All,

First, please use careful judgment about going above the MAX psi rating on your tires. It can get dangerous at high speed. I run my tires a little below their MAX rating, but above the PSI suggested by Toyota.

Second, I have seen a lot of talk about "break-in" improving MPG. The main factor in improving MPG is tread wear. My data does NOT indicate any "break-in" effect.

I ran my Michelin MXV4+ tires for 55k miles (they could have gone 60k, but winter was coming) in two years. They got 0.4 MPG (0.85%) better gas mileage in the second year, but most of this is attributable to the 0.64% increase in revs/mile due to reduced tire circumference and is not real.

There is a secondary effect that does improve MPG slightly with wear, a thinner tread generates a little less heat when flexing. This is too small an effect for me to measure due to other uncontrolled variables. The attached spreadsheet shows my MPG experience with the original Goodyear Integrity and my Michelin MXV4+ tires over almost 100k miles.

I'll report in a few months on the initial MPG performance of my new Nokian WR tires. My initial impression is good (seems to match the MXV4+, but too soon to tell) on MPG, great dry weather handling and traction, and no significant road noise noticed. We'll see about wet/snow/ice traction soon , but these tires should be significantly better that either of my first two tires in bad weather.

JeffD

Attached Files

PriusGasMileage.xls (72.0 KB, 10 views)

One thing I don't see anyone mention is the change in tire pressure when they heat up while driving. You will get at least a 2psi rise in pressure when the tires heat up to running temps.

2008 Prius Barcelona Red
All Options but leather interior
Getting 50mpg average

GoneGreen, I will summarize some old discussions on this topic from other Prius group.

Comparing the initial (cold) psi with the hot psi after many miles driving can be very instructive. If the hot psi increases by more than 10% it indicates that the tires are heating up too much. One will see less heating when starting out at a higher initial pressure.

If one still gets a 10% or greater "hot tire increase" even when initially inflating to the maximum cold sidewall pressure, this indicates that your tires are not adequate for the car, payload, and/or driving conditions.

So the cold tire pressure is what we use to set up the system, and the hot pressure can tell us if it is working appropriately. A tire pressure guage is a very handy little tool for fuel economy, tire lifespan, and driving safety.

A very few Prius drivers also look at their tires with non-contact infrared thermometers. Not surprisingly, they report high temperatures of sidewalls and 'edge tread' if the tires start out with too little air in them.

DAS

Thanks!!

2008 Prius Barcelona Red
All Options but leather interior
Getting 50mpg average

What sort of driving do you do? I keep the tires on our Prius at 42.5 (front) and 40.5 (rear), but we're only getting 48-50MPG with the colder weather recently. My wife does most of the driving - and most of it is on a 65-70 mile round-trip commute each day. Her speed is between 45-55 depending on traffic. I'm just curious to see how you're getting well over 60MPG - I'm jealous!

I switched to my Nokian WRs two months ago. I noticed little or no change in mileage, though it's dropping rapidly now due to the colder weather. I ran the stock Goodyear Integrities at 40PSI front and 38PSI rear (car came with 42 PSI all around - so much for dealer prep). I run the Nokians at the same pressure (40/38). The Nokians are rated up to around 50 PSI cold.

The cold rating on the sidewall is designed to allow for the increase in pressure as the tire heats up. It is usually (but not always - read it carefully) intended as a load carrying warning (XXXX lbs at XX PSI max). They give the maximum. If you exceed the load and/or the pressure you will be in danger of a blowout. Particularly if you hit an abrupt break in the pavement.

YMMV

I also can't yet comment on the Nokians in snow on Pearl. I can say they were fantastic on the anti-Prius (2001 Nissan Pathfinder) and on a 2004 Mazda RX-8. With any luck, I'll be quiet until after Christmas.

Pearl is a
2007 Driftwood Pearl Prius
Package "B" (everything but leather, nav, and rear camera)

I own a 2007 prius. I am looking for information if money was not an issue short term for the best combination of wheels, tires, and tire pressure. I go up and down a paved mountain every day and would like to squeeze out enough mpg savings to be able to hit 50 and above. I also do some higway driving every week, about 7 hours roundtrip. I have read what studies are that are out there and have not seen anything conclusive, it does sound like the Michelins are one of the best tires. I have heard that the tire can only be so light before its sidewall integrity is compromised. Are there any low drag light weight weels on the market that make sense? I have to run studded snows for 5 months every year so investment in a spare set of rims/wheels is an option.

Hi,

Welcome to the CLUB!

I would start with the Consumer Reports list of low rolling resistance tires:


Then realize that your tire pressure can range from what is on the door jam and the maximum side wall pressure. The higher the pressure, the lower the rolling resistance:


So you'd already seen my charts?
These are different requirements. You'll need to prioritize them.

GOOD LUCK!
Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

Bob,
Thanks for the chart. I am working with my local tire dealer as well to see what kind of information he is getting on the marketing end of industry studies. I am also interested to know if anyone done any studies looking at rim/wheel size and weight change for the Prius. I am looking at things scientifically so I want to gather as much info as possible and then make incrimental changes so I can monitor the improvements or lack there of on my end. I will keep you posted as I gather other information. William

You might consider joining the Yahoo Group, "Prius Technical Stuff" where I've been posting some technical analysis of tire rolling resistance. I've also been following the California energy board initiative on measuring tire rolling resistance.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.