What's the best Tire Pressure for FE/safety/handling?

Realistically, if truth be told, probably the manufacturers pressures are the best compromise of all those factors you've listed.

Both the tire Manufacturers and Toyota engineers do extensive research to give the end customer a unique balance of all those features, and the pressures they select are a good compromise of all those factors.

If you want a good ride, reasonable fuel economy, safety, good brakeing and pleasurable comfort, your best selection of tire pressures would be those of the manufacturers!

David (aka Blind Guy)

 

I don't know, but the sticker on the driver side door frame says 35 psi for the front tires and 33 psi for the rear tires.

My tires are 15 inch, and the brand is Yokohama Avid S33.

 

It's not an easy question to answer. Increasing pressure

- improves FE, tire tread and tire body lifetime (probably), cornering

- degrades comfort and possibly safety a very little bit

- hear contradictory opinions on handling

There is no "sweet spot" - it is a compromise depending on what you want. Over the three months I've had my G-3, I have gone from
32/32 to
35/33 to
46/44 to
56/54

so you can see what I like. :target: (OK, the ride's not that bad now)

 

As it relates to the Prius I think the absolute best all around pressure (ie good ride comfort, tire wear, braking, cornering, and fuel economy) is 44 front 42 rear. I have had my Prius for 2 1/2 years and have tried several different pressures. When I had my OEM set of tires I settled on 50 front 48 rear (yes just slightly above the max sidewall pressure). The higher pressure allows for higher fuel economy, but after 44 PSI I notice some braking losses as well as some handling and cornering losses especially in wet and snowy conditions. The comfort level is about the same unless you drive on some torn up back roads.
When I replaced my OEM tires I went with a slightly wider 195/60R15 tire and I still ended up settling on running at 50 front 48 rear.

 

My Volvo (and I believe other European cars) gave two sets of tire pressure recommendations:

One set was (I guess) the normal or default PSI recommendations.

The other set was expressly for better fuel economy and had higher PSI recommendations.

 

You know my wife's VW has that as well. I believe its listing says Standard Load and the other one says Full Load / 100 KMH+.
Anyhow the difference is about 5 PSI if I recall.

 

You need higher pressure if you increase your payload (weight) and to not overheat the tires (extended high speed driving). The extreme high pressure some people mentioned are just dangerous, plain and simple. As you exceed a certain pressure, your chance of blow outs are much higher.

 

With higher pressure you have more of a chance of popping a tire due to debris or pot holes, low pressure you have a higher chance of a blow out because of the high heat you would generate.
You don't have much to more to worry about either as long as you are within about 33% of the Max side wall pressure (between 29 PSI and 58 PSI on most tires) It's definitely the changes to handling and braking that someone should be more concerned with.

 

Nope, you also can break beads on a tire. I have seen it happened, not exactly pretty. Why do you think the tire installer wear goggles.

Overheating tire to a blow out, you have to be riding a flat tire for a LONG time before that happens. Also tread usually comes off rather than a big blow out. Remember the firestone Ford Exploder incident?

 

First, you probably should never simply trust anything a stranger says to you about safety -- you should double-check their advice. If you do so, I think you will find that there are a few reasons why you may NEED to inflate at other than the manufacturer's recommended pressure. As said here and elsewhere, they have to do with traveling at sustained speeds well beyond highway speeds, carrying loads over the expected load, and driving on unique surfaces (off-roading, race tracks). While most understand that underinflation is dangerous, overflating tires for normal use on ordinary roads is also dangerous.

While there are some who are obsessed with MPG and the few dollars it MAY save during the year, they seem unable to quote anyone other than like-minded people (usually just recycling opinions in other forum posts) to recommend overinflation. If there were engineering support for what they are peddling, I think we would have heard about it. We haven't, and I find that quite telling.

I'm not an auto suspension engineer, so I found a technical article that I think may be helpful (Google is my friend). Hunter Engineering Company apparently provides test and R&D equipment to automotive manufacturers (BMW, M-B, etc.) and has published a detailed discussion of suspension parameters, including the impact of tire pressure at Improved Automotive Suspension Testing Apparatus. I find it more persuasive than arguments like "so-and-so said it was okay in another thread." While I suggest that you read the article yourself, I will quote some of its relevant comments and conclusions.

First, let's start with the basics:

In case there is any doubt as to which factor is more important for safety:

Then, as long as you believe that traction is important, you might want to note that:

While there is a detailed discussion in the paper, the results seem to boil down to:

So, if I understand correctly, a 10 psi overinflation would reduce traction by about 12% on average and that increases to about 25% at 20 psi overinflation. And that reduced traction should result in reduced braking distance. That seems significantly unsafe to me even under normal driving conditions. But when combined with other unsafe hypermiler techniques such as drafting semi's and not slowing down for curves, that loss of traction must seriously compromise safety -- for the driver and others on the road.

