BEWARE WHEEL NUT OVER TIGHTENING

One click of a torque wrench is enough when tyres are replaced. The warning, from Norbar Torque Tools, is the result of increasing anecdotal evidence that too many wheel nuts are being tightened by professional tyre replacement operators using more than a single click of a torque wrench as it reaches the required load or are being tightened using power tools with no torque capability at all.

Julian Bremner-Smith, marketing manager at Norbar Torque Tools, says overtightening can leave drivers stranded at the roadside and is potentially dangerous.

“Overtightening risks bolt failure, but it can also leave motorists stranded at the roadside unable to perform basic wheel replacement procedures in an emergency. That second or third well-meant click with a torque wrench when tyres are replaced at a garage or MOT centre can result in the nut being at a torque nearly 15% more than the recommended level in the vehicle manual and very difficult to remove at a later date.”

Mr Bremner-Smith says the problem is exacerbated by many tyre replacement operators using power tools to tighten wheel nuts because they are faster. “Too often power tools are being used that have no torque setting capability and the nuts are therefore overtightened to a point that drivers cannot remove them.” What’s more, Mr Bremner-Smith says the break-off torque, the power that would need to be applied to the wheel nut in order to loosen it, would likely be much greater than the original torque applied.

“After only a few weeks of normal driving during with the wheel nuts exposed to wet weather, dirty roads and even salt, the torque that will need to be applied to undo the nut – the break-off torque - will most likely be nearer 50% more than the torque originally applied to the nut."

By way of illustration, Mr Bremner-Smith says that a Ford Focus has a wheel nut torque setting of 135 N·m. “If a wheel nut is tightened to 150 N·m, above the recommended torque, after a few weeks of driving it is likely to have a break-off torque of circa 225 N·m. This is something very few drivers will be able to apply with the typically short wheel brace supplied as standard with most modern cars.”

His advice to motorists is to insist on good torque practice when tyres are being replaced. “If a tyre replacement operative is using a power tool, drivers should insist that the correct torque is applied using a calibrated torque wrench. What’s more, if the tyre replacement operative tightens the nut beyond one click ask them to do it again. One click is enough.”