Why different tire pressure in front and rear tires?

[Tideland Prius]

<div class='quotetop'>QUOTE(poodlemaster @ Jan 17 2007, 08:47 AM) [snapback]376784[/snapback]</div>

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?
[/b]

Look under the hood of the Prius, then look under the hood of a regular car.

You'll see that the Prius' engine is ahead of the front axle while in most cars, the engine is on the front axles or slightly behind it (one exception is the Yaris which I also presume has a 2lb difference).

Hence, the Prius is quite nose-heavy and needs an exrta 2lbs to even things out. Check the door jamb. The manual should say 35/33 as well. You may be looking at the wrong section.

In a regular car, you can also put 2lbs higher in the front to gain a very slight handling improvement. It may not be enough to actually feel a difference but it may help in some cases (e.g. emergency manoeuvre). It's not necessary but you could if you wanted to.

[poodlemaster]

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?

[Tempus]

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

i'd tend to trust toyota over a prius owner. [/b]

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.

[Beryl Octet]

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.

[Schmika]

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

[qbee42]

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

[bomber991]

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.

[subarutoo]

"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.

[viking31]

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

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
[/b]

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

[qbee42]

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

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

Tom