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Michelin is leading the way in recommending a switch to the larger 315/70 tyre size.

Where the rubber meets the road: the importance of tyre husbandry

A tyre failure is an inconvenience for a commuter looking to get to work on time. For firefighters, such an event can be the difference between life and death. What steps should services take to keep firefighters safe on the road?

Firefighting is a tough job; so it goes without saying that anything associated with the profession needs to be equally tough: protective equipment, helmets, ladders, hoses – you name it. The same is true of the fire appliances the public rely on in their time of need – and of the tyres those vehicles roll on.

For fire services around the world, there’s no more important piece of equipment than their fire appliances. These trucks are put under stresses that other heavy vehicles employed by road haulage firms will simply never face. Under blue light conditions, fire appliances need to corner harder, retain traction in the worst weather, accelerate at a moment’s notice and transport a heavy load of crew, water and equipment faultlessly, efficiently and safely.

In order to meet these requirements, Michelin has developed technologies and working practices that are suited to the uniquely challenging nature of a firefighter’s work – and it all starts with weight.

Economies of scales

Unlike road transport firms, which have to consider the correct tyre pressures for vehicles running both fully-laden and empty, fire appliances have one advantage when it comes to establishing tyre pressures – they’re almost always running at about the same weight.

While this makes finding and maintaining optimum tyre pressures easier for fire services in the long term, it also throws up a unique set of challenges.

To illustrate: whenever a new vehicle type joins a fire and rescue fleet that Michelin works with, the company’s technical team puts the vehicle on the scales – complete with its normal crew complement, fuel, water, foam and equipment.

By subsequently weighing each wheel position individually to establish the vehicle’s axle loads, pressure suggestions are developed to provide optimal handling, stability and grip, whether the vehicle is moving at speed or heading home sedately following a call-out.

This weighing process also allows services to get the best from their tyres in terms of mileage performance and longevity, via tyre pressure management – although, naturally, this isn’t the key focus for most services, despite the ever-present pressure to reduce costs.

In fact, when it comes to tyre pressure management for fire and rescue services, the difficulty lies not in total weight, but weight distribution.

Fire services frequently aim to standardise the positioning of vital, life-saving equipment across vehicle types. With time always of the essence in an emergency, finding that vital bit of kit in an unfamiliar vehicle could be key. However, such a practice can also leave individual vehicle axles overloaded or underutilised, putting too much load (or too little) on their accompanying tyres.

Fire services should work with their tyre provider and vehicle manufacturer to examine weight distribution from an early stage. This would allow services to “spread the load” where possible, to ensure longevity, traction and handling in all conditions, without degradation of service or safety.

This issue of weight distribution is often more acute for services operating smaller vehicles, such as those rural services that are regularly faced with country lanes, mud-splattered corners and miles of track without a lamp post in sight. These vehicles still have to carry large amounts of equipment, and therefore tend to operate closer to their maximum gross vehicle weight. This then means that they have less spare capacity on the individual axles.

However, away from the vital need to find and maintain the correct tyre pressures and weight distribution on vehicle types across a fleet, consideration should also be made for selecting the appropriate tyre sizes, tread patterns and fitment policies.

X MultiWay 3D XZE tyres feature M+S and 3PMSF markings, highlighting their ability to deliver traction on snow and in mud.

X MultiWay 3D XZE tyres feature M+S and 3PMSF markings, highlighting their ability to deliver traction on snow and in mud.

Tread new ground

For many UK fire services, the move to 315/70 R 22.5 tyres (315 being the nominal section width of the tyre in millimetres, 70 the height of the tyre sidewall as a percentage of the nominal section width and 22.5 the nominal diameter of the wheel rim in inches) for larger appliances has been slow, but is gaining pace.

Michelin is leading the way in recommending a switch to the larger tyre size, as 315/70 tyres feature a wider nominal section width than the smaller 275/70 R 22.5 tyres previously favoured by services, providing a wider contact patch, and therefore a greater contact area with the road surface. This promotes even wear, with a high degree of tyre stability for improved vehicle handling – vital for blue light work.

These larger tyres also help with the weight distribution issue. The tyres offer up to 8 tonnes of load-carrying capacity on the front axle, a significant increase over the 6,300kg carrying capacity of the 275/70. This means that even with the increase in front axle loads due to the engines’ Euro VI emissions equipment, the 315/70 can cope with the weight transfer from hard cornering and heavy braking common when the sirens are sounding. Previously, when using the smaller tyre, these appliances could suffer from excessive understeer when the front axle loads were at the limit.

The Michelin approach to this tyre selection conundrum is a focus on ensuring the optimum tyre pressure is established and maintained for all axles, using a dedicated calculation specially derived for emergency response vehicles by the Michelin Technical Team. This ensures optimum traction, handling and stability. This, where possible, is accompanied by dynamic handling assessments, to fine-tune the vehicle handling characteristics.

However, selecting the correct tyre for the job doesn’t stop at tyre size – there’s also the tread pattern to consider.

