Uneven tire pressure?

It's on the door pillar. And in the Owner's Manual TOYOTA gave you with the car. Some might suggest adding a little extra - maybe add up to 10%, keeping the same proportion front-rear.

 

I use what is on door pillar too (36 PSI from memory I think) and I don't think I'm doing too bad MPG wise, even taking in x % over-reading display, nice smooth ride too on 17's

Just had 4 year service and all tyres are wearing evenly.

Never seen the point in using higher pressures than the manufacturers state, each to their own though I guess.

 

^ That

If you’re worried about gas then you’ve been keeping tabs on your fuel economy, right?
That means you have a baseline.
If you’ve been running 42/44 and your fuel economy is X...then drop the pressures down to OEM spec for two tanks and see if you can tell the difference.
Or start at the OEM spec pressures and work your way up.

There’s a school of thought that running the tires at 42/44 *might* give you a little better fuel economy and improve the life of your tires but you’re already close to the max sidewall pressure anyway - and if you’re running tires with eco-something in their brand name then they are already as hard as a billiard ball.

Priuses are BUILT for fuel economy,
Toyota cares about this SO MUCH that the efficiency numbers that are displayed on your dash are about as trustworthy as the news.
That’s why you should calculate YOUR fuel economy.

The point is...
If 42/44 were that much better than 36/38 then the sticker in your door jam would be different.

YMMV

 

First, let me say there should be nothing wrong with the door pillar numbers. I assume that very smart people came up with them.

But I find that running 42/40 still gives me a compliant ride as well as perfectly even wear side to side on the tread as well as excellent wet weather traction on the Yokohama Avid Ascend GTs my Prime wears. I assume that it also yields better economy given that there should be less energy wasted squishing the tires. But to know just how much would require running at lease one tank of gas over a closed circuit. It won't be enough difference to be quantifiable with all the variables in day to day commuting.

As for the pressure difference front to rear, that's most likely due to the weight difference front to rear. Gen 4 is 56:44 from what I've read. The Prime is perhaps not too different since the weight of the battery is partly offset by the carbon fiber hatch.

 

Have you actually tested that theory.......or are you just assuming it will be true ?

It is NOT in all cases. Maybe not even in many cases.
It depends on the exact tires in use, mainly.

And even if it does result in a tiny mileage increase, most people find that it results in a noticeably rougher ride.
AND some owners find that they have premature suspension failures as a result.

The probably is about 10 PSI above the recommendation and that is a LOT.

 

Whatever it says in the owners manual.......and on the sticker inside the drivers door.

 

What the sticker on the door jam says.
One or 2 isn't going to make a difference. Tires reading are most accurate at COLD . Coldest time of the day is at dawn.

 

Not exactly true.
The spec's are quoted as cold pressures so that is when you should check them.
That has nothing to do with accuracy.

 

It has been well documented in past threads here and elsewhere, with URLs pointing to various lab test reports that measured it.

It is small, many (most?) drivers won't find it worth the increased ride harshness, and additional improvements rapidly shrink with each higher pressure increment. But it is real and documented.

Yes, definitely. But the final numbers are a comprise between multiple factors, some conflicting. And those "smart people" include marketing types whose inputs lean very heavily towards ride comfort.

So the door placard numbers are the proper starting point, and will serve most drivers reasonably well. But for the others who put different weightings on those conflicting factors, e.g. less interested in ride comfort and more interested in certain types of performance than the 'average' driver, it is reasonable to make some changes.

 

You're absolutely right. I'm one of the drivers who makes some changes.

 

Weighing factors @fuzzy1 mentioned, and for practical reasons, I take the higher door jamb value, add a pound or two, and make all four thus.

And yeah, I'm using a tire gauge I like from an ergonomic point of view, but I know from checking against the rest of my collection, it's very likely reading 3 pounds high, so I add that amount.

 

Tire inflation also impacts things like traction and handling.
In case people have forgotten....
Firestone and Ford tire controversy - Wikipedia

One of the REASONS that TPMS is mandatory by our loving dot.gov is that a certain car company diddled with their door jam settings (to increase vehicle stability and ride comfort, in this case) and when bad things started happening they blamed the tire company!

It can go bad the other way too,
In other words....OVERinflating a tire can result in decreased traction---something not as easily measured at the pump.
If I lived in a state that regularly encountered tropical downpours......I'd be somewhat concerned about that too.....

Toyota has lawyers.
LOTS of em.....

I'm guessing that the door jam values are a compromise between efficiency and safety....ONE of which is more easily quantified than the other.

 

Well, there you go again......trying to throw facts and common sense into the discussion.
Good post.

 

I live in a climate zone that regularly encounters non-tropical downpours. And that is exactly one of my reasons for running a bit boosted inflation pressure -- onset speed of hydroplaning is proportional to the square root of inflation pressure. The research links are posted in old threads here.

A previous car with a low (by current standards) door placard pressure recommendation, initially suffered from premature hydroplaning compared to any other car I had driven. Boosting the tire pressure by 25-35% (from original 26 psi) cured it. And also cured uneven tire wear.

Now that the National 55 MPH speed limit has been abolished, average highway speeds are significantly higher, requiring even greater pressures to resist hydroplaning.

 

^ That's one of the reasons that it's "usually" a good practice to start at the door jam settings and adjust the tire pressures accordingly.
MOST of the time, hydroplaning issues will result from underinflated tires but OVERinflating tires will also reduce the contact patch and produce the same result.

