barspen Posted January 22, 2013 Report Share Posted January 22, 2013 I just replaced my OEM Goodyear Eagle F1's with a set of Continental ExtremeContact DW on my 2011 GT500. So far I like the new feel...much more grip and they seem to take corners better. But I noticed my MPG is lower by 10-20% based on built-in computer. With the F1's, I could do a steady cruise on the expressway around 70-75MPH and get close 23-24MPG. I'm lucky to hit 21MPG after the tire swap. The 10-20% hit seems to hold up in city driving and overall mileage too. I have the new tires set at about 36PSI (tire shop set them). Any idea why I’m getting less MPG or suggestions to get it boosted back up? My GT500 is a daily driver, so I'd like to get the best MPG I can. Link to comment Share on other sites More sharing options...
Bill Hamilton Posted January 22, 2013 Report Share Posted January 22, 2013 I just replaced my OEM Goodyear Eagle F1's with a set of Continental ExtremeContact DW on my 2011 GT500. So far I like the new feel...much more grip and they seem to take corners better. But I noticed my MPG is lower by 10-20% based on built-in computer. With the F1's, I could do a steady cruise on the expressway around 70-75MPH and get close 23-24MPG. I'm lucky to hit 21MPG after the tire swap. The 10-20% hit seems to hold up in city driving and overall mileage too. I have the new tires set at about 36PSI (tire shop set them). Any idea why I’m getting less MPG or suggestions to get it boosted back up? My GT500 is a daily driver, so I'd like to get the best MPG I can. Could be the colder weather taking a hit on your mpg. Cooler air will make your car run richer (and more power). I did the same tire swap a year ago in the stock sizes and my mpg has stayed the same. I feel much better driving in wet weather and also feel they grip in the dry as well as my stock F1 did. Mine's a daily driver also and the wet handling was most important to me. Link to comment Share on other sites More sharing options...
barspen Posted January 24, 2013 Author Report Share Posted January 24, 2013 Thanks Bill. Temps in AZ have been in the 70's and 80's this week and I still seems to get the lower MPG numbers, but I'll keep checking. Link to comment Share on other sites More sharing options...
Secondo Posted January 24, 2013 Report Share Posted January 24, 2013 Gasoline formulas are different this time of year, could that be it? What tire pressure were you keeping the F1's? Link to comment Share on other sites More sharing options...
barspen Posted January 24, 2013 Author Report Share Posted January 24, 2013 Didn't think about the Gas formula change...miight be a factor. I kept the F1's at 35PSI. Link to comment Share on other sites More sharing options...
Bill Hamilton Posted February 1, 2013 Report Share Posted February 1, 2013 Didn't think about the Gas formula change...miight be a factor. I kept the F1's at 35PSI. Make sure you don't have a brake dragging or something. Keep tracking your mileage. I've tracked my mileage here over the last year and amazed at what I'm getting. This is a record of my last 70 plus fillups: https://www.fuelly.c...tang?fu=2936123 Link to comment Share on other sites More sharing options...
Nitro Posted February 16, 2013 Report Share Posted February 16, 2013 Just curious, is the circumference of the new tire the same as the circumference of the old tire? If it's not that could account for the difference. Link to comment Share on other sites More sharing options...
ilmor Posted February 16, 2013 Report Share Posted February 16, 2013 Rolling resistance does vary with tire compounds and tread designs. Link to comment Share on other sites More sharing options...
barspen Posted February 16, 2013 Author Report Share Posted February 16, 2013 Nitro, Good question. Based on info from Tirerack.com and Goodyear, the Conti DW rear tires revolve 775 per mile. The Goodyear F1 rears revolve 777 times per mile. A slight difference, but seems hard to believe that 2 revolutions/mile would impact by 2MPG...Based on the rev/mile difference on the two tires, I think the MPG would be in my favor (unless I'm doing my math wrong). Ilmor, I agree that the tire compound could impact the rolling resistance. But I would think that impact would be very small. Tirerack.com has a small article on this...in their example, even a 20% increase in rolling resistance has about a 3% impact on MPG during highway driving. http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=29 Still havent looked into a break possibly dragging as Bill mentioned. I'm due for an oil change pretty soon and will have the dealership check that out. Thanks for all the ideas and recommendations! Link to comment Share on other sites More sharing options...
