[tnharley]

I have had a difficult time in keeping the tire pressures at the recommended 30 psi. Maybe because its cooler weather now and all. I will put 32 psi in all four tires using my guages but the TPM indicates about 1-2 psi lower. This morning when I came out it was showing only 27 psi in the front tires and 29 psi in the rears. I added more air up to 32 psi, but the TPM still indicates 30 psi. Just wondered about the accuracy of the TPM system. Also I guess since the tires are soft rubber they tend to let a little air pressure out more frequently than harder tires. I have never added air more than quarterly on my other vehicles. Seems like I am fiddling with these on a weekly basis. Just wanted some feedback if others are seeing the same thing.

 

[rdslon01]

Are all of your tires doing it, or just some of them? Has the temperature been dropping there regularly with the trend line going steadily down? Are you sure you don't have some slow leaks?

 

[U.S. Marine]

tnharley, when I checked my tire pressure "cold" I had 28psi both front tires, 29psi both rear tires. So I started the Vette and went to the screen section that indicated psi for all four tires. Filled each tire with 30psi and it has been two weeks and all four tires are reading 30psi. My tire gauge matches the TPM system readings. Like Rodney posted check for any leaks, valve stems etc.

SF
Rick

 

[jsvette]

tnharley the Stingrays TPM system (and for that matter most OEM TPM systems) are best used as a rough gauge of the actual tire pressures. You most definitely will find that your indicated pressure and actual pressure will drop 1 to a couple of pounds when the ambient temperature drop. Use an accurate hand gauge you trust to set your cold tire pressures where you want them, then note the relationship to what the TPM indicates (you will normally need to roll about a block or two for the revised reading to stabilize). I like to wait until I have been driving at normal (city) speeds for about 15 minutes to look at the TPM read outs. By that point any short term difference from one side being in the sun or near a warmer wall in your garage for example, will normally be equalized. Rely on your TPM to warn of low pressure especially after driving over questionable pavement, gravel or through a construction zone. But always revert to checking your tires with an accurate hand gauge on some schedule that is convenient for you.

 

[elegant]

In many parts of the country, it has been getting colder, and that old standard, "1 pound tire pressure up or down for every ten degrees in temperature change," is always worth considering, as is the other one, that most tires lose about one pound of air every month due to air molecules migrating through the sidewalls.

Most tire pressure gauges are inaccurate by a couple of pounds. The OP may have a super accurate one and his TPMS readings might be off a pound or two. On both my C5 and my C6, the factory TPMS readings perfectly agreed with my high-quality pressure gauge. Once however, one determines which one is most accurate (perhaps checking with a third gauge a friend has), one can adjust accordingly.

The least most accurate tire gauges I have ever found were located at dealerships, and consequently, for the last ten years, when I take my car in, tell them NOT to adjust my pressures.

 

[glen e]

Don't overthink this, your pressure will vary as temps change...let it swing between 28-32 and you'll be fine....

 

[ferd1971]

I actually had the same question this past weekend. My tires were inflated to 28 all around (according to the TPS in the car). Although the car showed the pressure as acceptable (in green), I decided to inflate the bit. When looking at the side wall of the tire, its max psi is 51. I decided to go with 40psi because I don't get an opportunity to drive it a lot and I didn't want to start developing flat spots. After inflating to 40psi, using a tire gauge, the tire pressure monitor in the car said the psi was 38psi. I guess there is always going to be variance depending on the quality of the tools you use to measure air pressure vs what the TPS system is saying. Which brings me to my next question...is 40psi too much? I find it odd the recommend psi is 30 if the tires max is 51.

 

[jsvette]

ferd1971 I think you will find you are running them too high with cold pressure reading of 40psi. It will lead to more rapid wear of the center of the tire, reduced traction and potentially serious problems if you are driving in warm weather at high speeds where the internal temp of the tires increases resulting in a related rise in tire pressure.

 

[ferd1971]

ferd1971 I think you will find you are running them too high with cold pressure reading of 40psi. It will lead to more rapid wear of the center of the tire, reduced traction and potentially serious problems if you are driving in warm weather at high speeds where the internal temp of the tires increases resulting in a related rise in tire pressure.

Thanks...your probably right. I will lower the pressure in the tire.

Fred

 

[glen e]

ferd1971 I think you will find you are running them too high with cold pressure reading of 40psi. It will lead to more rapid wear of the center of the tire, reduced traction and potentially serious problems if you are driving in warm weather at high speeds where the internal temp of the tires increases resulting in a related rise in tire pressure.

Agree with jeff, why would you look at tire and swag the guess? The pressure on your door sill is the one recommended by the engineers for this car, go with it....40 is way too high.

