Proactive tire maintenance

Abstract

Miloš Petrović Institute for research and design in commerce and industry, Belgrade, Serbia Objective of the paper is to promote the proactive approach in tire maintenance for commer-cial vehicles and application of the Tire Pressure Monitoring System (TPMS). Researches have confi rmed that the installation of TPMS on commercial vehicles is technically and economically justifi ed, namely traffi c safety and comfort of passengers would thus be signifi cantly improved and operating costs would be decreased. Example of articulated city bus shows that the invest-ment in the Tire Pressure Monitoring System would be recovered in the second year of operation.

Full text

465
doi:10.5937/jaes9-1267
Paper number: 9(2011)4, 211, 465 - 472
PROACTIVE TIRE MAINTENANCE
Dr Gradimir Danon *
University of Belgrade, Faculty of Forestry, Belgrade, Serbia
Miloš Petrović
Institute for research and design in commerce and industry, Belgrade, Serbia
* Faculty of Forestry, Kneza Višeslava 1, 11000 Belgrade, Serbia, gradimir.danon@sfb.bg.ac.rs
Objective of the paper is to promote the proactive approach in tire maintenance for commer-
cial vehicles and application of the Tire Pressure Monitoring System (TPMS). Researches have
confi rmed that the installation of TPMS on commercial vehicles is technically and economically
justifi ed, namely traffi c safety and comfort of passengers would thus be signifi cantly improved
and operating costs would be decreased. Example of articulated city bus shows that the invest-
ment in the Tire Pressure Monitoring System would be recovered in the second year of operation.
Key words: tire, pressure control, traffi c accident, costs
INTRODUCTION
From the end of the 1980’s a lot of attention has
been paid in professional and scientifi c journals
to the problems connected with tire use and main-
tenance and potential dangers if the tires are not
controlled and/or maintained regularly. It was
determined that tires are very frequent cause of
vehicle stopping. For example, in 2002 AAA (The
American Automobile Association, Inc.) received
2.4 million calls from drivers who stayed on the
roads because of defl ated tires [15]. It was more
than 50% of the total number of calls, namely
almost 0.5 of tire failures per million vehicle/ki-
lometres in the USA in the same year (2002).
Number of failures is probably higher as it can
be assumed that a signifi cant number of drivers
solved the “problem” and replaced the defl ated
tire with a spare one. The stated researches did
not confi rm usual statements that tire failures
during driving were mostly the consequence
of tire punctures. On the contrary, it was deter-
mined that more frequently these are failures as
a consequence of thermal-mechanic loads of in-
suffi ciently infl ated or overloaded tires, i.e. accel-
erated fatigue of material the tires were made of.
Researches conducted in the USA showed that
tires, beside the large number of failures, are not
frequent cause of traffi c accidents (only 0.5% of
6.3 million accidents that occurred in the USA
in 2003) [01], however they have a high partici-
pation in “technical” accidents i.e. the accidents
the cause of which was a vehicle system. For
example, tire failures compose 21% of all tech-
nical accidents of trucks [15] or even 50% ac-
cording to the data from Germany [07]. Figure 1
shows the structure of tire failures (causes of ac-
cidents with casualties or fatalities) in Germany.
Figure 1: Causes of tire failures causing accidents
with casualties or fatalities in Germany [11]
On the Figure it can be seen that negligence and
poor maintenance of tires are the most frequent
cause of accidents for which tires are marked as
the main cause (43%). Insuffi cient maintenance,
or negligence, primarily implies insuffi ciently
frequent control of tire pressure. According to
the researches of the National Highway Traffi c
Safety Administration (NHTSA) on over 10,000
passenger and light trucks conducted in 2001
[15], 36% of the tested passenger vehicles and
40% of light trucks were found to have one or
more tires under-infl ated (by more than 20%).
The situation was not better among commer-

Journal of Applied Engineering Science 9(2011)4
466
cial vehicles. According to the study [02], almost
44% of tires on trucks and buses had the pres-
sure ranging about 0.4 bar of the recommended
pressure, and about 7% of tires had the pres-
sure lower by more than 1.5 bar than the rec-
ommended pressure. Researchers in Serbia
reached similar results as well [14, 05]. The situ-
ation is especially worrying regarding the pres-
sure maintenance of dual tires for which (Figure
2) air pressure control could not be performed
due to the lack of valve stem extender [05].
