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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old June 30th, 2005, 06:29   #16
myke_w
 
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Default Re: Low Rolling Resistance Tires...Which is Best?

Quote:
I changed from Stock Contis to Michelin Energy and noticed a 2-4 MPG drop. Disappointing.
I think conti's all seasons use a pretty hard compound too. I used to run them on one of my gas a3 and they were stiff as all get out. seemed to last a while too.
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Old June 30th, 2005, 10:36   #17
ruking
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Default Re: Low Rolling Resistance Tires...Which is Best?

Quote:
Quote:
I changed from Stock Contis to Michelin Energy and noticed a 2-4 MPG drop. Disappointing.
I think conti's all seasons use a pretty hard compound too. I used to run them on one of my gas a3 and they were stiff as all get out. seemed to last a while too.
I think you point out some interesting phenonmenons. Because of a few factors, tires more worn tend to get better mpg than new/newer tires. They also get better traction. In most surveys, the Michelin's tend to get slightly better mpg than Conti's, and Conti's slightly more than the GY LS-H's. While there is always variation and variation between brands, I am thinking most is due to old vs new. In so far as Conti's using harder compounds than Michelin, the data indicates Michelin uses harder compounds than Conti. (UTOQ 400 vs 360)

I am sure someone can run the math for a 50,000 mile, lifespan, 2-4 mpg more/less, and M=107, C=55 GY=75. Even with 4 mpg better, the Conti's still are cheaper and you have to come up with 49% less money to get the Conti's over the Michelin's. To boot, Michelin and GY LSH's have no tread life warranty vs Conti's at 60,000. Does this warranty really guarantee anything? No but you can get a prorate if the tire does indeed fall below expectations. So the economics in the OEM tire fare are almost truly a no brainer.
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Old June 30th, 2005, 21:11   #18
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Default Re: Low Rolling Resistance Tires...Which is Best?

Quote:
I changed from Stock Contis to Michelin Energy and noticed a 2-4 MPG drop. Disappointing.
Sort of like the F1 race at indy.
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Old July 1st, 2005, 07:13   #19
VWannabe
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Default Re: Low Rolling Resistance Tires...Which is Best?

Check out this article for low rolling resistance tires. Pretty interesting. Scroll to the bottom to click on the link for the low rolling resistance tires.

http://www.greencarcongress.com/2004..._wings_of.html
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Old July 1st, 2005, 12:16   #20
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Default Re: Low Rolling Resistance Tires...Which is Best?

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Someone here estimated a 1 - 2 MPG mileage advantage of the Michelin Energy tire over the standard tire. I did a quick calculation based on the price, tread life, and fuel savings (1.5 MPG I picked) as compared with a Michelin Hydroedge and the Hydroedge came out cheaper over the life of the tire. The tread life of the Hydroedge is about 35% greater than the Energy tire.

--Nate
Nate I believe if you check, the HydroEdge is also an energy tire with low roll restance, but I've been wrong before. I think most tires that come with the 44 to 54 PSI rating are low rollers. I have the HydroEdges on my Magnum and run them at 40 F & 38 R in town. The Jetta has Michelin X1's with the max inflation rated to only 35 PSI and they are rated just about the same as the Hydro's for load weight, but they are oh so smooth riding with only 32 PSI.

That 1 or 2 mpg is not really noticable to most of use here, but just think what it means to total gallons of gas saved nationwide or world wide. Zillons of gallons.
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Old July 2nd, 2005, 01:56   #21
Ernie Rogers
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Default Re: Low Rolling Resistance Tires...Which is Best?

Philosophical thoughts about tires and rolling resistance--

Let's start with a formula. Most of us are satisfied with a simple proportionality constant between rolling resistance and load. (Of course it may not be exactly true):

RR = Crr L

So, the car has to push with an extra force RR to overcome the resistance of the tires, which are holding up a load L. The proportionality constant is the rolling resistance coefficient, Crr.

We know that the source of the energy loss is the work used in distorting the rubber in the tires, both the side walls and the tread. It is a curious truth somebody should be able to prove that doubling the load (L) on a tire doubles the about of work done in the rubber. Let's see where this takes us. (Note that the rolling resistance could be defined in other ways, to include other rolling losses like those in gears or bearings for example, but let's not go there.)

Now let's look at the contact patch, the surface where the tire touches the road. It's a good approximation to say that the contact patch area is proportional to the load on the tire:

L = P A

This is essentially a statement of force balance-- the force transmitted to the road, L, is applied by the air pressure P behind the contact patch area A.

