Scott said, in part:
...Bill said he managed to burn through
the mold release compound by, basically, driving the car sideways
through the first rally leg (on pavement, about 10 miles). His rally
computer showed 2 extra miles relative to the rallymaster's
instructions, but he finally got some grip in the tires.
Thus, here was Bill's recommendation (and who am I to argue with
Bill?): Shaving. RA-1s apparently come with a lot of tread anyway,
so just take off 2/32 to 3/32 of the tread. This will get rid of the
mold release compound and also put some heat in the tires, thus,
heat-cycling.
I'm tempted to try it. Roger Kraus sells Toyos and does shaving, no?
Just expressing an opinion here, haven't gotten deeply into tire chemistry.
Cycling is said to cause additional linking of the rubber molecules, and the
stressing that they are given by being rolled under load during the cycling is
said to make that more effective. Tire Rack says it's best if the tires are
not under load during the 24-48 hours after the cycling, probably just to keep
things even I imagine.
Mold release compound, if it survives the first lap in anger, must have soaked
well into the rubber. One would think that it would not do that by design,
since it's really just to provide slipperiness / minimize bonding between the
rubber and the mold, which I'll bet is steel or cast iron. If it does diffuse
into the tire a ways, then all the cycling in the world isn't going to get rid
of it, you'll just have to wear it off by using up that rubber. That may be
what your buddy experienced.
Additional cross-linking will tend to increase the strength of the rubber, and
its stiffness. There's a sweet spot for any particular compound, an age and
amount of cycling beyond which the grip will drop off. Age and repeated
cycling do harden tires. Loss of plasticizers by evaporation will do
likewise. Shaving will only take off rubber, it won't have any effect like
heat cycling. I did find that my Falkens came in nearly right away when I had
them shaved, versus the multiple events that others told me to expect when you
put them on new and full tread height. So maybe there is something to mold
release soaking in and having an effect. After I had 'em shaved, I put them
on, drove out the Altamont and back, and put them in the air overnight,
simulating as close as I could the Tire Rack treatment.
The last factor I can think of is surface roughness. The tires are quite
smooth right out of the mold. It will take a few miles to scuff them in.
Shaving shears off the surface layers and probably presents a better initial
surface for grip than the newly molded layer. Gentle driving won't take that
off right away. Driving sideways does it right quick, though!
Paul T. (materials engineer in his secret identity)
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