Tyres : Introduction
Tyres are the only parts of the car which are in contact with the road. Safety in acceleration, braking, steering and cornering all depend on a relatively small area of road contact. It is therefore of paramount importance that tyres should be maintained in good condition at all times and when the time comes to change them, the correct replacements are fitted.
(Source: TyreSafe)
UK Tyre Law : Tyre tread and the Law
The law requires a minimum tread depth of 1.6mm in a continuous band around the central three quarters of the tyre. To help you judge how much tread you have on your tyres, manufacturers often mould tread bars at roughly 1.6mm.
Tread depth indicator | 
This tyre is very close to being - or has just become - illegal |
If you can see these bars your tyres are about to become illegal and unsafe. However, for optimum safety, most manufacturers recommend that your tyres are changed at 3mm.
Tyre Maintenance : Tread Wear
Often tyres need to be replaced before their specified life has been reached mainly because of rapid or uneven tread wear. The most common causes of avoidable tread wear are: 
- Under-Inflating - Causing rapid wear along the edges of the tread.
- Over-Inflating - Causing rapid wear along the centre of the tread.
- Faulty brakes or shock absorbers - Can cause flat spots around the tread of the tyre.
- Incorrect wheel alignment (tracking) - can cause rapid wear along the inside or outside edges of the FRONT tyres. If you strike a kerb or hit a pot hole - the delicate settings of the steering geometry may become misaligned resulting in uneven wear. Wear and tear in the steering components can also affect wheel alignment so it's worth having your front wheels realigned every 6000 miles.
Tyre Maintenance : Damage
Cuts, breaks and abrasions can penetrate deep into the inner fabric of the tyre and can be dangerous, even capable of causing high speed blow-outs. However, penetration of the tread by a nail or shard of glass or metal can often be safely repaired. At National Tyres and Autocare only a special vulcanised plug patch is used which repairs the tyre to high standard in accordance with NTDA and BSAUl59 regulations.
Tyre Maintenance : Wheel Balancing
To keep the tread in constant contact with the road, the wheel and tyre have to be correctly balanced. If the vehicle was to be raised on a jack and the wheel spun by hand, an unbalanced wheel would always stop at the same point - with the heavier imbalance being of course at the bottom of the wheel.
On the road, wheel imbalance can actually lift the tyre from contact with the road creating vibration through the steering wheel, causing steering and braking problems. This vibration causes high-pressure stress in the steering, hub assemblies and suspension, resulting in excessive mechanical wear and high fuel consumption as well as tyre wear. Damage to the suspension, wheel bearings and steering components is unavoidable if the imbalance is left unattended.
Incorrect wheel balance is easily corrected by using a computerised electronic wheel balancer to measure the imbalance, and then adding small metal weights to even things up. It is essential that you have your wheels balanced whenever you replace a tyre or have a puncture repaired (Alloy wheels require specially coated weights to avoid corrosion caused by chemical reaction between differing metals).
Tyre Maintenance : Wheel Alignment
Every car has a specific steering track setting for its front wheels. If the setting becomes upset, by striking a kerb or hitting a pothole or simply by wear and tear, tyre wear can be rapid. Incorrect wheel alignment becomes obvious when either the inner or the outer edge of the tyres become unevenly worn or a "feathering" effect becomes noticeable. If you suspect your alignment has been disturbed - have it checked at National Tyres and Autocare immediately. We recommend having it checked every 6,000 miles or when tyres or steering components have been changed.
Tyre Maintenance : Tyre Pressure
It is important to keep your tyres at the correct pressure as wrongly inflated tyres will greatly shorten your tyres' life, and could make your car dangerous to drive. Pressure is measured by calculating the amount of air that has been pumped into the inner lining of your tyre in pounds force (PSI) or BAR pressure and the recommended pressure levels for your tyres can be found in your manufacturer's handbook or our inflation chart.
Ideally you should check your tyre pressure (including the spare) every two weeks when the tyres are cold, as the pressures increase after the car has been run due to the air inside warming up.
If you have a heavy load - for example before going on holiday - check your handbook and increase tyre pressures as per manufacturers' recommendations. Remember to reduce the pressures after removing the heavy load.
