NTDA Service Bulletin

We have a team of tyre technicians waiting to answer your technical problems – call our freephone number 0121 386 4624 (members password “explorer”)

NTDA Technical Help Line 0121 386 4624 (members only – password protected) 02/09

When fitting new tyres to a vehicle, should they be placed on the front or the rear axle? Does it make any difference whether the car is front- or rear-wheel drive?

Simple enough questions, you might think, but finding a definitive answer has proved nigh-on impossible and it depends very much on who you ask. We have sought the views of tyre manufacturers, car manufacturers and car dealers/servicing centres and about the only thing on which everybody agrees is that tyres should always be replaced in pairs, or in fours. Of course, replacing all four tyres makes the "which axle?" question redundant, but the customer may not be convinced that you are acting in his best interests if you suggest this.

Opinion is sharply divided, with most tyre manufacturers and fast fits favouring rear axle fitment and car manufacturers and their dealers either saying that it does not really matter, or suggesting that new tyres are fitted to the drive axle.

If there is confusion in the tyre industry, this is nothing compared to the motoring public, as any glance at a motoring magazine blog or question page shows. Motorists have strongly-held opinions and back these up with technical arguments, some of which are more convincing than others.

Getting back to the tyre industry, a selection of responses to the "which axle?" question is given here.

Tyre Industry Federation

The Tyre Industry Federation wrote to Mercedes Benz UK to seek clarification of a sentence in the handbook

of a C-class Mercedes which said that new tyres should be fitted on the front wheels first.

Enclosed with the letter was a copy of a briefing note from the BTMA, which said unequivocally: "The current recommendation on the part of the tyre industry is, as a general rule: NEW TYRES TO THE REAR. This applies to both front and rear wheel drive cars."

The primary reason given was safety, particularly in the wet, as test have shown that, with partly worn tyres fitted to the rear, the diminished water dispersal capability leads to a greater tendency towards over-steer and thus loss of control.

The BTMA accepts that there are occasions where rear-axle fitment is not appropriate – for instance if front and rear tyre sizes are different, where the new tyres are of a lower speed rating or where the car is fitted with a "system" concept of directional front and asymmetric rear tyres.

Mercedes Benz's Response

The TIF received a letter from Mercedes Benz, giving the following response from the MB factory in Stuttgart.

"The recommendation to mount singular new tyres only on the rear axle is based on an old technology and teaching. It recommends that singular new tyres are mounted on the rear axle for reasons of driving stability. By means of this, over-steering behaviour when braking should be compensated and/or counteracted.

"Due to the continuous improvement of our products, which are all equipped with stabilising monitoring systems (ESP), and because of their chassis and suspension set-up, today's cars show a neutral or under-steering behaviour.

"For the above-mentioned reasons, a higher potential of driving safety arises if singular new tyres are mounted at the front axle. In wet or aquaplaning conditions, the vehicles reveal a

FITTING NEW TYRES – FRONT OR REAR AXLE?

better steering performance and higher wet-road driving safety."

So, according to Mercedes Benz, the tyre industry is behind the times and has not taken into account the increased technology built into today's vehicles. Whether or not the company would take the same view if the car in question was 10 or more years old is not clear.

TyreSafe

TyreSafe describes itself as "Britain's foremost tyre safety organisation", so what are its views on the subject? The TyreSafe website reveals that its research shows that more than 50% of British motorists believe that new tyres should be fitted to the front wheels, while 30% did not know.

TyreSafe says that demonstrations have shown that it is more beneficial to fit new tyres to the rear, regardless of whether the vehicle is front- or rear-wheel drive. Again, better water dispersal and improved straight-line braking were cited as reasons and TyreSafe says: "…if the rear track is fitted with part worn tyres, the car often has a dangerous tendency to over-steer."

The statement goes on: "As the majority of cars on the road are front-wheel drive, it seems to make sense to have the new tyres up front. The demonstrations also showed that there is often a greater loss of control when a rear tyre suffers a puncture, so in fact it makes greater sense to fit the fresh, less vulnerable rubber to the rear wheels."

Plus, there is an economic reason too, which might appeal to motorists, as TyreSafe points out that rear tyres are subject to relatively low wear rates; meaning that the new tyres will have a longer lifespan on the back rims.

Car Manufacturers

The reaction of Mercedes Benz has already been given and a number of other car manufacturers were contacted. Responses were received from Honda and Volvo. Honda made the point that both tyres on an axle should be changed, even if only one has significant wear. This is "to ensure

optimum road handling and safety aspects of the vehicle."

Honda's statement goes on: "Under normal circumstances the tyres on the driving axle of a vehicle will need to be changed first. However, this is not always the case, as the surfaces and the way the vehicle is driven, alongside other influencing factors, all affect the wear of tyres."

