How much do you inflate your tires...tire spec or vehicle spec?

[chconline Veteran]

You realize you're talking minute fractions of an MPG, right? You'll be lucky if you save $20 a year.

The decreased rolling-resistance of an over-inflated tire is not nearly worth the decrease in handling, comfort and stopping power, and increase in road noise and risk of blowout.

False. It depends on your car and your tires.

Typically, you will want to fill it to your car's specifications as indicated on the door. This is the general rule of thumb. However, if you spend some time testing and tuning, then that is not always the best case.

Autocrossers like to run higher PSI for better handling and better traction. I run higher pressure for fuel economy as well. For example, in my 2007 Honda Civic LX sedan, I use Continental ExtremeContact DWS during the summer. These tires are rated for 51 PSI, obviously that is absurdly high. My car is specified for 32 PSI, which is absurdly low in my opinion (Car comes with Goodyear Eagle RS-A stock rated at 44 psi maximum). The ExtremeContact DWS has quite a soft sidewall, and running it at 32 PSI is just ridiculous. Also, for my car, I noticed tire pressure and rolling resistance makes a HUGE difference in fuel economy.

I normally run 41.0 PSI all around on my tires. Fuel economy during the summer is at a stable 5.9L/100km to 6.2L/100km with frequent A/C use (I check all my fill ups). I noticed no significant difference with regards to fuel economy if I drive at 80km/h, 100km/h, or even 140km/h consistently -- maybe 5 to 8% at most. However, one time my mechanic thought I was running my pressure too high, so he dropped it to 35.0 PSI all around. To see if it really makes a difference, I ran 2 tanks of gas in the exact same driving conditions, and it came out to be around 6.7L/100km for one tank and 6.8L/100km for the second. Keep in mind I ONLY use Shell gas at the same gas station (Gas quality also makes a big difference for my car). That's a 10% difference for a 6 PSI drop constant. Once I've inflated my tires back to 41.0 PSI, fuel economy is back to normal.

Overall, 41.0 PSI in my Civic with Continental ExtremeContact DWS gives me the best balance of fuel economy, handling, and grip. The tires make proper contact with the road, and after 40,000km the tire wear is completely even all across.

So yes, tire pressure makes a big difference in fuel economy in my particular case. It may not hold true for every car out there, and there is no universal rule for what PSI you should run it at. The number on the door is just a recommendation for those who are too lazy to check -- spend some time testing different settings with regards to wear, traction, and fuel economy with your specific configuration to get the best results.

Just for reference... right now I am running Continental ExtremeWinterContact tires in the winter right now, and obviously they have much higher rolling resistance, and as they are a completely different tire, I am still tuning at different pressures for the best result.

[Dan~]

32psi all round for my 205/55/16 TYRES

chconline - You said that your max psi for your tyres is 44psi, but you run it at 41, you do understand that when the tyre gets hotter the psi increases? So you'll be wearing out your tyres quicker plus your near to bursting point!

[moloko]

Ha i did not know it was on the door. I always went into the manual. But I do pressure by car weight.

[HawkMan]

32psi all round for my 205/55/16 TYRES

chconline - You said that your max psi for your tyres is 44psi, but you run it at 41, you do understand that when the tyre gets hotter the psi increases? So you'll be wearing out your tyres quicker plus your near to bursting point!

Actually he said the max psi was 51 ;)

[Haggis Veteran]

Use your common sense

put the door psi in that tyre

if it look as under-inflated as you say put some more in it

Under-inflated Tyres are dangerous and use more fuel

My Car says to put 40psi in the tyre if the car is fully loaded

I go with 34 as 40psi the car handles crap lol

[Iridium]

If you switch to pascals 1N/m? you find that you can actually get a much more accurate rating. My car has a rating of 35psi with 250kPa in parenthesis. I did a check and found that 35psi is only 240kPa. I did a check and found that the tyres are made in Japan, which like every country outside the US they they use metric units, so using the 250kPa rating is giving around 10kPa more per tyre.

[_neutrino Veteran]

I only buy the Tires specified by the vehicle manufacturer so they have always matched.

[threetonesun]

Autocrossers like to run higher PSI for better handling and better traction.

This is not technically true. Autocross limits the number of modifications you can do in whatever class you run, and at the bottom levels where most people compete, tire choice and suspension modifications are relatively limited. A driver might over inflate their tires to correct for a number of things, like cheap stock tires that have a tendency to roll over, or to adjust rear/front grip with just tire pressure, since they can't modify their sway bars. They also tend to overinflate since, unlike racing on a course, the tires cool off while waiting between runs.

In any of the open classes of autocrossing, where any modifications are allowed, the cars usually run racing tires and inflate them to their recommended pressures.

[chconline Veteran]

32psi all round for my 205/55/16 TYRES

chconline - You said that your max psi for your tyres is 44psi, but you run it at 41, you do understand that when the tyre gets hotter the psi increases? So you'll be wearing out your tyres quicker plus your near to bursting point!

The tire pressure rating on the door and your sidewall is COLD pressure.

The maximum pressure is NOT the bursting point. You can easily run 50-80% higher than that with no ill effects (Read EcoModder forums, not that I am suggesting it). You are running a much larger risk for tire blowout if you have insufficient pressure than overpressure. Of course at very high pressures, your ride will be extremely stiff, and if you hit a pothole or anything, the risk of damaging your tires is much higher. But it does not mean there will be immediately blows.

