full can/bottle to 1/2 tank for max results- do not do this while figuring mileage, it will mess up the numbers, then make them better! |
Originally Posted by 01tl4tl
(Post 10321382)
you can also do a quick fuel injector/induction cleaning with 1 can of seafoam or redline SI-1 fuel cleaner --6 bucks
Add full can/bottle to 1/2 tank for max results- do not do this while figuring mileage, it will mess up the numbers, then make them better! |
you thought you read in some official literature- got a link to that??
acura sells a 3 part process ($50 at honda dealer)-contains spray cleaner for the TB plate, some more you put into a main vac port on the intake, and some for the gas tank We do the same using other products that are well known and well tested- they cause no damage- are sensor safe and do a good job of restoring clean surfaces and injector spray patterns The extra stuff and higher ethanol percent now used in gasoline causes inefficient combustion and leaves behind a lot of residues. Those need to be cleaned out! Stop by your dealer and they probably have a sign or sent a coupon to you for Induction Service $149- suggested yearly/15k miles Guess what that is?! |
I also have recently purchased those same Pilot A/S tires, and love the hell outta them! As someone stated correctly above, the tires are more performance and the speed rating is higher than that of your previous, thus affecting your mileage. These tires are performance, as you should be able to easily feel sliding in/out of lanes at high speeds (which I hope you've tried already). The compound on these tires are more for stickier grip and longer treadlife, so these reasons may factor in to loss of MPG.
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Some tires are physically heavier than others this may account for the lost MPG's as well. I just switched from Sumitimo HTR ZIII's which are 24 Lbs. a piece to Eagle F1 All seasons which are 27 lbs. a piece. Even with the exact same tire pressures and driving in the exact same conditions I've noticed a big drop in fuel economy.
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27 lbs vs. 24 lbs? I don't understand how 3 lbs/tire can make a difference (I'm not saying you're wrong, just that I don't understand). I think more than likely one or more of the reasons outlined in post #3 are at work.
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Originally Posted by darksky
(Post 10327296)
27 lbs vs. 24 lbs? I don't understand how 3 lbs/tire can make a difference (I'm not saying you're wrong, just that I don't understand). I think more than likely one or more of the reasons outlined in post #3 are at work.
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Originally Posted by csmeance
(Post 10327429)
3 lbs can be a lot, the wheel rotates and thus 3 pounds is rotational mass. (forgot the right term). In the end in can equate to an extra 5 HP needed to drive just that extra 3 lbs.
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