Does running higher (40+ psi) really help MPG that much. Testing this weekend

I had a 2010 Honda Insight and bumped my tyre pressure to 40 psi. and noticed that my mileage increased quite a bit. I will more than likely do the same in my 2010 Prius II after the first tank of gas is done. BTW I just got my Prius II today 01/10/2011. Newbie to Prius but not a hybrid newbie.

 

Hi k...d...

Well, you need to take a class in design of experiments. I that , you need to do the exact same trip with the test variable changed, for the results to be meaningful.

So, repeat this exercise, only with the south ward travel using the high PSI setting. And the northward trip with the low PSI.

In this specific test, one possible comfounding variable might be wind direction. Traveling north, you might have a head, or front quartering wind (the worse for air drag). Which would then result in the worse mileage you saw. As the air speed could easily be 70 mph on the northward trip, and 50 mph on the southward trip. Espcially in a coastal enviorment.

An early car reviewer did the same thing, either by mistake or design. He favored the VW Diesel, so he drove that from Detroit to Washington DC, in the late winter/early spring. And then drove the Prius from DC to Washinton. Not supprisingly, the DC to Washinton trip mileage was worse than the other way around. As that time of year, there are strong winds out of the NW, W, SW along that route.

Mercedes did the best testing. They drove a CDi along with a Lexus RX Hybrid along the same route at the same time. The CDi won by a few MPG fuel volume, but if judged on energy used the RX won.

 

On my daily commute which is mostly in town running 40 psi all the way around makes close to a 3% improvement. I don't do enough hiway driving these days to post an observation.
Good Luck

 

It helps. My 06 averaged 50mpgs with 42/40. My 010 is averaging 45mgs with the same pressure but it's Winter and the car only has 1600 miles on it. We shall see when the warmer weather comes . FishHawk

 

Put them at the pressure for maximum load listed on the sidewall (44psi for your tires) and run them there for a couple of weeks. If your not happy with that lower them a little.

I use the same pressure in all 4 tires because the 2 pound difference front/rear doesn't seem to matter, of course it doesn't hurt either. I suspect that the 2 pound front/rear difference is based on an empty car and possibly an empty gas tank because that's the way curb weight is calculated, most of us carry some stuff in the back.