Hybrid Car – More Fun with Less Gas

Optimal Tire Pressure - Page 2

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Posted by News on December 24, 2007, 8:18 pm
 


Elmo P. Shagnasty wrote:

It certainly would.  After inflating to 100psi, you'd have the handling
and steering of any car with exploded tires.

Posted by Marc Gerges on December 24, 2007, 8:55 pm
 

Within limits that's correct. More pressure results in stiffer
sidewalls, giving crisper handling. I've found the 'sweet spot' on mine
(standard Michelin tires) at around 2.6-2.8 bar.

OTOH, my real world driving has many less than perfect road surfaces,
and especially smaller ripples are no fun with this tire pressure. Light
braking may even activate the anti lock system, and cornering makes the
car wander to the outside. By lowering pressure to around 2.4 that
tendency is completely gone, the car feels considerably safer at
comparable speeds. I have around 2.2 at the rear tires, because it make
the car somewhat less front heavy. This is with light load, usually only
driver or driver plus one passenger.

If your driving is mostly smooth roads and highways, higher pressure may
work.

cu
  .\arc

Posted by Mr. G on December 24, 2007, 9:52 pm
 I've found that running at 42/40 psi (front/rear) gives me the best
trade-off between ride, handling and MPG.  Using the factory pressure of
35/33 causes a significant drop in fuel economy, without (IMHO) an
offsetting increase in drivability.

Whatever pressure you decide to use, you should have the front pressure
slightly higher than the rear due to the weight distribution.

says...

Isn't 2.4/2.2 just at (or a little below) the factory recommendation?

Posted by Bob & Holly Wilson on December 25, 2007, 1:43 am
 

Thanks to Google books, I picked up the following graphs from:

Gyenes, L. and Mitchell, C.G.B., "The Effect of Vehicle-Road Interaction
on Fuel Consumption," Vehicle-Road Interaction, ASTM STP 1225, B.T.
Kulakawski, Ed., American Society for Testing and Materials,
Philadelphia, 1994, pp. 225-239.

http://hiwaay.net/~bzwilson/prius/pri_tire_010.jpg
Tire inflation lookup table:
kN/m**2 - psi
200 - 29
225 - 33
250 - 36
275 - 40
300 - 44
325 - 47
350 - 51
375 - 53

http://hiwaay.net/~bzwilson/prius/pri_tire_020.jpg
Speed lookup table:
km/h - miles per hour
80 - 50
90 - 56
100 - 62
110 - 68
120 - 75

Tire rolling resistance is not a linear function with speed and
inflation pressure and these charts give a clue about tire drag. For
those who prefer a softer ride, go for it. For me, local speeds and
roads are such that maximum sidewall pressure up front and -2 psi in the
rear works quite nicely.

Bob Wilson



Posted by Elmo P. Shagnasty on December 25, 2007, 5:34 am
  bwilson4use@hotmail.com (Bob & Holly Wilson) wrote:


You know, Mythbusters showed that the closer you tailgate a big rig
truck, the better your gas mileage.

Even down to the last inch, there were significant gains.

So pump those babies up, and plant your front bumper half an inch from a
big rig as you go down the highway.


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