When it comes to routine maintenance, tyres are the vehicle component consumers feel most able to handle themselves. However, tyre condition is also an important and frequently nuanced part of any service.
Spotting the warning signs of ageing or damaged tyres can be a valuable win for both the customer and the workshop. In this article, the Autodata team breaks down the factors leading to tyre damage and degradation, as well as when you should recommend a replacement.
Cracking
Several factors can cause tyres to crack. Ultraviolet (UV) rays or extreme heat cause the polymers in the rubber to expand. Once the polymers cool down, they contract, which weakens them over time. In colder climates, cold snaps can have the same effect.
Wet conditions can also damage tyres: any water that gets inside the tyre causes the rubber to wear from the inside. This results in a poorer fit and a greater chance of friction damage, creating small tears.
Under-inflated tyres result in more contact with the road and thus more wear, while over-inflated tyres place greater stress on the tyre wall – meaning potholes and uneven surfaces are more likely to cause cracks.
Typically, minor cracks on the tread do not fail annual vehicle inspection, but deeper cracks risk tread separation and can be hazardous. Cracks on the sidewall can be a sign of ageing tyres: the rubber becomes stiffer and no longer able to properly withstand shocks. This can potentially lead to a blow-out.
Flat Spotting
Lack of use can damage tyres. If a car is left to stand without the tyres being rotated , consistent pressure on one area will flatten the tyre where it’s in contact with the ground.
Temporary flat spotting will normally resolve after driving the vehicle for 10 to 15 minutes; however, after a longer period of disuse vehicle tyres can suffer semi-permanent flat spotting – especially when stationary under vehicle load for a month or longer.
Flat spotting can cause vibration, inconsistent handling, and even result in a puncture.
Jacking Points
Most vehicles have four jacking points. These are located on reinforced metal ribs along both sides of the car, and some include multiple notches or slots. Not all slots are suitable for all jack types and jacking up a vehicle incorrectly can cause damage.
For example, lifts should either use the points on the chassis or just place the feet on the chassis sills. Autodata’s Tyres module includes a jacking point diagram and details which jacks are recommended for which points.
The 2014 Jaguar F-Type Coupe, showing points for bottle jack, floor/trolley jack, and lift.
Manufacture Date Code
Sometimes tyres sit unused for a long time before they are sold. Because of rubber degradation, tyre industry associations recommend replacement after 7-10 years – even under conditions of low wear and tear.
For trailers and caravans, this number is reduced to six years. Spare and replacement tyres may reach end-of-life even sooner, as the oils added to keep the rubber flexible are only released with use.
This makes the manufacture date code found on the tyre’s sidewall particularly important. Tyres manufactured after 2000 will have four digits in the format WWYY (week-year).
For example, 0412 would indicate the tyre was manufactured in the fourth week of 2012 (January) and is therefore beyond end-of-life.
Torque
Over-tightening the wheel nuts/bolts can be as hazardous as under-tightening. Too much torque can strip the thread or even crack the bolt itself. Over-tightening can also lead to brake judder and even warp the brakes – which in turn puts further stress on the tyres.
A four-year study by the Tire Dealer Association of Canada found that 85% of wheel separations were caused by fastener failure. That is, the wheel nuts or bolts loosened most likely due to under-tightening.
Under-tightening can be the result of using an impact wrench to tighten the fasteners. Because of this, Industry associations recommend the use of a calibrated torque wrench to tighten wheel nuts/bolts.
Autodata’s Tyres module includes torques for both wheel nuts/bolts and the TPMS sensor bolt where appropriate.
TPMS
Tyre pressure monitoring systems (TPMS) became obligatory for new vehicles in the EU in 2014 and are now seen in the majority of vehicles visiting workshops. A faulty TPMS in the UK is an automatic MOT fail on vehicles registered after Jan 1st, 2012.
Workshops typically see two types of TPMS:
Spare tyres also increasingly have a sensor for triggering the TPMS. When diagnosing a persistent TPMS warning light, make sure the spare tyre in or under the boot has also been reinflated.
Driving over a pothole, speed bump, or other road calming measure can also trigger TPMS sensors: the sudden change in pressure as the wheel moves over the obstacle can trick the sensor into signalling a puncture.
Autodata includes vehicle-specific instructions including diagrams for TPMS operation and reset, as well as valve removal and fitting during tyre change.
Summer/Winter Tyres
Summer and winter tyres are formulated with different compounds and have noticeably different treads. Summer tyres have less grooves, are wider, made of a softer rubber, and profiled for high aquaplaning resistance.
Winter tyres have a greater number of grooves, are angled to grip snow and ice, and formulated with a compound designed to remain flexible at low temperature.
All-season tyres generally strive for a compromise between the two with a tread that offers lower rolling resistance and better energy efficiency than the winter tyre, but with superior performance in wet and snowy conditions than a summer tread.
Winter tyres are mandatory during the winter months in countries including Sweden, Norway, Finland, and the Baltic countries. German law requires the use of ‘tyres with winter properties’ in winter conditions such as snow or slippery or icy conditions. Snow chains must be carried in the vehicle in Norway, Austria, Serbia, and other countries.
Autodata sees most usage of the Tyres module in late autumn and early winter. A secondary peak occurs in spring. This indicates demand for tyre data continues to be driven by these seasonal requirements.
October 2020 saw over 25,000 requests a week for tyre data from the Autodata workshop application. Autodata also recommends a TPMS reset when changing from summer to winter tyres or vice versa.
Jamie Willis, Technical Support Supervisor for Autodata, said: “With various lockdowns and reduced usage of vehicles, customers may not realise that their tyre needs replacing because it looks in good condition . Technicians can recommend a change to head off issues which may come up due to old or degraded tyres.”
Autodata includes comprehensive tyre data including pressures, jacking points, torques and TPMS guidance. Willis added. “In the last 12 months we’ve added 2,480 tyre data items in addition to regularly updated modules on service intervals, wheel alignment, brakes, engine management, known faults and fixes, and more.”
Autodata is an online technical solution for workshops covering 34,000 models from 142 manufacturers. For more information or to try Autodata, visit www.autodata-group.com.