Suppose you have a different situation, where the load has been reduced, but the pressure in the tire was also reduced just so as to keep the contact patch the same as before. Since the rolling resistance is the result of the tire distortion, it must be exactly the same in this second case as it was before--

Then, we can combine the two equations to get:

RR = Crr P A,

And, since RR and A didn't change, the product Crr P is constant, thus giving an interesting fact: The rolling resistance is proportional to one over the tire pressure for a given tire.

That's all for now, will likely add to this tomorrow.

Ernie Rogers
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Old July 2nd, 2005, 10:13   #22
Ernie Rogers
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Default Re: Low Rolling Resistance Tires...Which is Best?

More philosophical thoughts about rolling resistance--

Let's assume that it is true that the rolling resistance is proportional to the amount of flexing going on in a tire. One measure of the amount of flexing would be the angle formed between the flat contact patch and the tangent to the tire tread face just outside the patch. Let's call this angle "alpha." (If you want to draw a picture, make a circle, then draw a flat spot on it for the contact patch. Alpha is the angle between the original circle and the flat (chord) line, or it's half the angle you get by drawing lines from the ends of the patch to the center of the circle.)

So, then it should be true (our assumption) that the rolling resistance is proportional to alpha:

RR = F alpha,

where F is the "flexing constant" of the tire.

As mentioned before, the load supported by the tire is equal to the tire pressure times the area of the contact patch:

L = P A

This time, we need to further describe the contact patch-- the area of the patch is equal to its length times the tread width, well roughly so:

A = W C

Where W is the width of the contact patch and C is the length, the chord across the circle. Now, I want to invoke a little geometry. The formula for the length of the contact patch is:

C = 2R sin(alpha), or C = 2R alpha

for small angles, that is for a small contact patch. Putting all this stuff together gives a relationship between the load L and the tire pressure, tread width, tire radius R, and alpha:

L = P W 2R alpha

Way up at the top we had a formula for the rolling resistance and now we have a formula for the load. Dividing one by the other gives a formula for the rolling resistance coefficient:

Crr = RR /L

Substituting,

Crr = F /(P W 2R)

Alpha was in both equations and cancelled out, that's cool. This is an interesting formula, but we have to be very mindful of F, the flexing constant. This "constant" depends on the construction of the tire. There is experimental evidence that it Might be true that F is proportional to the tire width, which is just about the same as W. This means that a tire's rolling resistance coefficient Might not depend on how wide the tire is. (But, remember, the aero drag DOES depend on tire width.) The only other new variable to talk about is the tire radius, R, or the tire diameter, 2R. Now, we have an expanded very interesting relationship for rolling resistance and tire properties:

Rolling resistance is proportional to one over pressure, and one over tire diameter.

Provided that we are talking about tires of identical construction except for the tire diameter.

Nothing has been said here about "dynamics", how the tire and vehicle behave when the car is accelerating, turning, and hitting bumps. (We have lots of those in Pleasant Grove, Utah.)

When choosing tires, dynamics considerations can affect choices too.

Ernie Rogers
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Old July 2nd, 2005, 10:49   #23
ruking
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Default Re: Low Rolling Resistance Tires...Which is Best?

Hard figures ER! Hard figures! If someone is asking the time, why are we talking about different theoretical methods of mechanical watch construction? Most folks have a hard enough time checking their tire pressures once a quarter! Just to enter a discussion on WHAT tire pressures are best is a herculean leap.

The other thing is there is no standard for rolling resistance measurement such as one that currently exists for tire tread (ie the UTOQ of 400, traction of AA and temp of A). While it is true that most manufacturers specify oem tires as being able to have lowest rolling resistance, even that is anecdotal to a certain degree. One does not really know what factors dominate such as cheapest cost vs the absolute best rolling resistance. My money of course is on the bean counting regime ruling out, but hey that is another story.
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Old July 2nd, 2005, 12:30   #24
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Default Low Rolling Resistance Tires...Which is Best?

Just my two cents worth...
I had the stocker Michelins (they really are junk tires, two out of four had inner cord failures and the tread actually moved sideways at one point in the tire, making the car bump sideways a bit on each revolution .) I had a neighbor suggest Nokian tires (nakapaletti is the model name I believe). They were expensive at $195.00 CAD per tire, but I went ahead and got them.

I was instantly impressed with their quality. I installed them before a long trip of over 400 kms and I got an 8% increase in mileage. I drive this long trip all the time so nothing else had changed that would have altered the mileage.

Incidently I have kept a log book of my beetle, including all fill-ups and mileages (something like you would for and aircraft) ever since it rolled off the lot and have proof of the mileage claims.

Anyway, I do recommend these tires, but they can be hard to find. Here in Canada, the only company that has them is Kal Tire. When I phoned around to look for them, even the other companies said they were a hard tire to match for quality. That basicly concreted my decision to but them.

