Tire Pressures

There are many threads, each with many posts, on this subject so be prepared to get lots of advice, some of it contradictory. Your first statement is that you want to inflate for best fuel economy. In general, the higher the pressure, the greater the fuel mileage. However, despite the claims by some zealots on this site, there is a safety risk in inflating beyond the maximum pressure shown on the tire sidewalls. So, to balance maximizing fuel economy and paying minimum attention to safety, you could inflate to the maximum sidewall pressure. However, this could result in less than optimum handling characteristics and ride comfort. Some argue that running consistently at maximum sidewall pressure also can cause uneven wear, with the center of the tread wearing more than the outer edges.
On the other hand, under-inflating adversely affects fuel economy, safety and wear. In this case, the outer edges generally wear faster than the center. Toyota recommends 35 psi in the front tires, 33 in the rear. A conservative approach would be to increase the pressures, keeping the 2 psi difference between front and rear tires, by a couple psi until you notice degradation in handling or ride comfort (the latter is certainly subjective) after driving for a few hundred miles at each set of pressures. A general rule would be to use the highest pressure (within the limits of the maximum sidewall pressure) that gives you a comfortable ride and good handling.
For what it's worth, after driving for around 11,000 miles since getting my Prius, I've settled on 38 psi in the front and 36 in the rear -- all measured when the tires are cool after sitting overnight. Many on this site prefer a couple psi higher but I feel that this results in a harsh ride and less road contact feel.

 

What he wrote :_> I settled on 42/40 PSI front/rear. Remember that tire pressures should be checked "cold", which for tires means "driven no more than one mile in the previous hour".

Modern tires will not change their wear patterns as a function of increased inflation (staying within the rated limit given on the side of the tire, of course) because the steel radial belts constrain the shape of the tire very strongly. That's also why it can be so difficult to judge the inflation of a radial tire by eye.

 

I've been told that bursting pressure is 4 to 5 times that of the max. on the sidewall. Of course I wouldn't recommend anything close to that.

PA P "zealot"

 

I've been running my psi at 44 front 42 back for over 4 years now ,and the tires are wearing even. Even with the heat we have here in Florida the tires are performing just fine.

 

I've been running over 55psi for 10s of thousands of miles and over 60psi since about winter? Tread wear is very even but does have a tiny bit of extra tread in the center, the opposite of what one would predict using such high pressures.

 

This begs the question-- Who is regularly running the highest psi on Integreties? Please reply if you are running higher than F8L's 60 psi.

Yes, we know many of you have concerns about this and F8L has heard too many times that his screen name is fitting, so those responses do not need to be added here.

PA P

 

sounds like a good poll question

 

Right. Now if I only knew how to set up a poll or how to search for a poll to see if a similar one already exists. It seems there should be a forum for polls....

PA P

 

DiamondLarry has me beat by a long shot.

 

You should also ask if they have a touring (16" wheels).

 

Raising pressures much above the recommended is bound to sacrifice handling and ride. These tires, in my view, are too narrow for the Prius, and are used by Toyota primarily for low rolling resistance and max. gas mileage. I would like to see Toyota offer a wider tire option in 15" wheels for those who value a combination of handling and gas mileage. Currently, a Goodyear dealer will not swap or sell a wider tire for the 15" Prius. I wanted to do a new tire swap and was told no because of the Toyota restriction. Toyota should lift this restriction which is unwarranted. Cornering and stability will be much better with a wider tire. I know from previous experience with an SUV.

 

In the current market, the Touring model is very difficult to get.

 

Wife and I both drive Tourings and have found 40 front/38 rear to be a good compromise between great MPG and ride comfort. Wife averages a little over 47 MPG and my current tank is averaging just over 53 MPG.

 

From this report (PDF document) Goodyear Integrity P185/70/R14 rolling resistance 0.0097. Minimum rolling resistance reported 0.0062. Maximum rolling resistance reported 0.0133. Mean rolling resistance reported 0.0102. Median rolling resistance reported 0.0104. I don't think the Integrity can be regarded as significantly "low rolling resistance". In fact, Toyota declaims that the tires are low rolling resistance although I can't find a cite for that assertion at the moment.

How do you know that the restriction is unwarranted? Your experience with an SUV is hardly applicable to a car as different in all respects as a Prius.

 

the old Gilligan's Island conundrum.

 

Try here:

http://priuschat.com/forums/fuel-economy/32512-tire-pressure-poll-where-yours.html

or here:

http://priuschat.com/forums/fuel-economy/23110-tire-pressure-poll.html

 

Thanks Danny.

PA P

 

What do you think is the reason for the big difference in mpg?