Extending the working lives of tyres – and improving their performance – can be achieved in a variety of ways. We investigate stopping distance, regrooving and minimum tread levels
Mark Cartwright, head of vans and LCVs at the Freight Transport Association (FTA) which manages the Van Excellence best practice initiative, sums up the issue: “Pretty much every truck operator I’ve ever spoken to has some form of tyre management policy. We can’t say the same for van operators.”
A recent FTA survey revealed that almost a third of its van operating members did not have a formal policy in place. What’s more, with tyre technology continually improving, a third of respondents had not reviewed tyre management policies in the previous 12 months.
The Van Excellence Code also calls on operators to undertake pre-use vehicle checks and that includes tread depth.
HGVs tailgating on motorways and dual carriageways is a familiar sight – often as a result of attempting to preserve hard won speed. A two-second gap or one yard for every mph is frequently highlighted as best practice, but that generally refers to cars and even that time span or distance may not provide enough road space for drivers to react to what’s happening ahead and the stopping distance required.
The FTA’s The Good Lorry Code/The Good Van Code says: “At 40mph a car needs a total of 36 metres to stop and at 50mph 53 metres. Commercial vehicles need far greater distances – almost twice those listed.”
Tyres are central to the calculations. While the law highlights legal tyre tread depths for all vehicles, experts say stopping distances for light and heavy commercial vehicles are influenced by numerous other factors including: overall tyre condition including pressure, tyre compound and tread pattern as well as the size, weight, load carried and speed of the vehicle and road surface and weather conditions.
Tread carefully: when to replace
Russell Adams, commercial vehicle engineer, corporate sales, Lex Autolease, believes it is best practice to have a 2mm minimum replacement policy. However, dependeing on the type of goods and services being delivered across various industries nationwide, there could be an advantage to changing tyres at 3mm, particularly in the cold and wet winter months.
“Tyres on commercial vehicles bear the brunt of heavy work, carrying loads or undertaking multiple drops, often in tough working environments. Rough ground or repeated kerb scuffing can also cause high levels of damage and wear way beyond that of a car tyre,” Adams says.
Tyres are complex components that have been engineered to work in harmony with a vehicle’s braking, steering and suspension system. When a tyre is under-inflated, it contains insufficient air to support the weight of the van properly. This can adversely affect acceleration, braking and cornering potentially making driving unsafe.
Under-inflated tyres experience rapid wear in the shoulder area of the tread as more of the load is supported here.
Therefore, it is vital businesses promote a duty of care and make drivers aware of their responsibilities and the risks faced if found to be driving on an illegal tyre.
“Driving on over-inflated tyres will also result in higher wear in the centre of the tread. Keeping tyres inflated to the recommended pressure for the vehicle and load ensures an even contact distribution and a more even wear rate, helping to make tyres last longer,” says Adams.
“All van operators should ensure that tyre checks are included in the driver’s daily vehicle walk round checks, and have a process in place for drivers to report any tyre defects and a facility to check tyre pressures at least once a month. It would also be best practice to have a tyre supplier carry out a monthly tyre report on all their vans to ensure they are operating within the law.
“Similarly, it would also be best practice to keep the tyre inspection reports for a minimum of six months.”
One of the most important things drivers should look for in their daily checks is tyre condition – deep cuts or damage to the tyre walls, ensuring there is no cord visible on the tyres, and that all wheel nuts are secure and tightened properly- tread depth and pressure.
Any irregular wear on the tyres should also be checked as that will severely affect the life, durability and safety of the tyres.
Kwik Fit recommends van fleets adopt a replacement policy at 2mm. However fleet director Peter Lambert is concerned about the discrepancy between legal tyre tread limits for commercial vehicles above and below 3.5 tonnes.
“The minimum tread depth that applies to cars and LCVs should be applicable to heavier vehicles unless there are very good reasons for the 1mm tread depth applying,” he says. “Two similarly sized vans, but with a gross vehicle weight either side of the 3.5-tonne mark, will be subject to different tyre laws.”
TyreSafe says it campaigns in line with current legislation and duty of care regulations, and as such focuses its message on fleets changing vehicle tyres before tread depths become illegal.
Chairman Stuart Jackson says that, to the best of his knowledge, there had not been a rigorous study undertaken on the impact of tread depth on LCV and HGV stopping distances. “As the legal limits imply, the impact of tread depth on LCV tyre performance is very similar to that on cars, while the extra weight of HGVs makes them less sensitive to tread depth,” he says.
