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Old 06-05-2008, 10:32 AM   #11 (permalink)
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So hows that 14" compair with some 13" 155's?

Just curious.. at 71 bucks each and the cost of rims how many sets of 155's would it take to make up for that set of LRR 14's and rims.. I just checked a few days ago and 155's were around 30-40 bucks each

you have to figure out the break even point on some of these things.. some times were throwing cash at stuff to not get gains that will repay you for a long long time.

However that 14" is a sweet resistance rating.. love to see what differences it makes in real world testing on the forums here.

Also its going to effect my end gear ratio.. it will be a 8.6% bigger than my stock size 13"... for me I'm going to need that.. but, these wont be for all of us.. only the ones who want to re-gear for more economy...

Also one other consideration.. tread wear rating these 14" have a rating of 240.. thats pretty low.. tires will be replaced pretty fast.

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Old 06-05-2008, 10:34 AM   #12 (permalink)
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The B381 in the 14" is a different tire from the other sizes of B381 - this is the OEM tire for the Insight.
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Old 06-05-2008, 10:46 AM   #13 (permalink)
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Also where are you finding those for $71... i see them in the $90 range?
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Old 06-05-2008, 10:50 AM   #14 (permalink)
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Quote:
Originally Posted by PaleMelanesian View Post
no 13" included.
ditto... where's the info on 13's?
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Old 06-05-2008, 12:17 PM   #15 (permalink)
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If you include 13's I would like to see 12's as well.
I have a Consumer reports sub. Tell me what you would like to know.
Or tell me how to find the info on 12 & 13 incher's.
I'm headed to CR right now.
S.
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Old 06-09-2008, 09:41 AM   #16 (permalink)
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There is not enough information for tires below 14", there wasn't much information for 14" either.... they provide lots of options for the most common sizes.... but not the lower sizes, which is why I didn't include it in the list :/
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Old 04-05-2009, 02:01 AM   #17 (permalink)
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Thanks, for the research.

I bought the Michelin MXV4 S8 tires when they first came out, have found them to be very good for mileage. I measured my rolling resistance coefficient as Crr = 0.0065 at 40psi. My tire size is 205/60R-16; my car is an 03 New Beetle TDI. Best one-tank mileage was 78 mpg (in a contest).
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Old 04-05-2009, 07:34 AM   #18 (permalink)
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Anybody have the specs on stock Prius and Civic/Insight Hyb tires? You would think those are super LRR.

Last year, I replaced GY Weatherhandlers on my wifes's Camry with Michelins from Walmart. Picked up grip but lost 2-3 mpg right away. They have super high threadwear rating (700+). I wish I knew what I know now.

Quote:
Originally Posted by Ernie Rogers View Post
I measured my rolling resistance coefficient as Crr = 0.0065 at 40psi.
You measured it yourself? How do you do that?
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Old 04-05-2009, 11:55 AM   #19 (permalink)
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Quote:
Originally Posted by Mpower View Post
Anybody have the specs on stock Prius and Civic/Insight Hyb tires? You would think those are super LRR.

Last year, I replaced GY Weatherhandlers on my wifes's Camry with Michelins from Walmart. Picked up grip but lost 2-3 mpg right away. They have super high threadwear rating (700+). I wish I knew what I know now.

You measured it yourself? How do you do that?
Hello, MPower,

Yes, you can measure your own rolling resistance, but if you do it my way it takes some work. First, the easy way-- rolling resistance is supposed to be independent of speed, so IF you find a section of sloping road where the car rolls very slowly at a constant speed, then the rolling resistance coefficient is equal to the slope (grade) at that point.

Now, the hard way-- Here is the formula for the retarding force on the car:

F = Cd A 1/2 rho V^2 + Crr Mg

and also F = M a

In words, the retarding force is equal to the sum of the aerodynamic drag and the rolling resistance. The aerodynamic drag is the product of Cd, the drag coefficient; A, the frontal area of the car; rho, the density of air = 1.2 kg/cu.m.; and the air speed squared, divided by two. The rolling resistance is the product of Crr, the rolling resistance coefficient, and Mg, the weight of the car. Remember that M is mass and Mg is weight. Use M in kilograms and to get Mg, multiply by g = 9.81

And when you are in neutral, the acceleration of the car (rate of change of speed) times the mass of the car equals the retarding force.

Okay, the test procedure is to find a lonely stretch of level road, and no wind. Speed up to about 75 mph, then put the car in neutral and roll. As you slow down, click the time with a stopwatch at say 70 mph, 60, 50, 40, 30, 20, and 10 mph. (Do this several times in both directions so you can get a good average.) Draw a graph of speed versus time. The slope of the curve is the acceleration. Now, plug all of the numbers into the formula above until you find a consistent result for both high and low speeds. That gives you both the Cd, the drag coefficient, and Crr, the rolling resistance.

Rolling resistance depends a lot on tire temperature and tire pressure. So, control the test conditions accordingly. And, remember that this rolling resistance value (as with the easy method) includes all of the friction in the drive train past the transmission.

As for your bad luck with the Michelin tires, a word of advice-- if you want a good price and long wear, you are doomed to failure. The low rolling resistance tires are made with soft rubber that won't last very long, no matter what brand. Find the tires with the low or no mileage warranty that are probably expensive-- they are sure to give good mileage.

By the way, I noticed that the Michelin Energy MXV4 S8 tires are being supplied at the factory for the new 2009 Jetta TDIs, showing the factory has agreed with me on the best tire for fuel economy, at least for VWs.

The next time you buy tires and they give bad mileage, TAKE THEM BACK. I did! Most reputable tire makers provide a 1000 mile satisfaction guarantee.
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Old 04-05-2009, 03:44 PM   #20 (permalink)
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Quote:
Originally Posted by blackjackel View Post
There is not enough information for tires below 14", there wasn't much information for 14" either.... they provide lots of options for the most common sizes.... but not the lower sizes, which is why I didn't include it in the list :/
I'm impressed with getting a rolling resistance value for the one 14" tire. I had tried to find the values for the Consumer Reports top rated tires and failed to find any metrics:
  • Michelin X Radial (Club Tire)
  • Michelin Agility Touring (Sears)
  • Michelin Harmony
  • Toyo 800 Ultra
  • Sumitomo HTR T4
I have had no luck finding rolling resistance values at Tire Rack and as for other sources, it has been a mixed bag. It is as if rolling resistance is being hidden.

Could you point me at where I might find the rolling resistance values for the Consumer Reports tires?

I recently measured my Prius Crr at 0.0102, which includes the transaxle drag. I'm not really happy with having to buy sets of tires to find the lowest rolling resistance tires.

I had been following the California Air Resources effort to measure tire rolling resistance but got the impression that it 'ran out of steam' last summer. I never saw their report much less some evidence of a continuing effort.

Thanks,
Bob Wilson

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