Buick35

Just wondering

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Sometimes thoughts come to me at night and here's a strange or silly one . If a car starts out for a drive and it's valve stems are at exactly in the six o clock position when you return and park it at the exact same spot would the valve stems still be at 6 o clock? Weird I know.

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Why would they be? In any case, if the car goes around any turns, the outside tire travels further than the inside tire so the valve stems would get out of sync. This is why cars have differentials.

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Also, in a turn, the rear wheels track a more "inner" line than the front wheels (with the possible exception of 4-wheel steering) ,

so all four wheels will have traveled differing amounts in any one curve or turn.

Edited by Marty Roth (see edit history)

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1 hour ago, Buick35 said:

Sometimes thoughts come to me at night and here's a strange or silly one . If a car starts out for a drive and it's valve stems are at exactly in the six o clock position when you return and park it at the exact same spot would the valve stems still be at 6 o clock? Weird I know.

 

Actually this is not the first time I heard this question asked, and it is a good question. There really is no such thing as a bad question, if we never ask we will never know.

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And if the circumference of the tires differs by a hair the cumulative difference adds up when they turn over a few thousand times.

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So, highly unlikely but possible.

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No.

1 hour ago, Buick35 said:

1. If a car starts out for a drive and it's valve stems are at exactly in the six o clock position when you return and park it at the exact same spot would the valve stems still be at 6 o clock?

 

2. Weird I know.

 

1. No

 

2. Yes

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28 minutes ago, padgett said:

So, highly unlikely but possible.

 

"Possible" only in the sense that my winning the lottery is "possible".

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We would play a game we called valve stems up you would drive around the school parking lot for a set amount of time and the car with the most valve stems up would win

 

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In a Gymkanna years ago, they had a test of getting all the valve stems to be at 12 o'clock. You were timed as to how fast and if all four ever got to the 12 o'clock position.😀

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Where the valve stem stops no body knows. The tracking of rear and front tyres , rear tyres following at a smaller circle is known as Murphy's Law.

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In my early and too much time on my hands days I would match front to back tire valve stems using my floor jack on my nice weather only car, a 1983 bright red Camaro Z-28 that I had bought new and took delivery on my birthday.   Side vs side didn’t matter but front to back did.  Then after I drove it a while I’d see how far off they were from where I started.  Its nice to know after reading the responses here I was not the only one doing weird stuff like that!

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8 minutes ago, TerryB said:

... I would match front to back tire valve stems using my floor jack... 

 

If your car has fender skirts, it's always a

happy experience when BOTH rear valve stems

are reachable (below the skirts) at the same time.

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The valve stem will stop in the same clock position only if the distance rolled by THAT wheel is an exact multiple of that wheels circumference (c).

 

However, there are many variables in the driving experience that can influence minute changes in the number of wheel revolutions when compared to the distance rolled (tire pressures, pot holes, turns...its a long list).  These variables will certainly mess-up your calculations!

 

Compressible rubber tires on vehicles means that you must measure from the center of the hub to the ground in order to determine the wheels radius (r).  For cars, r is not the overall diameter divided by 2 (as with theoretical math). 

 

c = 2 π r.

 

π = 3.14

 

Don't forget to keep all your calculations in the same unit of measure ('inches' for example).

 

This should give you enough ammo to play, and to help you sleep better at night.

If your kids ask whey you're laying down in the street with a measuring tape...tell them your doing math.

 

 

 

 

 

 

Edited by Real Steel (see edit history)
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Long ago, in a galaxy far away, a fellow wanted to know the pressure on the newly laid tiles in his garage.  I responded that the pressure per square inch was equal to the pressure in the tire, if one disregards tire sidewall support.

 

It was quite a circus.

 

This question somewhat reminds me of that, although the answer is much more slippery.  In a perfect world, if you drove forward EXACTLY in a straight line, and then backed up EXACTLY in a straight line, and the outside diameter and tire pressure in each tire was identical, and you held your tongue in your mouth in just the right place, the stems would theoretically end up in the same place.  There are so many variables in this equation that no way they would, of course.

