I`m a little cynical about claims in general..( maybe by being exposed to too many engine oil/additives/petrol, magic particle/bonding to metal and mileage claims in early life :)
Anyway, It turns out the van has *Firestone Fuel Savers* fitted.
I wondered if most new vehicles have similar tyres fitted these days and if so where is the hard, scientifically measurable evidence for fuel saving?
IMHO it must be easier than trying to measure something such as fuel consumption under road conditions.
I wondered if tyre rolling resistance could be tested outside the tyre lab by getting a steady air temperature ( perhaps in an aircraft hanger) and then using a spring measure of some sort to measure the force required to pull the vehicle by a low geared winch over a given distance?.
Or perhaps any claims ( i`m not aware of any other than whats written on the tyre) are vanishingly small?
I`m thinking here of a well known bookshop chain that has a shelf with "Up to 50% off" but many books on the shelf are full price. ( and thats quite OK and within the law according to a their manager...."Up to" meaning it *can* mean nothing off at all)
For example *up to* X % fuel saving would not impress me.
The reason I`m curious is that rolling resistance seems like a factor that could actually be measured and that *none* energy saving tyres lasted more than twice as long on my last van. ( when compared with a different * energy efficient* type tyre fitted as original equipment.
In Conclusion,
I`m aware of the other attributes or otherwise of tyre performance, but has any organisation/Motoring press ever tried to measure the rolling resistance of this type of tyre, as it would seem easy to pop different brands of new tyres on in comparison, under relatively simple controlled conditions.
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I wondered this too, I imagine as a tyre rotates faster, it balloons out which would reduce resistance, but equally, the faster something moves the exponentially greater drag is produced, so it looks like it's too complicated to get a meaningful single percentage fiigure measurement.
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Any reduction in rolling resistance, compared to "standard" tyres, will result in improved fuel consumption but aerodynamic drag and transmission losses will remain the same which ever tyre is used.
Since almost every vehicle manufacturer now fit "fuel saver" tyres as standard, excluding very high performance cars, these tyres have become the new standard.
Tyre manufacturers presumably test rolling resistance of all development tyres, in the laboratory, as a matter of course.
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Ah.... "The new standard" Good point, I had not thought of that.
So I guess all manufactures *have* to fit some make of fuel saver tyre as original equipment.
As the public now expects it?
But the non fuel saver Hankook van tyres lasted more than twice as long.
Guess I need a cure for being so cynical....
Oh, hang on, I need some engine oil tomorrow, maybe not :)
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I've seen the tests, simply a car is released and coasts down a ramp and the distance is measured, the tyres swapped and the same test is repeated. The fuel saving at the time, 6 / 7 years ago was said to be up to 5%. A car sat stationary in traffic would be no more effiicient.
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Cheers Dox, Its the "up to" that gets me though. Meaning to a cynic like me, that 5% was the very best they could get, no doubt compared with the stiffest, highest rolling resistance comparison tyres they could find. :)
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Lies, damn lies and statistics :)
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If the tyre is rolling it will save you fuel compared to a standard tyre, if the tyre is stationary (stuck in traffic) there's no benefit ;o)
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I agree that there isn't a great deal of useful technical information that is easily available that can be used to compare the performance of tyres.
If you are lucky enough to obtain a "full" technical data** sheet for a tyre, it should have two values, usually called A and B, which respectively describe the constant rolling resistance coefficient (which you multiply by the vertical load on the tyre to obtain the static drag force) and the speed dependent resistance coefficient (which you multiply by the vertical load and the forward speed obtain the speed dependent part of the drag).
A and B are both positive - i.e. rolling resistance goes up with speed. I imagine (although I'm not sure) that this is because more energy is absorbed by the viscoelastic deformation of the rubber at the higher local temperatures which will accompany higher speed.
If anyone knows a good source for decent technical tyre data, I would be keen to hear it.
* "full" technical data - by this I mean the technical data used for engineering purposes, not as part of the near useless sales blurb you find the in the local tyre fitters reception.
Number_Cruncher
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The tyre carcase remains the same, the tread contains silicon ;o)
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I should imagine a couple of extra pounds of pressure in each tyre would achieve a similar effect.
- - - - - - - - - - - - - - - - - - - - -
What\'s for you won\'t pass you by
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the constant rolling resistance coefficient (which you multiply by the vertical load on the tyre to obtain the static drag force) >>
I assume this is not constant because of verticle load related deformation.
rolling resistance goes up with speed. I imagine (although I'm not sure) that this is because more energy is absorbed by the viscoelastic deformation of the rubber at the higher local temperatures which will accompany higher speed.
