Space saver tyre warning issued

EXTENSIVE testing by Victoria’s state motoring body has revealed that braking and handling ability can be adversely affected by space saver wheels, also known as Temporary Use Spare Tyres (TUSTs).

In the worst case, the Royal Auto Club of Victoria’s tests found a vehicle without anti-lock brakes (ABS) and using a TUST took an additional three and a half car lengths (15.4 metres) to stop from 80 km/h.

The RACV has recommended that: * Car makers should fit a full size spare wheel in new vehicles where there is space available.
* Car dealers should inform potential buyers of the presence of a TUST in their vehicles.
* Car makers should provide prominent and comprehensive warning information for motorists on the safe operation of a vehicle when fitted with a TUST, as required by the Australian Design Rules.
* Replacement TUSTs must be readily available, in line with industry practices on other spare parts.

A TUST is any spare tyre that differs in width or diameter from the road wheels fitted as standard to a particular model. They come in a range from small diameter, limited speed and distance versions to wheels just slightly under the size of those fitted to the car.

“The public are in the dark about these tyres. Many people don’t even know their car has one until they have a flat,” said Michael Case, RACV Chief Engineer Vehicles.

“Motorists should check the spare whenever buying a car, and if they are not happy using a TUST, they should insist on a full size replacement wherever possible. If a motorist has a TUST on the vehicle, they should be sure to know how to use it and be aware of its performance limitations.” Extensive testing on TUST’s has been conducted by RACV engineers at the Army proving ground facility at Monegeetta. The testing was prompted by the discovery that no data was publicly available on how space saver wheels performed on the road. About one in four new car models on the market have some form of TUST.

The test results show the deterioration in road grip and therefore emergency handling that drivers are exposed to when driving on these inferior wheels.

Four different vehicle types were tested in three typical situations: an emergency brake test, a cornering traction test and a swerve test. All tests were first performed with the vehicles fitted with four standard road wheels, and then with a TUST on the driving axle.

“The worst result was attributed to a vehicle without ABS and running on a small space saver tyre. The space saver tyre increased braking distance by 15.4 metres or three-and-a-half car lengths, when braking from 80 km/h,’’ said Mr Case.

“RACV assessed cornering traction by driving on a 50 metre circle. The test showed that cornering traction suffered appreciably when a space saver tyre was fitted, particularly on heavier vehicles such as a large 4WD, where deterioration in grip levels was at least 13 per cent,’’ he said.

“Keeping control of a vehicle under emergency braking and swerving was also increasingly difficult on a space saver. The wheel continually locked without the assistance of ABS when attempting to stop quickly, causing the vehicle to pull to one side, and leaving significant flat spots on the tyre.’’ “TUSTs started out as a viable alternative in space-starved sports cars, but are now becoming standard issue for anything from small sedans to roomy 4WDs.”