Run flat tires and handling

Recently bought a used 2001 convertible.  This is my third Vette over the years, so I'm familiar with how they should handle, but this one is acting strange.  At speeds of 45 mph or higher, it seems a little squirmy....like it is floating in the back.  Just had a front-end alignment and have 30 psi in all tires.  The fronts are in good shape, but the rears are worn pretty good.
I suspect the rear tires may be the problem.  If you put a straight edge across the rear tread, there is a dip in the center section of about (two quarters) in thickness.  I have been advised this may be the handling problem as the rear tires are running on the edges only.  All tires are stock size and are Michelin (Zero Pressure) run flats.
I've never had run flat tires before, any thoughts on this.  Maybe just new rear tires will solve everything.

Yes
definately toss those rear tires, and get some new ones. They are worn, and the dip in the center of the tire you are talking about is caused from not having the correct air pressure in them.
I would say this is your problem, run flats or not, worn tires can play havoc.

30 lbs?  I'm running only 28 in my drag radials, but they are different.  On both the front on the 'vette (275 x30 -18), and my Porsche (225s and 285s respectively) , I'm running betwee 35 and 38 lbs.  They have a flat tread face and wear evenly at this pressure.  Before throwing away the tires, why not add 5 or 10 lbs and see if it pushes the middle out and gets you good handling.   

Since he said the tires were worn pretty good, sounds like he could use a new set anyway.
I keep 38 psi in mine also.
Whether moscooter buys new tires or tries to get a few more miles from his, Monitor that pressure, and keep those tires wearing evenly.

Thanks for the replies.  Next week, I'm gonna try a new set of rear tires.  Probably, the same Michelins that are on it now.  I'll let you know if that solves it.  Hope so.....

I keep my Goodyear GSD3s at 30 psi and they are wearing very evenly. This is what GM recommends for stock sizes and it's been working very well for me.
 
Dave

30 psi?   WoW
what is the maximum allowed psi for those tires?

Max pressure in the GSD3s is 51 psi, but really, that is irrevelant when it comes to the pressure that you should keep in your tires. The sticker on the door jam specifies the pressure that is recommended for the vehicle (for the C5, that pressure is 30 psi). Certainly, that pressure may be varied, depending upon ambient temperature, driving environment, and occupent weight. 38 seems kinda high to me.

Take a look at this video. The guy in the C4 accidentally set his tire pressure to 34 psi instead of 30 psi. You can see what happened. I was 4 cars behind him when this happened. Keep in mind that this person knows that road like the back of his hand.

http://www.corvettekillstories.com/photoga...ics/spinout.wmv

The moaral of this video is DO NOT OVERPRESSURE YOUR TIRES!

Dave

Wasn't able to see the video...
There are certain times when you need to utilize a max pressure for full load.
I have used my truck for towing for years, and I never ever start on a trip without maxing out the pressure in the tires to the rated pressure on the sidewalls. And I monitor this everytime I stop.
The sticker on the door is good to go by, as long as your tires are still the same as what came with the vehicle.
 
I take it the guy in the video lost control or spun out? And the tires were only at 34psi?

I always thought that the tire manufacturers recomendation would be best to follow. regaurdless of what the auto manufacturer says. the tire manufacturer sets the pressure in accordance to the compounds used in the tire and the intended use of it. Also concideration of generated heat affect on the air placed in the tire and ambiant tempareture when filled and temperature of the air at the source would have an effect as well. This is not really as important for daily driveing but the race guys have it to a science. There was a descusion about Nitrogin filling in another post here and air expantion was mentioned. I'm probably wrong like usual but ohwell.
 
 
http://www.corvetteforums.com/m_18442/tm.htm     verry interesting stuff here.

The tire manufacturer (of an aftermarket tire) has no idea what your vehicle weight is, so you will not be able to use a pressure specified by the tire manufacturer as a guidline. The pressure on the side of the tire is a maximum safe pressure - kinda like the max pressure on a spray paint pressure pot. This is the pressure you should never exceed, not the recommended daily driving pressure. There is a big difference.
 
Rich,
 
I guess the guy who made the video withdrew it from that site. Yes, the C4 guy (whom I know) was heading up a mountain road when he spun out. Luckily, neither he nor his car was hurt. He quickly realized that he had overpressurized his tires to 34 psi instead of the 30 psi to which he normally pressurizes them. Just 4 psi made his tires' contact area a bit smaller and hence, less "grippy".
 
Dave

Well I figured I was wrong but wouldn't the auto manufacturers pressure recomendation only work with the recommended tires? what if you replace your tires with tires of a harder or softer compound? I guess you would have to do your own testing huh? I never really paid much attention to the sicence of tires and tire pressure just always put 28 to 32 lbs and just replaced them when they wore out. some lasted longer than others but I just figured it to be the affects of driving habbits. the front tires on my '87 coupe are perfect and have little wear but the rear are about done, slightly more in the center than the out sides. they are at 32 all around. Coopers. lots of good stuff in this thread too.

That all sounds right on to me Blueshark.
At the track tire pressure is crytical, and you can win or lose races with not the right amount.
 
I can remember just a few years ago now, Firestone, and all the problems people were having with their tires blowing out. People were getting killed because of the accidents. And they were warning people to use the correct pressure in there tires, and not under inflate them.

I run 34-36 in front and 36-38 in the rear of my Porsche (both within the factory recommended range, but on the high end) and it works well.  It get only 20K miles per tire, but they wear very evently and that is par for the course for really extreme high performance tires. 
 
On my vette, the original tires wore on the edges mostly at factory pressures, so I increased the pressure.  Now, with oversize on all corners I have to guess, but I do an "ink pad" test on the tires until they seem properly inflated.  But about 36 in front (275s) and 28 in the rear (345 drag radials) seems to result in good handling and even wear. 
 
It could be that run-flats need less air pressure than normal tires: with the tough sidewalls for run I would expect that.  Still, if you replace the tires with the same model and inflat them the same way, you probably will get the same result.  

That was a good site never the less.
Quite a few interesting videos there.