> Sorry Jon, you completely lost me on your last blurb here...
Otay, I'll try it again. I'll pick apart my blurb and splain it bit by
bit.
The more grooves in a tire, the less rubber you have touching the pavement,
which reduces dry traction.
Picture a racing slick. It touches the pavement across its entire surface.
Where it touches the road is called the "contact patch'. Put grooves in the
tire, and you have reduced the amount of rubber in the contact patch.
There's now grooves in the patch. Less rubber in the contact patch = less
dry traction.
You can compensate for it with softer rubber,
which gives you better overall traction, especially in snow.
Now, if the tire was a hard compound to start with, if you reduce contact
patch by adding grooves, using softer rubber allows the contact patch to
mold to the pavement surface better, giving better traction.
Now, don't confuse that with performance tires, in which their rubber
compounds need to warm up to achieve good grip. That's why those Goodyear
Eagles and the like are so lousy in snow-they stay rock hard.
Performance tires use a rubber compound that doesn't grip well when
cold-they must warm up before the rubber becomes flexible enough to be able
to mold itself to the slightly irregular surface of the pavement. On snow,
they never get a chance to come to working temperature, so they get lousy
traction.
Modern tires don't have very much actual rubber in them any more, they are
pretty much a chemical cocktail they can change to achieve different
results. For instance, adding carbon black will increase wet traction. But,
add too much, you sacrifice mileage.
To the gentleman who talked about placing a blade on the tire just putting
slices in the rubber, I hear ya. You can do that with a hand groover also.
We have one with a thin knife blade for just that purpose-making a hard
compound tire act like a softer one without losing much contact patch by
making the surface of the tire flex a bit more. It doesn't matter too much
on a race tire on dirt, we don't really care too much about mileage. On the
street, it needs to be done right, or the tread blocks now become too
flexible and create heat-which reduces mileage. Or, they start chunking off
at high speed.
Some motorcycle tires that have large tread blocks with long grooves that
run from the center of the tread at a shallow angle of attack "cup" more
than tires with smaller blocks with grooves that run at a sharper angle.
This is because the edge of the "block" on the tire with the grooves that
run more parallel to the circumference must flex more when it hits the
pavement as the tire rolls. This tire will have better dry traction, as
there are fewer grooves, putting more rubber down. Make the grooves shorter
by running them from the center to the edge at a greater angle, you reduce
that long block where the edge must take the impact and distribute it across
more "blocks", thereby reducing cupping. It also can make a harder compound
tire act like a softer one, yet increasing mileage.
Notice off road truck tires are very noisy on the street? What you are
hearing is the edges of those huge rubber blocks hitting the pavement. When
they are worn, you will see the leading ede of the rubber blocks are worn
more than the trailing edges. This is the "cupping" I referred to earlier.
Sipe the tires, and you have more, smaller "edges" hitting the pavement, and
that tire gets quieter.
I'll bet by now folks are more confused than ever. Sorry, I read a lot of
technical stuff. I like to know how stuff works. Plus it splains why the
front tires on my bikes wear differently. I also tend to get long on the
explanations.
Hope this helped and not hurt-I'm back quiet.
Jon
STL MO
This archive was generated by hypermail 2b29 : Fri Feb 06 2004 - 11:48:14 EST