Fit the pattern

Historically, UK fire services fitted identical tread patterns to both axles, as this offers the best handling balance. Then – following some particularly challenging winters – some services, particularly in the north of England and Scotland, instead opted to fit drive-pattern tyres to the drive axle, and steer-pattern tyres to the front. While this compromise had a marginally negative impact on vehicle handling balance, it provided improved traction on snow-covered roads, ensuring appliances made it to the call safely, quickly and reliably.

Today, tyre technology has advanced to a point where fitting the same tread pattern to both axles can again be considered, even for challenging conditions.

To illustrate, Michelin’s latest-generation regional X MultiWay 3D XZE all-position (steer) tyres carry both the Mud + Snow (M+S) and Three Peak Mountain Snowflake (3PMSF) markings.

Traditionally an M+S tyres’ tread design generally had lateral grooves in addition to the circumferential grooves found on ‘standard’ steer tyres, and are specially designed to improve performance in mud and fresh or melting snow. The 3PMSF symbol, meanwhile, is only applied to tyres which meet the requirements specified within ECE regulation 117 for traction and braking in defined snow conditions – all of which adds up to a better vehicle handling balance when fitting multi-position tyres on each axle, and with minimal impact on traction in bad weather.

As a bonus, fitting only one type of tyre means storing only one type of spare, ultimately cutting costs and streamlining the supply chain.

New tyre strategy for Scottish Fire and Rescue Service

The Scottish Fire and Rescue Service is benefiting from improved tyre life, durability and traction for its frontline appliances after adopting the latest generation truck tyres.

The service became the first emergency service in the UK to fit a set of 315/70 R 22.5 Michelin X MultiWay 3D XZE all-position (steer) tyres in 2011. Five years on, the fitments are still fitted after more than 58,000 km in service and are projected to achieve in excess of 71,000 km – an approximate 94 per cent increase in mileage performance over the previous fitment.

Fleet Manager Scott Roberts pioneered the shift from 275/70 R 22.5 XZE2+ tyres – previously the favoured tyre size for an 18 tonne fire appliance – and says that the move to larger tyres, combined with the new Michelin tread pattern, ticks all of the boxes.

Critically, the all-position X MultiWay 3D XZE tyres feature M+S and 3PMSF markings, highlighting their ability to deliver traction on snow and in mud.

Previously, even urban-based appliances on all-position tyres could struggle for traction in challenging conditions. However, the new tyres’ credentials enable the Scottish Fire and Rescue Service to specify all-position tyres as an all-round fitment on new heavy appliances – even those for rural areas, which previously required drive pattern tyres to ensure sufficient traction when road conditions deteriorate.

As well as fitting the latest generation tyres on its 18 tonners, the Scottish Fire and Rescue Service is also fitting Michelin’s new X Multi range of tyres on its smaller 15 tonne trucks. 285/70 R 19.5 X Multi Z tyres have been specified as original equipment on 15 new Volvo appliances.

The new X Multi Z tyres stand out for being safer, more fuel-efficient, quieter and longer-lasting than the previous generation Michelin XZE2s they replace.

The service was the UK’s first to fit a set of 315/70 R 22.5 Michelin X MultiWay 3D XZE all-position tyres in 2011.

The service was the UK’s first to fit a set of 315/70 R 22.5 Michelin X MultiWay 3D XZE all-position tyres in 2011.

Top tips

To conclude, here are my ‘top tips’ for fire service tyre husbandry best practice:

Select the right tyre for the job

In consultation with the appliance manufacturer and tyre supplier, services must first consider the particular vehicle’s desired application. Once this has been established, the manufacturers can provide suggested tyre sizes for the vehicle as well as an appropriate tread pattern.

Weigh your vehicles

Following the selection of the tyre type, services should have their vehicles professionally weighed. Once the technical weighing exercise is complete, the tyre manufacturer’s technical team should be able to offer bespoke tyre pressure settings for each axle on the vehicle type.

Maintain optimum tyre pressures

Services should adopt a consistent maintenance programme to ensure these pressure settings are maintained, while also making sure the tyres comply with legislation in terms of tyre condition. Services could consider making tyre maintenance part of the crews’ daily routines as a team task, with responsibility shared among crew members.

Review your tyre policy

Utilise the tyre manufacturer’s technical expertise to review and optimise your existing tyre policy. The Michelin technical team collectively has more than one hundred years of tyre industry experience with the company. Paying a little more at the point of purchase can bring multiple benefits in terms of increased tyre life, improved fuel economy, reduced downtime and, particularly in bad weather, enhanced mobility and safety. The difference in tyre performance from one brand to another can be significant

Firefighting is a tough, demanding job, but tyre husbandry needn’t be. Advances in tyre technology, combined with proactive, in-depth analysis and regular maintenance, can help fire services get to the call quicker and safer than ever before. All that’s required is some careful thought as to precisely what rubber your appliances should be rolling on.

For more information, go to www.michelin.co.uk

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Dan Lamb is a Technical Manager at Michelin covering the north of England and Scotland, alongside fire and rescue and government contracts. Previously an Account Manager working with truck fleets, Lamb is a regular visitor to fire services and road transport firms, using his 22 years of experience within Michelin to ensure customers get the best from their tyres.

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