7th Gen ('06-'07): Wheel Swap = mpg drop?
#1
03-05-2012, 07:33 AM
Wheel Swap = mpg drop?
I swapped out the stock 16" wheels for a set of SS 18" wheels this weekend. I drove to work this morning and couldn't believe the drop in MPG! I went from 30.5 mpg to 24.5 mpg! Did I really lose 6 mpg by swapping into the bigger wheels? 
Holy crap!
Is this normal?
Holy crap! Is this normal?
#2
03-05-2012, 07:48 AM
Wow, that's quite a reduction in mpg, but I suppose it is possible. The larger wheels probably weigh more and it also takes more effort to get them rolling. The engine will also operate in a different rpm range to sustain the same mph. I went from a 16" to 17" wheel but my mileage increased by about 2mpg because I shaved almost 40 lbs of unsprung weight off the vehicle with my wheel choice.
#3
03-05-2012, 07:58 AM
Join Date: Sep 2008
Location: Southeast PA
Posts: 25,136
Is this from the car's computer instant readout? Or did you calculate this yourself?
Also what size tires are you running on the 18s?
Also what size tires are you running on the 18s?
#5
03-05-2012, 06:36 PM
Join Date: Sep 2008
Location: Southeast PA
Posts: 25,136
My assumption is that the computer is completely wrong because you are running the wrong size tire.
Compared to stock you are running a 5% different size, the speedo is completely wrong, so when it does revolution math you are going faster than you really are. This is probably throwing the computer way off.
Do the real MPG calculation by hand, you should see a much smaller difference.`
Compared to stock you are running a 5% different size, the speedo is completely wrong, so when it does revolution math you are going faster than you really are. This is probably throwing the computer way off.
Do the real MPG calculation by hand, you should see a much smaller difference.`
#6
03-05-2012, 10:35 PM
go here and punch in your tire sizes: Tire size calculator
more than likely you'll lose mpg anyways because of the bigger and heavier wheels. basically your car is working harder to stay the same speed.
more than likely you'll lose mpg anyways because of the bigger and heavier wheels. basically your car is working harder to stay the same speed.
#7
03-06-2012, 09:14 PM
Join Date: Apr 2010
Location: Mentor, Ohio
Posts: 12,156
I would also be concerned if the car is mis-calculating MPG, is it mis-displaying your speed. I know when people get their PCMs tuned, adjusting for change in wheel size is one of the options.
#9
03-07-2012, 10:41 AM
wow i guess going to big 20s and heavier rim must be making a huge difference on mine also....i m reading my computer and says 27.8 hwm and really low on back roads like 19.9 ???does this seem right and can snap on dionoastics changed wheel size in computer ???how do i go about changing the wheel size is what im tryn to say ??
