When is the best time to change tyres?
04 July 2017
Author: Daniel Puddicombe
New research is splitting the tyre industry on when is the best time for fleets to change rubber, after Michelin claimed that premature switches could hit businesses both in the wallet and environmentally.
The French manufacturer found that changing tyres with 3mm of tread left - almost double the current UK legal minimum of 1.6mm - could cost European drivers an extra £6.9bn a year in additional tyre purchases and extra fuel consumption through increased friction on the road surface.
Michelin also claimed that changing tyres too early would result in an extra 128 million tyres a year being used, causing an additional nine million tonnes of CO2 emissions through increased friction on the road and extra tyres being manufactured. The firm likened changing tyres early to throwing away shoes because they needed to be cleaned, or putting a half-full tube of toothpaste in the bin. In addition, Michelin said it could not see a correlation between a decreased tread depth, down to a minimum of 1.6mm, and increasing accident rates.
However, Continental - a company that has long campaigned for the tread depth limit of tyres to be upped - disagreed with Michelin's views on the grounds of road safety. "A number of tests over decades proves without a doubt that the wet braking characteristics of summer tyres and the snow grip of winter tyres reduces disproportionately with tread depth of less than 3mm and 4mm respectively," a spokesman for Continental told BusinessCar. "Therefore, for safety reasons, we have been recommending for years to change summer tyres with tread depth of 3mm and winter tyres with tread depth of 4mm."
The spokesman added: "Continental continues to recommend a tyre change before reaching the legally mandated minimum residual tread depth of 1.6mm because the influence of physics on numerous safety-relevant tyre characteristics cannot be denied."
However, the idea of changing tyres at 3mm was branded as "ridiculous" by one fleet manager, with Andy Hyatt, transport and fleet manager at Ashford and St Peters Hospitals NHS Foundation, telling BusinessCar he asks the leasing company responsible for his vehicles to swap rubber when 2mm of depth is left "as by the time they've got their stuff together it's down to 1.6mm anyway".
He added that if he were to change tyres at 3mm, 2,000-3,000 miles' worth of usable tread would be wasted and suggested that the legal limit should be upped to 2mm. "At 2mm, people will push their luck and change at 1.6mm. At present, people chance a change at 1mm and that's dangerous," he added.
Michelin's advice of replacing tyres early goes against that of fast-fitter Kwik-Fit too, which earlier this year urged fleets to follow the lead of UK emergency services by changing tyres well before the 1.6mm threshold. According to results of a Freedom of Information request made by Kwik-Fit, 73% of the UK's police, fire and ambulance services change tyres when between 2.6mm and 3mm worth of tread is left. Of the 95 units that responded to the FoI request, 73% have a formal tyre-change policy in place, while the remaining third have an accepted practice on when to switch rubber.
Falken Tyre also advises changes at 3mm. However, Matt Smith, UK director of the company, told BusinessCar tread depth isn't the only thing to take into account when choosing the right time to switch and urged fleets with concerns to visit a tyre centre for a safety inspection. "Tyre safety is not merely about tread depth and consumers need to consider other factors to maintain their safety. These include tyre age, how they are stored and using the appropriate tyres for the vehicle and conditions," he said.
A number of factors need to be considered when deciding to replace tyres, a spokeswoman for Goodyear told BusinessCar, although the company recommended that tyres should be changed when the law dictates.
Michelin conceded, however, that factors other than tread depth play their part and called for an overhaul of the way new tyres are tested in light of its findings. At present, tyre safety is ranked when the rubber is brand new, but the company called on the industry to conduct tests with worn tyres as well: "There is no consideration given to how their levels of performance will change over time. Michelin is now raising this issue - the fact that the only factor for safety is tyre performance not tread depth. Michelin is calling on industry test bodies and consumer organisations to start comparing and testing tyres when they are worn to the legal limit."