Figure 2: Results of air pressure control on city
busses /16/
Common conclusion that can be made based
on these researches is that the present main-
tenance of tires on passenger and commercial
vehicles is not on adequate level, users do not
pay suffi cient attention to tires and they do not
realize the importance of tires for safe driving.
Also, it can be concluded that a large num-
ber of failures with happy ending was found
which could act as a reminder that luck can
be changeable and that lack of tire mainte-
nance can signifi cantly jeopardize traffi c safety.
One of the available opportunities for solving
the problem of monitoring air pressure in tires is
wider application of the Tire Pressure Monitoring
System (TPMS) on cars and commercial vehi-
cles. This idea is not new. More than fi fteen years
ago (in 1996) an article on TPMS for passenger
and freight vehicles was published in “Commer-
cial Carrier” journal [06]. The article analyzed
devices used for monitoring air pressure in tires
available at that time, as well as devices that en-
able pressure equalization in dual tires or pres-
sure regulation, i.e. air infl ation in tires. Based on
this article and the information obtained from the
companies that developed or sold these devices,
an impression could be reached that these were
already developed systems already commercial-
ly applied [09]. Unfortunately, the situation was
not such. Lack of legislation (which appeared
much later, fi rst in the USA) and their price at
that time limited the application of these devices
to luxury passenger cars equipped with run-fl at
tires. Only after Ford – Firestone scandal [10]
did the extensive researches start in the USA re-
garding the justifi cation of using these devices
[13]. These researches resulted with the TREAD
regulation [11] that forbids the sale of new pas-
senger cars without a TPMS device in the USA
after 2006. The European Community adopted
a similar regulation in 2009 with obligatory ap-
plication for new vehicles from November 2014.
Based on positive experience with passenger
cars, the introduction of obligatory installation
of TPMS also on trucks and busses is expect-
ed as the next step. To that effect, adequate
researches have been conducted for several
years already focused on the quantifi cation
of the impact of maintaining proper air pres-
sure in tires of commercial vehicles in busses
on safety and operating costs. Conclusion of
these studies [02, 04] is that the realized sav-
ings in tire and fuel costs for commercial ve-
hicles would pay off the investment in installing
TPMS already in the second year of operation.
TIRE PRESSURE MONITORING SYSTEM
(TPMS) DEVICES
Drivers traditionally avoid their obligations re-
garding tire maintenance. Despite various edu-
cational activities, no special advancement has
been done and producers of tires and vehicles
have searched for solutions which would “make
the drivers’ life easier” eliminating at the same
time the main cause of tire failures, namely (in-
stantaneous or gradual) loss of air pressure in
tire. The simplest way is the sealants injected in
the tire through the valve stem. The advance-
ment in this area was made by Goodyear which
offered tires with built-in sealants between two
tire layers several years ago [12]. The best solu-
tion, however for passenger vehicles only, is the
so called “run fl at” tires. Run-fl at tires are always
accompanied with TPMS devices. These devic-
es are, as previously mentioned, obligatory for
all new vehicles sold in the USA from 2008 and
from 2014 similar law will be in force in the Euro-
pean Community countries. Today, there are two
types of these devices on the market, namely the
ones that indirectly measure air pressure in tires
by calculating the change of wheel radius from
extensive tire speed and the others that directly
measure the pressure (usually the temperature
as well) and send the data to the driver’s cab.
Dr Gradimir Danon and etc. - Proactive tire maintenance
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Journal of Applied Engineering Science 9(2011)4 467
Indirect systems – use the speed sensors of
anti-lock braking systems. These sensors mea-
sure angular velocity of each wheel and based
on this the computer calculates rolling radius
which is in correlation with tire pressure among
other things. Smaller rolling radius on a wheel
means lower tire pressure. Too large differences
in the calculated rolling radii activate alert sig-
nals in the driver’s cab. Advantage of this system
is that additional costs of installation are small if
the vehicle is already equipped with ABS system.