Hope that helps...
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Old July 2nd, 2005, 19:19   #25
IndigoBlueWagon
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Default Low Rolling Resistance Tires...Which is Best?

Interesting. I've been intrigued by the Nokian NRHi, and one dealer in the Boston area (Direct Tire) can get it for me but it's a special order item. I think they run about $100 each, which is about the same as a Michelin Energy.



Anyone have any experience with this tire? It might be a good option for my A3.

You can read about it here: http://www.nokian.com/passengercars_...e=NOKIAN+NRHi#
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Old July 2nd, 2005, 23:42   #26
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Default Low Rolling Resistance Tires...Which is Best?

Quote:
I had the stocker Michelins (they really are junk tires, two out of four had inner cord failures (snip)
__. Interesting. I just replaced my stock Michelins ('02 Jetta sedan) at ~86K miles. They were worn evenly and smoothly and gave mileage in the 60-62 MPG range with "summer fuel". I'm constantly amazed at how different people get different results with similar parts/conditions, etc.
'
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Old July 3rd, 2005, 01:21   #27
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Default Low Rolling Resistance Tires...Which is Best?

Tires...Schmires. There are way too many variables to say if one is going to be better than another. I replaced my stock GY Eagle LS's with the BF Goodrich Traction T/A H, in 195/65R15. My mileage went down about 4mpg. Why? The tire is slightly heavier; the compound is stickier; and who knows what else may be a factor. However, it was well worth the trade off. These tires stick like glue and handle great! Plus they show virtually no wear after 20K miles. The tirerack's website now gives shipping weight for tires; you can use this to help determine rolling resistance. The UTQG treadwear number is just a number that the manufacturer pull out of their ___. The government doesn't regulate it at all. When comparing tires of one make, the number will give an idea of what wear to expect, but they mean absolutely nothing compared to another manufacturer's numbers. What good is a low rolling resistance tire, if you lose control/traction and crash? Get a tire that will grip well in the environment that you drive. Everything else should come second. This is supposedly one of, if not the, lowest rolling resistance tire. My $.02.
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Old July 3rd, 2005, 07:41   #28
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Default Low Rolling Resistance Tires...Which is Best?

This Nokian could be perfect:
light: 17.9 lbs at 195-65-15, low rolling resistance: claims up to 5% increase in fuel economy, durable: long tread life



<ul type="square"> Nokian NRT 2 Ė the cream of small car tyres

Roads roughened by winter traffic place great demands on summer tyres as well. <font color="red">One of the qualities Nokian Tyres has particularly emphasised in the development of NRT2 is durability. Thus the tyre retains all its great properties for a longer time.</font>

The pioneer of environmentally friendly summer tyres

First in the world, Nokian NRT 2ís tread features a rubber blend in which toxic highly aromatic oil has been replaced by low aromatic oil.

Safety on wet roads

Designed especially for northern conditions, the treadís rubber blend retains good grip on cold and wet asphalt roads as well. The directional lateral grooves and the deep longitudinal grooves effectively remove water from under the tyre and reduce the risk of aquaplaning.

Economical and quiet

Nokian NRT 2ís rolling resistance is one of the lowest on the market. This makes tyre noise pleasingly quiet and <font color="red">reduces fuel expenses by up to 5 per cent in normal driving conditions</font>.

Nokian NRT 2 is an environmentally friendly and economical quality choice for small and medium-size cars.[/list]
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Old July 3rd, 2005, 08:57   #29
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Default Re: Low Rolling Resistance Tires...Which is Best?

I've had both Michelins &amp; Contis (both OEM and both came off a car other than mine). I've noticed no mileage difference between the two. The drive is nicer with the michelins... especially quieter. The Michelins also seem grippier on wet roads. I would certainly consider Nokians... they are the Rolls Royce of tires according to everything I've read about them.
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Old July 3rd, 2005, 13:25   #30
gdr703
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Default Re: Low Rolling Resistance Tires...Which is Best?

Ernie,
I think you need to factor in the dynamic bounce factor. What I mean is that as the tire pressure gets up there, the tire transmits alot of bounce (at 60 - 70mph) into the suspension. This lack of damping within the tire itself I think causes the extreme tire pressures to be less effective in minimising rolling resistance.
My observations indicate that I get the best mpgs in the region of 40/44 psi.
Any one else concur?

Oh, I have a 2 door Golf, pressures should be 26F/28R I currently run 40F/42R.
The tires are Michelin Energy Plus on the front rated 44 psi, 3/4 worn at 71kMiles, and Michelin Energy S8 on the rear rated 51 psi, 1/8 worn.

cheers.
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