Tip: Run Flats - experience explained

[Yellow32]

Hey folks,

I'm chipping in my $.02 on the Michelin run flats that our SRT-10s come equipped with.

I have read and heard from several sources that the Viper SRT-10 can 'give way without any notice' ...most if not all of these comments were with new cars, presumedly using the run flats.

So, here's my tip:

Run flats are different from other tires and for proper handling they need one thing, SUFFICIENT AIR PRESSURE!

It really is that simple.

I have tracked my SRT-10 twice in the past 30 days. For the first event (the higher speed track) I used 36 pounds at each corner (each tire) COLD PRESSURE ---meaning the air pressure in the tire was 36 pounds after the car had been sitting overnight. I did not have one single experience with the tires getting "greasy" or slipping away with no warning. In fact, I didn't have any tire slippage that wasn't extremely well communicated.

Now, day one at the second event (shorter more technical track -lots of turns, not as high speed) I, at first, ran with 34 pounds at each corner cold. Again, no problem (I did use the first lap to warm up the tires since there are a lot of hard twisties, but, I would have done this with any car using any tire). In the afternoon of the first day (after running twice in the morning) I dropped the pressures to 30 at each corner (cold pressure equivalent). This time it took 4 laps to get the tires hot (6 miles!) and on the second time out I spun with absolutely no warning whatsoever in the first lap! (the tire was quite 'greasy', like I hit an oil patch, but, I didn't of course).

For day two of the second event, I put the cold pressure to 36 at each corner, ran 4 times that day, very hard, no problems, none, tires very predictable.

Previously, on the street I had "weird" sliding motions with the tires...they were at 26 pounds then (cold). This seems to corroborate with the lower pressure I tried at the track.

So, bottom line, run at least 34 pounds cold pressure in the run flats and you should have no 'out of control' experiences with the tires (I would recommend 36 but at 36 you feel a lot more of the road's imperfections, 34 seems to work well and still be sufficient pressure to keep the tire manageable and predictable).

If the dealers would air up the tires there just might be fewer folks going off road on their first trip home...

I know "29" is the factory manual recommended pressure, I completely disagree that that is a safe pressure to use. I just think that's the recommended pressure because it is what gets the best gas mileage and tire wear...

That's my $.02,

J

 

[Kai SRT10]

I have found much the same thing.

I run 34 psi for the street and 38 psi (cold) for the track with the runflats.

 

[vincent_esq]

Thanks for the tip. Will do just that!

 

[ViperRay]

How about getting some tire pyrometer readings on the track to support your impressions?

I'd be interested to see that data.

 

[Yellow32]

Before I continue, please know that I had a professional driver in my passenger seat...he agreed with what I wrote.

As for the pyrometer, not going there, I am not going to risk spinning out again. I mean I could set it to 30 and drive around for a few miles on the highway after the car had been sitting overnight and then repeat the next day with the tires set at 36 (after sitting overnight so the tires "are the same coldness" for each run...), but, that would require I purchase a tire pyrometer...(someone always has one at the track...)

As for the track, I originally was just trying to see what tire pressure I needed. Anyway, if I did run the pressure low again I would be on the track and not able to jump out and measure the tire temps "right then"...

I can tell you this, the tires at the end of the run were much more gooey when the 34 / 36 tire pressure than with the 30 (felt hot and while driving in the paddock, all the little bits and pieces on the tarmack were being picked up quite readily).

Hope this helps.

-J

p.s. if you have a tire pyrometer and run flats on your '03 SRT-10, you could test the temps for us and let us know...

 

[GoldenVenom]

Great tip . Thanks! I will keep them at 36 psi.

 

[GR8_ASP]

I will try it this weekend. I have kept mine in the 30-32 range. They have been slick when cold but never uncontrollable. I am never afraid of breaking the tires loose in the SRT like in a Gen I/II, where spinning the tires leads to enexpected oversteer in a snap. But kess spin would definitely be good.

 

[DSR207]

I have always heard the opposite, meaning for more traction, lower the pressure, unless run flats are different...I will try 34 and see what happens.

 

[Chuck 98 RT/10]

I have always heard the opposite, meaning for more traction, lower the pressure,

For dragracing yes. For tracking no.

