SAFE PREVENTIVE MAINTENANCE OF TIRES

The most fundamental and important procedure is maintenance of the specified air
pressure for tires under established load and service conditions.
For a tire to successfully perform the function for which it was designed, care must be
taken to ensure that neither underinflation nor overinflation occur, as both will seriously
detract from tire performance. The operation of tires with too much or too little air is
similar to the operation of an engine with too much or too little oil. Such an operation
brings about predictable disastrous results.

1. Underinflation -- When inflation pressure is less than specified for a given tire
load, the desired percentage of deflation is surpassed and any of the following
conditions are likely to occur:

Ply, tread or bead separation
Tire fatigue/stress
Radial sidewall cracks
Liner failures (tubeless tires)
Irregular or rapid wear
Poor handling

2. Overinflation -- Excessively high pressures for a given tire load and ply rating
create excessive stress such as:

Punctures
Cuts
Rock penetration
Impact breaks
Bruise damage
Cut separations
Cut growth
Irregular and rapid tread wear
Spin cuts

Additional disadvantages can result from overinflation causing decreased mobility
or damage to mining equipment:

Loss of traction
“Hard Ride” and excessive vibration
Excessive shock loads
Poor handling
Payload spillage
Operator fatigue

Specified inflation pressures must be set “cold,” that is, after allowing at least 24
hours of idle time. Most mining equipment manufacturers include
recommendations for inflation pressures, but whenever possible, actual tire loads should
be used to determine the required inflation pressure

3. Cold Inflation Check -- Cold inflation pressure is determined by the actual tire
load. Inflation pressures should be periodically checked. Cold inflation pressure
should be adjusted to the correct pressure as often as possible -- in all cases at
least once a week.

4. Hot Inflation Check -- During the time between cold pressure checks, it is
advisable to check and record hot inflation pressures. This program has great
value as it detects under-inflation or leaking tires, which if found in time can be
properly corrected to avert needless damage. For the most effective results, hot
inflation pressures should be taken at about the same time every day and the
readings recorded for each tire on the vehicle. Once this data has been
accumulated, a comparison can be made with the previous day’s pressure for the
same tire and a judgment made as to the air retention.
If a steady drop is noted for one tire, but pressures of the other tires are relatively
stable from one day to the next, it is reasonable to assume that a leak exists. For
the hot inflation program to be effective, it must be frequent, regular, and factual.
A tire or tires with what appears to be abnormally high pressure should never be
“bled,” that is, air released from the tire. The high pressure can often be attributed
to some service irregularity which should be investigated to determine the cause
rather than attempting to eliminate the effect by bleeding air.