PSI question

[Frankenstipe]

I'm taking a 330 mile trip tomorrow and have a lot of stuff packed into the trunk and some in the back seat. I've heard you're supposed to inflate your rear tires more to accommodate for the added weight. I was already planning on pumping up my tires to 40 psi from 32 psi, so my question is how much more should I pump them up in the rear? Should I pump them above 40 psi, or would 40 psi all around be enough to take car of that extra weight?

[GasSavers_Erik]

Read on the recommended max load/pressure rating that is written on the tire, if it states 44psi, then it will be perfectly safe to go that high- although the car may not handle/brake the same.

Personally, I'd go up to 42-44 psi on any tire, but that's just me and I don't want to give advice that may lead to an accident!

[theholycow]

I'd go to the maximum rating, and if it's squirrelly or sketchy, back it off a little. Do you know the normal weight distribution for your car? Tire pressure depends on weight, and the front is probably heavier. According to Edmunds.com the 2009 Corolla is distributed 59% front / 41% rear, and the 2007 is probably similar, so you'll probably be evening it out, or at worst, making the rear a bit heavier.

See also the link in my sig about tire pressure, if you want.

[Frankenstipe]

The Max Sidewall PSI is 51 PSI @ 1,356 lbs, however it also says on the sidewall not to inflate beyond 40 PSI, so I'm a little confused as to which it is. I'd like to try 50 PSI soon to see how much better MPG I can get, but not while it's loaded up so heavily.

The weight distribution is 60/40 and the total weight added is just shy of 200 lbs.

[GasSavers_Erik]

It likely warns to not inflate above 40 psi to mount the tire (seat the bead). This is something that the tire shop had to worry about when they put the tire on the rim.

If the tire states that the max load is 1356 pounds at 51 psi then its safe to run at 51psi.

51 is an odd max psi (no pun intended), what brand is the tire?

[Frankenstipe]

Ahh ok yeah it did say to seat beads I just didn't know what that meant hehe.

It's a Yokohama YK520, Discount Tire specific tire that is closely related to one of Yokohama's other tires, not sure which. 225/45/17 as opposed to stock size of 195/65/15, obviously I could do better on stock size but I'm an enthusiastic mountain driver and I like grip.

[theholycow]

Originally Posted by Frankenstipe

I'd like to try 50 PSI soon to see how much better MPG I can get, but not while it's loaded up so heavily.

The weight distribution is 60/40 and the total weight added is just shy of 200 lbs.

When loaded more heavily, you should use more pressure. If there's ever a time to try 50 PSI, heavily loaded is the time.

However, an additional 200 pounds isn't "heavily loaded". If I sat in your back seat I'd be more extra load. If my wife did too...well the two of us wouldn't fit...

Originally Posted by Erik

51 is an odd max psi (no pun intended), what brand is the tire?

The Continentals that came on my VW are rated for 51, also.

Originally Posted by Frankenstipe

225/45/17 as opposed to stock size of 195/65/15, obviously I could do better on stock size

Take a look at the other canned tire post listed in my sig, the one about tire width. Assuming all the other variables are the same, the wider tire will have less rolling resistance.

[Frankenstipe]

Originally Posted by theholycow

Take a look at the other canned tire post listed in my sig, the one about tire width. Assuming all the other variables are the same, the wider tire will have less rolling resistance.

I read that earlier today but if that's true then why is my gas mileage less than it was before the new rims/tires? They should weigh about the same I think.

Edit: Nevermind about the weight thing, I think the stock rims weigh about 16 lbs and the new ones are about 20, is this why the gas mileage is lower or is it something else?

[theholycow]

Could be weight (don't forget about weight of the tire too), aero, differently constructed tires, or any of a million other variables. If your new rims are a larger diameter, then that will affect the way the tire has to deflect; less sidewall means more sharp deflection, so more RR.

It's a good piece of info to add, I think I'll try to add something like that to the post. Thanks.

[Lug_Nut]

51 psi is a rounding of the S.I. pressure measurement of 3.5 bar.
44 psi is similarly a rounding of 3.0 bar.