I have a new car and I recently went to see if the tires needed any air. I’d never inflated these tires so I didn’t know what psi they were. The first thing I checked was the tire itself. 51 psi. I’d never heard of a tire taking that much air pressure, so I checked the placard and that said 32 psi. Baffled by the huge disparity, I looked around online and saw these tires variously recommended at and around 44 psi. From what I’ve been reading here and elsewhere, the placard is the thing to follow, but other people who mention this problem don’t seem to have so huge a disparity between what the tire says and the car says. All this has me kinda nervous.
The tires are Goodyear Eagle RS-A P205/55R16. The car’s an 09 Pontiac Vibe.
Is the 51 psi on the side of the tire, or what you measured? Either way, it’s the placard, period. Just make sure you measure the tire cold, before any driving, with a quality (dial or digital) gauge.
On the side of the tire.
In addition to the placard, you might find additional information in your owner’s manual.
51 psi is the maximum inflation safe for the tire, follow the placard that gives the psi your vehicle is designed for.
When the tire manufacturer made the tire, they had no idea of what vehicle it would be on. The MAXIMUM pressure for the TIRE is on the sidewall. The tire pressure recommended by your car’s manufacturer is what you should be using.
If you someday find a tire with a LOWER maximum pressure than what’s on the car’s placard, then you have selected the wrong type of tire.
Good for you for checking your tire pressure. It doesn’t say much for the dealer prep though. Just to be on the safe side, check the fluid levels; oil, coolant, transmission, etc.
Ed B.
I agree that it’s poor dealer prep. Tires are commonly inflated to higher than normal prssures for shipping, and they should be adjusted by the dealer in prep.
yes, the correct pressures are those listed on the placard.
Been busy with calculating tire pressure from 2007 with use of the formula the car-manufacturers also use to determine the advice-pressures.
Last made Excell-spreadsheet
http://cid-a526e0eee092e6dc.skydrive.live.com/browse.aspx/.Public/Recalculating%20tyre-pressure
Always use the newest version in this map, and there are excamples.
The maximum pressure on the tire-side-wall is not a verry meaningfull term.
In some countries they have to put it on the tire by law.
Important is the Reference pressure ( at xxx psi or kPa)
Most normal cartires have a RP of 250kPa( 36psi) but there are exeptions.
This is the pressure at wich the tire can bare its maximum reference load ( on the tire in KG, LBS, or the load index. So for lower loads on the tire u can use a lower pressure. That is why the stikker advices ar much lower then the maximum pressure of the tire.
for higher speeds then mostly 160 km/h and when the tires are aligned not so|-| but so /- more then 2 degrees, this reference pressure has to go up.
With this knowledge you can calculate the pressure needed with use of the actual weigt on the tire with the formula. So it can be higher then 36psi when you use the car for higher speeds and camber angle. For the advice-pressures the manufacturars fill the axle-loads in. For heavy use , they fill in the maximum permissable axisloads of the specific car.
with use of the formula the car-manufacturers also use to determine the advice-pressures.
Actually they do test track testing. No formula is going to beat out real life track test.
No formula is going to beat out real life track test.
How does that not-too-old saying go; all models are wrong but some are useful.
It’s hard to beat empirical research for such varied and complex interactions…
If they dont put the data in the formula,but determine the advice-pressures bij testing, then why the figures are completely the same as on the stikker, when you fill in my sheet for the original tires???
Mayby they do some testing afterward, but I think the most important for them is that you cant hold them responsible for to low pressure.
That is why, I think, last time there ar so many high pressures, especialy at the back ,maximum of the tire.
Classic method was for heavy use the maximum axle loads and for normal use a by the car-manufacturer calculated axle-loads for 3 persons and some lugage. I think after the Ford-Bridgestone afaire they got frigtened and began to give higher advice-pressures.
Tire- specifications havent chanced that much since the introduction of the Radial tire. This formula is probably used for more then 30 jears, a tire-manufacturer answered me, and has since only been chanced on minor points.
In My spreadsheet, I give 6 advices, for normal use, Heavy use and vacation-use, all 3 for up to mostly 160 km/h and up to maximum speed of the car.
The sticker nowadays gives the advices in my sheet for normal use and vacation-use up to maximum speed of the car, to be on the save side.
But if you know you never drive faster then 160km, most dont, then you can use the advices for up to 160, and when you are always alone in the car, you can use the normal for up to 160km.
