Have been a vette owner for about 2 years now and currently have an '07 C6. This car (and the former C5) have run flats. I only drive the vette about twice per week with normal city and interstate driving. My problem is the tires will not hold 30psi. After about 2 trips, the pressure falls to 27-28 psi and the tires have to be topped off (about once per week) which is getting to be a bit of PITA. Is this normal?? What do the rest of you guys do?? Nitrogen??

 

Well......you'll have your hardcore nitrogen advocates say that nitrogen will help, but considering that normal air is 78% nitrogen anyway, unless you're doing some special stuff with your car (such as taking it to 35,000 feet where you don't want moisture condensing out of the air and making ice cubes in your tires) I don't think the fact you have normal air is the problem.

You might have a small nail creating a slow leak, but if all tires are losing air about the same, then that's unlikely.

I would get some soapy water and slop it around your valve stems and see if there is a leak. I'd suspect either the nut securing the valve stem might need tightening, or your valve (inside the valve stem) might be loose or need replacing.

The nuts that hold the sensors in the valve stem hole are only torqued to a real low value (62 inch-lbs., about 5 ft-lbs.). If you replace the valves in the valve stems, they are supposed to be nickel plated (like the silver ones below) so they don't corrode the aluminum valve stem like a standard brass one might do.





I think you've got a simple problem that you, or any tire shop, should be able to take care of pretty easily.

Good luck,

Bob

 

I agree with beezeye, you've got a leak in all 4 tires.

I'm on my 3rd C6 and have never had any of the runflats leak like yours. When the temperature drops, the tire air pressure gets lower, but when the temps drop to stay for awhile I add more air. When it warms back up in the spring, I have to let some out. That's the only time mine have to be changed - about 1 psi for every 10 deg. F change in temperature.

 

"I think you've got a simple problem that you, or any tire shop, should be able to take care of pretty easily."

Except it is the dealers responsibility to fix it, I would be have this conversation with my dealer.

 

No offence but you could drive it more, no usey you lucy air...

 

Not normal. Sounds like the tires aren't seated on the rims properly. Just reseating them may do it. Have to find a shop that sevices runflats.

 

I read that in my manual that it is the dealership and or a Goodyear Tire place. BUT dealership told me they don't do tires and they just send it out.
BUT is it covered under any kind of warranty on these factory Good Year runflats? or another expense that you have to cover?
There is 15,400 miles on 2005 C-6 now with lots of tred left.

 

Being a runflat I was told you can't just take it to any Goodyear shop but one that has the proper equipment to work on these tires.

 

Thanx for the comments...I'll start with the valve stem nuts!

 

I'd say check the stems, & if not, then the tires weren't sealed/seated properly onto the rims....Hope all goes well!

Ron

 

FWIW:

Jay Leno uses nitrogen in all of his cars.

http://www.popularmechanics.com/auto...51.html?page=2

A Porsche dealer in Dallas uses nitrogen in all of its tire applications also. They'll do the nitrogen "fix" on any make of car with an appointment.

 

FWIW: That's all Costco uses when they install new tires on all cars. The cap is green.

 

Ah....NITROGEN!

According to that link, Jay says your wheels won't corrode with Nitrogen. Yeah, Nitrogen is an inert gas, but the main thing is that it's generally dried out so there's no moisture in it - you can do the same thing with air. And, of course, air is 78% Nitrogen, so you've already got almost complete Nitrogen in your tires already.

As far as his claim that the pressure won't change with temperature

I say again: BULLSH!!!!!!!!!!!!T!!!!!!!!

Get out your old physics book and review the info on Boyle's, Charle's, and Dalton's Laws. Temperature/Pressure/Volume are all directly related in all gasses.

The General Gas Law is: pv=nRTIf volume is constant (such as in a tire - well the rubber can expand with an increase in pressure, but for all practical purposes it is solid enough to be considered a constant volume), the number of molecules is contant (i.e., you don't put in or take out any air), the Gas Constant is, obviously, constant, then the only 2 variables are p and T.

Therefore, Pressure is directly proportional to Temperature, QED. If you increase one, you increase the other. That is an immutable fact of physics (at least in our universe at macro levels - maybe it's different in a parallel universe or in quantum mechanics in a singularity in a black hole or at the instant of the big bang).

In a restricted/constant volume (such as a tire), if the temperature goes up, the pressure will increase.

Also, why is "pure" Nitrogen (as opposed to normal air with only 78% Nitrogen) used in aircraft tires? Primarily due to fire in a wheel well.

Aviation Airworthiness Directive 87-08-09 requires that tires on wheels with brakes installed (the brake overheating can cause the tire pressure to increase until the tire or wheel fails) to be serviced with NITROGEN-which will suppress any fire caused by overheating.

