Tire PSI and Mileage

[UseTheEarth]

Dealer or Factory put 28-29 PSI
Sticker on Driver Side door opening says 33 PSI
Tires say 44 PSI MAX

I just put 37 PSI in. Is that dangerous?
If not let's see if I improve from 41.3 MPG!

[Zangetsu57]

Originally Posted by UseTheEarth

Dealer or Factory put 28-29 PSI
Sticker on Driver Side door opening says 33 PSI
Tires say 44 PSI MAX

I just put 37 PSI in. Is that dangerous?
If not let's see if I improve from 41.3 MPG!

You will be fine . I've had my I2 since May of 2009. I've gradually increased the tire pressure from factory to 36, 38, 40, and 41 PSI. I find that the ride and mileage is quite good at 39-40 PSI, so I keep them at that pressure.

The max sidewall is 44 PSI. This is the maximum pressure at which the factory recommends tires before bulging begins to occur. It is NOT the max pressure before explosion. Anyway, you need to take into account that the pressure inside the tire will increase due to the ideal gas law (pV = nRT). That is, the pressure times the volume is equal to two constants times the temperature. Since the volume remains the same but temperature increases due to road friction (heating up the air inside the tire), the pressure also increases to balance the equation.

That said, I'd imagine the pressure to increase a few PSI after sustained highway driving, but haven't done any calculations to quantify the amount. It won't be a huge amount though (just a few PSI), so inflating to about 40 PSI is fine.

In summary:
Modern tires are steel-belted tires. You are safe to run up to the max sidewall, but take off a few PSI to allow for increased pressure due to heat. Your ride will get more bumpy, but fuel economy will increase. In fact, it is better to run the pressure higher than the factory recommended in some cases, otherwise you will see increased wear on the outer edges of the tires due to sagging in the center.

[cheesie]

i always keep them at 38
how americas tires always keeps them
im scared of going higher

[MN Driver]

Originally Posted by Zangetsu57

[snip]You are safe to run up to the max sidewall, but take off a few PSI to allow for increased pressure due to heat. Your ride will get more bumpy, but fuel economy will increase. In fact, it is better to run the pressure higher than the factory recommended in some cases, otherwise you will see increased wear on the outer edges of the tires due to sagging in the center.

You are safe to fill the tires to the max inflation pressure on the sidewall when COLD, the fact that they warm up while driving is factored in and there is even more of a fudge factor too, the tires are underrated to account for pretty much every condition including a few patches, some damage, and terrible roads. Many people in the 1st Gen forums run higher than the sidewall max and I haven't seen any issues come of it, but do so at your own accord. The fuel savings of running above what Honda suggests is significant, especially with the front of the car where it is heavier.

[Zangetsu57]

Originally Posted by MN Driver

You are safe to fill the tires to the max inflation pressure on the sidewall when COLD, the fact that they warm up while driving is factored in and there is even more of a fudge factor too, the tires are underrated to account for pretty much every condition including a few patches, some damage, and terrible roads. Many people in the 1st Gen forums run higher than the sidewall max and I haven't seen any issues come of it, but do so at your own accord. The fuel savings of running above what Honda suggests is significant, especially with the front of the car where it is heavier.

I wasn't aware - thank you for clearing this up!

[firsthonda]

Going from 33-40psi, how many mpg do you typically gain? Is it significant?

[freddy the mug]

Lately i've been running 49 psi and am liking it.

[freddy the mug]

i don't know how to delete this.

[firsthonda]

After 6 months of owning my Insight I've come to the conclusion that running higher than 36 psi does nothing for MPG. All it does is increase road noise and make a harsher ride. The best MPG gains can be made by adjusting the nut behind the wheel.(and running the ac as least as possible)

[TepuruMan]

I have a brand new I2 ex Nav. I recently bumped the psi up to 39. I would say that the first tank after the bump had a small, but noticeable improvement in mileage. The road noise did increase, too.