Nitro Posted February 17, 2013 Report Share Posted February 17, 2013 Clearly the tires are not the same circumferance and therefor you will need to reprogram the computer with the right revs for the car to give you accurate information. I suspect that this is your problem. If you have a Ford ProCal tool you can do it yourself, otherwise your local dealer can do it for you. Phil (2010KonaBlueGT) here on this site might have some more information about this to help you. Link to comment Share on other sites More sharing options...
barspen Posted February 19, 2013 Author Report Share Posted February 19, 2013 Thanks again for the advice Nitro. I'll be headed to the dealership soon and will ask them to reprogram the computer for the correct revs/mile Link to comment Share on other sites More sharing options...
WJinLV Posted February 19, 2013 Report Share Posted February 19, 2013 Instead of correcting computer, how about you dont pay attention to the MPG youre getting and just see if you need to fill-up more often? Link to comment Share on other sites More sharing options...
ingram4868 Posted February 19, 2013 Report Share Posted February 19, 2013 Ask the dealer how much they charge to make the computer change. It may not be cost effective and there is no assurance it will correct your concern. Link to comment Share on other sites More sharing options...
AndyGJ Posted February 19, 2013 Report Share Posted February 19, 2013 Nitro, Good question. Based on info from Tirerack.com and Goodyear, the Conti DW rear tires revolve 775 per mile. The Goodyear F1 rears revolve 777 times per mile. A slight difference, but seems hard to believe that 2 revolutions/mile would impact by 2MPG...Based on the rev/mile difference on the two tires, I think the MPG would be in my favor (unless I'm doing my math wrong). Be careful of simply accepting the Tire Rotation values that are posted on Tirerack and manufactures sites as well. When I replaced my stock tires in December (BF Goodrich g-Force 235/50/R18s) for new BF Goodrich g-Force Comp-2 (255/45/R18), Tirerack called for a value of 746 I believe and BF Goodrich called for 766 (just from memory). In using both of these values, my speedometer was WAY OFF the mark. I have a local school zone that has active speed radar readings to get folks to slow down in the school zone, so I was able to adjust the computer with my SCT-X3 tuner, drive by both signs with radar readout at either end to check the actual speed by sustaining 40 mph, and one time I hit 50 once fully dialed in to double check 4th and 5th gears. The end value that I used to nail it 100% correct was 795....way off from what both websites stated. I even called Tirerack to ask which one was better to use the first time I programmed the change and they said to use the manufacturer's website over theirs if the information is posted. I have since double checked this with several different radar locations with similar signs to cross check, and all is 100% accurate now. Another way to calibrate is to use a GPS watch set in MPH mode...Garmin makes several, so if you know someone who has one of these, they work like a charm as well. I've had to use mine to calibrate my Mastercraft boat speedometer readings since they have an adjustment switch built directly into the dash for both speedos. Just make sure this is accurate...mine was 7 mph off when first set at the BFG value...a huge difference! Andy. Link to comment Share on other sites More sharing options...
Nitro Posted February 19, 2013 Report Share Posted February 19, 2013 The easiest way to do this is to measure the circumference of the tire and do the conversion. Works every time. Link to comment Share on other sites More sharing options...
barspen Posted February 19, 2013 Author Report Share Posted February 19, 2013 Thanks Andy. Sounds like I may need to play with the rotation/mile number a bit and cross check with a with a speed radar location and/or GPS. Looks like I might also want to invest in a tuner. I'm assuming the dealership will be 'OK' with me using a tuner assuming I only play with the tire rotation number? I've stayed away from using a tuner since I have an extended warrantee on the car, I have plenty of horsepower for a daily driver and dont plan on doing any performance mods. Link to comment Share on other sites More sharing options...
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