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The real meaning of MPH


Kent2406
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No, she's right! Think about it! At 80 miles per hour your tires are going so fast that based on their circumference, there's no way in hell that they could travel that far in an hour so you cut it about in half. It's a compromise so you can be fair to both large and small tires. Simple!

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No, she's right! Think about it! At 80 miles per hour your tires are going so fast that based on their circumference, there's no way in hell that they could travel that far in an hour so you cut it about in half. It's a compromise so you can be fair to both large and small tires. Simple!

Please don't, my head hurts.......

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I believe the appropriate response from the husband would have been to reach over open the door, ask her how many times will the human body roll when it hits the ground at 80 mph, the push her out. If he didn't want to go to that extreme then stop at the next layer office and begin anulment proceedings based on the grounds of her being a fucking idiot.

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The doctors asked if she was sexually active and she said," No, I just kind of lie there and try to figure out how long it takes to go 60 miles if I'm driving a 60mph if all my tires are different sizes". :lol:

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Showed my wife this video last night. Within 5 minutes we were debating the statement; "I don't know how you would measure that. (the number of revolutions of a tire within a mile) and we sat and calculated a formula based upon tire ratio (215/45 on a 17" rim came to ~850 revoutions. 400 revolutions would require a 4' diameter tire)

Then we go into a heated debate about whether a slightly un-inflated tire would affect that number. She though the diameter of the tire woudl be affected by the bulging at the contact patch, and I argued that circumference remains the same unless the tire is almost flat.

Total nerdgasm there.

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Showed my wife this video last night. Within 5 minutes we were debating the statement; "I don't know how you would measure that. (the number of revolutions of a tire within a mile) and we sat and calculated a formula based upon tire ratio (215/45 on a 17" rim came to ~850 revoutions. 400 revolutions would require a 4' diameter tire)

Then we go into a heated debate about whether a slightly un-inflated tire would affect that number. She though the diameter of the tire woudl be affected by the bulging at the contact patch, and I argued that circumference remains the same unless the tire is almost flat.

Total nerdgasm there.

Boy, you two really know how to keep the magic going in a relationship. :D But at least you seem to have mutual interest and there's no video with her arguing that pie is round, so your wrong saying pi R squared. :lol:

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Then we go into a heated debate about whether a slightly un-inflated tire would affect that number. She though the diameter of the tire woudl be affected by the bulging at the contact patch, and I argued that circumference remains the same unless the tire is almost flat.

I think you are both correct. Under inflation would definitely change the diameter not the circumference of the tire and would require more rotations to match the speed of a properly inflated tire. How much of a difference it makes would be calculated like this

(tire sidewall size from ground to bottom of the wheel x 2) + wheel size = rolling diameter (yes I made this term up)

If the tire is under inflated the side wall height is going to be smaller which will require more rotations to equal the fully inflated tire.

Edited by JStump
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im going to go with underinflated tires dont change the speedo. the whole tire has to rotate around along with the rim if this changed just because the tire is underinflated it would mean the tire is spinning on the rim.. this is all logic and could be way wrong.

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My logic is you are basically riding on a shorter but wider tire when it is under inflated. Think of it on a bigger scale, say this truck for instance..

hybrid-truck.jpg

right now that tire is inflated so the rim is about to the top of the hood, now imagine it was only inflated so the rim cam up to the bottom of the bumper. You would not be going nearly as fast as the speedo indicates because that speedo is calculating speed for a 10 foot tire but it is only inflated to 8 feet now. Does this make sense? This would be much more minuscule on a car but it is still a difference in speed. This is also why when you are buying new wheels for your car, if you go up in size on the wheel you go down in size on the tire. But in this case, the wheel stays the same size but the tire is now smaller in diameter. Its all about the diameter, not the circumference.

Edited by JStump
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Diameter and circumference are proportional to each other, so its really about both. The thing is, an under inflated tire still had the same surface area, just a larger contact patch, so it should not make a difference in Speedo reading, or at least not a notable one. The same amount of surface feet are still pissing over the road per rotation of the wheel.

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1) how the hell did he marry a bitch that dumb

2) she better give the best fucking blow job in the world for withstanding pushing her out of the car

3) shes not hot enough to be THAT stupid

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A tire that deflects has an effective circumference of a circle with the same radius as the point of max deflection. The "flatter" the tire is it will travel less distance for the same rotation. That's why they say fill your tires up for best MPG.

However the guy said "going 80mph" not "the speedometer says 80mph" so tires and the effect on the speedometer has nothing to do with it.

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A tire that deflects has an effective circumference of a circle with the same radius as the point of max deflection. The "flatter" the tire is it will travel less distance for the same rotation. That's why they say fill your tires up for best MPG.

However the guy said "going 80mph" not "the speedometer says 80mph" so tires and the effect on the speedometer has nothing to do with it.

This is exactly what I was trying to say, except I forgot all the technical terms I learned in my engineering classes lol. It would be like putting a tank tread on your car and expecting the car to go 5 times faster because the tread has 5 times the circumference of the tire but you would actually go slower since the radius is smaller and you are practically riding on the rim.

Edited by JStump
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