 

In a corollary to this discussion, one must realize that the tire that needs air will always stop with the valve stem at the most inconvenient location.  A Murphy law, perhaps...

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What are the odds that the stems will randomly all match location? Not putting them that way, but randomly parking and having them match? In theory it is possible.

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I recall reading about one of those famous old time movie producers who was a fanatic for little details in his films. It was said that he would have crew members jack up a car that was about to be in a scene in which it rolled up in a driveway for a dramatic entrance by the star(s) of the film. He insisted that the wheels should end up with both hubcaps on that side of the car being oriented so that the name on the hubcaps should be exactly level and right-reading. The article that I read said this was harder than it sounds, and it took many takes to get it right...much to the annoyance of the some of the rest of the film crew. 

 

This may have been Cecile B. DeMille...but I'm not sure. 

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9 hours ago, Billy Kingsley said:

What are the odds that the stems will randomly all match location? Not putting them that way, but randomly parking and having them match? In theory it is possible.

 

Always 50-50, either they will or they won't. Just like flipping coins.

 

Luckily when I wake up during the night I usually only think about money or sex.

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37 minutes ago, lump said:

I recall reading about one of those famous old time movie producers who was a fanatic for little details in his films. It was said that he would have crew members jack up a car that was about to be in a scene in which it rolled up in a driveway for a dramatic entrance by the star(s) of the film. He insisted that the wheels should end up with both hubcaps on that side of the car being oriented so that the name on the hubcaps should be exactly level and right-reading. The article that I read said this was harder than it sounds, and it took many takes to get it right...much to the annoyance of the some of the rest of the film crew. 

 

This may have been Cecile B. DeMille...but I'm not sure. 

 

This was only done in one movie which was at the very beginning. I think the car was a Yellow or White Rolls or Bentley, and yes, they took many takes.

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9 hours ago, Billy Kingsley said:

What are the odds that the stems will randomly all match location? Not putting them that way, but randomly parking and having them match? In theory it is possible.

 

Around one quintillion.

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If you are taking pictures of a vehicle to sell it is well worth the effort to orientate the hubcaps properly and to make sure not trees or utility poles are sprouting from the vehicle.

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"What are the odds that the stems will randomly all match location" - depends on what you mean by "match". Within two degrees ? one degree ? Some people (artists and engineers usually) can measure very closely by eye. Others can't. As said, all it takes is a jack.

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OP is among the silliest/wierdest/stupidest ?'s I have seen posted here for a while. Since a valve stem can be in 360 different locations around a rim (or more if you split degrees in half or more), and considering the degree of accuracy one would need to "exactly" park in same spot (i.e. within what tolerance, a millimeter?), the precision needed to even test the theory would be a nightmare. Even rolling a car forward 5 feet and then back would be a major challenge to get in precisely the same spot. I hope next time you wake up in the middle of the night you aren't faced with a more logic based question " If your fish tank has 12 goldfish and all but 9 die, how many do you have left?" LOL

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20 hours ago, Real Steel said:

The valve stem will stop in the same clock position only if the distance rolled by THAT wheel is an exact multiple of that wheels circumference (c).

 

However, there are many variables in the driving experience that can influence minute changes in the number of wheel revolutions when compared to the distance rolled (tire pressures, pot holes, turns...its a long list).  These variables will certainly mess-up your calculations!

 

Compressible rubber tires on vehicles means that you must measure from the center of the hub to the ground in order to determine the wheels radius (r).  For cars, r is not the overall diameter divided by 2 (as with theoretical math). 

 

c = 2 π r.

 

π = 3.14

 

Don't forget to keep all your calculations in the same unit of measure ('inches' for example).

 

This should give you enough ammo to play, and to help you sleep better at night.

If your kids ask whey you're laying down in the street with a measuring tape...tell them your doing math.

 

 

 

 

 

 

Interesting. I was taught pie r squared. I know it’s the same, just never saw it expressed as 2 pie r.

(Don’t have the proper pie or squared keys on my phone). 

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