Re: Tire pressures

[rdh@sli.com (Robert D. Houk)]

   I have an experience ( and questions! ) relating to tire pressure. I have 
   some tires, that are not very highly rated ( $100 or so ) with a 60,000 
   miles warentee ( read " not sticky rubber - family style M+S tires " ) 
   and I was up the canyon driving the other night. I drive FAST through 
   those curves, and I could feel my tires loosing grip around most of the 
   turns. When this happened, it was a sort of skidding grab-jump-grab-jump 
   kind of traction. It was sort of disconcerting at first, but I got used 
   to it. I was wondering : Do all tires lose traction like this? I thought 
   tires would actually skid, not bounce-skid...? I drove the same tires 

I betcha you have 70-series (or "worse" -- higher aspect ratio) tires?

Sounds like your whole tire/sidewall/suspension is "bouncing" . . . not
uncommon with "family cars", tall skinny wimpy tires, RealLife roads,
etc.

   through a yellow light/left hand turn about 40-50 mph on cement, and they 
   slid (did I mention that they squeeled? they did. ) the way I would expect 
   tires to skid. I feel that it is because of the cement, and that for 
   whatever reason, it doesn't have as much friction as asphalt (Sp?).  Am I 
   correct?

Actually, "concrete" has a much higher grip than asphalt -- in general.
(True, you can smooth and polish concrete till it's slick as <insert fa-
vorite stupid graphic luridity here>, and that stuff has no friction to
speak of! But then again, neither does fresh oily asphalt with wet fall
leaves <Ouch!>)

   after this little mountain escapade, I looked at my tires in the morning. 
   They all had little bruise/scrape/burn marks around the first couple or 
   three inches of the sidewall. Was I actually folding the sidewall over? 

Yup. Makes a nice "spring" to bounce you around. Ruins traction, too!

Watching a drag race (*real* top-fuel five-second quarter-milers!) is
fascinating. When the TV replays a launch in slow-mo, you can see the
monster rear wheels start to rotate while the tire remains in place -
it winds up like a spring! Then later, as the tires catch up to the
wheels' rotation, you can see the whole tire expand radially to a sig-
nificantly larger diameter under sheer centrifugal force (what a great
automatic transmission! No gears needed, tire just gets bigger as you
go faster...heh heh heh)! 

And you thought tires were a passive component . . .

   I was running street/dirt road pressures of 35 psi. Usially if I go 
   'mountain racing' I jack them up to 40-45. Would this have helped me? 
   Should I just go spend the cash and get some good Z rated tires with 
   stiff sidewalls? Or should I keep trying to play the 'beat the 60,000 
   mile warentee so I can get new tires for free game'?

My own philosopy is that any tire that lasts 20,000 miles is way too hard
and not nearly grippy enough . . . (but then again, I don't have to drive
50 miles each way to work every day, either, except maybe sometimes on
my motorcycle on a nice spring day...).

					-RDH