Disadvantages of these devices are numerous:
Proper functioning of the system requires re-
set after each infl ation and set-up of the new
condition. If the device is not set on the rec-
ommended pressure, calculation of rolling
diameter will not be correct and the system
will not react timely;
Current indirect systems have different re-
actions for different speeds usually reacting
only when the pressure drops to 30% lower
value than the recommended pressure;
Tires of different producers can have different
elasticity characteristics and different rolling
diameters (for the same load and air pres-
sure), which can also impact the moment of
system reaction;
Insuffi cient pressure on all four wheels at the
same time (which is a frequent case) is dif-
fi cult to detect because of the manner of de-
vice operation.
If the vehicle is not already equipped with
ABS system, installation costs for indirect
TPMS are signifi cantly higher.
Direct systems – TPMS measures actual
(over)infl ation and temperature of air in tires. Sen-
sors can be placed in the deepest groove on the
wheel rim interior (in tubeless tires) or integrated
with tire valve stem. Device in the cab receives
signals from the transmitter and compares them
with the previously given limit values for pres-
sure and temperature. If the measured pressure
or temperature exceeds the set limits, sound and/
or light alert is activated in the driver’s cab.
Advantages of these systems are:
Sensors are factory calibrated and do not
have to be recalibrated;
They operate with all usual tire types;
They can also be used as measuring devices of
air pressure in tires if the driver does not have it;
•
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It alerts the driver when the pressure drops
below the set limit (which the driver can also
change) and identifi es the wheel where it oc-
curred.
Disadvantage of direct TPMS systems is costs
of procurement and installation in new and exist-
ing vehicles.
Regulations in the USA and Europe so far give
preference to direct systems, therefore only
these systems will be discussed hereafter. The
set consists of a certain number of sensors (de-
pending on the number of wheels on a vehicle)
and receiver installed in the driver’s cab. Exam-
ple of the system for monitoring air pressure in
truck tires is given on Figure 3.
•
Figure 3: Example of tire pressure monitoring
system for freight vehicles
Appropriate sensors (5) are installed on each
wheel. Sensors measure air (over)infl ation and
temperature in tires. Signal from the sensors is
transmitted via antennas (6) to the receiver (3
and 4) and fi nally to the display in the driver’s
cab (1). The measured (over)pressure is recal-
culated in the receiver for standard conditions
(20oC) and compared with the set limit values.
Many devices with sensors can be found
on the market which are mounted on wheel
rim by means of steel belt (see Figure 4).
Sensors for passenger cars, light trucks and
heavy trucks are developed.
The second group consists of the sensors in-
stalled on the interior of the valve stem of tube-
less tires (see Figure 5).
These sensors and valve stems are specially
developed for the installation on the wheels of
commercial vehicles. The sensor is installed
on a standard valve stem and does not hinder
Dr Gradimir Danon and etc. - Proactive tire maintenance
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Journal of Applied Engineering Science 9(2011)4
468
infl ation and manual pressure control. There
Sensor for passenger vehiclesTransmitter installed on wheel rim Sensor for passenger vehicles
are two types of valve stems: the one made for
steel and the other made for aluminium wheels.
The advantage of these systems is that they
are tougher, they have low profi le, they are not
easily damaged when mounting/dismounting
tires and there is no need for a special anten-
na because the valve stem itself acts as one.
The third group consists of TPMS installed as
valve caps. They are a simple and cheap do-it-
yourself solution, which can be used for passen-
ger and freight vehicles (Figure 6).
Disadvantage of these sensors is that they have to
be removed during infl ation and they could become
the target of inquisitive persons. Technical solu-
tions allowing manual control or infl ation of tires to
their proper pressure without taking off the sensors
can also be found on the market (Figure 7). These
are the so called “Flow–Through” sensors which
can be dismantled by means of special tools only.
The simplest solutions do not have this option.
Sensors act as valve caps at the same time.
