Reparing Leak in Tire Side Wall

Page 7 of 9  


But the ratio is so low that it's kinda like the heat in your freezer when you put a candle inside. I'm all but certain the candle makes heat, but the ice cubes are not going to melt, so the freezer is still a freezer.
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On 11/10/2014 9:36 AM, Jeff Strickland wrote:

Are you certain...have you calculated the actual fill percentage and compared that to the 95% claimed needed to be effective? I've not taken (nor am I going to) the time but it's the underlying question.
I've seen reference to purge cycles; the question is is that a routine needed when using N to make it effective to the extent it is, anyways, (which really isn't much as shown in another subthread). Interestingly enough, our Costco tout hasn't answered/responded to any of the more factual aspects of the topic.
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On 11/10/2014 10:03 AM, dpb wrote:

Actually, it's not that tough to get pretty good estimate...
14.7/(14.7+30) = 0.33 --> 33% air by fraction of total pressures. So w/o purge you're only going to be 2/3rds or so N...
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nitrogen, and 2/3 will be 98% =/- Notrogen - so closer to 96% nitrogen.
That's so, yes...the 1/3rd is air:N, my bad.
OK, guess that may be "close enough" to make some difference. Wonder what the Consumer Reports test data would've been if they'd just done N fill instead of purge.
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KNOWS certain vehicles are always sold at a loss - certain very popular models have never earned the company a cent, and others lost money for several years before becoming "mainstream" and making money.
For years, Toyota lost money on every Hilux sold in North America, but they sold them for what they could get for them to allow them to import more Celicas, Coronas, and Corollas - models they could sell all they could get and more.
The same has happened with virtually every other manufacturer/dealer at one point or another.
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I'm paying 950 for 2 vehicles with full coverage. Ones about 10yrs old the other about 8, I guess I've got a good deal then
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On 11/10/2014 1:02 PM, ChairMan wrote:

Can't compare just rates; need to know about limits of liability, deductibles, all that other stuff that changes the rates drastically for differing levels of the same basic coverage items.
And, liability in particular is _very_ jurisdiction dependent. In VA it was roughly 3X the KS rate for the same vehicle/coverage and that was 40 yr ago. I'd expect it to be an even wider disparity now.
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nitrogen, and 2/3 will be 98% =/- Notrogen - so closer to 96% nitrogen.
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much if you drive in Toronto vs, say, Wiarton.
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snipped-for-privacy@snyder.on.ca wrote:

That's understandable, particularly if you spend much time on the Mac and Jack Speedway.
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wrote:

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That cannot be right, but I have no idea the formula that is needed.
An "empty tire", one with 1 atmosphere of air inside will not pollute with any significance the contents it takes to bring that tire to 30+ psi. The empty tire will contain air, no doubt. But filling the tire to 30 psi will most certainly result in a dillution of the "empty" contents to far less than 1/3. Surely the anology of a candle in the freezer has to be pretty accurate, even if not the same type of thing.
An "empty," balloon has air inside, and filling it with helium still results in a balloon that floats.
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On 11/11/2014 9:30 AM, Jeff Strickland wrote:

It _IS_ right for what it is... _Air_:N ratio. I just didn't go ahead to then account for the 80% N content in the entrained air (as clare pointed out the oversight). See the followup there.
All it takes for the He balloon to float is that the density be less than that of air--nothing even close to the 95% fraction would be required so it's not a useful comparison.
I was thinking the ratio wouldn't be quite so high altho the 80% N in air is the saving grace; just hadn't computed the actual fraction previously.
It would be interesting to see the CR data/experiment w/ a control population that were just backfilled w/ N alongside the purged set they did just to see if it showed up.
After the above computation I'll concede it is sufficient to likely be able to produce the net savings of roughly 1.3 lb less diffusion pressure drop over a year than air; I'll still contend that isn't sufficient difference to be of any real value to the end user.
In large part that that's so can be shown because the temperature swing from yesterday afternoon's high of 80 F to this morning's low of 19F (it's all the way up to 22 F now at 10 AM) results in a pressure swing of (20+460)/(80+460)*30 psi = -3.3 psi or 2.5X that annual loss differential. It's just not significant difference in what happens w/ N in lieu of air for passenger car applications.
So the car this morning is underinflated but by this time two weeks from now if were to correct for it it'll be back to seasonal normals and they'd be over-pressured by about that much.
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On 11/11/2014 9:50 AM, dpb wrote:

*ADDENDUM*
...It _IS_ right for what it is... _Air_:N ratio....
More precisely, it's Air:Total ratio.
And, to explain if don't see it, it's simply the absolute pressure ratio instead of gauge pressures. 14.7 is normal atmospheric pressure; hence when the tire gauge reads '0' that's what's there. The total pressure when the gauge reads 30 psi is then roughly 45 psia (or 30 psig).
Dalton's Law says partial pressures are additive.
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On 11/11/2014 10:30 AM, Jeff Strickland wrote:

Most empty balloons I've seen were collapsed flat before filling.
- . Christopher A. Young Learn about Jesus www.lds.org .
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On Tue, 11 Nov 2014 07:30:07 -0800, "Jeff Strickland"

can be said for a tube, but not a tire. A tire has it's full volume of air at 1 atmosphere. That 1 apmosphere is roughly 80% nitrogen. Inflate to 3 atmospheres is 3 times the mass - correct? So 2 thirds of the volume is 96-98% nitrogen and 1 third is 80% nitrogen. Lets say the nitrogen fill is 98%., so 98+98+80/3%.
Close enough anyway, unless it takes the addition of more than twice the volume of the tire to raise the pressure to 3 atmospheres from 1.
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wrote:

else was selling the same tire for less and they didn't want to loose market share. If they can sell 100 at a dollar profit they make more than selling 48 at 2 dollars profit
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On Tuesday, November 11, 2014 5:41:26 PM UTC-5, snipped-for-privacy@snyder.on.ca wrote:

That's part of it. The other part is that an important part of where supply and demand curves meet for a product are the total cost of production. Nitrogen costs money. Unless you believe that it actually saves the tire company money, by less warranty claims, less customers coming back, etc, which I don't. If you add cost to a product, then economics 101 says that the result is a higher market equilibrium price.
That's the economics behind it. What Costco actually does, none of us know. They management could set the price based on astrology. But SMS keeps insisting that costs have nothing do to with it. That's just not true. Costs directly affect prices. It doesn't have to be that Costco figues their cost and adds X%. Per the above, market forces determine the price, but costs are directly involved in what the price is. Also, IDK about Costco, but typically businesses know their costs, keep and eye on their margins, etc. I would be surprised if Costco didn't know to the penny how much their cost is to install a tire, including the nitrogen and they keep that in mind when setting the price.
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I'm late to the party so maybe someone's also mentioned this, but perhaps Costco figures if someone is dumb enough think they have to drive miles to top up their tires instead of doing it in the comfort of their own garage they might also, while there, go in and buy an impulse flatscreen.
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The way I price tires is to ask for the total out the door price including tax and anything else.
As you say , some places dollar you to death adding things on like mounting and valve stems. The way I look at it is I am not buying a tire to take home, I want it on the car and ready to drive off. I doubt very many people go to a store and buy tires and take them home. Maybe a few to make planters out of, but usually those are old tires.
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