[Tigeo]

I have noted what to me, seems like a significant drop in my highway mileage (I mainly drive highway) since installing new tires a little over 1000 miles ago. Is this common? Went from the stock Cooper Zeon RS3-As on my 2013 Focus that had ~48.5K on them to General G-Max AS-03s. I realize that the General's have a bit more aggressive tread pattern but I wouldn't think it would make that much of a difference. I see it as a consistent 3 mpg drop since getting them.

 

[n8 dawg]

Tire rolling resistance generally declines as the tires wear. When you replaced the worn tires you now have better grip which creates more rolling resistance which decreases the MPG. Also in the winter months people typically get worse gas mileage because of the winter mix gas, and also letting their cars warm up longer.

 

[Tigeo]

^^^Thanks. I get the winter part and corrected for that and even then I lost ~3mpg. Its got to be the tires.

 

[spacemanspif]

Change in compound also has an effect. If the new ones are softer for more grip it will cost you as well. Did you change size too? What tire pressure are the new ones inflated to compared to the old?

 

[n8 dawg]

3 mpg isn't too bad considering our cars get pretty good MPG to begin with. I would think your old tires having close to 50k miles were probably pretty worn out, so the new tread and grip just adds resistance causing the difference. Also as stated by spacemanspif, softer tires offer more grip, which adds to this resistance. I think I heard someone say once that new tires will decrease MPG by about 5% over worn tires.

Tire pressure is another issue, but with them being new tires I would hope that they have the correct pressure, but it never hurts to double check.

 

[Tigeo]

Pressure is 35, same as I ran on the old ones. Tire are the same size. Its just the new tires. It was just in for service for an unrelated issue where they checked/ran diagnostic so if something were off they would have noted it. I also just popped the K&N out and cleaned it but it wasn't dirty enough to impact the mpg.

 

[rambleon84]

the weight can be different as well...though sounds like a decent drop in mpgs just from tires

 

[[email protected]]

A 3 mpg loss is more than usual staying in the same category of tire, 1 or maybe 2 being more the norm going from worn tires to full tread depth in my experience.

 

[bringler26]

I would guess that the tires may weigh 2-3lbs more each which has a surprisingly large effect on mpg. I went from Bridgestone RE970 at 23lbs ea to General DWS tires at 21lbs ea. I gained 2 mpg. I had been averaging 26mpg and with new tires was getting 28.

 

[JFrye]

I cant find the link to it now, but the tread pattern also comes into play with MPG, which is why most tractor trailers use a groove style tread as opposed to lug style (or however you want to word it).

 

[thenorm]

two factors.
taller tread block which have more flex or squirm which eats up energy
your high perf tires probably have a higher rolling resistance than the OEM tires.

combined I can see those two things making 3mpg differnce

 

[felixthecat]

friction & weight. friction is traction & rotational weight.

 

[Tigeo]

So today I was a bit more scientific and started my mileage tracking again on my 100% highway commute (45 miles). I actually think the mileage is about the same when compared to older data collected in the exact same manner. The issue I am seeing is that the dash computer that used to typically show ~400 miles to empty on a tank has now has dipped as low as 320 on the last 1/2 dozen tanks. Could be the holidays and being off work so mainly city driving...or maybe I am just paranoid! You know though that when you drive your car as much as I do (30K/year) you really notice things when they are different and the mileage to me has been really off (in the 20s vs. 30s). Will collect data for a week and see what the real answer is.

 

[felixthecat]

We shall see...

 

[Tigeo]

The issue seems to be the distance to empty figure. The MPGs seem to be within the normal range I am used to seeing on the highway (resetting when I get on in the morning, use cruise the whole way, drive speed limit) – 33-35 mpg with average speeds in the low-to-mid 60s and temps in the 30s-40s. What is throwing me off is the distance to empty figure. In the past, with my normal commuting, when I fill up this will be in the 380-400 range when I reset it. Now I am seeing low 300s and it creeps up VERY slowly vs. the faster increase I was seeing before. Example: Fill up, reset computer, see DTE ~380, do 5-10 miles of city-type driving then 3 days of nearly 100% highway commuting. DTE quickly increases to 450 or more once the highway driving sets in. Now that is gone. Could a computer reset have caused this? I recently had it in for service for a faulty component and they did some engine diagnostics. Last fill up I calc'd the mpg and got 31.5 for mixed driving which is v. normal so it looks like the mileage isn't as far off as I thought.

 

[JBZZX3]

I've noticed this with a lot of cars in the past. I have compensated in a variety of ways. Sometimes I increased air pressure 1 or 2 lbs. or started using premium. Sometimes the new tires require a little different air pressure then stock ones did. Winter hurts a lot too... if you have aluminum rims they might be losing a few lbs... even if the tire pressure sensor doesn't alert you... 2-3 lbs might be too much for MPG. My GF's son was telling me up and down about how his Nitrogen air tires and TPMS would tell him if he was low and that he was fine on his Chevy Impala. So we took a tire gauge and checked. His tires were down 4lbs. He has since switched to using dedicated winter tires with the steel police rims and he sees no variance in tire pressure this winter. I did the same thing with the Caprice I had many years ago (when I was still driving it in the winter) and the air holds in the steel rims so much better. I did the same with my new 14 Focus HB by using 1998 Ford Taurus 15 inch steel rims and my tire pressures do not fluctuate more then 1 lb. The 15 inch rims ride so much better in pot hole season too!

 

[pintoman]

Just food for thought.....on the '13 Titanium with the 18's, they have to run at 39 psi for the low resistance tire that they are.....maybe you can check to see if you can raise the tire pressure higher without damaging the tire...and ride....again, food for thought!

 

[dfens42]

The issue seems to be the distance to empty figure. The MPGs seem to be within the normal range I am used to seeing on the highway (resetting when I get on in the morning, use cruise the whole way, drive speed limit) – 33-35 mpg with average speeds in the low-to-mid 60s and temps in the 30s-40s. What is throwing me off is the distance to empty figure. In the past, with my normal commuting, when I fill up this will be in the 380-400 range when I reset it. Now I am seeing low 300s and it creeps up VERY slowly vs. the faster increase I was seeing before. Example: Fill up, reset computer, see DTE ~380, do 5-10 miles of city-type driving then 3 days of nearly 100% highway commuting. DTE quickly increases to 450 or more once the highway driving sets in. Now that is gone. Could a computer reset have caused this? I recently had it in for service for a faulty component and they did some engine diagnostics. Last fill up I calc'd the mpg and got 31.5 for mixed driving which is v. normal so it looks like the mileage isn't as far off as I thought.

Winter blend gas can do it too, or 15% ethanol vs 10% fuel when you fill up.

Winter blend gas can be 1-2 mpg worse, combine that with being slightly down on PSI and that would account for the difference.

Have you used any fuel additive lately?

 

[Tigeo]

^^^I believe you are correct; currently seeing 15% ethanol vs. what I seem to remember a few months ago saying 10%. PSI is the same; I have always run 35 psi in my tires per the recommendation from Ford. I had a bad experience running too much air...it wore out the center tread of the tires I was running on a former vehicle plus it will make it ride rougher. No fuel additives to speak out since owning - what do you recommend?

 

[dfens42]

Techron is always the one I hear recommended.