Air pressure control in tires is done in various
ways depending on the applied technical solution:
a) for passenger vehicles b) for freight vehicles
Figure 6: Valve caps – sensors for monitoring tire pressure
In the driver’s cab – most existing technical
solutions also have adequate display in the
driver’s cab where it is possible to read tem-
peratures and pressures in each tire sepa-
rately. Driver can react on time and infl ate
•the tire on the fi rst petrol station or in the
garage. Also, the system should react with
sound or light signal if the pressure in one of
the tires is lower than the set threshold (usu-
ally 80% of the recommended pressure);
Dr Gradimir Danon and etc. - Proactive tire maintenance
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Figure 5: Sensor installed on valve stem
Figure 4: Devices installed on wheel rim

Journal of Applied Engineering Science 9(2011)4 469
Figure 7: „Flow–Through“ sensors for external installation
Figure 8: Control point for remote control of air
pressure in tires
In the garage – a stationary device is mount-
ed which controls tire pressure on vehicles
that enter or leaving the facility provided that
they have adequate transmitters installed on
wheels (see Figure 8). These way vehicles
with defl ated tires can be prevented from
leaving.
The system is primarily intended for garages
with a lot of vehicles whose daily movement
radius and daily kilometres are relatively low.
By means of a handheld device – mainte-
nance worker has a personal digital assistant
(PDA) and adequate software by means of
which it can read air pressures in tires and re-
cord air pressure in tires in contact-less man-
ner. If RFID (Radio frequency identifi cation)
is also installed in the tire, this device can
also be used to read other data about tires.
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fi rst line intended by 10 mm.
Double spacing should only be used before
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in this example. Position and style of headings
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spaces should be placed between paragraphs.
JUSTIFICATION OF USING TPMS
ON COMMERCIAL VEHICLES
In the last several years, a lot of researches have
been done with the objective to reject or confi rm
economic justifi cation for applying TPMS devic-
es [02, 08, 12].
Frequency of tire failures on passenger and
freight vehicles, causes and consequences of
these failures were researched. Objective of
these researches was to determine if the real-
ized savings would be higher than the costs of
procurement, installation and maintenance of
this equipment. Results of these and many oth-
er researches unambiguously indicate that im-
proper air pressure in tires reduces the safety
of passengers and vehicles and increases to-
tal operating costs. To quantify the effects of
improper tire infl ation, it was necessary to use
“impact profi le curves,” which describe the cor-
relation between the amounts a tire is under-in-
fl ated or over-infl ated and the percentage impact
on tire life, tread wear, and/or fuel economy [02].
Reduced tire life (total useable kilometres includ-
ing all retreads - Inadequate tire infl ation, spe-
cifi cally underinfl ation, causes a reduction in the
useable life of a tire because the tire is running
in an overloaded condition. Overloading causes
the sidewall of the tire to extend and contract,
causing heat generation inside the tire. Exces-
sive heat leads to fatigue of the rubber and cords
thus further exacerbating the sidewall fl exing.
The weakened structure increases the likelihood
of punctures and cuts, and the increased temper-
ature leads to premature separation between the
tire cords and the rubber. In effect, the increased
heat and motion reduces the number of times that
a tire could be safely retreaded (see Figure 10).
A common rule is that a constant 20% under-in-
fl ated condition will reduce the life of a tire by 30%
and 40% under-infl ation will reduce tire life by 50%.
Dr Gradimir Danon and etc. - Proactive tire maintenance
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Journal of Applied Engineering Science 9(2011)4
470
Figure 10: Underinfl ation impact of tire life [8]
Increased tire wear (miles between retreading)
- In addition to impacting the usable life of a tire,
improper tire infl ation also affects tread wear.
Both over and under-infl ation change a tire’s
footprint thus affecting tire traction and leading
to irregular wear (see Figure 11). Under-infl a-
tion causes many types of irregular and accel-
erated wear patterns including shoulder wear,
block-pumping wear, spot wear, diagonal wear,
rib wear, and block-edge wear. Over-infl ation
also can cause shoulder and block-edge wear,
and accelerates heel and toe wear.
• A common principle is that a constant 20% un-
derinfl ation will increase tread wear by 25%.