Changing Tyres : When to Change
If your car doesn't handle or grip the road as well as usual in wet weather or it takes longer to stop when you apply the brakes, this could be a sign that your tyres need changing. Because your tyres wear down gradually it can be difficult to identify these changes so we recommend that you have your tyres checked regularly by a qualified National Tyres and Autocare technician.
Tread depth indicator |
This tyre is very close to being - or has just become - illegal |
Many manufacturers now include a Tread Wear Indicator (TWI) within the grooves of the tyre tread which become more visible as the tyre wears down. Whilst these markings are an indicator, always check the tread depth using a tread depth gauge and check your tyres regularly for bulges or wear.
Changing Tyres : Valves
The tyre valve is often the most neglected and overlooked component within the wheel and tyre assembly, yet an efficient valve is important for the safe operation of the tyre.
Wear on the valve seal, damaged screw threads, dirt and grit in the valve itself can lead to failure of the tyre at speed. Even a poorly sealed valve can cause fairly constant under inflation of the tyre which will reduce the life of your tyre by up to 25%. As it is impossible to replace the valve without removing the tyre casing from the wheel - National Tyres and Autocare recommend that the valves are replaced EVERY time a tyre is replaced.
Tyre Repair : Puncture Repairs
Puncture repairs are carried out in accordance with NTDA and BSAUl59 regulations which stipulate that:
- Tyres can only be repaired in the area marked 'T'.
- For tyres rated 'V' and above, only one repair is allowed.
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NOTE: NEVER FIT AN INNER TUBE WITH A TUBELESS TYRE EXCEPT ON A TUBE TYPE WHEEL
Minor penetration repairs are not permitted in this area. |
In every case the tyre should be inspected and if any of the following are noted then it shouldn't be repaired:
- Illegal tread depth (below 1.6mm across the central ¾ of the tyre tread throughout the entire circumference)
- Run flat damage - breakdown of the tyre's structural integrity
- Secondary damage - caused by the injuring object
- Ageing/deterioration of tyre rubber
- Bead damage
- Exposed cords
- Faulty/poor previous repairs
Tyre Information : How to read a sidewall
Every tyre sidewall shows information about the manufacturer, size, model etc. Here's a summary of the most important information and what it means.
Example: 165 70 R13 79T
- 165 - means the tyre has a nominal section width of 165 millimetres
- 70 - is referred to as the aspect ratio and is the height of the tyre sidewall as a percentage of the nominal section width.
- R - means the tyre has a radial construction, the most commonly used of three different types of tyre construction: cross ply, radial and bias belted.
- 13 - means it fits a 13" diameter wheel
- 79 - is the load index. This identifies the maximum load capacity of a tyre when driven at maximum speed. Overloading a tyre, by carrying more weight than it is designed to or running at a lower than specified pressure can cause heat build up and blow outs. Load indexes for passenger cars usually range from 70 - 110 and the maximum load per individual tyre is shown in the table below.
| Load Index and Maximum Load per Individual Tyre |
Load
Index |
Load
(kg) |
Load
Index |
Load
(kg) |
Load
Index |
Load
(kg) |
Load
Index |
Load
(kg) |
| 70 |
335 |
81 |
462 |
92 |
630 |
103 |
875 |
| 71 |
345 |
82 |
475 |
93 |
650 |
104 |
900 |
| 72 |
355 |
83 |
487 |
94 |
670 |
105 |
925 |
| 73 |
365 |
84 |
500 |
95 |
690 |
106 |
950 |
| 74 |
375 |
85 |
515 |
96 |
710 |
107 |
975 |
| 75 |
387 |
86 |
530 |
97 |
730 |
108 |
1000 |
| 76 |
400 |
87 |
545 |
98 |
750 |
109 |
1030 |
| 77 |
412 |
88 |
560 |
99 |
775 |
110 |
1060 |
| 78 |
425 |
89 |
580 |
100 |
800 |
|
|
| 79 |
437 |
90 |
600 |
101 |
825 |
|
|
| 80 |
450 |
91 |
615 |
102 |
850 |
|
|
- T - is the speed rating. This represents the maximum speed that a tyre can sustain at full load. The example shown is rated for speeds up to 118mph.
