I had an old set of Cooper Discoverer ATs on my 97 F-150. They were worn to about 4/32" and I replaced them with a set of Cooper Discoverer ATRs. The new ATRs had about 100 miles on them when I took a trip. This is the same trip I took a month ago with the old ATs. I filled up at the same gas stations, traveled the same direction, and kept everything else the same except for the tires. With the old ATs I got 18.4 mpg and with the new ATRs I got 16.7 mpg. Is this drop in gas mileage because the tires aren't broken in yet or is this something I'll have to live with? The old set and the new set are the same size tires.

 

If your new tires have a more agressive tread this will happen. Some tires have a better rolling resistance than others.

 

Are they the same size? New tire could be heavier, as in an LT w/ more plys.

 

The new tires are the same size as the old ones 235/70-16 (I know they're small but I was getting great gas mileage with the old ones and didn't want to screw this up with bigger tires). The Cooper ATRs are suppose to be Coopers newer better version of their Discoverer ATs. The ATRs do have a different tread design so this may be the cause of the lost gas mileage.

 

time of year - winter gas?

 

Wind speed/direction, temperature...

 

Agreed, outside temperature makes all the difference in the world. Plus if it was more windy thats a huge factor as well. For example, I do a 2 hour drive every now and then and it takes more time and gas to get there because Im driving straight into the wind. And since its relatively flat and open theres a bit of rolling wind. On the way back the I have a nice tailwind and I manage to make it back 10-15 minutes faster and get better mpg.

By theory you should get better milage because you travel a farther distance per tire revolution, but if the tread design is a mudd clogger you should expect bad mpg. Winter gas sucks too. All bad things!

 

also check tire pressure & alignment
those two factors can have a huge toll on gas mileage, especially tire pressure

 

A new tire will cause a reduction in mileage due to the increases in rolling resistance of full tread depth vs that of worn tires.

Check out this info. http://www.everytime.cummins.com/eve...Whitepaper.pdf

Granted it's directed to commerical vehicles, but what works there can work for us too....