Reduced fuel economy - Fuel economy is
also impacted by inadequate tire infl ation.
Increased fl exing and the irregular footprint
caused by underinfl ation, yields increased
rolling resistance which leads to increased
fuel consumption as more power is required
to move the vehicle. In fact, for every 1 bar
underinfl ation there is a 0.75% reduction in
fuel economy. Figure 12 shows the impact
profi le of underinfl ation on fuel economy.
•
Tire failures from sudden loss of tire tread
and blow-outs, leading to an out-of-service
condition (road calls) - Under-infl ation causes
excessive deformation of the sidewalls and
heat built up, which weakens adhesion be-
tween the rubber and steel cords. Improper
tire infl ation also increases the potential for
•tire failures from sudden loss of tire. Over-in-
fl ated tires also can lead to major tire failures
since they are more vulnerable to tread sur-
face cutting, impact breaks, punctures, and
shock damage.
Based on the data from the same source [02],
impact of under-infl ated tires on operating costs
Figure 11: Infl ation pressure versus tread wear [8]
Dr Gradimir Danon and etc. - Proactive tire maintenance
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Journal of Applied Engineering Science 9(2011)4 471
Figure 12: Underinfl ation impact on fuel economy
Reduction of tire life Increase of protector wear Increased fuel consumption
-7.67% +6.89% +0.19%
Table 1: Impact of improperly infl ated tires of an articulated bus on operating costs [02]
is calculated using a city bus in Belgrade as an
example (see table 1).
Due to the reduction of tire life, the average of
7.67% of the price of a new tire is lost. Tire wear
is 6.89% higher, which impacts the reduction of
life of a new or renewed protector. Regarding fuel
consumption, it is about 0.2% higher due to neg-
ligence in tire maintenance. Table 2 gives the re-
quired data for the calculation of possible savings.
For this example, based on the assumed input
data (given in table 3) and on the assumption
that effects amounting to 80% of the expect-
ed effects are realized with the introduction of
TPMS, savings for one articulated bus in the
amount of 471 EUR annually would be obtained.
Vehicle with installed TPMS does not require
frequent controls of air pressure in tires; how-
ever, they are needed for occasional controls
of proper functioning of the installed devices.
Taking into consideration all these points and
assuming that it will be possible to realize only
80% of the expected benefi ts, a bit reduced
amount of savings is obtained (see table 4).
Number of wheels on articulated bus Number 10
Average annual kilometres km 70,000
Average tire life km 54,000
Average consumption for articulated buses l/100km 70
Coeffi cient of tire retreading – average number of retreading in tire life - 0.11
Price of a new tire EUR 300
Price of diesel EUR 1
Average price of retreading EUR 150
Price of intervention in the fi eld for 1 tire EUR 65
Number of interventions per vehicle annually Number of
interventions 1
Table 2: Input data required for the calculation [03]
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Journal of Applied Engineering Science 9(2011)4
472
New tires EUR 298
Retreaded tires EUR 15
Fuel EUR 93
Interventions on the road 65
Total 471
Reduced amount of savings for tires and
fuel (80% of 471 EUR) 377
Retreaded tires EUR 80
TPMS maintenance for one year EUR -50
Possible savings EUR 407
Receiver EUR 300
Sensors (10*40) EUR 400
Total* EUR 700
Item Amount
Costs of installing TPMS on
articulated city bus EUR 700
Possible annual savings EUR 407
CBR (Cost-Benefi t Ratio) 1.72
Table 3: Possible savings that would be realized
by installing TPMS on articulated bus [14]
Calculated savings should be compared with the
costs of the user. These are the costs of procur-
ing receivers and sensors (table 5).
* Costs of installation are included in the price
of a new bus. Now possible costs and possible
benefi ts of installing TPMS on city buses can be
determined (table 6).
It arises from the analysis that the funds invest-
ed in the installation of the system for controlling
and monitoring air pressure and temperature in
tires would be returned in less than two years
or 21 month, i.e. by installing these systems the
traffi c would become safer, more comfortable
and cost-effective.
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Table 5: Costs of installing TPMS on articulated city bus
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