Why different tire pressure in front and rear tires?

i've noticed on several posts that people say you should put 2 less lbs in the rear tires, so 42/40, 40/38, etc.. why? i know people say it affects the handling of the car, but i don't buy that. first of all, i just purchased an 07 prius a couple of weeks ago and the dealer had 42psi in all four tires. secondly, the manual says absolutely nothing about this, and i'd tend to trust toyota over a prius owner. i just don't understand why so many people believe this is the best setup. anybody have any thoughts on this?

 

<div class='quotetop'>QUOTE(poodlemaster @ Jan 17 2007, 11:47 AM) [snapback]376784[/snapback]</div>

Then check the door sill on your drive door where it lists the 'recommended' inflation which is 35 front 33 rear (ie two pounds more in the front).

I believe it's because the front of the car is significantly heavier than the rear. Tire Load Ratings are pressure sensitive.

 

Higher pressure in front is for attempting to compensate for the weight balance of the car, basically trying to keep maximum stickiness of the rear tires with respect to the road. I have found that I like 38/35, but experiment and see what works for you, as someone noted, lots of folks run 42/40. Higher than recommended pressures should help with MPG. Note that keeping all 4 the same could result in some surprises of the unpleasant kind if you have to make any drastic moves.

 

if your question is- Is it REALLY important....the answer is no. However, for handling and the weight differential, it is a help.

 

The extra two pounds in the front tires makes the Prius heavier in the front, which causes it to roll downhill during normal driving. This is the real secret to great gas mileage, but don't tell anyone else.

Tom

 

Hey guys, what about wear on the tires? You know, the reason the tires get rotated every 5k miles, or whatever it is, is to ensure even wear on the tread of the tires.

So don't you think that the front having 2 more pounds of air than the back also has to do with ensuring even wear on the tires? Especially since there's more weight at the front. Just a thought that it probably has more to do than just with ride comfort.

 

"i'd tend to trust toyota over a prius owner."

Why do you waste time talking to Prius owners? Why not ask Toyota?

Its common knowledge that in understeering cars (99% of cars on the road, including Prius) more air in the front than rear will balance out the handling a little. If you carry heavy luggage in the trunk, pump the rears a little more to compensate for the weight change front to rear. Front heavy cars need more air in the front tires, as a general rule. 2 psi can make a difference. Of course, I'm just a Prius owner.

 

<div class='quotetop'>QUOTE(qbee42 @ Jan 18 2007, 11:21 PM) [snapback]377583[/snapback]</div>

That's why I put nitrogen only in the front. My Prius goes faster downhill and gets much better mileage to boot.


Rick
#4 2006

 

<div class='quotetop'>QUOTE(viking31 @ Jan 19 2007, 03:30 PM) [snapback]377906[/snapback]</div>

I tried that, but it's hard on the brakes and I had trouble backing up.

Tom

 

<div class='quotetop'>QUOTE(qbee42 @ Jan 18 2007, 08:21 PM) [snapback]377583[/snapback]</div>

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Tom -

You have raised a cloud of puzzlement from over me. Thanks, so much!

Maybe...you can also tell me which came first: The chicken or the egg?

 

I just put helium in the front tires and nitrogen in the back. Now the car weighs the same all the way around....

PS: For the spare, I tried helium, but it floated away... so, I am using a blend now....

 

Regarding why the car was delivered with the tire pressure at 42/42; mine was actually delivered at 45/45 and my understanding is that is how toyota ships their cars. Apparently some dealerships are too busy to reduce the tire pressures to their recommended values. It seems that it should be part of the "vehicle preparation service" but I guess not.

BTW: I also have mine set at 37/35 which has given me good mileage (52 MPG lifetime) and better handling than it did with higher pressures in the tires.

 

<div class='quotetop'>QUOTE(John in LB @ Jan 20 2007, 03:21 AM) [snapback]378185[/snapback]</div>

Don't tell me you forgot and opened the hatch!

Tom

 

I would like to know why do people use a higher pressure then what is recommended by the manual? Is it for the higher mileage? Better handling?

Just wondering.
Thanks

 

Yes, Toad, you have it exactly: Better milage and better handling. But also tire wear. Many have experienced wear on the outer edges of their Integrity tires when inflated to the Toyota specification of 35/33, so bumping up the pressure a bit prevents underinflation wear.

<div class='quotetop'>QUOTE(fphinney @ Jan 19 2007, 11:16 PM) [snapback]378179[/snapback]</div>

Isn't it obvious? The egg.

Why are you always so bold, fphinney?

 

<div class='quotetop'>QUOTE(toad @ Jan 21 2007, 12:42 AM) [snapback]378562[/snapback]</div>

Both. I'm going for better handling, usually, but higher pressures do help with MPG, less rolling resistance. 42/40 seems to be the magic number for MPG. I like 38/35, but when in doubt, don't exceed the limit stamped into the tire, or go below the car manufacturer's ratings.

 

Thanks for the answers

...but, aren't you at greater risk of blowing your tires?

It doesn't appear to be a problem since it seems everyone is "over-inflating" the tires.

Thanks!

 

<div class='quotetop'>QUOTE(subarutoo @ Jan 19 2007, 03:19 PM) [snapback]377896[/snapback]</div>

toyota said 42lbs all around when i bought my new car.

 

<div class='quotetop'>QUOTE(poodlemaster @ Jan 21 2007, 07:13 PM) [snapback]378805[/snapback]</div>

I suspect you meant to say that a Toyota Dealer told you that. Not Toyota.

They are not the same thing.

I would certainly trust a Prius Owner, especially one on here, before I'd trust a random Toyota Dealer