Again I assume that this is offset to a degree by the speed induced centrifugal "roundening" forces on the tyre structure.
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They can reduce the rolling resistance by a lot more than 5% very easily but at the expense of grip;you can't get both at the same time!
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With the demonstration I saw the stopping distance remained the same or improved. No tyre manufacturer would make a tyre that was fuel efficient at the expense of safety, well the one I'm talking about would'nt.
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Cheers Dox, Any comments about the wear rate of this type of tyre?
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All aspects of the tyre remained similar, the only disadvantage was a huge static shock when you got out of some cars on the early versions. lol
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No tyre manufacturer would make a tyre that was fuel efficient at the expense of safety, well the one I'm talking about would'nt.
Michelin 'Energy' tyres are famous for their reduced grip compared to normal Michelin.
You cannot get something for nothing...
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Michelin 'Energy' tyres are famous for their reduced grip compared to normal Michelin.
No one else has posted a similar response, could you ellaborate?
You cannot get something for nothing...
Using this annalogy, we may as well give up developing anything, what we have is as good as it gets?
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>>I assume this is not constant because of verticle load related deformation.
For any particular car, typically you do treat it as a constant. The mass, hence weight, of the car is assumed to be near enough constant for performance estimation. Obviously, if you are considering a car with a large amount of aerodynamic downforce, at high speeds, the effective vertical load on the tyres will increase, and this will cause an increase in rolling resistance.
>>Again I assume that this is offset...
I don't know - I've never done the sums! Although, on my list of things to look at (purely as a bit of fun), there is a model of tyre behaviour, called the Pacejka string model which I would like to play about with.
Number_Cruncher
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oilrag
I have, on one occasion, paid considerably more for the fuel saver version of a tyre (P6000). To be fair I am comparing against the tyres I replaced, which did not claim to be fuel saver and not against the equivalent P6000 but I did not see any fuel saving.
I know it's a flawed test, I'm not comparing apples with apples but I very much doubt that I got back the extra I paid for the fuel saver variant.
JH
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The following article may prove interesting:
snipurl.com/11z5u
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Very interesting, thanks for posting the link.
I particularly like the way that the CRR trailer works on page 16 - quite elegant IMO.
Number_Cruncher
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Since fitting Goodyear Eagle F1 GS-D3 tyres all round to my BMW 530i, I have noticed a decrease in fuel economy by up to 10%.
This would support the arguement that fuel saver tyres exist.
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Michael, Have you any data re comparative wear rates?
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Wear rates are on the side wall, mainly for the USA. If you go to an American tyre site you may find the info there ;o)
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>'Michelin Energy are not designed for roadholding.' Prove it.
Have a read of www.ostlestyres.co.uk/michelin.html and then tell me if you really believe that Michelin Energy are designed with roadholding in mind. (Michelin's own website does not seem to have such a handy reference guide.)
Michelin Pilot Exalto - 'The wet road tyre'. (The only reference to Energy's performance in the wet is to say that it's better than the first generation Energy's performance in the wet.)
Michelin Pilot Primacy - 'perfect dry handling' (compared to Energy's 'precise handling in the dry').
Michelin Pilot Sport - 'The ultra high performance tyre' (whatever that means, it's not the way they describe Energy).
So in summary: Michelin Energy - well, it's not the best in the wet; it's not the best in the dry; it's not the best at ultra high performance; it saves you petrol. In other words there is a sacrifice in performance as a tyre in exchange for saving petrol.
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They are still using *up to* ( that great little term that can actually mean nothing or even less :)
Given that they actually compare the energy with the classic, they will have lower figures too.....
As well as the best ( presumably) figure of 5%.
This seems to mean 5% fuel saving was the best we ever achieved in testing.
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Not a perfect test by any measure, but the Scenic had Michelin Energy tyres fitted as original equipment and now has Firestone Fuel Savers. Grip in bends (especially wet bends) has improved in that, while the Scenic isn't a car to hustle, I'm no longer afraid of it sliding off into the ditch on a damp road.
The Firestones are claimed (on Firestone's website) to reduce fuel burn by up to 5% compared to the previous "non fuel-saver" version of the same tyre, provided the car is fitted with four tyres of the same type, correctly inflated. I haven't found any noticeable change in fuel comsumption since switching to them.