Notice it doesn't say the pressure won't increase with temperature - because it will no matter what gas you put in the tire.

However, a normal fire requires oxygen to support combustion. In a confined space, such as an aircraft wheel well with the gear up and doors closed, if a fire starts for any reason and the tire bursts, if the tire is filled with regular air (about 78% Nitrogen, 21% Oxygen, 1% Argon/CO2/water vapor/other gases), then there is a shot of Oxygen from the exploding tire that could fan the flames. Pure Nitrogen might help supress the fire when the tire bursts.

Additionally, tires on large aircraft are pumped up to pressures far higher than car tires. On the B-767's I flew, the main gear tire pressures were in the range from about 160 psi up to 195 psi for the high ply rated tires on the heaviest extended range aircraft we flew. Here's an excerpt from a review of the TWA 800 accident, which speculates that a burst tire could have caused the accident:
Anyway, if you feel good putting pure Nitrogen in your tires, go for it. Me, I'll stick with 78% Nitrogen.

Bob

 

I will assume, Bob, that since I said "FWIW" about Leno using nitrogen in all of his car and motorcycle tires that you were merely being instructional and not pedantic as are far far far too many university types, not to mention former Navy fixed-wing jocks.

Most civilian pilots, in my experience, are usually pretty decent sorts, perhaps you're still in training to get the military and uni-prof out of your system. You're probably familiar with - but others may not be - Ayn Rand's _Atlas Shrugged_, which has an interesting look at college professors.

Others of us on here have fair amounts of education and experience too. Some of us teaching at the university level upon occasion as well.

You familiar with the Clemson report titled _Freight Sustainability Demonstration Program_? And the _Improving the Energy Performance_ results in Canada? - there are other studies - this is just to mention two. They apply to vehicles other than aircraft, specifically trucks.

NASA doesn't quite deal with Boyle's the same way you do: yes, your formula is correct, it's just that NASA deals with it wherein the temperature is the constant, which affects pressure. With automobile and truck tires the whole point is that the temperatures are not constant. This tread is about inconsistent pressures and leaks in automobile tires, which deals with fluctuation in our Corvette tires, not potential high-pressure problems and fires - with 767s - or Navy P-3s.

Since tire structure is somewhat porous - albeit it small - and nitrogen molecules are larger than air molecules, nitrogen is lost at a slower rate than is air which, as you point out are 78% nitrogen. It's probable then that nitrogen will maintain a more constant pressure in our tires than will "plain" air.
I could be mistaken, I often am.

As I said earlier, I'll just "assume" you were being instructional and not pedantic.

 

 

Overrated.

 

Jay Leno also washed all his cars with expensive bottled water during the L.A. water shortage when the average person couldn't run a hose to wash his car.

For the average driver, filling your tires with nitrogen is a gimmick with a skewed cost-benefit ratio. If it's free and you want it fine, otherwise, don't bother with it.

 

Well here the only place I know of is Costco that fills tires with Nitrogen. The air here used to be free now they charge you for that too.

 

Thanks, and I'm sorry, and apologize to you and all on the forum. Thanks for the whack up 'side the head to bring me back to reality - my wife has to do that regularly!

Yes, my rant was supposed to be instructional. The thing Jay Leno said that set me off was:
You know that's flat out false, but I should have just said that, I guess.

I'm not an academic - I'm an nuts'n bolts, practical application, dumb operator kind of a guy. They brought me on to teach the practical application of all the theoretical crap the students learned in other courses and to try to bring all that junk together in a "how to apply it operationally" kind of way. Butt....after 2 years of doing that, I'm retiring (again) at the end of this semester. They'd be happy for me to just teach for a couple of more semesters, but ultimately they want you doing research, publishing, presenting, getting grants, etc., and I'm not into any of that - although I do love teaching what I teach.

I was not aware of the studies you cite above, but I Googled the FSDP and saw the Round 7 study of truck tires that expects:
My car is driven regularly (26,000 in the 2 years I've had it, on my third set of tires), but I guess if a C6 owner doesn't drive the car much, and their tires might last many years, tire casing life might well be a factor that Nitrogen might help.

My reference to 195 psi tire pressures in aircraft tires was simply to show that our street car tires are not the same as those on aircraft that the FAA requires to be filled with Nitrogen or other inert gas - it's a fire supression thing that we really don't have to be concerned about in a street car.

Anyway, I learn a lot more on this forum than I'm able to pass on. If I pass on bad info, please call me out on it and straighten me out - my wife tells me I'm wrong all the time (and she's right ).

Bob

Edited to add this link to some pictures of the Christmas Day Tornado damage to our school:

http://www.leadingedgesim.com/mkaprocki/ERAU/

 

Someone has been sniffing too much nitrogen