Fuel consumption - tyre choice

Mikex

Just seems a timely subject to discuss.......

I have just done a comparison using some real figures obtained from 2 motorists who have changed their tyres. They have both opted for heavy duty winter type tyres and have noticed an increase in their fuel consumption in the region of 4 MPG. This equates to increased fuel costs in the region of £322 pa for someone doing 10,000 miles pa. £1,608 for the life of the tyres assuming 50,000 miles.

There are a couple of factors that have an effect fuel consumption to do with tyres.

One is the rolling resistance of the tyre. Some tyres are designed to have a low rolling resistance (LRR). These are fitted to electric vehicles Toyota Prius etc. I note some tyres are now advertised as fuel savers.

The other factor is that irrespective of the tyre you have fitted it will have a much higher RR if underinflated. Like trying to pedal a bicycle with half flat tyres! and a much lower RR if pumped up to the MAX as indicated on the tyre wall.

With the fuel price set to go to £10 gallon & beyond I guess we should all be thinking of replacing our worn tyres with new fuel savers. I guess if these tyres are a few quid more the fuel saving will quickly cover the initial purchase price.

The thing is although there is much information available about tyres such as speed & load rating I have been unable to find any information about rolling resistance.

My own tyres are 7.50 x 16 Michelin XPC

Unless I can find the RR of these and of the tyres I am considering purchasing I am unable to make an informed choice.

As well as the financial saving running these fuel saver tyres has environmental benefits also.

Mike

hubert_cumberdale

would the RR not vary for the same tire depending on the weight of the car thats sat on them

i.e how much it squishes the rubber into the little holes in the tarmac - as a heavier car would have higher friction

i also wouldnt reccomend drving your car with the tires pumped up to the max as stated on the side wall my tires have 80psi max written on the side but i would never drive with them that hard

davidjwest

Agree, would never over-inflate my tyres by any great amount, I imagine they would wear unevenly if you did and cost more to replace prematurely than any fuel saving. I tend to over-inflate mine by a couple of PSI but that's about it.

I bought some Michelin Pilot Primacy tyres last year for my Mondeo as they got good reviews and claim to improve MPG as well. I've noticed a ~3 MPG improvement since I got them which basically means the tyres will pay for themselves over their lifetime, perhaps a little more if I can get them to last a few more months.

Lum

I would worry that the lack of friction needed to get low rolling resistance would also mean a lack of friction when it comes to grip and braking.

This certainly seems to be the case with the Michelin Primacy HPs fitted to my Mondeo, but I have not had the opportunity to try a different type of tyre on the same car to do a fair comparison.

If it comes to a trade off between losing a few MPG vs worse stopping distances then I'll go for the better stopping distances, it's not worth the risk just to save a few quid.

marlot

Mikex wrote: »

I have just done a comparison using some real figures obtained from 2 motorists who have changed their tyres. They have both opted for heavy duty winter type tyres and have noticed an increase in their fuel consumption in the region of 4 MPG.

There are likely to be some other variables too - such as winter diesel (gives about 2mpg less for me), cold running etc.

But winter tyres do increase fuel consumption slightly. The tread is designed to move around more, so creating friction.

mikey72

My winter tyres are advertised as a low rolling resistance.

"The tyre’s low rolling resistance reduces fuel consumption and

carbon dioxide emissions"

Rolling resistance is the amount of force it takes to peel the tread of the road as the wheel turns, grip is the amount of force needed to move the tread sideways across the surface.

Wouldn't dream of guessing how that works, but they no doubt spent millions on it to improve one and reduce the other.

Lum

mikey72 wrote: »

grip is the amount of force needed to move the tread sideways across the surface.

Not strictly true. Lateral grip is the amount of force needed to move the tread sideways across the surface.

When you're braking lateral grip isn't going to help you and, all other things being equal, a tyre that is easier to peel away from the road surface is a tyre that isn't going to stop your car as quickly, unless they find some other way to improve stopping distances but presumably those improvements could also be applied to high rolling resistance tyres to improve stopping distances even more.

That said if you are switching from £10 Linglong ditchfinders to a premium brand low rolling resistance tyre you're probably going to see an improvement in stopping distance anyway!

Inactive

mikey72 wrote: »

My winter tyres are advertised as a low rolling resistance.

"The tyre’s low rolling resistance reduces fuel consumption and

carbon dioxide emissions"

Rolling resistance is the amount of force it takes to peel the tread of the road as the wheel turns, grip is the amount of force needed to move the tread sideways across the surface.

Wouldn't dream of guessing how that works, but they no doubt spent millions on it to improve one and reduce the other.

That looks like sales hype to me..

leosayer

I recall a magazine (perhaps Which?) doing a tyre test a while back which found that some 'fuel saver' tyres actually used more fuel than some non fuel-savers.

mikey72

Lum wrote: »

Not strictly true. Lateral grip is the amount of force needed to move the tread sideways across the surface.

When you're braking lateral grip isn't going to help you and, all other things being equal, a tyre that is easier to peel away from the road surface is a tyre that isn't going to stop your car as quickly, unless they find some other way to improve stopping distances but presumably those improvements could also be applied to high rolling resistance tyres to improve stopping distances even more.

That said if you are switching from £10 Linglong ditchfinders to a premium brand low rolling resistance tyre you're probably going to see an improvement in stopping distance anyway!

No, even when you're braking, you need grip to stop the tyre sliding across the surface. When you are rolling, you're lifting the tread from the surface. The harder it is to lift, the more force will be used.
The trick is getting the least of one without affecting the other.
It needs to be "grippy", but not "sticky".

bigjl

If I was doing high miles again, have done up to 70k a year in previous jobs, I would try an stretch to Michelins, the Michelin Energy on a budget or the Micheline Primacy if I had the money.

Though many manufacturers make tyres that they say are more economical but I am biased towards Michelin, have been for years, money permitting.