Often nowadays they dont give the advice-pressures for normal use.
Then the calculatin back to the weights they used for that, cant be used.
I haven’t gone through the entire spreadsheet, but I see a flaw!!
You assumed the maximum pressure imprinted on the sidewall of the tire is somehow connected to the load. It isn’t. I explain that here:
http://www.barrystiretech.com/loadtables.html
Plus, it doesn’t appear you’ve accounted for the change from Standard Load to Extra Load (and vice versa).
So until I have had a chance to fully explore the spreadsheet, my advice to everyone is:
DO NOT USE THIS SPREADSHEET!!
*****WARNING
DO NOT USE THE LINK POSTED ABOVE.
*****WARNING
jadatis,
Please edit this post to remove the link. It has a flaw that will cause folks to underinflate their tires - VERY DANGEROUS!!!
Contact me at Barry@BarrysTireTech.com
Mayby they do some testing afterward, but I think the most important for them is that you cant hold them responsible for to low pressure.
I would not be surprised if they start with a formula, but they also do test track work.
Yes car manufacturers are serious about not recommending low pressure after the Ford Explorer/Firestone mess. Of course they are also concerned about recommending too high a pressure.
I would trust real life testing to a formula. It is possible that the formula you are recommending might be a good choice for a non-standard (OEM) tyre size situation.
Joseph E meehan wrote:
"Yes car manufacturers are serious about not recommending low pressure after the Ford Explorer/Firestone mess. Of course they are also concerned about recommending too high a pressure. "
I think to high pressure can be dangerous too, because you dont have maximum grip then. For campers the camper-manufacturers sometimes stripe troug te advices of the car-manufacturer here in europe, and set all 4 tires at maximum tire-pressure.
I think it will have to take some accidents too, before they will chance that back.
You may try to overload the front-axle of a car, almost can not be done.
The rear-axle of campers are often over-loaded , so maximum tire-pressure is mostly needed at rear. When you put front at maximum tire pressure too, you create understeer and it is possible you slide away if you go a little to fast in the curve of a High-way exit. So I doubt if the car-manufacturars are also concerned about not recommending to high advice-pressures.
@ capri racer
Mail is on the way to you , first to the yahoo adres from the link ,later sent troug to of you reaction here.
Pay little to no attention to the number on the tire. You have a pretty big tire on a smaller, lighter car. Therefore you’d need less tire pressure than the same size tire on a car that is say 700 lbs heavier.
If you are headed for the race track for track day you’d likely want a few more pounds in the tire for better performance. If you are a serious racer you’d do test laps with different tire pressures to dial in the best pressure for racing.
Assuming you don’t go to track day then the only other time to go a few pounds above the placard on the car is if you are loading up the car for the trip to college or family vacation. If the car is near it’s weight capacity running 34 or 36 lbs for the trip can’t hurt. Drop the pressures when you get back to normal daily commuting.
If your car’s placard says 32 psi and the tire says 32 psi then you shouldn’t raise the pressure above 32. In your case if you ran your Vibe with 51 psi in the tires you’d have very squirrely handling, a very hard ride, and excess treadwear in the center of the tire. With the 32 psi on the placard you should have the proper tread footprint on the road for good traction, decent ride, and good mpg.
I think to high pressure can be dangerous too,
True.
After discussion with capri racer, I adjusted the spreadsheet so it gives a trusworthy advice for TRA-typed tires too. Also warnings when normal advice can not be used,wich nowadays is seldomly given.
His concern was that sometimes the ETRTO formule,wich I use, gomes to lower pressures then the TRA formula, but I still am sure that the Advice in the spreadsheet is a good one then for heavy use and vacation-use with tow-bar load.
What I wrote about advices being the same as the plancard advices, when using the original tires in the sheet, only goes for when the plancard is made with the ETRTO formula, wich I thougt was the only one. When it is made with the TRA-formula, this goes wrong, but I give a warning now not to trust it in that case.
So now I again place the link to the map, with the spreadsheet and examples.
http://cid-a526e0eee092e6dc.skydrive.live.com/browse.aspx/.Public/Recalculating%20tyre-pressure
After discussion with capri racer, I adjusted the spreadsheet
Does CapriRacer now fully agree with your updated advice? The fact that you discussed it doesn’t convey whether you reached agreement or not.