 

[treynor]

Hrmm - this does make some sense. In particular, with somewhat lower tire pressure "normal" tires will expand the contact patch and begin to compress the sidewalls. Run-flats presumably transfer more of the car's weight to the stiff sidewalls, decreasing traction much more than would otherwise be expected. I wonder if there's a pathologic condition under hard cornering where the tire is under side load and actually transfers *more* weight to the sidewall, meaning that it loses traction as the load increases. That'd lead to some very unpredictable handling...

 

[quick2tr]

Yellow32 -

I have tracked my SRT-10 twice in the past 30 days. For the first event (the higher speed track) I used 36 pounds at each corner (each tire) COLD PRESSURE . . .

Now, day one at the second event (shorter more technical track -lots of turns, not as high speed) I, at first, ran with 34 pounds at each corner cold. . .

I dropped the pressures to 30 at each corner (cold pressure equivalent). . .

Previously, on the street I had "weird" sliding motions with the tires...they were at 26 pounds then (cold). . .

Can you (or Kai) recall what the "hot" pressure readings were after lapping?

 

[Yellow32]

Yes,

Good question.

At 36 pounds cold my tires were at 42 pounds hot (measured right after the run). At 34 pounds cold, my tires were at 40 hot. At 30 pounds cold, 36 hot.

Each "run" was about 28 miles.

Hope this helps.

-J

 

[vegas guy]

Increased tire pressure to 34 psi last night. Will let you know the outcome.

Thanks for the tip!

 

[Viperfreak2]

Could that have been my problem all along? At the drag strip I lowered the pressure from 34 to 26. I thought this would help, but I felt no real difference in traction. I left the tires at 26 all through the winter, again thinking it was better.

 

[GARY J]

36PSI... CHECK. I WILL TRY THIS.

 

[Chuck 98 RT/10]

Could that have been my problem all along? At the drag strip I lowered the pressure from 34 to 26. I thought this would help, but I felt no real difference in traction. I left the tires at 26 all through the winter, again thinking it was better.

Dunno about runcraps but best psi for Pilots on the dragstrip is somewhere in the 19 to 22 range.

On a track I would start with 34-36 front and 32-34 back.

On the street I run the recommended 29.

 

[Jay Lopez]

Before I continue, please know that I had a professional driver in my passenger seat...he agreed with what I wrote.

As for the pyrometer, not going there, I am not going to risk spinning out again. I mean I could set it to 30 and drive around for a few miles on the highway after the car had been sitting overnight and then repeat the next day with the tires set at 36 (after sitting overnight so the tires "are the same coldness" for each run...), but, that would require I purchase a tire pyrometer...(someone always has one at the track...)

As for the track, I originally was just trying to see what tire pressure I needed. Anyway, if I did run the pressure low again I would be on the track and not able to jump out and measure the tire temps "right then"...

I can tell you this, the tires at the end of the run were much more gooey when the 34 / 36 tire pressure than with the 30 (felt hot and while driving in the paddock, all the little bits and pieces on the tarmack were being picked up quite readily).

Hope this helps.

-J

p.s. if you have a tire pyrometer and run flats on your '03 SRT-10, you could test the temps for us and let us know...

I rode with him at both of these events in his SRT. I agree that he was much more in control with the higher pressure, with a quicker tire temp warm-up to proper operating temperature with good grip. For another datapoint, I also drove my 97 GTS at those tracks (Texas World Speedway and Motorsport Ranch), using Kumho ECSTA 710s slicks and I run them at 34 lbs (not run-flats).

 

[Sellshomesdrivesviper]

bump

 

[VIPER D]

I hate run flats. Its like a copier and a fax machine in one unit. Its does two jobs but not as good if you have a dedicated machine for each. Run craps are at best ok. But not a supercar like a viper. I don't see them being used on the ford gt, nor the enzo.


vd..

ps i have been driving hi hp cars for over 10 years now and have never had problems with any tire make or style until runflats were intoduced.

 

[Racer Robbie]

Hi Yellow,

You quoted above:"Yes,

Good question.

At 36 pounds cold my tires were at 42 pounds hot (measured right after the run). At 34 pounds cold, my tires were at 40 hot. At 30 pounds cold, 36 hot."

What was the outside air temperture and track surface temperture? Did you take tire temps aacross each tire in three places? By this I mean the left, middle, and right side of each tire. Whay you are attempting to do is get even temperture across the complete surface of the tire. I always tell fellow racers that you need to adjust your tire pressures after the tires are hot so as to even the temperture across the complete surface of the tire. Adjusting tire pressure cold is a waste of time as the outside air temperture and road/track surface tempture changes. Thanks for an informative post. Robbie