- Other common speed ratings are:
Q - for cars with max speeds up to 100mph (160km/h)
R - for cars with max speeds up to 105mph (170km/h)
S - for cars with max speeds up to 113mph (180km/h)
T - for cars with max speeds up to 118mph (190km/h)
H - for cars with max speeds up to 130mph (210km/h)
V - for cars with max speeds up to 150mph (240km/h)
Z - for cars with speeds over 150mph (240km/h)
W - for cars with max speeds up to 168mph (270km/h)
Y - for cars with max speeds up to 186mph (300km/h)
You should always replace a tyre with the same or a higher speed rating and we recommend that you check against the speed rating approved by the vehicle manufacturer.
Tyre Information : Runflat Tyres
Run flat technology allows your car to keep on running after a puncture or blow out, even when the tyre is completely deflated. Self supporting run flat tyres are designed to provide a run on period following deflation. The range of the tyre when running on flat is dependent on the condition of use (i.e. vehicle load, vehicle speed and driving conditions). However, you should be able to keep ongoing for a minimum of 50 miles at a constant speed of no more than 30mph.
This is made possible due to the tyre's reinforced sidewalls. The highly resilient rubber inserts support the weight of the car even when the air pressure, which normally does this job, is gone.
Replacement tyre fitting - Always consult the vehicle handbook or tyre manufacturer's guidelines regarding which vehicles are suitable for fitment of run flat tyres. These tyres may only be fitted to vehicles equipped with a tyre pressuring monitoring system (TPMS).
Fitting of conventional tyres to vehicles originally fitted with run flat tyres will remove the vehicle's run flat capability and will leave you with no spare tyre. This could potentially leave you immobile in case of deflation and it is therefore recommended to consult your vehicle or tyre manufacturer before replacing a run flat tyre with a conventional tyre.
Mixing run flat tyres with standard tyres - The handling characteristics of run flat tyres are different to those of conventional tyres and therefore should not be intermixed on a vehicle.
Mixing different brands of run flat tyres - As with standard tyres, there may be different characteristics between different makes of run flat tyres so it is advisable to consult the tyre manufacturer regarding mixing different brands. It is recommended that the same make and pattern of tyre is fitted across the axle of a vehicle.
Service Life of run flat tyres v standard tyres - The tread rubber compound used in run flat tyres is generally the same or similar to that used in conventional tyres. Therefore, tyre wear rates should be similar. The best tyre performance is achieved by maintaining correct inflation pressures for the loads and vehicle's use.
Use of run flat tyres on towing vehicles - in their inflated condition, run flat tyres may be used in the same way as standard pneumatic tyres. However, any experienced towing caravaner knows that the stability between their car and caravan is of primary importance to road safety. Whilst a deflated run flat tyre is designed to cope with the demands of the solo vehicle, the additional mass of a caravan or trailer will subject the tyre to higher stress levels and impact on the tyre's inbuilt lateral stability.
Therefore, even travelling at a restricted speed of 50mph may negatively affect the stability of the car/caravan combination and reduce road safety. To avoid this potential hazard, it is recommended that the distance travelled and maximum speed on the deflated run flat tyre be reduced. As the vehicle itself has an influence on the tyre's performance, please refer to the vehicle manufacturer's handbook for further information.
Use of run flat tyres on caravans and trailers - run flat tyres must only be fitted to vehicles which have a tyre pressure monitoring system (TPMS) as a visual/audible warning to drivers of a deflating tyre. As yet, no caravans or trailers are equipped with TPMS systems, hence they should not be fitted with run flat tyres.
Repairability - all major tyre retailers, the National Tyre Distributors' Association (NTDA) and TyreSafe do not recommend repair of run flat tyres or fitting run flat tyres to vehicles not designed with this type of tyre in mind.
Tyre Information : Energy Saving Tyres
20% of a car's fuel consumption is due to the tyre. To reduce fuel consumption, the forces opposing the vehicle's movement need to be decreased. Therefore a decrease in tyre rolling resistance leads to a reduction in fuel consumption.
Energy saving tyres have low levels of rolling resistance, therefore providing a reduction in fuel consumption, and subsequently reducing vehicle CO2 emissions.
Check out our range of energy saving tyres which provide the following benefits:
- Reduced rolling resistance
- Less fuel consumption
- Decreased pollution levels
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