Rocketsfan

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.

erick3

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

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...

darksky

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)

darksky

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.

01tl4tl

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

01tl4tl

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

Rocketsfan

Don't laugh... parts of Houston got about 2-4 inches of snow a few weeks ago... lol.

I thought the same thing, but I thought I noticed 30-33 mpg on my trips there consistently since I had the Bridgestones. I'm not positive, though.

Yeah, I was going to get another set of 960's because they lasted so long and held up pretty well, but the Pilots were on clearance for a lot less, so I figured I'd give them a try.

Rocketsfan

This is based purely on the MID. I consistently got 30-33 mpg on the Bridgestones on several trips to Houston and back. I had some PZeros in the past that also got similar numbers if I recall. Even if the MID isn't always foolproof, I would think it's one heck of a coinicidence that the dorp in mileage it displays is right after I get the new tires. Hmm...

It was definitely colder than usual ... probably in the 40's, but then again in the 60's when I got to Houston... by the time I got back to Dallas it was in the 30's-40's again. One thing I noticed was that the mileage was low no matter when I looked at the MID and no matter the temp. Meaning I filled up in 40 degree weather in Dallas, drove about 100 miles and noticed how low the mileage was. I filled up in Houston in 60-70+ degree weather, drove back about 100 miles and still noticed the mileage was low (the trip each way is about 300 miles for me).

Possible. I did pump gas at 2 different gas stations in 2 different cities (same brand).

It may have sprinkled a bit, but no ice or snow in either direction.

I averaged 64 mph on the way back and I usually average about 65-67 on the way down there.

Hardly any traffic (I travel really early in the morning and late at night). Of the 300 miles each way, there was possibly 1-2 miles of slow down in any traffic.

This is a possibility. It was windy both ways.

Yup! All my tires have been A/S tires. I would've been ok with maybe a 1-2 mpg difference, but 4-5 mpg is huge to me.

I just checked - this could possibly be one of the problems. I noticed one tire at 32 and the other 3 around 30 or 31. I'll get them all up to at least 32 and try again in about 2 weeks to a month.


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).

darksky

@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.

01tl4tl

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

01tl4tl

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!

darksky

Does Acura recommend using either product? I thought I read in some official literature that such products are potentially harmful and not necessary.

01tl4tl

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?!

dero79

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.

Lerlactl

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.

darksky

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.

csmeance

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.

Lerlactl

^^^ Well put, Thanks.