THE PROCESS
1 Before you even think about firing up your tire truer you have to
determine what you are trying to do with your foams. Whether you are
starting with a fresh set or just cleaning up an older set you must
determine your desired tire diameter. If you are working with a used
set of tires and want to match sizes or flatten out a few coned tires,
you are best to start working with the smallest diameter tire and match
the rest to that one so you are removing the least amount of material.
This offers you the longest tire life when you are finished with the
truing process. 
2Assuming that you are working with brand new tires that are usually
way oversized, you first need to rough them down so you are close to
the size you want before you do the precision truing to the actual race
size. Make sure there is no flashing on the rim or debris on the tire
truer hub to ensure that the wheel assembly mounts flat to the machine
and provides an even cut. Also be careful not to over-tighten the
mounting nut or you may warp the wheel, causing an untrue finished
wheel. Some truing machines have an option as to what direction you
want the truer to rotate the tire. If you have the option, rotate the
tire towards you for this step. Rough cut all of the tires down to
about 1mm bigger than you want, and set them aside in the order you cut
them. Temperature can affect the final size of the tire, so to ensure
accurate tire diameter you want to let the tires fully cool down before
you make the final cut to size. After you rough down the last tire,
mount up the first tire you worked with (which should be cooled down)
before you move onto the next step. 
3 With your first tire mounted to the machine, you are ready to do the
final cut. Most tire truers have some sort of a measuring device and
lock, so the cut diameter stays consistent. It is recommended that you
use a set of calipers to verify the tire diameter of your first tire,
but once you know the size is accurate, lock the machine for the other
three tires. It is a wise idea to pass the cutter over the face of the
tire a few times to ensure all of the material has been removed and to
create the smoothest finish possible.
ROUND OR SQUARE?
Rounded tire edges with a radius between 1/16" and 1/8" is the most
common setup for foam tire racing. This setup offers the most
consistency when it comes to on-track performance, but Josh says you
can round the edges even further if the track is super high-bite but
really rough. This offers you a more controlled slide without losing
too much grip. A rounded tire edge will keep the tire on its contact
patch better and you'll have fewer worries of the tire rolling over
onto the side wall which will break the car loose through a turn.
Rounded edges will also help to reduce foam tire chunking, which can
become a huge issue, especially during longer nitro main events.
The least common cut when it comes to foam tires is a
square edge. A tire with a square edge will always be riding on that
edge, thus taking side grip away from that area. If you run a square
edge on the front tires you will get less steering. A square edge at
the rear causes your car to be very inconsistent--it offers increased
forward grip but much less side traction. The track surface has to be
very smooth for square edges to work on the rear tires.
Josh will usually run the same type of edge cut front and
rear except in 1/12 scale where it's common to run a square edge at the
front and a rounded edge on the rear tires. Josh also used a mixed cut
when he raced at the Gas Nationals in Texas. The track was really rough
with very little grip, so he ran square fronts but rounded rear tires
with an excessive amount of radius cut into the edge. The square cut on
the front prevented his car from over-steering while the rounded rears
stayed consistent over the bumps, making his car easier to drive.
Truing Camber Into Tires
Truing camber into your rear foam tires is a trick used for longer
nitro mains. It is almost unheard of in electric classes where race
lengths are much shorter, so if you're racing electric you are best to
stick with the good old fashioned flat tire true. With nitro racing, if
you don't run enough negative camber at the rear your tires will wear
flat or cone to the outside. This greatly increases your risk of
chunking a tire during your hour long main, so to combat this Josh
usually trues his rear foams with about 1 degree of camber into them so
the diameter of the outside of the tire is larger than the diameter of
the inside of the tire. Nitro front tires are always cut flat. The rear
camber is set within the chassis to maintain the 1 degree of coning
towards the center of the car within the tire. In some rare cases where
traction is "stupid high," Josh says he'll cut a bit more camber into
the rear tires to a maximum of 2 degrees.
4 Your tire now has square edges that need to be addressed. Use a file
or sandpaper to round the edges slightly both on the inside and outside
of the tire, and smooth the face of the tire even further to help it
break-in quicker on the track. You can hold a piece of sandpaper in
your hand, but it is usually better to get some adhesive sandpaper and
adhere it to a stick to give you better grip and keep your hands away
from the moving tire. 120-grit sandpaper is usually good, but you can
go coarser for harder tires or finer for soft tires or to smooth the
face of your tire even further by removing most of the tire grain left
by the truing machine. If possible, the direction of the truer rotation
should now be away from you, but if you are using a directional file
you want to hold it backwards so the tire is rotating into the cutting
edge of the file. This will prevent you from having the tire rotate
towards you, which could cause the file to fly in your direction if it
catches on the tire. 
5 Repeat the above steps for the other three tires after ensuring that
they've had enough time to cool so their diameters are in check. After
you've done all four tires let them cool down, and verify their
diameters one last time before you mount them onto your chassis and hit
the track.
Multiple Tire Sizes
Foam tires mounted at the front and rear and left to right of your
chassis won't always wear at the same rate during a race, so Josh likes
to experiment with varying tire diameters around his car to match wear
as best he can. For indoor carpet racing Josh will estimate wear
patterns and set up a stagger with his foams, run three or four
practice races to scuff his tires in and bring them to equal sizes,
then set them aside for a big race. This ensures that all of his tires
are the same diameter for the shorter electric races while still
scuffing them in on the track. Once he starts racing with these perfect
tires he'll swap the left and right tires back and forth after each
battery pack run. Josh will only practice with his electric car on
different tire diameters to match them; he will never start an actual
electric race on staggered tires.
Racing nitro cars on foam tires is an entirely different
game. Josh will sometimes run multiple tire diameters during qualifying
but always for the longer mains. You'll have to do some experimenting
to determine tire wear characteristics for your chassis on your
specific track and then use some common sense to estimate starting
diameters. Josh says that with a track that runs clockwise he'll
usually start with the left side of the car with tires that are 0.5mm
larger than the right side on both the front and rear. If his rear
tires are wearing more than his fronts then he'll run both rears
another 0.5mm larger than the fronts. Here is an example of a starting
tire diameter setup that Josh would try for a longer nitro race. Let's
say he wants to run a 60mm tire. He'll experiment with the front right
tire cut to 60mm, the front left tire to 60.5mm, the right rear tire to
61mm, and the left rear tire to 61.5mm. After this initial setup he'll
do some testing on the track and alter his stagger from there.
Track direction for this type of setup would be clockwise. You'll need
to experiment with different diameters that suit your chassis and track
layout or conditions.
CLOSING
As most racers will tell you, if your tires aren't right it doesn't
matter how good your chassis setup is; you aren't winning. With that in
mind the perfect prep of your foam tires is crucial to success on the
track, so read this article carefully to ensure you carve your tires to
perfection every time. Don't forget to experiment with some of these
tips from Josh Cyrul and you'll see why he's got more National Titles
than most people have sets of tires. |