Also, for those who cannot feel the more violent wheel hops caused by the overinflated tires, that may not mean that the laws of physics are suspended around you. It just suggests that the Prius suspension is "soft" enough to isolate the impacts. But I think the suspension components are still taking a greater beating than they were designed for.

And for those that keep saying that US tires are also underinflated to provide comfort:

First, for that response to even begin to make sense, foreign versions of the exact same car would have higher pressure recommendations. I don't think that is the case.

Second, the tires just transmit road defects, and the pressure makes that transmission more or less efficient because:

Now, if there is an equally detailed discussion that offers another conclusion, I would certainly be pleased to read it. Until then I'm not buying the overinflation pitch.

 

well to be fair most BMW's and Euro cars come with low profile tires where there are a whole new set of problems. Better for performance, handling, braking, and cornering, and horrible for ride comfort. In low profile tires even if you are at the recommended pressure you have a high chance of breaking one of the steel sidewall belts. Yes I've seen that happen too.

 

I still have a hard time believing that if it was just as safe, that manufacturers wouldn't pump up the tires as much as they could to achieve higher EPA ratings. They could then put a notice to owners how they could "lower" pressures for additional comfort. There is such a push to increase FE that they would be stupid to overlook this if it is a legitimate option.

 

You would think..... But maybe the engineers just aren't drinking the right Cool-Aid.

 

Haven't you heard comfort always rules out of fuel economy to the general consumer. Toyota and Honda have done it for years with the increasing FE by equipping their smaller cars with tires that are arguably too small for the size of the vehicle.

 

The most important thing for the pressure is the load it must carry.
I once got a copy of a formula in the standards manual of the ETRTO. This is the formula the car -manufacturars also use to determine the advice-pressures .
Made an Excell-form to re-calculate advice-pressures, for when you put non-standard tires on.
Translated it to Englisch (from Dutch, I am from Holland) and placed it on my Sky-drive from my hotmail-adres in the next map. Allways take the newest version in that map.
Sorry,when I made 5 posts I can give you the link, so ask me for more information so I can react.

At making this form ( and others) I concluded that what another member here wrote is wrong, Te manufacturars determine the pressures not by testing, they just fill the right loads in the formula.
This weigt is sometimes diferent from what other manufacturars do.
BMW for instance only give the pressure for what I call Heavy use, and users explain them as normal use. My vacation use with towbar-load is what most manufacturars use for maximum load, and only then the rearpressure( and load they filled in) is higher, mostly the maximum of the tire.

That is why I introduced the load-percentage.
And this is what you need to calculate your own pressure.
If you calculate back the load of a sertain tire-pressure, and the actual load on that tire is 100% of that , then you have the smoothest ride up to 160km/h\ 100m/h, and the best grip. The lower you go with this persentage, the harder the ride and lesser grip , but the lowest fuel-consumption and stiffer in curves. Under 85% you will notice discomfort bij bouncing ( conclude this myselves throuch reactions, but can be discussed). 95% gives the less tire-wear, so you tires last the longest, 100% and 90% gives more tire-wear and about the same both. So it is just what you want, for the tire-pressure.
That is why you get so many different answers.
if you play with my form , you get what is nice for you.

 

Oh.. I forgot something
You may not go over 100%, then the tire gets to warm and gets damaged.
But mayby someone with more posts wants to glue the http thing in front of it and place the link for me.
cid-a526e0eee092e6dc.skydrive.live.com/browse.aspx/.Public/Recalculating%20tyre-pressure

 

Rodjo wrote
From testing over 100 different vehicles, an increase of one p.s.i of tire pressure decreased adhesion by an average of 1.2%. So, if I understand correctly, a 10 psi overinflation would reduce traction by about 12% on average and that increases to about 25% at 20 psi overinflation.

Then you asume it is a liniair scale, but probably it works another way. I think you should see the pressure adding asl a persentage op the pressure you start from. concluded by studying the formula they use for that, which I can send you in a personal mail, the formula is made so that the tire-surface gets the right temperature.
And that is a balance between warming up bij the energy there is put in bij deforming the tire-surface, and the cooling down by windcooling and rotation of the tire. I dont know yet what the ideal temperature is for summer and winter tires, and howmuch more grip they have at that temperature then cold (20dgr celcius)
Say it is 1.5 times as much and at 10degr C lower 1.4times as much, then it is verry important to use the right , and not to high pressure, otherwise you slide easyer out of a curve. Is it for instance only 1.1 times as much , then it is not so important and you can take a higher pressure for less fuel-consumbtion, then it is only for comfort that you dont go to high.