At 01:09 PM 5/22/01 -0700, The Fortinis wrote:
>I'm sure you all have covered this before we came along, but how do I best
>tell when our tires are toast? We run on a variety of surfaces and lengths
>of courses throughout the season, so counting runs is kinda like voodoo
>(e.g. how many 35-second asphalt runs equal a 60-second concrete run?). I
>know Hoosier Tom has told people "when everyone starts kicking your a$$, buy
>new tires." But by that standard, I'd need a new set every weekend. And that
>rule-of-thumb doesn't make sense when your CODRIVER/spouse is one of those
>a$$ kickers ;->.
>
>A kind competitor (Pat Bullis) gave me his durometer, which in theory seems
>like a good tool to monitor tire life. He said new Hoosiers showed as 40 (40
>what?) on the scale, but didn't know quite what value meant "cooked." I know
>most of you run GYs in CenDiv, but any rules of thumb and/or measurements
>you could share would help immensely.
>
>Thanks in advance,
Here is my very opinionated view from nine years of trying to figure it out:
Tires are "toast" when your desire to win combined with your budget exceeds
your $$$ sense:-)
More specifically, Durometers are essentially useless to compare brand new
tires with ones that are still "pretty good". Under the exact same
temperature conditions I get the same durometer readings from new tires and
decent old tires. Exception, if you have REALLY cooked a tire or portion of
the tread, it may read high duro numbers. So will real old tires. Sometimes
the high duro number is the DOT street tire, etc. rubber you have picked up
from the course. Sometimes a high duro number is because the tread is
simply thinner. If you want to see the variability, get two otherwise equal
tires and put one in a cool area and one in the sun for a while. If your
car setup tends to overwork a portion of the tire surface, it will "harden"
somewhat. However, it will also tend to wear more so you can see what has
happened.
Tire feel and balance changes are the best way to tell, other than my lead
in suggestion. However, you must pay attention to other variables including
but not limited to: surface, temp, types of corners, other changes to the
car, location of driver's head vs. other parts of driver's anatomy, etc.
The first run after a couple of weeks or a month off may be terrible, if
for no other reason that the tire surface is hard from the tows and/or the
time. Combine that with cold tires and they feel like junk (not to mention
where the driver's head may be). Next run and they are fine. (thats one
reason why codrivers should alternate who runs first)
Since I generally set my car up for "when in doubt, oversteer" and tend to
spin the rear tires due to Pro Solos, etc. I generally can tell by the
balance shifting to even more oversteer. An "understeery" car will probably
get more so. Also, at about half tread depth for the rears they become
"practice or I don't care . . . as much" tires.
Another way to tell is how sticky they feel AFTER a run, all else being
equal. If they no longer pick up gravel on a warm day, they are probably
only good for practicing car control.
Just remember, the older your tires, the more excuses you have. However,
the more money you save on tires, the more runs you can take to get more
practice. The "fast folk" at any given even will beat the "slow folk" most
of the time even if the slow folk are on new tires and the fast folk are on
older but not dead tires. If you get so you get the max out of older tires
you will be real fast on new ones . . . and you will be able to tell the
difference!!! Just be carefull about adjusting for balance changes as the
tires age. Best way to understand this is to pay attention to what the oval
racers (open wheel or NASCAR) say about their cars balance between new and
old tires.
That's enough at my attempts at wisdom. Your results may vary!
Dick Rasmussen
CM 85
85 Van Diemen RF-85 Formula Ford
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