“However, a tyre with lower tread depth is less effective at removing water from the road, leading to longer stopping distances and reduced road safety. It has been shown that braking distance in wet weather from 50mph to standstill of a tyre with only 1.6mm of tread depth is almost 12 metres longer than with a new tyre, which dramatically raises the chances of a collision.”
Thousands of van tyres are replaced because of damage and long before tread depths become an operator concern, according to Jamie McWhir, customer engineering support manager, car, van and 4x4 at Michelin.
He says that one of the most important issues was for fleets to teach van drivers to mount kerbs at an angle so “the tyre tread takes the hit rather than the side wall”.
McWhir estimates that 20-25% of van tyres are replaced early due to in-life damage, rising to up to 40% on vehicles operating in urban areas.
While tyre tread depth is important, he says checking for tyre damage was “at least as important, if not more so”. Drivers and managers should be keeping a watchful eye out for any bulges, lumps or cuts to tread and sidewalls, while also checking for stones or other objects that may be embedded in tread, as tyre damage can result.
‘Twinning’, regrooving and ‘turning on the rim’
Most car and van tyres have a tread depth of 8mm when new, with some up to 10mm, while truck tyre tread depths vary enormously and can be up to about 22mm.
Best practice indicates that tyre replacement should take place when tread depths are at 2-3mm, but truck operators are able to preserve tyre life through a variety of techniques such as regrooving and turning on the rim.
Tyre firms say self-imposing a 3mm limit is ideal for a number of reasons, including the ability to regroove tyres at that depth to give improved grip and traction and extending tyre life while also delivering fuel efficiency improvements of up to 10%.
With less tread there is a higher risk that the recutting blade will cut through to the base rubber and to the cords, which in turn can damage the tyre.
Regrooving is advocated by Michelin and typically improves tyre life by 25% with the tread depth rejuvenated to that of a half-worn tyre. Regrooving consists of cutting a pattern into a tyre’s base rubber to effectively regenerating the tread depth pattern thus giving improved grip.
TyreSafe, the not-for-profit tyre safety organisation, says budget tyres might not be designed with enough extra rubber to regroove.
Chris Smith, Michelin head of truck marketing, says fleets are more likely to regroove premium tyres, adding that the policy is most likely to apply to “road-going” operators and not trucks that operate in particularly arduous conditions such as quarries and construction sites where “stresses and strains would rip rubber to pieces at low tread”.
Additionally, as few trucks return to their home depot daily, adopting a 3mm replacement policy provides flexibility around the 1mm legal limit.
“Transport operations are not running as much risk as they would be if operating to the legal limit,” says Smith.
Meanwhile, a ‘turn on the rim’ is when a tyre is demounted and refitted after being turned around so that the inner and outer lanes of tread are effectively swapped over to maximise tyre life. ATS Euromaster calculates that turning a tyre extends its life by 20%.
Marc Preedy, commercial director at Goodyear Dunlop UK and Ireland, is seeing more fleet attention to ‘tyre husbandry’.
“We are finding customers are increasingly adopting highly vigilant tyre maintenance policies,” he says.
“Strong tyre husbandry not only improves safety and reduces any downtime for the fleet, but it can also reduce the total cost of ownership of tyres. Many of our larger fleet customers opt for a bespoke on-site service from TruckForce, our dedicated fleet services provider.
“It is a common occurrence on trucks that one side of the tyre tread will wear greater than the other. Turning a tyre on its rim compensates for the varying shoulder wear and allows the difference in tread to balance out. Simply turning the tyre before the tread is below 3mm, on the side which shows the greater wear, will help it reach its optimum life.”
Preedy also advocates ‘twinning’ to prolong tyre life. “When two of the same tyres are mounted on either side of the axle, operators may think that they will wear at the same rate,” he explains.
“However, the contact that the individual tyres have with the road throughout a journey may differ. As a result, an uneven tread depth can develop between the tyres; this can cause uneven wear and increase the chances of a puncture. This requires monitoring. Twinned tyres should not have more than a 3-4mm difference between them.”
Ray Engley, head of technical services at the Road Haulage Association, says the way operators manage tyres varies enormously. Many fleets operate a tyre management scheme with manufacturers or retail outlets, where the maximum tread life and casing viability is managed.
“In these scenarios tyres are regrooved at 2-3mm to maximise first life use, casings are then recycled as remoulds for second and third lives depending on the types of operation vehicles are involved in,” he says. “Other operators will maximise first life casing and only use new tyres.”
