Re: [ST] Tire pressure experiments?

[chuck boatwright <dirac@xxxxxxxxxxx>]

Alex wrote:

>Has anyone played much with their tire pressures?  I know that 
>"lower" generally should give improved grip at the expense of 
>tread life, but has anyone attempted to quantify the effects?
>  
>

I have been wrong before (charlie m will correct me if I am).

basic rule: You lower the tire pressure to get more heat into the tire. 
 Tires have a window of ideal temperature.  Too cold, and they will 
slide (cornering force on tire exceedes coefficient of friction because 
the rubber isn't warm enough to reach the designed coef. friction), too 
hot and they will slide (the rubber starts to come off the tire -- this 
is the "my tires got greasey" comment racers make).  On the track, using 
typical DOT race tires, recommended pressure  is between 29-32 psi.  The 
tire reps at tracks always have a sign out with the days suggested 
pressures.  These pressures are learned from the pros who participate in 
tire test days (dunlop just did their daytona test a couple weeks ago).

The guidelines which I have learned from the track is as follows.  When 
the tires are warm, you want a 10% increase in pressure between cold and 
warm readings.  I don't run DOT race tires on my race bike, I run bias 
plys, and the tire reps don't usually have info on these tires.  I 
"figure out" the tire pressures at track days, and based on my level of 
skill, the tire pressures are between 28 and 30 psi .  This rule is 
track specific, as you rarely get the tires that warm in normal riding. 
 There are exceptions.  deals gap, california rt1, rt 128, mines road, 
rt 9.  These are roads that are all curves.   But, even when doing 
spirited riding on these roads I don't bother with adjusting tire 
pressure.  You really shouldn't be pushing that hard, as full lean on 
public pavement doesn't leave you much of a safety buffer.

I run my ST at the recommend PSI.  When riding two up with luggage, I 
run a couple pounds higher on the rear.  So in short.  Run normal 
suggested pressures, unless you are in the habit of riding DOD nominal 
all the time (you probably won't have an operators permit if you ride 
like that and the tires outlast your license.)

Heat cycles do play a role in tire stickyness (not address), but how 
many people count the number of heat cycles on their street tires?  

"shutup and ride"
- --chuck
02 ST





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