Tire pressure confusion

different pressures for different needs and priorities.

 

42/40 gives better mpg and wear without sacrificing safety. Just harder to put on your make-up or text .

 

It is your choice.

'Best' tire pressure is a compromise between many competing factors. You, the manufacturer, and others may place different values the various component factors, and thus arrive at different answers.

 

I got ~ 70,000 mi on a set of Michelins by running 42/40. If you run 35/33 as shown on the door sticker, you will probably see a wear pattern with the outside edges worn more than the center tread; this is typical of a underinflated tire. Toyota values ride characteristics over tread life with the door sticker recommendation.

 

Pressure on the placard could be considered as a "minimum" and what Toyota represents that would make the car ride the best for creature comfort. Those who use the higher pressure do so to help to achieve greater MPG along with other techniques such as hyper miling and so forth.

What ever pressure you choose to run, do not exceed the pressure that is stamped on the side of your tire. Maintain a two pound difference from front to rear with the front tires set two pounds higher than the back. Experiment with different pressures until you are happy with the ride, comfort, and MPG you are experiencing. It seems that those who run the higher pressure seem to get the best wear and longevity out of their tires also, whereas those who run at the placard setting tend to see their tires wear out quickly with the edges wearing out before the center of the tire wears out.

General rule of thumb. Check tires first thing in the morning before the heat of the day hits. Set the pressure at that time before you drive the car. Be aware that ambient temperature does affect the pressure in your tires. And take the time to check and maintain your pressure at least once a month. Some do it once a week. All tires will leak over a period of time, that is why it is important to check and maintain your pressure.

Best of luck to you,
Ron (dorunron)

 

The good news is Costco probably filled with N2 which should hold pressure better than regular air. I am not the tire pressure expert, but I'd be inclined to increase a few more lbs maybe 38/36 with regular air. As the warmer summer temps come upon us, you will probably see some further pressure increase. The increase in MPG starts flattening out above 35 psig or so, so unless you are really trying hard for the last +1 MPG, the returns of higher pressure are diminishing.

PS- there seems to be something funny about this thread...it does not show up in some browsers or searches.

 

This is a simplified and exaggerated drawing of the effects of tire pressure on tread life. The under inflated tire runs on the edges of the tire and wears out there first. An over inflated tire wears out the middle first. The correctly inflated tire wears evenly. I watch my tire wear to guess if I need more or less air.

From a safety issue, isn't it obvious that the correctly inflated tire would stop quickest, turn better?

From a comfort standpoint, look at the side walls, the under inflated tire can flex, while the over inflated tire is pushing those bumps straight up the side walls. The correctly inflated tire for tread life is sacrificing some comfort. This is why Toyota is recommending lower pressures.

(Ignore this advice, it is dangerous) If we only care about MPG, that over inflated tire sure would roll well. (Do not do this, it will not be safe to drive on public roads)

This harder to see, but the more you inflate your tires the lower you THINK your MPG is, as the tire diameter changes. A modern belted radial does not change as much as this diagram implies, but it does grow as you inflate them. (set a yardstick by your car to see this) Edit: See below I had this backwards. In any case, changing tire inflation can change how you measure MPG.

 

A couple problems here --

* As increasing pressure causes the tire (and vehicle) to rise, the tire's rolling circumference does not proportionately increase. That circumference is set mostly by the length of the belts inside the tread, not the apparent tire diameter at the moment. Things mush around where the tire flattens at the contact patch, messing up the simple equations of circles.

* If the effective circumference does increase a bit, it will reduce (not increase) the apparent MPG as measured from the odometer. Over a fixed surveyed distance, the wheels will rotate slightly less, and that is the only way the car measures distance. And this becomes a double-dip issue if the driver uses the speedometer to maintain 'constant' speed, because the speedometer gets hit by the same shift.

 

I have my tires rotated at Sam's Club and they will always report the tire pressures at 35 psi whether they actually decrease to the door placard rating or not. Most of the time they leave the pressure alone but I always have to check after rotation. I usually just have to adjust a little since after rotation they are at 38/40 instead of 40/38.

This weekend they actually lowered the tires to 35 psi all around so I had to pump back up to 40/38.

 

The few times I've gotten new tires through Costco, I accept that:

1. They are going to set tire pressures to the car manufacturer's specification. Likely their legal department insists on this, I don't bother to debate it, can see their point of view.

2. They're going to put green valve caps on, what can you do.

Accordingly, coming home, I pull into Chevron (last bastion of free air in our area) and raise the pressures (with ordinary air) to my preference, and replace the green caps with the caps I took off just before rolling into Costco.

To the OP, maybe just raise the pressures modestly at first, say to around 38 psi, see how that works for you?

 

If you can settle on a single pressure for all four tires it saves this hassle at rotation time.

 

This is only safe if you drive slow on clean, dry roads. In other conditions you'd better keep pressure +2 psi higher in front to ensure proper car stability, as recommended by manufacturer.

- Alex

 

Understand but it only takes a couple of minutes to adjust the pressure. I prefer the 40/38 to a single pressure mainly due to above comments.

 

I'm sorry but that statement struck me as kind of funny.

You seem to be OK with increasing the pressure over the recommendation by 5 lbs or so......but then are concerned that the RELATIVE difference be maintained ??? What ??

I think it has a LOT more to do with ride comfort than "stability".

 

The manufacturer spends A LOT of time and money engineering the vehicle. If you want to deviate from their recommendation, it's just backyard mechanics...not thoughtful engineering.

 

I whole heartedly and absolutely agree with that, which is why I have my tires at or just a couple over the recommendation.

HOWEVER.......not KNOWING what the considerations really were for the engineering model, it is possible that some owners have different priorities than the engineers did.

In this case SO MANY hybrid owners of all different models and even a good many owners of high mileage gas only cars are running their tires at +5 or so with seemingly no adverse impact, except maybe a little rougher ride, that I think your indignation that anyone would DARE to do that is misplaced........at best.

I also believe that excessive air pressure wears out the suspension components faster.......but we live in an age of instant gratification so it's no surprise that most people don't care about that.

 

^ I'm thinking that too, that firmer tires equals more wear-and-tear on the suspension. At lower pressures the tires are acting more like part of the suspension, absorbing minor bumps and dips. I guess the thing is to just not go to extremes.

Doubly so with our 215/45R15: the spec pressure for them is lower, 33 front / 32 rear, and just having raised them to 38ish I feel like a bobble-head when going over speed bumps.

 

so the answer is...

 

uh huh