Wheels and Tyres
Wheels and Tyres
Wheels and Tyres
4.
WHEELS
AND TYRES
the hub of
successful off-roading
4. Wheels & Tyres 14/8/00 11:40 PM Page 128
T
he pressure a tyre exerts on the ground and the effect the
tread pattern has on the surface over which the vehicle is
passing will determine the ease and efficiency with which
the vehicle will travel. Although motor manufacturers go to a
great deal of trouble to research what type of tyre will work
best with a particular vehicle, they are normally shod with general
purpose tyres or just road tyres with aggressive treads.
TYRE SELECTION
Mud tyres
A tyre suited to sand or normal road use clogs rapidly and loses
traction in mud. The large gaps and chunky look in the tread of
mud tyres facilitates ‘self-cleaning’. As the wheels rotate the mud
embedded in the tread is released and is thrown out. Heavy treads
tend to make more noise than fine treads and this is most notice-
able on tar at speed. Purpose built mud tyres do not have good wet
road performance, so extra care is needed in these conditions.
Sand tyres
The main feature of a tyre designed for sand is not, as is commonly
thought, broad width, but a tread pattern that compresses the sand
beneath the tyre instead of penetrating through it – which is what
happens when a mud tyre is used on sand. The gaps in the sand
tyre tread are narrow and the tread pattern runs longitudinally
around the tyre. Good sand tyres flex well when used at low
pressures.
Sand tyres must also be tough enough to withstand rough tracks
and sharp stones of semi-desert regions, since rarely do pure sand
conditions last for long before being interrupted by sections of
sharp stones and gravel.
Broad tyres
Not all vehicles are designed for very broad tyres. On some
vehicles the tyres may rub the steering arms, brake hoses or
chassis when the steering is on full lock. If your vehicle is blessed
with good axle articulation, oversized tyres may rub against the
body when the axles are extended in off-road travel. They also put
undue stress on transmissions not designed for the use of big tyres.
Snow tyres
A mud tyre will perform well in virgin snow conditions. On com-
pacted snow, as found on well-used roads, a less knobby tyre will
be more effective. Typical effective road/mud and snow tyres are
indicated M&S (mud & snow) and have squared shoulder and
block tread.
Damage to a sidewall is
a common occurrence
in rocky terrain. The
thickness of the sidewall
is a good indication of a
tyre’s resistance to
damage. Three-ply
sidewalls are
recommended for off-
road conditions
Summary:
• Heavy tread far apart: good for mud, mediocre in sand.
• Medium tread close together: good in sand, mediocre in mud.
• Thick tread: good for sharp rocks, often combined with hard
compound rubber which will wear well on rough tracks. Will
not flex well – a disadvantage in sand.
• Thick sidewall: good for sharp rocks. Good load rating. Less
ability to flex in sand. More resistant to damage when at
lower pressures due to the strength of sidewall.
OTHER FEATURES
Speed ratings
The maximum permissible speed is printed on the tyre sidewall.
Tyre damage will result if this is exceeded. When a tyre is deflat-
ed for reduced penetration, the permissible speed rating no longer
applies.
Load ratings
The maximum permissible load is printed on the tyre sidewall.
Tyre damage will result if this is exceeded, particularly if high
speeds are attained.
Radials
Radials are superior to cross-plies in almost every respect except
price. They offer superior traction, safety and comfort, both on a
paved surface and off-road.
Radial tyres are made by laying strips from bead to bead (the
bead is the point where the tyre meets the rim). The advantage of
this design is that flexing of the sidewall does not affect the tread.
They flex independently of each other. So, decreasing pressures will
flex the sidewall and tread area, while keeping the tread pressure
evenly spread and increasing the tyre’s contact area with the
ground, thereby decreasing the ground pressure and the tyre’s pen-
etration.
Valve stems
The length of valve stem fitted to tubed heavy duty tyres fitted to
a 4x4 must be the short type. Long stems are vulnerable to
damage by rocks, grass and undergrowth and are subject to failure,
often when the tyre is working hard in a remote location. Tyre fit-
ment centres may assure you that it makes no difference – but it
does, so insist on short valve stems. If you use tubeless tyres, carry
a few spare valves with you.
235R16C
108Q
375kPa
235/85 R 16 112 N
Tyre width
Design (radial)
Load index
Speed category
Key to Charts:
• Mileage: reputation for distance covered before replacement.
• S/Wall: number of sidewall plies and resistance to penetration.
• Tread: strength of tread and resistance to penetration.
• Punct: resistance to punctures. A heavy tread does not necessarily
mean high resistance. For example, some tyres are like magnets
to nails. Nobody seems to know why.
• Mud: performance in mud.
• Sand: performance in sand at below normal pressures.
