TRD Sport Wheels on SR5

I have a 24 SR5.
mpg lists as 21/26
It has 245/70 17 tires on it.
I am about to put wheels and tires from a TRD Sport on it (265/65 18)
I’m wondering if I should expect TRD Sport type MPG (20/24)
Or are there other differences between the Sport and SR 5 that account for the MPG difference. Thanks for any help.
j-

 

The loss of MPG is due to the larger wheel and Tire. You're adding an inch to your diameter but I doubt your MPG loss will be noticeable.

 

Don't forget that putting bigger tires on will make your speedo inaccurate. Make sure you account for this when calculating your new MPG.

 

Those size wheels and tires are tuned to the sport suspension too. The sr5 has different shocks. Just a thought it could change the ride quality as well

 

It’s interesting, as it is now with the stock wheels and tires, the actual speed is 2 mph slower than indicated on the speedometer. So my thought is that a slightly larger wheel could actually make the speedometer more accurate.

 

Putting 33's on my 2nd gen made the speedo accurate...

I think they put Mickey Mouse tires on all trims to improve MPG ratings but they know you're going to change them so they at least put the speedo where it will be right when you get the right tires for the truck.