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Michelin Energy
For all-year-round performance and fuel saving, nothing matches this. Energy offers improved performance, safety and grip, even in snow and offers braking distances reduced by up to two metres*. But the real benefit of this tyre lies in its special silica-based tred compound, which creates low rolling resistance - and that can mean up to a 5%** reduction in fuel consumption. Ideal for everything from small hatchbacks to family saloons.
All-year-round versatilty
Up to 5% fuel saving
Precise steering and handling in the dry
Michelin 'Energy' tyres are [>famous for their reduced grip > normal Michelin
Reads pretty good for a general use tyre would'nt you say? Braking distance reduced by 2 metres
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Reads pretty good for a general use tyre would'nt you say? Braking distance reduced by 2 metres
'Braking distance reduced by 2 metres' is a completely meaningless observation unless you state what the braking distance is being compared with. Go on, go back to the website and find out what.
I'm sure it's a fine general use tyre, I've got it on my car; you miss my original point, I think, for which I was asked to find evidence.
The point is, that the saving in petrol is offset by a reduction in road-holding or braking performance compared to Michelin's other tyres. Surely that's no surprise to anybody.
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I would'nt fit an energy type tyre to an Impreza where ultimate performance and handling were the reqirement, I would fit them to a familty hatchback for which they were designed.
You seem to be dissagreeing with your own link, they say 2M reduction in braking distance and you say the opposite.
You pays your money and take your chance ;o)
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You miss my point! 2 metre reduction in braking distance compared to what?
There is a little asterisk next to the point in your extract. At the bottom of the website page it tells you what they're comparing the performance to. If you read that, you'll be less impressed (if I have any luck).
I don't think that you disagree with my original statement that a gain in economy is coupled to a reduction in performance.
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Michelin 'Energy' tyres are famous for their reduced grip compared to normal Michelin.
Its your statement about that made me ask the question in the first place, normal michelin, then you compare them to the sporting versions.
They're "famous" for being a good all rounder which is a compromise in all departments and compared well to the "normal" tyres they replaced. ;o)
DDs going to tell me off again for "attitude" again now when all I'm doing is getting my point over, says discussion above ;o(
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I must be really really stupid, Dox, because I am unable to deciper the point you're trying to make. So far as I can see you're agreeing with me - so if you're trying to have an argument with me, it's not working; the only person with whom you've disagreed so far is yourself. Sorry, you said that you wouldn't fit them to a high performance car, thereby presumably accepting their limitations at remaining attached to the road.
QED!
As you correctly state, 'a good all rounder is a compromise in all departments,' i.e. there is a trade off between road holding and petrol consumption. Thatwas my original point that you doubted and so asked me to justify.
As you cannot be bothered to go back to the website to look, I'll do it for you. You will see that the 2m braking distance improvement is compared to the first generation Energy. Woo hoo! Michelin's advertising bumf says that mk ii compromise tyre is better than mk i. Way hay!
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I saw the tests for the MK1 and its predessesor, the two cars fitted with the energy ( 406 / Xantia)compared favourably to the non energy tyre fitted to the same cars.
The car manufacturers tested them and bought them.
Everytime I question the often repeated and exagerated norm on this site teddies go flying.
All I've said is compare like with like thats all.
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Dox, and Mapmaker,
Thats *up to* 2 metres braking distance. Not an absolute figure.
That might be from 100 miles an hour for all we know.
It would not seem to be in michelins interest to give a figure other than the best obtainable.
The question is, What speed was needed to get ( presumably)the best case braking distance of 2 metres between the different tyres.
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All cars are different, so I'd imagine that the figure would be a test bed or dyno / brake tester.
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Sure, But for me the devil is in the detail. Thats the *up to* ( with all that seems to imply,) in both the fuel saving and braking distance categories.
My car can do *Up to* 120MPG..... Ok thats at 56mph, on a motorway downgrade, tailgating an HGV to reduce drag.
But a true figure, It CAN do up to 120MPG
It occurs to me that we are fortunate that *official* fuel consumption figures are not based on *up to* or we would really be in cuckoo land.
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If a set of Michelin Energy tyres reduce fuel consumption by, say, 2mpg, whilst lasting an equivalent distance to a standard tyre, but cost, say, 30 quid more a corner than a standard tyre, how many miles do you have to travel to get your outlay back on them?
Away you go!
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They don't cost that much more than the non fuel saver type
Simple maths, a set of tyres lasts 40K miles when swapped front to rear to wear out all 4 at the same time.
40 MPG = 1000 gallons
5% = 50 gallons
50 gallons X average of the fuel cost over the 40K miles
50 x £4 = £200
All are guestimates
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