Tyres and stopping distance
Michelin says that linking tyre tread depths to stopping distances is “too simplistic a view” and points out that with the 2012 introduction of tyre labelling it is easier to see vast differences in the performance of new tyres.
Tyres are graded according to wet grip, fuel efficiency and external noise.
“Even at the top end where tyres are labelled A, B or C with budget tyres lower down the labelling regime, there is a 15% swing between the wet grip performance of tyres within a grade,” says Michelin truck tyre technical manager Rob Blurton.
“That equates to a stopping difference of around 4.5 metres for two new tyres.”
He estimates that stopping distance performance would be even greater on two-thirds worn tyres, but sees a difference when it comes to quality.
“Michelin tyres when two-thirds worn have very comparable stopping distances to new because of the investment made in innovative technology,” he says.
Lower quality tyres can take up to an additional 13 metres to bring the vehicle to standstill, Blurton claims.
Those 13 metres are the equivalent of three family hatchbacks in a queue of traffic; under emergency braking conditions that’s potentially the difference between avoiding a collision and a multi-vehicle pile-up.
Smith says: “Looking at tread depth alone is too simplistic and so much is based on tread design, compounds, materials and the investment in new technologies.”
And commercial vehicle stopping distances are further impacted by vehicle weight and the load carried.
“Stopping distances for cars are equally simplistic in our view and that multiplies for HGVs,” adds Smith.
“An empty 18-tonne truck and a full 44-tonne truck will not stop in the same distance, while the choice of tyre brand and make will also have an impact.”
Michelin’s van tyres are designed to run to 3mm and below. McWhir says that stopping distances between new – up to 10mm of tread – and 3mm were marginal and “not even a van length”.
However, he argues that crucial to stopping quickly is for drivers to hit the brake pedal uniformly, notably when tread reduces to below 3mm.
Tyre compound and tread pattern have a major influence on stopping distances, according to McWhir. “I would rather have 3mm of tread remaining on a premium tyre than more than 8mm of tread on a budget tyre,” he says. “If the compound and tread pattern do not function as they should then tread depth will not make a huge amount of difference.”
McWhir recommends that fleets run as good quality of tyre as possible. “Cheap tyres can be a false economy in terms of their fuel efficiency, performance and safety as well as the need to replace more frequently than a premium tyre – and that impacts on vehicle downtime,” he says.
Engley emphasizes the significance of new labelling. “With the advent of tyre labelling operators are able to gauge the suitability of individual tyre patterns in respect of stopping distances in dry and wet conditions – the difference can be quite significant,” he says.
Continental Tyre Group recommends tyre replacement at 3mm for light vans. The company’s general policy for HGVs is 2mm but, says Steve Howat, general manager technical services, that can vary dependant on vehicle usage and application. “The role of the tread pattern is to help eliminate the water between the tyre and the road surface,” he says.
“Many factors, including speed, the depth of water on the road surface, the load being applied to the tyre and inflation pressure, will all impact on how efficient the tyre is in dispersing water between the tyre and road surface. On light vans up to 3.5 tonnes, the remaining tread depth has a much higher influence on wet performance.”
Tests by the Motor Industry Research Association (MIRA) provide a “very clear” indication of the deterioration in wet braking performance, says Howat, with a difference between a new tyre and a tyre at 1.6mm being five vehicle lengths. Where the new tyre had stopped, a tyre at 1.6mm was still travelling at 35mph.
“For larger commercial vehicles the correlation between wet braking distance and tread depth is not so straightforward due to loading, higher inflation pressures and speed – it is unlikely a truck will experience an aquaplaning situation,” he adds.
Other factors that can reduce a tyre’s lifespan
Experts also emphasise the importance of operating vans on the correct tyre pressure for the load being carried.
“A 10-15% reduction in tyre pressure, which is not unusual on a van, can extend stopping distances by 2-3 metres,” says McWhir. “Checking tyre pressures and for tyre damage is vital.”
Preedy agrees, adding that tyre length of service is also affected. “Tyre pressures are key to an effective tyre management programme: under inflated or overinflated tyres can significantly impact on tyre life,” he adds.
Vehicles will always stop more quickly in the dry than in the wet because there is greater friction. In the wet, stopping distances will vary hugely due to the type of road surface and the speed and weight of the vehicle, but will typically be extended by 25-30%, according to McWhir.
“The best way to maximise stopping distances is to take account of all factors in terms of tyre quality and condition and add in elements of driver training,” he says.
