Thanks, Racer.
I’d expect to see colors indicating higher compression in the middle of the treads, but I do not.
I wish they would measure the footprint widths and show the differences in percentage.
The over-inflated tires will make the car ride VERY hard and can damage the suspension after a while…
If those tires were on a pickup and the truck was loaded to its maximum capacity, the tires may then be inflated to 44 PSI. That is the only time to do it. The owner’s manual may even have a chart that shows exactly what tire pressure to use for what vehicle load. It is almost impossible to figure out but it may be fun to look at if you need a good laugh.
“What about using a narrower tire? They allow a range of sizes.”
If you are not using the recommended tyre size the recommended pressure no longer applies. If they list a range of sizes in the same place they provide the recommended pressure, it applies, but if the tyres are listed in another place, like a different chapter of the owner’s manual the recommended pressure does not apply and you are on your own.
"Does it really make a difference in footprint? Between 35 and 44 I see no difference. (Only 9 psi more.) " How are you measuring foot print? It is not easy to do without some rather expensive tools generally only found on the test area of an auto manufacturer.
That is the same place they test different pressures to decide which ones are the safest.
"I ran brand new tires at 44 psi down to their wear bars and they were surprisingly even from center to sides! "
Not surprising. That became the norm when steel belted tyres came in.
“If there is a slightly smaller footprint, would not the greater weight/area continue the same traction?”
NO!
“I have not noticed any difference in handling or braking, but I also drive gently and have not panic braked (skidded) so don’t have a comparison.”
You answered that one yourself. That is why the manufactures use test tracks and test different speeds, surfaces etc.
“I suspect vehicle manufacturers would like us to feel a more comfortable ride by lowering the tire pressures.”
You suspect wrong. That changed with the Ford Explorer/Firestone mess. No automaker today would even think about using that trick. Ignoring it cost a number of people their lives.
"But WE pay for it with higher fuel costs." No you benefit by safer driving.If you look carefully, you will see exactly what you were looking for: Higher pressure / lower load = more pressure in the center. This particular tire is has an excellent footprint. I have seen others that are much more dramatic.
In terms of percentage: A good estimate is a 10% change in pressure or a 10% change in load = a 10% change in area. For this tire, the width of the footprint is almost the same for all conditions - again, this tire has an excellent set of footprints - other tires, not so much.
BTW it is not true that you can calculate the area of the footprint knowing the pressure and the load. Here’s what I wrote up on the subject.
What about using a narrower tire? They allow a range of sizes.
A narrower tire with the proper tire pressure is NOT the same as running a wider tire with higher tire pressure. The narrow tire is DEIGNED to run on a smaller foot print…the wider tire ISN’T.
Does it really make a difference in footprint?
Between 35 and 44 I see no difference. (Only 9 psi more.)
Yes…about a 20% difference in foot print.
I have not noticed any difference in handling or braking, but I also drive gently and have not panic braked (skidded) so don’t have a comparison.
I’m glad that you have such a commute that you can guarantee that you’ll never need to brake hard or turn hard because someone cuts you off or a kid comes running out into the street out of nowhere. I’d LOVE a commute like that.
I suspect vehicle manufacturers would like us to feel a more comfortable ride by lowering the tire pressures.
True…I agree completely. I keep inflate my tires 1-2 lbs above what is recommended. That way it’s NOT adversely effecting the cars handling or graking. But adding 9-10 extra lbs can/will adversely effect handing.
But WE pay for it with higher fuel costs.
If you’re concerned about fuel costs…then WHY are you driving a Expedition???
Good point. I raise the pressure of my rear tires when ever I tow our trailer. I just add about 6 extra lbs. Then when I’m NOT towing anymore I lower the pressure back down to safety levels.
"If those tires were … loaded to … maximum capacity, the tires may then be inflated to 44 PSI."
That is what I thought.
Which means they will go above 44 psi during driving.
The higher 44 pressure diminishes the flexion of the tire which keeps the flexion heat less.
Apparently it is a matter of keeping the foot print the same size.
Less load, less pressure keeps the footpint a certain size.
More pressure would make the footprint less, but the greater load makes it larger.
There may be a misconception floating around this thread.
If a tire says the maximum inflation is 44 psi, it is a passenger car tire. This doesn’t mean it can only be used on passenger cars. It means that the tire is designed to passenger car tire standards - and not light truck tire standards (or a standard for another type of tire).
Passenger car tires are designed such that at lower inflation pressures, the maximum load carrying capacity is less than the maximum load stated on the sidewall. Using more pressure increases the maximum load carrying capacity, but those increases in load carrying capacity stop at 35 psi.
Using pressures between 35 and 44 psi is PERMITTED, but there is no increase in load carrying capacity.
You could say the load vs pressure relationship is related to the size of the footprint - and that would be somewhat correct - but it is really tied to the amount of deflection - the difference between the unloaded height of the axle above the pavement vs the loaded axle height above the pavement.
For a more detailed explanation, please see what I wrote up here: