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9/20/02
17" tire options
for the dirt
by Rick Washek
I spent all of the 1999 and half of the 2000 dirt track
season in a failed experiment of dirt tracking an yz
426 with 17 inch wheels. Throughout this season of going
sideways everywhere, including the straights (not always
a fast way around the track) I learned 17 inch wheels
don’t work very well on a clay oval. But if you
wanted to run 17 inch wheels and still haven’t
outgrown that burning desire to play in the dirt, these
seemed to work the best. Now keep in mind spinning a
rear tire all the around a blue grooved clay oval can
be very abusive to the rubber, possibly more abusive
than what you guys do due to the fact the spinning is
so continuous.
Pirelli MT 60 R and RS
The version I used was a Super Sport road race rain
compound called the Corsa. I don’t think it is
available in the US because the AMA banned the tire
after a German gent walked away with the Daytona 600
Super Sport race run in the rain in, I believe 1999.
It worked probably the best of all the tires I used
but it didn’t last very long. I got about 3 race
events (5 classes or 10 races per day) before I had
to re-groove the tire. I could do this 3 times before
I ran out of rubber. The RS is a supermotard compound
so it’s probably a little softer than the R. These
are both DOT tires so a little harder than road race
rains. The tire I had was probably somewhere in between.
These are the tires that come stock on the KTM Duke.
Metzler MEZ 2 or 3
This tire, in a race compound, seemed to offer the
best balance of traction and longevity. I grooved it
up 3 times and would get 3-4 race events between grooving.
It was the only tire I tried that offered any traction
in the cushion (loose dirt). I have friends that hand
groove these tires with additional rain grooves and
run them as road race rain tires. They are pretty happy
with them and they don’t go away the way rains
do on a drying track so the longevity on dry asphalt
should be very good.
Metzler also makes a rear called the Tourance. It comes
in a 150-60-17” size for the rear and it’s
a v rated radial. They also make lots of dual sport
bias ply sizes for the Sport Motard guys. I have used
2 on the rear of my TDM 850 and they rock in the dirt,
grip great on the street (at go to jail speeds) and
seem to last forever. They may be a bit hard for the
asphalt but you would get lots-o-races out of it.
Avon Gripster AV 37 and AV 38
This is a DOT rain tire. Not nearly as soft as a full
race rain, but softer than most super sport tires. This
is not the cobby Gripster that the BMW GS bikes used
to use. I never had a chance to try this tire, but it
has the same tread pattern as the Michelin rains that
all the 80 cc bikes use on the dirt (they run fronts
front and rear and they stick like glue) You can run
these tires either direction, so if you shag one side
you can turn the tire around and shag the other side.
I quit running the 17’s before I tried this tire,
but it was going to be my next guinea pig.
Maxis
Maxis makes a dirt track tire in an equivalent to a
120-70-17. It is designed for 80cc bikes for use in
the front and rear. It has directional arrows but you
can run it either way. I used this tire on the front
for a whole season and it was barely starting to show
signs of wear. We now have it on the back of a very
low horsepower out put (shagged) xt 250 practice bike
for 2 years and showing no signs of wear. I have no
idea of how long it would last on the asphalt but they
are very cheap, right around 100.00. As far as staying
together at speed, the 80cc bikes average 86 mph around
a mile oval. It has a very round profile as opposed
to the very “v” profile most rain fronts have.
It was the best of all the fronts I used. This included
Dunlop and Michelin rain tires.
Michelin
I never used the Michelin rains, but they are heavily
used in the European motards and with a little additional
grooving, I’ve read, they work very well in the
dirt. You simply grove across the tire and then add
some side sipe grooving from the outer groves to the
edge. This makes them squirm a little under heavy acceleration,
but greatly improves the grip on the dirt. The Michelin
fronts are heavily used by the 80 and some 125 bikes
on the dirt and don’t last quiet as long as the
Maxis but provide better dirt grip. There is a guy that
wins Pikes Peak about every other year that uses the
Pilot Rains and is very happy with them but longevity
is not its strong point.
Bridgestone
The reason I started running 17’s in the dirt
was because of a kid, Shawn Burr that runs them on his
125. You have never seen someone turn a more technically
perfect line and form in the world. He is sponsored
by Bridgestone and ran them exclusively. He would toss
them instead of regrooving them but they run a slightly
shallower carcass and you would only get about 2 regroovings
out of them. I never tried them, but spent enough time
looking at his rear tire to know they work very good
in the dirt.
Hand grooved slicks
I tried this also. I tried 4 different patterns, 2
modeled after dirt track patterns (Goodyear and Maxis)
and 2 loosely patterned after the Michelin rains. No
tread pattern stood out as better than another. The
key seemed to be to have a nice sharp fresh edge contacting
the dirt.
Other things to keep in mind
Tire pressures, anything over 20 lbs will be a bit
much on the dirt. I always ran mine at around 18 lbs.
This wont work so good on the asphalt, but more than
likely what your running now wont be optimum in the
dirt.
Heat sipping, when we run on the mile ovals we put
a diagonal shallow razor slice in each tread block to
dissipate heat. Keep in mind you need fairly large tread
blocks for this to be beneficial.
Mag wheels, if you run mags and run 22 lbs or less
you will need to put a tube in the tires. If you don’t,
the tires will roll off the bead just enough to allow
dirt to get between the bead and the rim, resulting
in a slow leak that will show up at the worst possible
time. I have a big dent in a the fence with my name
on it to prove my point.
Regrooving, almost all tires have enough rubber to
simply deepen the existing grooves when you start to
consume the rubber. A tire groover is available from
your dirt trackin buddies or from White Brothers for
about 50.00. DO NOT attempt to groove a tire with a
knife of a razor blade. No matter who you are, you don’t
have that much free time and need all your digits.
Tire series; avoid the low profile 70 series if possible.
The taller the profile the longer your shiny rims will
stay shiny. However no matter what you do, the dirt
beats up the edges of your rims.
That is about as much info as I have gathered. If you
have any questions, give me a call at 612-432-4077.
Thanks Rick.
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