• Wet tar: compromises that make a tyre good off-road are often
felt on wet tar.
• Dry tar: grip and noise levels.
• Rocks: performance and resistance to punctures.
• Sizes available have been omitted because of the rapid changes
made to tyre designs and it would probably take about ten
pages to list all of the manufacturers and their products.
• Ratings: P=Poor, F=Fair, G=Good, E-Excellent.
BF Goodrich
This US manufacturer makes a number of off/on-road products and
all appear to have a good reputa-
Left: Mud Terrain T/A
tion. Their tyres fit 14, 15 and 16- Right: All-Terrain T/A
inch rims. The All-Terrain T/A
has a particularly good repu-
tation for robustness and
good mud traction. They
are more expensive than
most.
BF GOODRICH
Model mileage s/wall tread punct mud sand wet tar dry tar rocks
Long Trail T/A G G F G F F G G G
All-Terrain T/A F G E E E F G G G
Mud Terrain T/A F G G G E F F F F
Continental (Gentyre)
Gentyre and the Continental brand are
home-grown products all of which were
developed for local needs. The General
listed here is the Super All-Grip radial, once
supplied as OE (original equipment) on
Land Rover Defenders and is an excellent
tyre for a working 4x4. The Conti Trac AT
is Continental’s flagship model and is
ideally suited to luxury 4x4s that are also
required to tackle off-road conditions and
long stretches of unpaved roads. It is
currently OE on the Defender.
The second generation Conti Trac AT
was available from early 1999. It can be
told from the first generation by a serrated
seam on the sidewall. This tyre has Left: Conti Trac AT
Right: RVT280
improved tread life and a tougher sidewall.
Conti Trac is available in a range of 15 and
16-inch sizes.
CONTINENTAL
Model mileage s/wall tread punct mud sand wet tar dry tar rocks
Conti 180N G F F G P E G G F
Conti 280 G G E E G G F G E
Conti Trac AT (new) F G G F G G E E F
Gen SAG radial G G E E G G F F G
Firestone
The two products that Firestone have built from local needs is the
R4S and the ATX. Both are available in 14 and 15-inches, the ATX
being the most widely used for off-road work. Its reputation is one
of ruggedness and excellent puncture resistance. Their road man-
ners are not as good and they can be a little noisy. They do not
work well in mud. The Town and Country is a very old design and
FIRESTONE
Model mileages/wall tread punct mud sand wet tar dry tar rocks
ATX G G E E P G F G E
Town & Country P P F F P F F F P
Goodyear
The Wrangler is one of the best known multi-purpose tyres and has
an excellent all-round reputation. OE on the Hilux for some time,
the Wrangler is a light duty off-road tyre with a good balance of
toughness and road grip. Its only short-
coming is its narrow tread pattern
which clogs with mud quickly. Its una-
gressive tread belies that fact that it is
robust and able to cope with fairly
tough off-road work although sharp
stones can and do penetrate the tread
with heavily loaded vehicles.
GOODYEAR
Model mileage s/wall tread punct mud sand wet tar dry tar rocks
Wrangler G F F G P G F G G
Michelin
Undoubtedly due to its fine reputation for making excellent road
tyres, Michelin is, in my opinion, overated as a maker of off-road
tyres. I drove on Michelin for well over a decade and the day I
changed, my problems with tyres came to an abrupt and pleasing
end. Michelin’s offer traction as good as their competitors but some
reason every Michelin I drove suffered repeated punctures. And, to
back up my opinion, I still receive as steady flow of stories about
the lack of strength or resistance to punctures of many Michelin
products.
Michelin was the first manufacturer to tackle the leisure 4x4 mar-
ket in a big way with the 205/16 M+S radial fitted
OE to the Range Rover. In South Africa many suf-
fered sidewall failures at high speed, some with
fatal consequences. Michelin’s conclusion was that
the cause of the problem was that local Range
Rovers were overloaded with air-conditioners,
winches, power steering, bull bars etc. combined
with under-inflation. The fact that it was always
rear tyres that blew and my own imported vehicle,
which suffered three such blowouts, had none of
these fittings did not influence their conclusions.
Michelin LTX A/T
MICHELIN
Model mileage s/wall tread punct mud sand wet tar dry tar rocks
XC M/S 200 F F P P G F G G F
LTX A/T F F F F G F G G F
LTX M/S F F F P F G E G F
Yokohama
One of the best Japanese off-road tyres is the Super Digger, a well
known brand with a reputation of extremely long life and atrocious
manners on wet tar. This has been changed with new models and
it appears that the softer compound has improved the tyres
performance in all but longevity. The Y815 is
OE on the SWB Pajero and suits the vehicle
well. The Y826 is the choice for those
who like the ‘fat takkies’ look.
