So I recently upgraded from the stock 15x6 +52.5 wheels wrapped with 195/60R15 Hankook Optimos (OE tires) to 18x8 +35 Team Dynamics Pro Race 1.2 wrapped with 215/35R18 Nitto NeoGens. I've been experiencing a severe decrease in fuel economy lately and the only explanation I have left is the increased unsprung weight from the new wheel and tire combination.
I currently attend college at Auburn University in Auburn, Alabama and I am originally from Maryland. One way from my apartment in Alabama to my home in Maryland is 798 miles and a round trip of 1,596 miles.
I made the trip home in August during the break between summer classes and fall classes and I averaged about 42 MPG on the stock wheels and tires. I then made the trip again a few weeks ago for Thanksgiving break on the new wheels and tires and could barely muster 31 MPG.
The stock tires were inflated to Ford factory specifications of 32 PSI (I believe that is the spec) and the new tires have been constantly inflated since installation to 46 PSI (per recommendation from the seller, users on this forum, and my engineering/car friends). I doubt the tire pressure has any play in this situation, as all of the users on hypermiling forums recommend maximum sidewall pressure for best fuel economy results.
I had recently been getting pretty terrible fuel economy while at college. Primarily, because it is a college town with a large population and a lot of stop and go driving. The last tank I had before I left Auburn garnered 16 MPG! I have never had a tank that horrible since I've lived here. The lackluster numbers on the ride home confirmed that I have a problem somewhere.
I initially thought it was an issue with my tuner, that I had input the wrong tire revolutions per mile value or that I should have left it alone to begin with. The stock tires have a manufacturer reported revolutions per mile value of 851; but if using a tire size calculator, the value is 833. The new tires make 843 revolutions per mile (I went with the value from a tire size calculator, rather than looking for manufacturer values). The tuner only uses increments of 5, so I had to choose between 840 or 845. The first time I changed it, I used the higher value of 845, then I used the lower value the second time. There was an increase in fuel economy, but not by much and it wasn't the same type of interstate driving as before. The only thing I never did was calculate fuel usage with the stock tire value because I changed it as soon as I got the new tires mounted.
The only explanation I have left is the change in unsprung weight from the stock wheels and tires to the new ones. The stock wheels and tires weigh 33.2 lbs per corner, with a total of 132.8 lbs. The new wheels and tires weigh 40.8 lbs per corner with a total of 163.2 lbs. That is an increase of 7.6 lbs per corner for a total of 30.4 lbs for the whole car. It also just occurred to me that the reduced sidewall may have an effect, but I'm not sure how much.
Is 30.4 lbs of weight really reducing my fuel economy by 26%? I'd kind of expect it if I had a large sedan and put some 26" wheels on it, but not under these circumstances.
Thoughts and opinions are appreciated on this matter. I hand calculate every tank and I literally have every receipt from every tank of gas that I use to report my fuel consumption on a graphing tool on a hypermiling website, so this is really irritating to me right now.
TL;DR Increased unsprung weight by 30.4 lbs, fuel economy decreased 26%
I currently attend college at Auburn University in Auburn, Alabama and I am originally from Maryland. One way from my apartment in Alabama to my home in Maryland is 798 miles and a round trip of 1,596 miles.
I made the trip home in August during the break between summer classes and fall classes and I averaged about 42 MPG on the stock wheels and tires. I then made the trip again a few weeks ago for Thanksgiving break on the new wheels and tires and could barely muster 31 MPG.
The stock tires were inflated to Ford factory specifications of 32 PSI (I believe that is the spec) and the new tires have been constantly inflated since installation to 46 PSI (per recommendation from the seller, users on this forum, and my engineering/car friends). I doubt the tire pressure has any play in this situation, as all of the users on hypermiling forums recommend maximum sidewall pressure for best fuel economy results.
I had recently been getting pretty terrible fuel economy while at college. Primarily, because it is a college town with a large population and a lot of stop and go driving. The last tank I had before I left Auburn garnered 16 MPG! I have never had a tank that horrible since I've lived here. The lackluster numbers on the ride home confirmed that I have a problem somewhere.
I initially thought it was an issue with my tuner, that I had input the wrong tire revolutions per mile value or that I should have left it alone to begin with. The stock tires have a manufacturer reported revolutions per mile value of 851; but if using a tire size calculator, the value is 833. The new tires make 843 revolutions per mile (I went with the value from a tire size calculator, rather than looking for manufacturer values). The tuner only uses increments of 5, so I had to choose between 840 or 845. The first time I changed it, I used the higher value of 845, then I used the lower value the second time. There was an increase in fuel economy, but not by much and it wasn't the same type of interstate driving as before. The only thing I never did was calculate fuel usage with the stock tire value because I changed it as soon as I got the new tires mounted.
The only explanation I have left is the change in unsprung weight from the stock wheels and tires to the new ones. The stock wheels and tires weigh 33.2 lbs per corner, with a total of 132.8 lbs. The new wheels and tires weigh 40.8 lbs per corner with a total of 163.2 lbs. That is an increase of 7.6 lbs per corner for a total of 30.4 lbs for the whole car. It also just occurred to me that the reduced sidewall may have an effect, but I'm not sure how much.
Is 30.4 lbs of weight really reducing my fuel economy by 26%? I'd kind of expect it if I had a large sedan and put some 26" wheels on it, but not under these circumstances.
Thoughts and opinions are appreciated on this matter. I hand calculate every tank and I literally have every receipt from every tank of gas that I use to report my fuel consumption on a graphing tool on a hypermiling website, so this is really irritating to me right now.
TL;DR Increased unsprung weight by 30.4 lbs, fuel economy decreased 26%