12 fastlane
techtorque
TURN, TURN, TURN
FIGURING OUT TUBES, TYRE
SCREWS AND BEAD LOCKS
Go to a drag strip and you’ll see
cars with beadlocks, tyre screws and
what appears to be nothing holding
the tyre bead to the wheel rim.
Some cars will run tubeless. Others
will have tubes. Ponder all of the
combinations and the big picture
starts to get a wee bit confusing or
at least a wee bit muddy. What do
you need?
Honestly, it depends upon the
recommendation of the tyre
manufacturer along with the
application. As Jerry Bickel is quick
to point out, tube-type tyres must
always have inner tubes installed to
prevent leaks. Tubeless drag slicks
on the other hand may be run with
or without inner tubes. From Jerry’s
experience, most racers prefer to
run tubeless drag slicks without
tubes in order to reduce tyre mass.
With less mass, there is less inertia
to overcome. As a result, the tyres
will accelerate faster and you’ll most
likely be rewarded with a lower ET
slip.
When it comes to tubes, There’s
always a risk of rupturing the tube.
That means rapid air loss in the
tyre. What causes this? Bickel notes
these are the most common causes
of inner tube rupture:
Wayne Scraba
Photo Credits: Jerry Bickel
Race Cars, Wayne Scraba,
Summit Racing
1 WRONG TUBE SIZE
2 WRONG TUBE TYPE
3 INCORRECT INSTALLATION
4 TYRE TURNED ON RIM (TEARS
OFF VALVE STEM)
5 INNER TUBE IS DRY ROTTED
When it comes to tubes, you should
only use new natural rubber racingtype tubes correctly sized for your
slicks. Any other type of tube cannot
withstand the constant flexing that
comes from low inflation pressures
and of course, sidewall wrinkling.
That’s not the end of it either. Bickel
notes: “I have see tyres rip through
the rim screw on a particularly hard
tyre-wadding launch. If the tyre turns
at all on the rim, the tube turns with
it and pulls the valve stem off. This
causes a sudden loss of air pressure.
If you must install tubes, have them
mounted by professionals. Many
inexperienced racers have damaged
inner tubes by installing them in a
twisted condition or with the valve
stem under tension.
keep the tyre in place. If a slick turns
on the wheel rim, balance is upset
and the result is vibration. If you run
tubes, it becomes even more critical.
As Bickel mentioned earlier, the inner
tube tends to turn with the tyre. If
the tyre turns on the wheel rim, then
the valve stem will be ripped off and
causes a sudden tyre deflation.
“If an inner tube develops a slow leak
the lost air forms a pocket between
the tube and inner tyre. This can
cause tyre balance problems and a
gradual bleed down of air pressure. If
you suspect this may have happened,
dismount the tyre and check the inner
tube for leaks in a water tank or with
a soapy water spray.
Over the years, it’s been possible to
buy drag race wheels that come predrilled for rim screws. If you have to
drill your own holes, Bickel suggests
you locate the holes symmetrically
around the wheel in order to maintain
balance. Bickel also staggers the
alignment of the screws from side to
side on the wheel rims.
“I prefer metal valve stems over the
pull-in rubber types for tubeless
tyres. A nut holds them securely in
place, preventing them from popping
out under high centrifugal force.
One drawback to tubeless tyres is
that they all leak slightly. Over time,
air bleeds through the thin rubber
sidewalls or may leak around rim
screws. Some wheel rims may leak if
they are made from porous aluminum
or have poor w elds.”
If your racecar is parked for long
periods of time (shop or trailer)
there’s a good chance the tyres will
lose pressure (bleed down). Some tyre
brands are more prone to bleed down
than others, and it can become a pain
to deal with flat tyres. When a slick is
sidewall is left in a severely wrinkled
(flat) condition for long periods
of time, the damage can become
permanent. The best solution is to
monitor the tyre pressures regularly.
Or you can simply swap to “tow tyres”
– these can be anything that hold the
race car up.
That brings us to methods of securing
the tyre bead to the rim. You can use
tyre screws, bead locks or glue to
WHEEL RIM
SCREWS
According to Jerry anywhere from
eight to sixteen screws on each side
of the wheel is enough to get the job
done. Some folks have used as many
as thirty-two screws used per side,
but Bickel figures this is unnecessary
overkill.
Bickel installs all wheel rim screws
straight in (horizontal) around the
perimeter of the rim flange. Jerry tells
us that some racers prefer to alternate
between straight and angled screws.
The angled screws are threaded into
the bead on the radius between
the outer flange and inner rim. The
figure below shows the installation of
straight and angled rim screws.
According to Jerry:
“The stated
purpose for the angled screws is to
hold the bead against the rim lip as
centrifugal force pulls outward on
the tyres at speeds over 200 MPH.
I think this logic is questionable
at best. Funny car type tyres are
generally designed to run with bead
locks, not rim screws. Over time,
tyre manufacturers have changed
bead-lock recommendations and you
should always consult with them
before you select a method for your
car.
“The best rim screws to use are
hardened #12X3/4-inch sheet metal
types. Hex-headed plated screws are
easy to install ant resist corrosion.
Drill 5/32” holes through the rim, but
not into the tyre. Deburr all sharp
edges. As they are installed, the
screws cut threads into the rim so
that they may be tightened without
stripping the rubber. Only the ends
of the screws thread into the bead
of the tyre. I like to apply a small dab
of RTV silicone on the screw threads
prior to installation to prevent leaks.
“Air the tyres up to 20 PSI before
installing the screws. Don’t over
tighten them, or you might break
off the heads. After numerous tyre
installations, the self-tapping action
of the sheet metal screws strips
the holes in the rim. At this point,
the wheels should be repaired or
replaced.”
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