What’s more, replacing a tyre early in its life means optimum fuel efficiency is not being obtained. A new tyre has more rolling resistance than a part worn one, so replacing a tyre at, for example, 5mm impacts on fuel economy as with lower tread there is less rubber.
Safe stopping distances are not affected by tyre tread alone and, say experts, it is “marginal gains” in areas such as compound, tread pattern, tyre pressure and overall tyre condition as well as the size, speed and weight of vehicle that are critical. While most truck fleets’ policies stipulate a 3mm tyre tread depth limit, the advent of new technology enabling the automated inspection of tyres is likely to see a concerted move downwards towards a 1mm legal limit.
Indeed, commercial fleets that have outsourced their tyre management to Michelin Solutions – 70,000 commercial vehicles are currently managed, with the majority being HGVs – have already started to migrate policy limits down to 2mm because they want to obtain the maximum amount of tyre life. Apart from management report information, the move is aided by a tough mandatory inspection regime that is further supported by in-house checks.
“The next five years will be a massive transition period for the tyre industry as it moves forward in terms of technology and improving tyre performance,” says Smith. “That will give fleets more confidence in moving tyre replacement policies down to 1mm.”
Currently, the monitoring of tyres is largely manual, but the advent of digital tools is set to change the face of inspections and give confidence to operators to extend tyre replacement policies.
Michelin calculates that each millimetre of tread equates to 9,000-12,000 miles for truck operators with an estimated 15% of the potential performance of tyres remaining unexploited equating to a 15% hole in fleets’ budgets.
Developments to plug that hole have already started with last year’s launch by Michelin of ‘Tire Care’, which initially comprises a suite of three digital and connected solutions.
The new tools include ‘TireLog’, a free smartphone app that includes the ability to monitor tyre wear, and two chargeable services: ‘iCheck’, a tool to monitor pressures, tread depths and general condition of tyres with data reported online, and ‘iManage’ which involves the collection of all tyre-related data, including tread wear, via radio frequency identification tags fitted to tyres and connected to the Tyre Pressure Monitoring System and fleet’s portal.
The latest DVSA data reveals that, in 2014/15, tyre condition was the number one prohibition defect of all vans inspected at the roadside (at 29.3%). For HGVs tyre condition (5%) was the second most common.
Last year, TyreSafe, in partnership with Highways England, conducted a national survey of the tread depth of tyres at the point of replacement across Britain. More than 100,000 car and van tyres were surveyed from more than 800 outlets across England, Scotland and Wales.
Of the almost 6,000 tyres removed from LCVs that were studied, 1,220 (21.7%) were illegal and 2,299 (40.9%) were classed as “borderline” meaning that less than 2mm of tread was remaining.
Kwik Fit says 15-20% of tyres it removes from vans are illegal with “a lot” borderline. A “significant number” are replaced at about 2mm.
Automotional, which provides risk management services, says tread depth ‘company limits’ typically range from the legal minimum up to 3mm.
However, director Andy Neale says, particularly in respect of van tyres: “With modern service intervals being what they are many company vehicles are being driven with illegal tyres fitted and not just from worn-out tread patterns but from cuts and splits to being poorly inflated. The latter being particularly relevant in light and medium-sized commercials with the disparity between laden and unladen.
In contrast, Michelin says that the number of illegal tyres removed from trucks is “a low single figure percentage at worst” and that’s because of the regulatory inspection regime – independent inspections ordered by many fleets and operators – requiring drivers to undertake daily checks.
“Commercial vehicle operators are more careful with tyre maintenance,” says Smith. “If they fall foul of the DVSA they could be out of business.”
CASE STUDY: Ginsters Van Sales
Savoury food brand Ginsters Van Sales operates 150 vans with fortnightly tyre inspections carried out by the company’s tyre supplier.
Fleet continuous improvement manager Andrew Gibbons said: “Vans average 1,000 miles per week and all tyres with less than 2mm of tread remaining are replaced at each visit. Any tyre with under 3mm of tread remaining is reported and replacement arranged at the next inspection visit.”
CASE STUDY: Travis Perkins
Best practice dictates that fleets typically replace tyres when tread depth reaches 2-3mm, but experts say the daily checking of overall tyre condition is a critical aspect of managing safety.
Travis Perkins, which operates 4,000 light and heavy commercial vehicles, operates a 3mm replacement policy across the board.
Group fleet director Graham Bellman says drivers should do their own checks. Highlighting that it is easier for van drivers to undertake tyre checks than for a truck driver, Bellman says: “If the tread is down to 3mm on a truck then it will possibly be close to 1mm somewhere on the tyre.”