Left: Super Digger 815
Right: Super Digger 826
TYRE PRESSURES
The pressure a tyre exerts on the ground is something that can be
adjusted – the lower the air pressure in the tyre, the less the
ground pressure will be and therefore the less the tyre will pene-
trate the sand or mud over which it passes. In sand, penetration
will halt progress, while in mud and snow this can sometimes be
an advantage. Reducing or increasing tyre pressure is therefore a
way in which the driver can change the effect his tyre will have on
the ground before difficult terrain is negotiated.
The key element in deflating tyres for off-road driving is that low
pressure increases the length of the tyre footprint (not the width),
thus exerting less weight per-square-inch and thereby reducing
On the bonnet
When the release knob is pulled from inside the vehicle to open
the bonnet, the catch often does not release due to its added
weight. It is therefore difficult for a single person to open the
bonnet if a spare wheel is stowed there. Forward vision is also
restricted and safety in a head-on collision is compromised. An
advantage of this position is that it offers excellent weight distrib-
ution. Removing the wheel and replacing it requires some physical
strength and will scratch the bonnet’s paintwork.
On a roof-rack
A spare wheel carried on a roof-rack is ideal because it is easily
accessible, can be secured well forward to aid weight distribution,
and the bowl of the wheel rim can be sat in when game viewing.
Swing-away wheel
carriers are the most
convenient way of
carrying a spare.
If you tow a trailer
make sure that
additions to the trailer
draw-bar allow the
wheel carrier to be
swung clear of the
tailgate. A single and
twin-wheel carrier is
made by Outback
Extreme (011 397
8883)
Spare wheels are usually heavy and it may take two people to lift
it onto the roof rack.
WHEEL RIMS
Steel rims
This type of rim should be selected for serious off-road use. Steel
rims are constructed in two parts: a pressed steel centre boss and
a rolled circular bed for the tyre. These parts are either rivetted or
welded together, rivetted types being the strongest and most reli-
able. Steel rims are sometimes of inferior quality and in some cases
severely warped rims are supplied with new vehicles, making per-
fect balancing impossible.
sure that wheel studs are clean and lightly oiled otherwise stud
nuts can tighten against dirt and rust. Running with loose wheel
nuts can cause severe rim distortion which is irreparable.
Slight damage can be easy to repair, eg. bending of the outer
bead. This can be straightened using a shifting spanner and light
use of a hammer. Make sure the bead is returned to its original
shape and the distortion has not been transferred along the bead.
Because wheel rims are made from high grade steel, welding
should not be undertaken owing to the possibility of the temper
being altered by the heat and resultant weakening of the rim.
Split rims
Some older vehicles were fitted with split rims of a two part design.
This facilitates the removal of the tyre from the rim. These rims are
unsafe and should not be handled by the
uninformed. It is imperative that the tyre
be totally deflated prior to splitting the
rim as air pressure remaining in the tyre
will cause the rim to split with explosive
force which could cause serious injury.
Also, when a tube is fitted onto a split
rim, a gater consisting of a ring of
shaped rubber must be inserted between
the rim and the tube. Not fitting a gater
with a tube will result in the tube wear-
ing and eventually rupturing at the joint
between the rim halves.
Right: A carrier
attached to the rear
of the vehicle is a
very handy place to
carry recovery gear.
Above: Cosmetic
rims covers should
be removed and left
at home during long
trips.
Left: The Thomas air pump is one of the more expensive pumps available.
Right: The Bush Buddy air pump, sometimes called Volcano, a little smaller than the
Hurricane pump but much cheaper and almost as efficient. It is excellent value for money.
Next page top: An example of a Hurricane pump mounted in an engine bay. Mounting a
pump here saves space and is very convenient. Note the similarities with the Volcano.
REPAIRING A PUNCTURE
Tyre repair kits
A repair kit should comprise a set of a minimum of two tyre levers,
a rubber repair kit with patches
of varying sizes, a valve spanner
and a pump. A tyre repair kit
designed specifically by the
author for the African off-roader
is stocked by most 4x4 gear
shops, AA stores and Makro. Ask
for the 4xForum tyre repair kit or
call 021 785 5752.
For punctures that can be repaired without removing the tyre from the rim
follow these instructions:
As these plug repair systems differ slightly, read the instructions
that came with your kit. Locate the item causing the puncture and
draw a circle around it. Do not assume that if you find what seems
to be a nail/thorn in your tyre that this is the only cause of the
puncture. Look carefully at the entire tyre including the inner and
outer sidewalls marking all irregularities. Remove the nail/thorn.
Insert the plug into the spiker and apply cement (some systems do
not require cement) to the plug. Insert the plug and withdraw the
spiker according to kit instructions. Inflate the tyre and splash
water over the repair and over any other suspect areas checking
for bubbles.