As I have said, different tires and different cars have different configurations. Normally it's better to run it at a higher pressure than lower from my experience. Also, after 40,000kms on my ExtremeContact DWS, there is no uneven wear across the tread. I know people who run much higher pressure than me on other forums due to the softer sidewall with absolutely no issues at all with the same tire and the same car.

Honestly, if you think your tires are going to blow because you run it at a pressure that's too high, or think that the sidewall maximum is the point of failure, you need to do a little more research. Engineering maximums have HUGE tolerances.

Additionally, you effectively ignored 95% of the stuff I just said and just picked out 2 or 3 sentences in my post and started arguing about things I've already addressed clearly.

[JackBlack304]

The door pressure is for a smooth ride. The auto manufacturer's don't want their customers complaining about a harsh ride. Crank it up (my tires last around 90,000 miles).

[_neutrino Veteran]

I always go with whatever the tire has to say, then again if you get the correct tires then they should match anyway.

[sc302 Veteran]

I always go with whatever the tire has to say, then again if you get the correct tires then they should match anyway.

Yes do this, and when you see a high wear on the center of your tire go back to the door.

[xendrome]

Yeah the PSI rating on the door of the vehicle assumes you are running the OEM size tires and factors in the standard weight of the vehicle, so you should use that.

[thejohnnyq]

Always go by the Tire if the tire has been changed from the original set. It is best to keep the tire at about 10% the maximum fill.

the perfect example of why not to use the vehicle numbers is FORD f-150 and Firestone tires, the truck called for pressure of 26 lbs the tire called for minimal 35 lbs. Firestone and others pointed out it was to little air to allow proper cooling of the tire and not enough pressure to stabilize the sidewalls.

No one car manufactures can test for all types of tires and rubber mixes.

I use the advise from my experience as a mechanic in the past and from where i purchase all my tires from, Tire Discounters, which has never steered me wrong.

[Growled Member]

I usually end up running the things until they are nearly flat and then throw some air in there until it looks right. Not proper at all, I know.

[EddieF]

I can't believe how split people are on this. (and the person who registered to resurrect this topic haha)

Anyways, government recommendation: ;)

Tires are manufactured for many different vehicle makes and models of vehicles. And the psi number on the side of a tire only reflects the ?maximum permissible? inflation pressure for that tire ? not necessarily the correct psi for your vehicle. When filling your tires, always follow your vehicle manufacturer?s psi recommendations. You?ll find this psi number on yourvehicle?s tire information label, as well as in your vehicle owner?s manual.

http://www.safercar....Information+FAQ

[peacemf]

if its not on the door, its on the fuel cap!

[tsupersonic]

if its not on the door, its on the fuel cap!

Certain cars have it on the driver side door, and other cars have it on the fuel cap. On my car, it's on the fuel cap.

[neo1911]

32psi all round as suggested by manufacturer.

[jmhobson]

Though my first instinct was to go with the vehicle's PSI recommendation, I think that going by the tires' stated PSI is just as good, if not better. Here's why:

 

1 - Though this is just a theory, it seems vehicle manufacturers would recommend a lower PSI rating so that traction is increased and safety specs improved (such as those advertised in commercials like shortest stopping distance, best handing, etc...). Though perhaps better to show off specs and in bad weather, it's probably wise to go higher for everyday, average-use purposes.

2 - Auto manufacturers might assume that a tire is inflated before being mounted. Thousands of pounds of car is sure to increase the pressure, so maybe the auto's recommended pressure is just in case the average consumer doesn't;t take that into consideration and max-fills the tire before mounting.

3 - Are the tires factory-originals? Even if the tire size and ratings are the same the recommended PSI can vary greatly from brand to brand and make to make. In this case the auto's PSI recommendations are likely irrelevant, unless you get the exact matching tire models.

4 - My car "disapproved" of its own door-mounted PSI.    The TPMS light kept coming on in my 2006 Mazda Tribute (a.k.a. Ford Escape, Mercury Mariner). I had all tires inflated to and slightly above the recommendation of 30 PSI, but still the light was on and I could tell there was a lot of excess drag when turning. So I switched to the tires' specs of 44 PSI, and now the TPMS is off, no more high-drag feeling from the tires, and at least 2 MPG gained!!! No bulging or excess wear points to be seen. (similar scenario with my Chevy Tracker too)

 

So based purely on what I've experienced, go with the tires' ratings. As long as the PSI is taken with the load of the vehicle already being applied there should be no problem.

[TCA]

32 for all tires. I don't go by the door I go by the tires themselves.

[The Evil Overlord]

2012 thread guys

[Draconian Guppy]

2012 thread guys

So? Still informative, you  Jelly just cause you didn't start it huh?

[T3X4S]

vehicle spec all the way

[thejohnnyq]

Never follow the door, once the Tires have been replaced.  You should do 15% less then max.   

 

Following the door recommendation is why FORD and Firestone had issues, the tires max was 44, and the trucks door said 25-27, way to little to allow the tire to cool.  

 

This is not the only example, but the car door tag was for the original spec'ed tires (not necessarily the ones that ship with the car