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Old 01-01-2009, 12:43 PM   #21 (permalink)
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I just check my odometer at a mile post on the highway, then check it again 30 or 40 miles later and see what the discrepancy is.

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Old 01-01-2009, 03:30 PM   #22 (permalink)
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And the Clarifying continues:

Quote:
Originally Posted by Jim Allen View Post
Capri: Is that,
"Interesting, that's the dumbest thing I've ever seen!"
or
"Interesting, cool way to do it!" ( : < )
Actually, my reaction was "I wouldn't have thought anyone would do it that way, even though that's a pretty good way to do it."

Quote:
Originally Posted by Jim Allen View Post
..........

Either way, it's not my idea. It's how the programmer wanted you to find the circumference. Easy to do. I though it was cool. My other method is to measure the loaded radius with the tire inflated to the pressure I will use.
No!! The loaded radius is not the way to do this. BTW, this is called the Static Loaded Radius and it only affects ride height - which is why some find it a useful statistic to have.

Long story, but the short version is that the axle is off center both from the top and the bottom of the tire. The tire kind of hangs from the top and pushes down on the bottom.

Quote:
Originally Posted by Jim Allen View Post

..........

If you have other methods, would love to hear about them!

As to centrifugal forces, a tire engineer told me regarding one particular tire (a big, high profile, 38 inch diameter, 15 inch rim, mudder) that the tire grew in circumference by several mm at high speed (he did not define "high"). I never did get to question him further to see if this was a general phenomenon, or something found just on that tire, or others like it. That's why I asked you about it.

This is probably a bias ply tire - and yes, those types of tires will grow. You can see this phenomenon in drag racing - especially Top Fuel where the speeds are high and the tires are exposed.

But we are talking about radial tires with a belt which restricts the growth. In fact, growth of this nature is such a problem for radial tires that higher speed rated tires will have a circumferential overlay which further restricts the growth.
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Old 01-01-2009, 05:28 PM   #23 (permalink)
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Quote:
Originally Posted by CapriRacer View Post
Actually, my reaction was "I wouldn't have thought anyone would do it that way, even though that's a pretty good way to do it."
Folks that are into bicycling (as I am) that need to calibrate bike computers will measure this way too (rather than use a tape measure around the circumference)... not that bike computers need to be all that precise, but still the same idea. I usually use chalk on the tread which then leaves a mark on the pavement for several revolutions before becoming too faded, and then measure between the marks.
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Old 01-01-2009, 06:45 PM   #24 (permalink)
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All tires are subject to the centrifugal force which can make them bulge slightly while rotating. The faster the rotation, the greater the chance of distortion/bulge.
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Old 04-11-2009, 09:43 PM   #25 (permalink)
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Hi,

I recently got a TireRack.com catalog in the mail and they actually have a blurb on low rolling resistance, and they list three tires that are low(er) rolling resistance:

Michelin "HydroEdge Green X" (UTQG Rating 800 A B)
Goodyear "Assurance Fuel Max" (UTQG rating 580 A A)
Bridgestone "Ecopia EP100" (UTQG rating 400 A B)

Has anybody tried any of these, or have you heard anything about them?
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Old 04-12-2009, 03:58 AM   #26 (permalink)
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Accuracy of speedometer and odometer? Why not just check them with a GPS?

If you are comparing fuel economy, best to make sure both cars are going the same speed, otherwise, what have you proved? With my car, a one mph error in speed makes a one mpg change. I apply corrections to both speed and odometer when it's important to know.

If you increase tire diameter, fuel economy will usually increase, but it will SEEM to go down unless you correct for guage changes.

/Ernie Rogers
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Old 04-12-2009, 04:47 AM   #27 (permalink)
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Ernie -

Yeah, I periodically use a GPS correction for my one-size-up-from-stock tires :

http://ecomodder.com/forum/showthrea...ires-2642.html

I apply the correction to my fuel log, so it's like a mini-bonus.

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Old 04-17-2009, 04:46 AM   #28 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
Hi,
Has anybody tried any of these, or have you heard anything about them?
I contacted Michelin directly a few months ago, and they recommended the Hydroedge.

Another one that looks good is Nokian i3.
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Old 07-30-2009, 11:53 PM   #29 (permalink)
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What do you think the rolling resistance is on these?
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Old 08-01-2009, 05:20 AM   #30 (permalink)
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I contacted Nokian also, and they said the i3 is good but the H is better.

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