Tire Pressure (Avanza)

[1D4LV]

Ano effect ng underinflated sa tires?

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meron pa aside from what is stated...... ang hirap ng steering.....

[oj88]

If you prefer not to follow the manufacturer's recommendation, just remember that you're SAFER with a slightly over-inflated tire than one that is under-inflated.

An under-inflated tire will generate heat due to continuous friction/rubbing on the pavement and excessive flexing. If the tire gets too hot, it causes the tread layers to lose cohesion which may cause them to separate and burst.

[1D4LV]

If you prefer not to follow the manufacturer's recommendation, just remember that you're SAFER with a slightly over-inflated tire than one that is under-inflated.

An under-inflated tire will generate heat due to continuous friction/rubbing on the pavement and excessive flexing. If the tire gets too hot, it causes the tread layers to lose cohesion which may cause them to separate and burst.

aside from this, if the tire is under-inflated, you run the risk of damaging the tires dahil tumatama sa rolling surface yung sidewalls ng tire.

[TireWhisperer23]

This thread might be old, but some of the comments in here have inspired me to come clean about how those numbers on the door frame tire pressure stickers were picked.

Ten percent contributing factor of how they were picked? Experience, with similar sized tires on similar sized rims on prior vehicles of similar size and weight.

Ninety percent? Science:

Tire size and load tables are part of it. Every tire size known to man has an ultimate max. load capacity, at a standard(35-36psi) or heavy duty(40-41psi) pressure.

For our example vehicle, "Project X", we want a tire size that satisfies both traction and load capacity.

Tire "C" is a medium-profile(60-series sidewall), with a hypothetical max load capacity of 1,500lb at 35psi.

Project Car X has a GAWR(gross axle weight) of 2,200lbs in front, 2,600 in back. Now remember, "gross" means max, as in: the most you'd ever hope to fit in a given vehicle: 6 adults, their luggage for the weekend, several cases of bottled water, a full tank of gas, and the dog. The tire & load placard on the door pillar might remove one adult, or the dog plus bottled water. But you catch where I'm going.

Now, since one tire is not expected to carry the total front or total rear gross axle weight, we have to cut those GAWRs in half:

Front: 1,100

Rear: 1,300

Tire "C", of a size and ratio picked as suitable for our Project X, satisfies, according to standardized tables, a 1,112lb load at 29psi, and a 1,307lb load at 32psi. Again, these figures are hypothetical, and I'm using them to underscore a point, which I'll reveal momentarily.

So we've found pressures that safely carry the gross axle weights for our project car.

But now we want to consider other aspects:

A. Handling

B. Ride

C. Fuel economy

D. Consumer ease of maintenance, and potential over loading of the vehicle*

(*overloading not just weight, but overloading as in excessive speed, hard cornering, and other operational extremes, intended or otherwise)

A. A lower cold tire pressure will maximize grip, acceleration, and braking. It may also induce oversteer, or slow reaction to steering wheel inputs. A higher pressure will make the car more responsive, more nimble, at the expense of grip and traction.

B. Self-explanatory: Lower cold pressure = softer, comfortable ride. Higher = rougher, harsher.

C. Lower cold pressure = lower mpg, higher = more mpg - up to a point!
If your overinflated tires spin and deposit their tread on the pavement, where is the fuel savings in that? Not only that, but overinflated tires will skid on a wet surface during sudden stops.

D: People are human. They do dumb things, such as overload their vehicles.

For others, it's easier to remember one cold tire pressure number for the tires on both axles. Especially in North America! Maybe 1/5 passenger vehicles have different specified cold tire pressures for the front and rear axles.

In the Philippines, mainland Asia, or Europe, passenger vehicles specifying different front and rear tire pressures might represent at least half the total on the roads.

Now getting back to our Project X:

We have determined that a cold tire pressure of 29psi satisfies the front gross weight by, IE, 2 percent, and 32psi satisfies the rear gross weight by 1 percent.

And the ride at those pressures is sublime: Soft, smooth, quiet. Even over the worst manhole cover. But we want a safety margin, typically ten percent for the comfort market, fifteen for a broader swath desiring a blend of ride plus handling, twenty percent, for more load capacity and/or maximizing fuel economy. We'll add fifteen percent to the per-tire gross axle weight:

Front: 1,265lbs

Rear: 1,495lbs.

Consulting the tire tables, we find that the size of tire chosen for this car - "Tire C" holds 1,280 at 31psi, and 1,500 at 34psi.

After more road test, the tire and load placard is printed and affixed, with the final cold recommended pressures of Front: 32psi, and rear, 34psi.

That was a rough and dirty example, and the point I'm trying to make is that the cold tire pressures specified for your personal vehicle support normally 110 to 125 of its gross weight. So your vehicles tires, at door placard pressures, are not underinflated there really is zero reason to inflate then by more than 1psi over.

The engineers all of the brain work and road tested, so you don't have to.

Getting back to North America, and specifically the U.S., one reason for having same cold recommended tire pressures front and rear:

Easy to remember!

So the North America version of Project X might have recommended pressures of 33 or 34psi for all four wheels, even if it means satisfying the lower front axle weight by 20 or more precent. For a busy American, Front & Rear 34psi might be easier to remember than Front: 32psi Rear: 34psi.

A secondary reason for same front/ rear tire pressures: A lower spring rate(softer springs) at the lighter axle. So no need to specify different front/rear tire pressures in that case.


If you have read this far and are still with us, congratulations! You've just delved into the secrets and science of how a vehicle's cold tire pressures come to be calculated and determined.