Volvo is even more emphatic, saying: "Generally speaking, the tyres with the most grip should be fitted to the wheels that drive the car. In a front wheel-drive car, this means that new tyres are usually fitted to the front. This is dependent on the amount of tread left and the wear patterns and we would always recommend that tyres are inspected by an authorised Volvo dealer."

So, as far as the vehicle manufacturers are concerned it seems to be "drive axle first" unless there are good reasons why not.

Car Dealerships

Phone calls to Honda and Volvo car dealerships showed that they agreed with the manufacturers that drive axle tyres should be replaced.

However, a phone call to a Ford dealer revealed a different viewpoint, where the man said that new tyres should go on the rear axle. His reasoning was that, if the driver loses grip at the front, then he can use the steering wheel to adjust the vehicle's direction, whereas, if grip is lost at the rear, it is much harder to keep the vehicle on track. He added that this was what he had been taught "when I worked in the tyre business".

Was this point of view universal to Ford dealers? Apparently not, as a phone call to another dealer elicited the response that new tyres should be fitted to the driving wheels. This, I was told, was not a policy handed down by Ford, but was just common sense and was the course of action followed by most car dealers.

Tyre Manufacturers

The attitude of tyre manufacturers is evident from the letter sent by the TIF to Mercedes Benz and most advocate rear axle fitment.

A section on the Michelin website explicitly states that "whether you have front or rear drive, we recommend that you use newer tyres for the rear set, for extra safety in unforeseen or difficult conditions (emergency braking, tight bends etc.) particularly on wet surfaces."

Fitting tyres to the front will reverse the balance between front and rear, says Michelin, and the driver, who is used to a car with less grip at the front, will be taken unawares. It continues: "On a slippery road, the rear will lose traction before the front of the vehicle. The driver will have no chance of controlling the rear and will be tempted to accelerate further, which will amplify the spin effect. Only an experienced driver will be able to recover from this dangerous situation."

Should the new tyres be fitted to the rear, the handling of the vehicle will be similar to that before the change. Says Michelin: "Rear traction will be better and the driver will be able to control and steer their vehicle without a problem by decelerating and turning the steering wheel in the direction of the bend."

Other tyre manufacturers' websites have little to say on the axle question, but it is probably worth mentioning the Bridgestone website, which suggests rotating tyres regularly (every 5,000 km) to prevent irregular wear.

Tyre Dealers

A straw poll of tyre dealers proved unanimously in favour of rear axle fitment. Indeed, a number, including a couple of independents, a Kwik-Fit depot and (not surprisingly) ATS Euromaster, said that they went by the Michelin guide to tyres and fitting.

A National Tyre & Autocare depot said that there was no official policy, but they tended to go for rear axle fitment. He added, as indeed did practically every one of the dealers, that they would fit the tyres to whatever axle the customer asked for. And if he didn't specify an axle? "Then we'd probably fit to the rear" was the answer.

Conclusion

So, what is the answer – rear or drive axle fitment? It depends on who you think knows more about tyres and vehicle handling – is it the tyre industry, or the car manufacturers and traders?

To say that it is up to the customer is undoubtedly correct, but it could be seen as a cop-out, as the customer may well be relying on the knowledge and expertise of the tyre professional. From our enquiries (which by no means are wholly representative) it seems that tyre professionals prefer to fit tyres to the back axle.

Whatever the preferred fitment, it is as well to have the reasons to hand to explain to the customer exactly why you chose that particular axle. At the end of the day, however, if he points to the vehicle handbook and it says "fit new tyres on axle X" then are you really in a position to argue?

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, mechanical, photocopying, recording or otherwise, without the prior permission in writing of the publishers.

Although great care has been taken in the compilation and preparation of this bulletin to ensure accuracy, the publishers cannot in any circumstances accept responsibility for errors or omissions or advice given in this publication.

Copyright ©NTDA 2009

Published by the NTDA in association with

entyrety,Tyre Fort, 88-89 Wingfoot Way,Erdington, Birmingham, B24 9HYTel: 0121 382 4825 Fax: 0121 382 6109e-mail: info@entyrety.co.uk

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, mechanical, photocopying, recording or otherwise, without the prior permission in writing of the publishers.

Although great care has been taken in the compilation and preparation of this bulletin to ensure accuracy, the publishers cannot in any circumstances accept responsibility for errors or omissions or advice given in this publication.

Copyright ©NTDA 2008

Published by the NTDA in association with

entyrety,Tyre Fort, 88-89 Wingfoot Way,Erdington, Birmingham, B24 9HYTel: 0121 382 4825 Fax: 0121 382 6109e-mail: info@entyrety.co.uk