 

[Fdxpilot]

I actually had the same question this past weekend. My tires were inflated to 28 all around (according to the TPS in the car). Although the car showed the pressure as acceptable (in green), I decided to inflate the bit. When looking at the side wall of the tire, its max psi is 51. I decided to go with 40psi because I don't get an opportunity to drive it a lot and I didn't want to start developing flat spots. After inflating to 40psi, using a tire gauge, the tire pressure monitor in the car said the psi was 38psi. I guess there is always going to be variance depending on the quality of the tools you use to measure air pressure vs what the TPS system is saying. Which brings me to my next question...is 40psi too much? I find it odd the recommend psi is 30 if the tires max is 51.

Your tach says 6500 rpm is max. Do you routinely operate at 6490 rpm? 51 psi is the highest pressure at which the tire is guaranteed to not separate from the rim.

I've varied my tire pressure a pound or two, based on how the tires were wearing (excessive wear in the center,) but never just 10 psi for no particular reason.

And I agree with Elegant, tire pressure drops about 1 psi with every 10 deg F. With the changing seasons, you will probably have to add air.

 

[mjw930]

Max tire pressure is more about load ratings and overall integrity of the tire. The tires max load rating is only valid at max pressure. This is not max cold pressure, it's max absolute pressure whether hot or cold. It's a reference point, not the pressure you are supposed to operate the tire at.

As others have said, the engineers gave us a set of numbers (road and track). Unless you are tweaking the tires for competition use, have an accurate air pressure gauge and pyrometer then simply use those temps and don't over think this.

 

[tnharley]

Thanks for the input from everyone. I think that the engineer in me is causing me to overthink the issue. I have a couple of motorcycle air pressure gauges but they have the long extension hose attached to them and doesn't work out real well on an auto tire. I need to pick up an accurate gauge for automobile, maybe a nice digital one like the Sears Craftsman one and use it exclusively. We have had a considerable temp drop lately too from the mid 50s at night down to the low 40s, so that probably is contributing to the dropping air pressure indicated. First Corvette, so I guess I am paying much more attention to it than I should be

 

[Milliwatt Rob]

Generally, you raise tire pressures above the recommended rating, up to the maximum rating, when you are carrying a greater than normal load in the car. Save that 51 pounds for when you have a 860 pound passenger with gold ingots for luggage.

 

[ferd1971]

tnharley...sorry for your thread getting hijacked. I had the same questions you did about the TPS system.

 

[U.S. Marine]

tnharley, you didn't overthink anything, you had a great question about the TPM system and we all received some great feedback!!

SF
Rick

 

[glen e]

Whenever i say "dont overthink it" - its not a slam, we all do it! But for others reading here, let it be an example. Yes, he did. He bypassed the owners manual, he bypassed the sill label that tells you what to do and decided on his own measurement for filling the tire which was based on a wrong spec on the tire.

Thats overthinking, IMO.....It really pays to see what the engineers want you to do first....the most recent stat i saw in the industry was something like 70 pct of all car owners have never read the manual and opened the hood.

 

[U.S. Marine]

Whenever i say "dont overthink it" - its not a slam, we all do it! But for others reading here, let it be an example. Yes, he did. He bypassed the owners manual, he bypassed the sill label that tells you what to do and decided on his own measurement for filling the tire which was based on a wrong spec on the tire.

Thats overthinking, IMO.....It really pays to see what the engineers want you to do first....the most recent stat i saw in the industry was something like 70 pct of all car owners have never read the manual and opened the hood.

Glen, my post was not referring to your previous post. I was responding to tnharley's statement: "I think that the engineer in me is causing me to overthink the issue" I normally select "Reply With Quote" to reply back to a members statement.

SF
Rick

 

[glen e]

I know...my point is we all overthink......its what enthusists do!

I dont need to tell you a story of a rubbing compound I used a few years ago on my camaro where "I knew everything about it" and did not read the label....

After a $400 hood repaint, all was ok again.....

 

[ferd1971]

Whenever i say "dont overthink it" - its not a slam, we all do it! But for others reading here, let it be an example. Yes, he did. He bypassed the owners manual, he bypassed the sill label that tells you what to do and decided on his own measurement for filling the tire which was based on a wrong spec on the tire.

Thats overthinking, IMO.....It really pays to see what the engineers want you to do first....the most recent stat i saw in the industry was something like 70 pct of all car owners have never read the manual and opened the hood.

glen e...I appreciate your expertise with all things corvette. I enjoy reading your posts because you seem to be very knowledgeable. However I do not appreciate your continued slams about an honest mistake I made about tire inflation. I'll be honest...I did not consider looking at the sill label and when I looked yesterday, the owners manual did not mention the recommend psi level. If I had all of the answers to my questions about my C7, I wouldn't be on this forum. I welcome your comments, but please keep in mind some of us are still learning