Tire PSI for daily driving

I know letting out some air can help with ride quality a little bit but how much is too much? My ome setup is pretty rough but I can tolerate it (so don’t suggest new/better coilovers)
At what point will mpg and other factors be effected? What psi are you running? This is my DD. 285/70/17.

 

Having a 285 size tire will reduce your fuel efficiency regardless of tire pressure due to the tire height being greater than that of the stock tire as well as the contact patch being larger, resulting in more rolling resistance. Higher PSI will result in better fuel efficiency, but can also result in less tire tread life. Personally I would recommend you do a chalk test to determine the correct PSI for your circumstance in particular.

 

Chalk test? Never heard

 

34 +/-

 

Chalk test would be the best to show "How Low Can You Go". But I would error on the side of a little more pressure. Going to low will cause premature wear on the tires. Tires are too expensive to sacrifice them for ride quality.

 

Start at a higher PSI than you think you would want, rub some sidewalk chalk on the tread of your tire (front and back tire on either passenger or driver side) maybe about 6’-10’ of the tread. Then either drive forward or reverse without turning the steering wheel till the tires have made a few revolutions. You will be able to see that the chalk will be nearly gone, or at least less vibrant in the middle of the tread. The goal is to get the same appearance across the entire width of the tire, meaning you have a perfect contact patch. Keep lowering your pressure a little at a time and continue repeating the chalk test (with a fresh chalk mark on the tire each time) until you get the desired results.

You also do not want to run too little of pressure as some claim it can cause premature wear due to overheating. However, I ran around 28 PSI with my 285/70/17’s and they still lasted for nearly 40k miles, so personally I just get a near perfect contact patch and don’t worry about longevity as in my case it doesn’t seem to effect it.

You can also use a tread depth gauge to check your tire across the entire width of the tread ever 5k miles or so. If you find the middle is worn more than the edges than you can slightly reduce your pressures or do another chalk test.

 

Got it. I’ll consider that thank you

 

Chalk test to know for sure, or just run ~30-35.

Too low and you'll wear out the outside edges prematurely, too high and you'll wear out the middle prematurely.

Only air down when off road.

For a "better" ride on the road, C rated tires will minimize the weight.

 

That’s another thing I don’t know much about are tire ratings

 

Chalk test. You will be surprised how low psi to get a good test. That being said on aggressive tires I run 26 to 28psi.

 

Keep an eye out for any abnormal wear resulting from too much or too little pressure.
https://www.knowyourparts.com/technical-resources/info/understanding-tire-wear/

 

C rating is a lighter weight tire meant more for street driving. Thinner sidewalls means they are lighter, but generally less durable.

For people who go offroading, most use E rated tires. Thicker sidewalls, and much more durable, but also heavier.

D rated tires are a happy medium between the two, but not as many tire options available.

 

Keep in mind on the chalk test it's recommended once you find the pressure that gives even wear across the width to raise the pressure 10% for daily driving.

You'll also want to complete a temperature rise test once you've found the pressure. This involves a 10-15 highway run and verifying the pressure (temperature) hasn't increased too much. With stiff sidewalls you can get a good result on the chalk test, but have an underinflated tire that flexes too much and will prematurely wear the tire.

Probably the best writeup for setting pressure.

 

Noted. Thank you

 

I don't know how well this translates to passenger vehicles, but in the realm of bicycles, for the longest time the conventional wisdom was that higher pressure = lower rolling resistance. Somewhat controversially, some bicycle tire manufacturers did some laboratory tests, which validated this conventional wisdom, but only when the road surface was perfectly smooth. At the same time, they discovered that in real world conditions with rough road surfaces, very high tire pressures actually increased rolling resistance, as additional energy was required for the bicycle/rider combination to ride up and over surface irregularities, whereas a tire with lower pressure could absorb more chatter, preserving forward momentum.

With respect to cars and trucks, rock hard tires will transmit more harshness through the suspension and the rest of the vehicle, which can contribute to increased component wear. In view of cost effectiveness, the ideal daily driver tire pressure probably needs to account for typical road surfaces as well as the potential cost of accelerated component wear in order to accurately calculate the actual savings of increased fuel efficiency.

 

Lowered them to 30 psi. They all fluctuated around 32-35 at first so we’ll see how they feel now.

 

Chalk test

 

I had never heard of such a study but it’s pretty interesting. I know that when I ride BMX street I run around 40 PSI to give my wrists a break, and if my wife wants to ride on the local walking trails I increase my tire pressure to around 80 PSI so I can keep up with her and her cruiser styled bike without having to constantly pedal (very small front sprocket size).

 

Reference to such a study can be found here.

Here is a graph from the same article illustrating the effect. In a nutshell, for a given tire, power to maintain speed decreases as pressure increases, until a certain point, between about 100 - 115 PSI (this is for a 25mm road bike tire), after which the power requirement increases. The precise PSI at which this occurs depends on the roughness of the road surface:

 

Well my door plate says 26psi all 'round. 26! My belief is they recommended 26 as to the ORIGINAL tires from factory, to balance ride quality with whatever else. To me, 26 is under-inflated. So my general rule, again, my own rule, is to run psi at a medium between what the door plate says and what the MAX psi states on whatever tire I run. So currently, my tires state MAX as 44. Hence I run 37psi all around.
Running them low like they want is not going to much improve ride on a truck that's narrow, pretty long, kinda light, having a rigid full frame and half-ton leafs out back.