Good tyre husbandry can extend the life of tyres and on trucks that includes turning tyres on the rim and regrooving, both advocated by Bellman.
“Tyre technology is progressing at a rapid pace,” says Bellman. “Kerbing is the number one tyre damage factor on our trucks. Our professional drivers are trained to spot that if tyre lettering is worn off it needs turning. With an eye on environmental impact we need to get the most out of tyres. Regrooving has come a long way and is something we are comfortable with.”
CASE STUDY: Pimlico Plumbers/Chivas Brothers
London-based Pimlico Plumbers operates a fleet of more than 150 light commercial vehicles, with tyres replaced at the 1.6mm legal limit.
However, workshop manager Andy Wilsher says: “All of our vans come into the workshops at least three times a year for inspections and service. If tyre tread depths are about 2mm or below, and there is a belief the tyre will not make the next scheduled inspection, we will replace.”
Tristan Campbell, in charge of whisky firm Chivas Brothers’ fleet, which includes 60 LCVs, operates a 2mm tyre replacement policy as recommended by vehicle supplier Lex Autolease.
He says: “Operating to 2mm provides the company with a little flexibility above the 1.6mm legal minimum.”
What the law says on tyre tread depth
There are different legal minimum tyre tread depths for vans and commercial vehicles with a gross vehicle weight above 3.5 tonnes.
The legal minimum tyre tread depth for vans as well as cars, eight-seater vehicles and light trailers, including caravans up to 3.5 tonnes is 1.6mm. The 1.6mm should be in a continuous band throughout the central three-quarters of the tread width, throughout the whole of the circumference.
Any vehicle with a gross vehicle weight above 3.5 tonnes – or a motorcycle above 50cc – must have tyres in which the grooves of the tread pattern have a depth of a least 1mm throughout a continuous band measuring at least three-quarters of the breadth of the tread and round the entire outer circumference of the tyre. The same regulation applies to regrooved tyres.
The driver of the vehicle is responsible for making sure all tyres are legal and in a roadworthy condition. The penalty for driving with an illegal tyre is £2,500 and three penalty points per tyre.
Businesses can also be prosecuted for committing offences such as fitting illegal tyres. The maximum penalty is £20,000 under the Health and Safety Offences Act.
CASE STUDY: Hitachi Capital Commercial Vehicle Solutions
Gary Banister, national account manager at Hitachi Capital Commercial Vehicle Solutions, says the decision on when to replace tyres on vans and trucks was customer-dependent.
“Some customers look to maximise a tyre’s life so will run tyres to the safe, legal depth before replacing. Other customers can be more cautious and therefore have a 3mm limit, requiring a replacement for any tyre under this depth,” he says.
“Replacing ahead of the legal limit offers a wider safety margin and ensures all vehicles are always compliant. Some argue this also increases safety, but regular checks – which are part of a company’s duty of care and operational requirements – will ensure all vehicles are compliant.
“The disadvantage of this approach is increased operating cost. Replacing a tyre ahead of schedule generates additional waste and fleets are losing some of the operating life of that tyre by replacing early.”
As a result, there is no single depth that Hitachi Capital advises fleets for changing their tyres, as each business is different.
However, the majority of customers choose to replace tyres at 2mm, which Banister calls “a good balance between safety and cost effectiveness”.
Vehicle mileage and usage schedules also impact fleet operator attitudes to tyre replacement. “Vehicles, such as a road gritter, may only cover limited mileages but at critical times or in poor weather conditions,” says Banister. “Here, it could be advised to replace the tyres ahead of the tread limit, as tyre performance is critical.”
CASE STUDY: O’Donovan Waste Disposal
London’s leading construction waste management company Waste Disposal, which has won a host of fleet safety awards, operates an 85-strong HGV fleet.
Managing director Jacqueline O’Donovan, leads the company’s significant occupational road risk management focus.
“Company policy is to always put new tyres on the front axles and remoulds on the rear,” she says.
“That’s because the rear tyres get abused more due to the ground conditions we operate in. We set our own tyre tread depth limit of 3mm but we change as soon as they reach 5mm to be on the safe side and send back the remoulds for re-cutting. We monitor tyres with our own tyre fitter when they’re flagged at 7mm to ensure they’re changed at 5mm.
“Additionally, we have a monthly tyre audit carried out by our tyre company to check all tyres are safe and in good order.”