New tires and decrease in MPG...Why?

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Originally Posted By: CapriRacer
Long Version:

http://www.barrystiretech.com/rrandfe.html

Short Version:

1) New tires have more rolling resistance than worn out tires - all other things being equal.

2) There is a technology triangle between rolling resistance, traction - especially wet traction- and treadwear. To get improvement in one area you have to sacrifice another area (or both)

3) OE tires generally go after rolling resistance.

4) You went after treadwear.



Well, I can see....



But after reading about the ratings of the tires, barry wants me to buy H rated tires (14 inch, mind you) for my Cavalier because they are less likely to blow that the S and T rated tires....
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Originally Posted By: daves87rs

But after reading about the ratings of the tires, barry wants me to buy H rated tires (14 inch, mind you) for my Cavalier because they are less likely to blow that the S and T rated tires....
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...and?
 
Originally Posted By: Quattro Pete
Originally Posted By: daves87rs

But after reading about the ratings of the tires, barry wants me to buy H rated tires (14 inch, mind you) for my Cavalier because they are less likely to blow that the S and T rated tires....
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...and?



So I should go against what I'm told to put on? (S rated)
 
Originally Posted By: daves87rs

So I should go against what I'm told to put on? (S rated)


Dave,

That is just one person's opinion - one I highly respect, but nevertheless, one opinion. You need to decide for yourself.

But one way to look at it is that you really aren't going "against", you're upgrading.
 
Same thing happened to me back in 1996. I had a Chrysler Lebaron Convertible and a 72 mile commute between East Lansing and Farmington Hills. Switched out the OEM tires for Eagle GT+4's. Mileage went down 3-4 miles per gallon and stayed there for the life of the tires. I was not a happy camper.
 
Originally Posted By: CapriRacer
Originally Posted By: daves87rs

So I should go against what I'm told to put on? (S rated)


Dave,

That is just one person's opinion - one I highly respect, but nevertheless, one opinion. You need to decide for yourself.

But one way to look at it is that you really aren't going "against", you're upgrading.



True, it's a very good point.
 
Originally Posted By: Quattro Pete
Originally Posted By: CapriRacer

That is just one person's opinion - one I highly respect,

So, Barry is not you?


No, that's me - and that's why I highly respect his opinion.

::Boy, do I love how well this sockpuppet stuff works!::
 
Originally Posted By: opus1
Dumb question but I have to ask (it's my forte'
lol.gif
); are the tires exactly the same size as the ones you replaced? Not a different size but +0, but exactly the same size?

The reason I ask is that when I replaced the tires on my Dakota, even though I got a different size that's advertised as a +0 change, there is enough of a difference that my speedo is off slightly.


The sizes aren't absolute, they represent a range of dimensions. Check the Tire Rack site and compare different models and brands, you'll see that the tire diameter can vary a little.
 
This is my first post here. Thanks to everyone who contributed so far.

I was considering the Pirelli P5 until I learned about rolling resistance and the effect on fuel cost over time due to increased rolling resistance. The P5 seems to have the highest rolling resistance of all the tires I have looked at followed by the Goodyear Tripletred. As such, I have narrowed my search down to two other tires and would appreciate any constructive feedback.

Fuel cost over time is an important issue for me, along with wet traction, snow traction, and cornering on a 2003 Dodge Sport Caravan (tire size: P215/65R16). I'm willing to compromise in the areas of noise and comfort. I normally approach (but never exceed) the upper limit cold PSI specified by the tire manufacturer, as in the past this has given me better cornering, even tire wear, and better fuel mileage. The tires I am now considering are the Michelin Destiny and the Goodyear Assurance Fuel Max. I realize the Goodyear will likely have lower rolling resistance and consequently higher mileage per gallon, but I am unsure about the trade-off in cornering and traction between these two.

Thanks in advance!
Dave
 
The reason is the OEM tires were built specificaly for the oem under contract. When the vehicle was designed, the tire design went out to bid. The tire companies bid to build to that spec. Even though the replacement tire might be the same model and brand, it is different. If you check your OE tires sidewall and DOT, they usually have a different plant code and material code than the ones you bought. The OE tires have a lower ply turn up and lighter nylon overlay. Nylon has an excellent memory effect so the oe tires are built to resist flat spoting when the vehicles sit on the dealers lots for an extended time. They are also built to help obtain that MPG on the window sticker.

The replacement tires are built more robust usually with heavier ply multi strand nylon instead of monofiliment. Tread compounds are altered slightly too. That is why they usually don't ride as well or get the same fuel mileage. Also, OE tire do not come with a mileage warranty from the tire manufacturer unless they offer a concession.

I analysis tire durability and failures with the engineers for one of the big tire brands. I've spent a lot of time in a tire plant.
 
Tire design on OTR trucks can affect mpg by 15%. That is why you see ribbed tires on the trailers and also on the cab when possible. The difference between ribbed and M/S tires is about 15%. The difference between new and worn tires can also be quite high depending on how aggressive the pattern is to begin with. Near bald M/S that have been worn down past the warning bars will give mileage comparable to ribbed tires.

Road surfaces can make a difference of up to 15% also between smooth concrete highways and rough asphalt.

When I switched from Firestone rib-like tires on my excursion to Pirelli Scorpions M/S My highway mpg went down 10%. I reclaimed some of my 10% when I went to Michelins LTX M/S. Probably about 5%.

If you would like to know more about the factors which can affect mpg, google Dr. Diesel. There is a 30+ page paper on the subject. Sorry, I don't know where I put my copy or if I still have one.
 
Last edited:
Difference in weight and traction
More tread = more weight.
Better traction = more friction.
 
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