Help...new tires = lower MPG and speedo off?

I replaced my worn out at 35,000 miles OEM Integrity's last month and put on the slightly wider Goodyear Assurance Fuel Max. My mileage has also gone down some, but I knew that would happen from reading here on PC. Still playing with tire pressure as the Max can go up to 51 ! psi.
The grip is so much better and the improvement in ride is just great!

 

Hi Hbarron. There's really two issues here.

One is the break-in period for new tyres. I've read lots of information that suggests that new tyre don't roll quite as well as more well worn ones. So fortunately you should find that the milage improves over time. I've read that some users here have had to put in quite a few thousdand miles on their new tyres before they're really broken in.

The second issue is the speed change. Obviously this is due to a slightly larger rollout distance, but whether this is because the new Fuel max's are just intrinsically a bit larger or whether it's the deeper initial tread of the new tyre that's behind this I'm not sure. In either case it's important to realize that this means that at least part (perhaps even all) of your MPG hit is only apparent. Why so? Because it means that your Prius's computer will think that you've travelled less km than you actually have. This of course means that the Prius would compute a lower MPG than before even if in reality there was no difference.

 

You were running on bald tires which gives the best possible mpg. You can expect the mpg to improve with age. Tiretrac did a test of tires on gen II prirus and the Goodyear Assurance Fuel Max did not get good marks for mpg.

 

As I recall the stock Integrity's rolling resistance is better than the Goodyear Fuel-Max. Although you should have a better and quieter ride with the Fuel-Max.

 

I think the rolling resistance of the Fuel Max is slightly better than the OEM Integrities, and eventually they will get you better gas mileage than the Integrities.

In the recent tests of (mostly) fuel efficient tires by TireRack.com, the Fuel Max got slightly better gas mileage than the Integrities on the Gen II Prius test car. See this thread:

http://priuschat.com/forums/gen-ii-...ity-against-energy-saver-ecopia-fuel-max.html

And the Fuel Max should outperform the Integrities in other areas as well -- such as wet traction (see TireRack.com article where the Fuel Max dramatically outperforms the Integrities) and tread life (compare tread life warranties) --- with the possible exception of snow traction (with respect to which, Goodyear itself rates both tires equally).

If I were you I wouldn't worry about your Fuel Maxes. From what is known so far, they should prove to be a better tire than the Integrities.

 

I just put on a set of FuelMax (OE size), and the indicated mpg has initially increased. I have seen other posts of this same thing happening. I think this is due to them being .1" larger in diameter than the OE Intregrities, not to mention they were almost down to the wear bars after 24K. So I went from almost "bald" to .1" over. On a mile post speed check zone the speedo still seems to be close. (Sorry, I'm the only person without a GPS.) Correct me if I'm wrong on the mpg.
The FuelMax are rated better in most areas than the Intregrities, plus a 65K warranty, up from 50K. Time will tell how they will do in the long run. They are quieter and a little better in cross-winds.

 

I was on a road trip and picked up a screw. replaced all 4 integerites with kelly springfield ultra gt tires and within a few tanks refills went fron 42-43mpg. tire shop was in the middle of nevada. so didn't have muck of a choice. but put the only size tires they had. very happy sofar as the car has much more grip. tires were very inexpensive, run them at 40psi just like before but picked up a few mpg. anyone else try these tires?. was planning on getting tires at costco. but that didn't work out these tires cost $52.99 and I'm getting better milage.big surprise. car has 28K miles and was getting 42.4mpg now getting almost 44mpg driving the same.

 

I bought the Fuel Max in June so we’d have good tires for our 4 week road trip. After putting 7,000 miles on the tires my mpg is only in the high 49’s and low 50’s compared to the mid 50 range with the old tires. Yeah, the ride is better but the mpg really sucks and I’m even more cautious on how I drive.