[QUOTE="fuzzy1, post: 3133784, member: 48224"
Now that the National 55 MPH speed limit has been abolished, average highway speeds are significantly higher, requiring even greater pressures to resist hydroplaning.[/QUOTE]

"Now that?"
We were freed from that law almost 35 years ago.

The 55mph was the third most ludicrous federal law since Prohibition....and like those other two laws it actually created a cultural shift TOWARDS the behavior that it was trying to regulate.
Even today...people speak easy about speakeasys and the Cannonball Baker Sea-to-Shining-Sea Memorial Trophy Dash (an actual event!) resulted in at least one book and two movies.


Fortunately, common sense usually breaks out following federal over-reach.

 

According to the tests linked here, overinflating the tires never produced the same hydroplaning results as underinflation. The pressure-vs-onset-speed function was strictly monotonic.

Only partially, and only in some states.

I was experiencing premature hydroplaning in my 1986 Honda (which was kept until getting my 2010 Prius). Partial rollback, allowing states to raise speeds to 65 mph only on certain rural interstates, didn't begin until 1987, and my state was not among the early adopters.

Several additional easing were passed, but full repeal did not happen until 1995. My math says that was just 26 years ago, not "almost 35".

And states didn't immediately raise speed limits to today's levels. It has been a gradual and continuing ramp up. And the damn-the-speed-limit behavior of drivers has been producing continually rising average speeds. And the Pandemic has produced an additional bump up.

=============================

On an note unrelated to rising traffic speeds , modern traffic crash fatalities first fell below 40,000 (barely) in 1992, but rose back a bit above that the next year. Deaths would not fall below 40k again until 2008. Functionally speaking, despite continually improving vehicle and road safety improvements, annual deaths were nearly flat from 1991 through 2007. Only in 2008 did the modern trend of decreasing annual deaths resume ...

... until 2015, when it bumped back up again. (Smart phone distractions?)

Very preliminary figures indicate that in 2020, despite a substantial pandemic-related drop in vehicle miles traveled, crash deaths shot up to 42k, 6k more than the year before.

Any association to increased speeds will be left to readers' imaginations.

 

I heard of a peer-reviewed study once that associated vaccines with autism.
So...here's the "real world" thing with passenger tires.
It is very difficult to over-inflate modern passenger tires, so I will leave the baseball statistics arguments for another forum.

If anyone out there rides a motorcycle though, I would advise that you take an MSF course.
They might introduce you to radical new thinking about how excessive air pressure can distort the shape of the tire.
This is because they are not entirely rigid, which is sort of the whole point of tires.
Tire over inflation (in the real world) CAN lead to decreased traction and increased wear and tear down the center of the tire.

For those not interested in the useless "six" versus "half a dozen" type of arguments.....Just stick with the manufacturers "door jam" recommendations and if you decide to take a walk on the wild side......vary the pressures by a pound or two and see if it your mileage varies.
Just remember to stay within the max sidewall pressures if you decide to bump the pressures up a bit and you'll be OK.

MOST of the tire problems encountered by norms occur wen people don't CARE about their tire pressures and cannot be bothered to even regularly check to see if they are properly inflated.

Fact check: True.
I was wrong.
I concede to the superior 'fact' warrior.

However (comma!) I believe that my underlying points are still valid.

OBVIOUSLY.....YMMV.

Absenting "science and data"....that IS INDEED what we are left with....as is also true with increased alky consumption during and since Prohibition, and sales of 'those things that shall not mentioned"..... following another (failed) federal ban.

 

Since I use better tires than Toyota puts on Prii, Nokian WR "H" rated tires that have a cold max rating of 51 PSI, I fell safe putting 42/40 in my tires. The higher pressure does produce a small MPG improvement (the tire flexes less and I have done some experiments), better tracking and not too harsh a ride.

JeffD

 

This is a DANGEROUS myth that you are spreading around.

Tread design and depth (wear) has a LOT more to do with it than simple pressure......across the whole universe of "all tires".

At one end of the spectrum is a racing slick. NO tread and max. rubber on the road. Will hydroplane at very low speed no matter what the pressure.

At the other end of the spectrum is something like a truck snow tire or a rear tractor tire......with HUGE deep tread grooves.
That will shed water so good that it will almost never actually hydroplane......but it will loose traction without a lot of water on the road.
Again, it's resistance to hydroplaning has almost no relationship to the pressure.

In the middle are "all other tires". Some of which will be better in deep water with higher pressures and some that won't depending on the specific tire design.

And finally, every time a tire loses traction on a wet road it is NOT a case of hydroplaning.
Quite often you will loose traction just because of the wet surface way before an actual hydroplane happens. And THAT is where your higher pressure can actually become dangerous.

Since you seem to be so fixated on "facts", how about looking up the general impact on overall traction......in varied conditions.......of over-inflating your tires.
Pretty sure that you will NOT find that extra inflation makes it better.

 

You bring lots of jaw-jaw but little or no evidence.

Show me the evidence on the later. I've been watching for it for years.

Hydroplaning is a more severe hazard than the reduced traction of simple wet surfaces. Drive prepared for the worst, and the lesser stuff takes care of itself with margin to spare.

Driving for just the lesser hazard, is dangerous.

Show me. I'm still waiting for something more solid than the jaw-jaws of self-styled but conflicting "experts".

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P.S. I showed mine a couple years ago, and am still waiting for a response from the other side.