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question?
Send it to satreads@mweb.co.za
Q
Do I need special tyre changing machines to service run-flat tyres?
A
While most extended mobility tyres appear to be the same as a regular
tyre, the sidewall areas are usually reinforced and much stiffer. Without
the proper equipment to depress the sidewall during the demount and mount
processes, the likelihood of torn beads and damaged rims increases. In order
to properly service most run-flat tyres, the machine must have the hydraulic
arms and/or rollers to keep the bead in the drop center.
Q
Is there still a global shortage of OTR tyres?
A
The only shortage that still remains to some degree is the large
earthmover tyres with 57- and 63-inch rim diameters. Small- and
medium-sized OTR tyres are in good supply, and with the global demand
for new earthmoving equipment continuing to shrink, we expect inventories
to remain at high levels for most OTR tyres.
44 • Ask the tyre experts
Ask the tyre experts
With Marvin Bozarth and Kevin Rohlwing, Tire Industry Association
Q
How many splices are acceptable on a
pre-cure retread?
A
Most retreaders will only allow one splice
per retread, but some companies will allow
two splices with shallow tread depth rubber where
the vehicles do not operate at highway speed or
are fully loaded.
Marvin Bozarth
Q
Can inflation gauges be calibrated?
A
Yes, truck tyre gauges have a small screw on
the bottom of the “stick” that pops out when
Kevin Rohlwing
the air pressure is checked. When the gauge is checked against a master
gauge or at a calibration station, the screw can be tightened or loosened to
read the exact pressure.
Q
How can I improve envelope life in my retread plant?
A
The most important thing you can do is check the sealing rings,
hooks and platforms for any sharp edges or burrs. A small nick or
burr can poke a hole in an envelope or start a small cut that eventually
works it way all the way through rubber. It’s also important to store the
envelopes flat but off the ground on a platform without sharp edges or
protruding nails, which is why we don’t recommend using a wooden pallet.
Another important thing is to let the envelopes cool evenly and make sure
that housekeeping in the plant minimizes the number of staples and other
objects on the floor that may puncture an envelope. Finally, choosing
the correct size and ensuring no foreign material is trapped between the
envelope and the tyre will improve envelope life.
Q
I read that tyres run cooler when inflated with nitrogen. Is that true?
A
None of the tyre manufacturers can produce any data showing that
nitrogen makes a tyre run cooler or last longer. The main factor that
contributes to heat inside a tyre – besides the proper inflation pressure for
the load – is moisture. Moist air retains more heat than dry air, so installing
water separators or air dryers will almost eliminate the moisture and allow
the tyre to run cooler. While nitrogen does bleed out at a slower rate than
regular air (which is already 80% nitrogen), regular inflation pressure
maintenance combined with dry air will yield the same benefits attributed
to nitrogen.
Q
What is the best bead lubricant for truck tyres?
A
We always look for vegetable- or animal-based products that contain
a rust inhibitor with no petrochemical products. Paste lubricants are
typically best for mounting tyres, because they don’t dry as quickly and
typically result in a tyre that is concentrically seated on the rims. One of the
biggest problems we see is technicians who lube the beads with a waterbased
lubricant on a bunch of tyres and then proceed to mount them all
at once. The first few still get the advantages of bead lube, but the last few
are basically dry. Paste lubes don’t evaporate as quickly and also create less
mess in the service area.
To submit a question to be answered in a future edition of Southern
Africa Treads, please send your questions to satreads@mweb.co.za.
Marvin Bozarth is the senior technical consultant for the Tire Industry
Association (TIA) and has more than 40 years of tire and retreading
experience. Kevin Rohlwing is the senior vice president of training for TIA
and has over 26 years of tire experience. TIA offers some of the most
comprehensive tyre service training programs for both commercial
and automotive tyre service professionals in the world. For more
information on these programs, or for more information on TIA, visit
www.tireindustry.org or email training@tireindustry.org.