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Technical how-to's: Inflating tires
What could possibly be difficult about inflating tires? You pump them
up and that is it, right? Wrong! Unfortunately, there are quite a few
things that can go not as planned, possibly making this a much more
tricky operation than you expected.
Again I have to thank the members of Pete Muller's karting mailing list,
which helped me with their advice when I faced these problems. The
following document is a compilation of their recommendations which have
worked for me.
Now it is time for the usual disclaimer:
Inflating tires bears the risk of serious property damage and/or injury,
including but not limited to: Stained carpets, broken bones, annoyed
neighbors, blindness, damaged rims and tires, injured pets and other
by-standers, death and various other inconveniences. I am describing a
way to inflate tires which worked for me. Of course, I am not implying
at all that you will under all circumstances be successful and kept
free of harm when following the procedures outlined below. I certainly
will not be held responsible for any damage, injury (physiological and
psychological) or other negative side effect that may occur when you try
to inflate a tire. Don't follow my advice if you can't live with that!
What's the problem?
Kart tires are tube-less, i.e. the air is held inside of the tire
due to a tight seal between the tire bead and the wheel rim. When
you have just freshly mounted a tire on a rim, you might notice that
there is actually a gap between the tire bead and the material of the
wheel rim. The wider the rim is in relation to the tire, the bigger
this gap tends to be. So, with a gap there, i.e. no seal between tire
and rim, how can you possibly even begin to inflate the tire?
This problem is not always experienced with all tires and all rims, but it
will really depend on your combination of the two and the individual
tires, since there are differences even between individual tires of the
same make. Count yourself lucky if you do not experience that problem.
Furthermore, even if you managed to get a seal between tire bead and
wheel rim, you might still not like what you see when the tire inflates:
One tire bead may seat properly against the lib, i.e. one of the outside
edges of the wheel rim, while the other seems to be stuck somewhere
along the way to its edge of the rim. You may also experience a partial
seating of the bead, i.e. the bead does not seat against the lip of the
wheel rim all the way around.
What's the solution?
Well, in order to do any inflating, it is most important to get a good
seal between the tire bead and the wheel rim. If you don't have a good
seal there after you mounted the tire, the air you pump in through the
valve will escape rightaway out of that gap, making a nice hissing sound,
but nothing more. There are several tactics which you may use now
(either one or a combination of them):
If you try a combination of these three methods, you really should get
your bead seated and have the tire ready to be inflated (after screwing
the valve core back in).
- Closing the gap by applying pressure around tire
If the gap is not too big, you can try to close it sufficiently
by tying a broad belt very, very tightly around the circumference
of the tire. The hope is that the pressure which is applied from
all sides, will be enough to press the rubber of the tire bead down
onto the rim material, thereby creating a seal. The softer the
tire compound, the better this will work. Instead of a belt, you
may also use a special tool if you have one. In general, though,
harder tire compounds will resist such a compression so well, that
this really works for only very minor gaps.
- Using a substance to seal the gap
The smaller the gap, the better this works. Whatever sealing
substance you use, make sure it does not damage the rubber of
the tire. The substance should be thick and withstand some air
pressure. I once tried dish washing liquid on a relatively
large gap, and it was simply blown away by the air pressure.
The tire didn't inflate, but I had some nice bubbles hovering
all around me in the air. Dish washing liquid may work on
very small gaps, though, as was reported to me. Other substances
are 'bead sealers', which might be available in local tire stores,
and can be applied to the gap (let dry).
- Pumping air in faster than it can escape
This actually seems to be the most effective way to solve the
problem. If you have a very high pressure air tank or compressor
(don't even try a foot pump), you can try to force air in at such
a high rate, that it actually cannot escape from the gap(s) fast
enough. Consequently, the rubber of the tire will rapidly expand
(mostly sideways, espcially if the belt is still tied around the
tire), until it reaches the rim material, temporarily providing a
seal. At that moment any additional air will stretch the tire
further very quickly, providing a very tight seal, which will
typically remain, even if the air is let out of the tire. The valve
will resist the fast inflation, though. So it is necessary to
remove the valve stem beforehand. This can be done with
a handy little tool, called the valve stem remover, which
should be available in automotive parts or tire shops. It has
a tip which allows it to 'reach' into the valve. You can then
simply screw out the valve core. Of course the tire won't hold
any air that way, but once the beads are seated, the core can be
inserted again and the tire properly inflated. Be careful
when using the high pressure method! Faulty tires may explode
if the pressure gets too high. Use equipment which allows you to
step back while blasting the air into the tire. Speaking of
Where do you get such high air pressure from? Depending on how
wide the initial gap is, a high-pressure air tank or compressor
may do. You can also go to a garage or tire shop and ask if they
can give it a try with their air pumps. There are tools available
which are actually designed to seat beads by blasting air into the
tire using a very short, almost explosive discharge of air. They
consist of a special air tank with some attachments and can be had
for some $300 or so and are called bead seaters.
CAUTION: These devices are typically designed to handle
big truck tires. I don't know what they would do to a much
smaller kart tire. So please use extreme caution!
Now, as you proceed in inflating the tires, the pressure will grow, and
the tire's beads will start to slide up the rim material, towards the
lip where the beads should eventually get seated. You should assist
in this process by doing the following things:
When a bead seats under high pressure, it will usually produce a loud
metallic sounding POP. Don't be alarmed, that's normal. It
did startle me, though, when I experienced it for the first time.
- Applying pressure around the tire
The idea here is to strap a broad belt around the circumference of
the tire very tightly. Especially with softer compounds, this will
help to squeeze the tire walls outward. Ever held a Marshmellow
and squeezed it? Sure you have. You will have noticed that the
sides seem to pop-out when you apply pressure. It's the same
effect. One difference is that most of the pressure is actually
applied from the inside, as the air pressure increases. Since the
rubber cannot expand around the circumference, because of the
belt, it is forced to expand sideways, thus helping to advance the
tire beads closer to the lips of the rims.
- Applying lube
You can reduce the friction between rubber and rim material by
applying plenty of lube. Be sure the lube will not damage the
rubber of the tire. Dish washing liquid is quite popular for this,
but other stuff might work as well. Even KY Jelly was
- Pumping up to a higher pressure
Again, when you apply very high pressures (40 or 50 lbs or even
more), you will probably exceed the recommendations of the
manufacturer and all bets are off. Take safety precautions.
Don't stand next to the tire, or hold it next to your face or
some such thing. Use a longer hose between the pump or air tank
and the tire, just to give you some safety distance in case
something happens. The higher pressure may be required to force
both beads against their ends of the wheel rim, providing the
One bead often seats much earlier than the second bead, so keep lubing
and carefully keep increasing the pressure. Eventually, this time with
a really loud POP, the second bead will seat as well.
Be careful not to get your fingers between the wheel lib and the tire
bead when the bead seats! As you can imagine, whatever is capable of
producing such a loud POP sound when hitting the lib of the
rim, will also be capable of seriously squishing your fingers if they
should be in the way. Make sure your fingers are nowhere near the
tire and rim when you are trying to seat the bead! In general, during
all of these procedures, keep yourself (face, hands, etc.) as far away
as possible from the tire. For all you know, that thing may not have
been manufactured properly or you applied too much air pressure, in which
case it might just explode!
Once both beads are seated, check that they have even contact with the
lip of the wheel rim all around. Then reduce the air pressure to either
the desired value for a track session if you plan on going out right
away, or to an even lower value if the tires need to be stored first.
Don't leave the extremely high pressure in for too long, since this could
over-stretch the tire.
For comments or suggestions,
please contact J. Brendel
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