Author Topic: Tire Circumference  (Read 540 times)

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tooseevee

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on: September 07, 2020, 01:48:04 pm
       I've got a simple question, no, two.

          (1) Does a tire increase in circumference as it goes from 0 internal pressure to operating pressure?

           and (B) What websites can be trusted on this subject?

           I thought of a 3rd one: (3) Are there ANY websites now that you can trust on ANYthing  :) ? ??? ???

           I wonder if my garbage guy is going to come today ???
« Last Edit: September 07, 2020, 01:53:44 pm by tooseevee »
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DavidGraves

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Reply #1 on: September 07, 2020, 03:08:13 pm
Most do yes...

And to some degree a tire will expand with RPM.

The human may not notice it.

Certain drag racing slicks for cars were designed to change diameter on Rev and essentially provided a gear change down the track.

But you knew this eh ?

DG


AzCal Retred

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Reply #2 on: September 07, 2020, 03:18:15 pm
I think I'd need a nitrous infused blower & new-crank-auto-injection to ever see this phenomenon on my trusty Bullet!  :D  - ACR -

"The science behind the massive 48-pound Top Fuel tires | 2018 NHRA DRAG RACING"

https://www.youtube.com/watch?v=6N8NXpvHWW0
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tooseevee

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Reply #3 on: September 07, 2020, 04:18:51 pm
Most do yes...

And to some degree a tire will expand with RPM.

The human may not notice it.

Certain drag racing slicks for cars were designed to change diameter on Rev and essentially provided a gear change down the track.

But you knew this eh ?

DG

           Nope, I don't mean expansion from a Don Garlit's trip "through the Christmas Tree"  :) :) :) 

            I mean just sittin' there. And would the increase be measurable with instruments that use light waves and not electrons  :)

            I don't think there's any increase at all that a tape measure would care about. And I'm talking reasonable pressure not blow up an oxygen tank pressure.

            And dontcha' just love a 1/2 hour of Top Fuel once in a while?  :)[/img] They're like insane wild animals that would love to kill and eat you. Stainless Steel Rats.
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Toni59

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Reply #4 on: September 07, 2020, 05:57:36 pm
Well, regarding your first question:

     
          (1) Does a tire increase in circumference as it goes from 0 internal pressure to operating pressure?
         

I would say it depends on what you mean:

If you ask, whether the radius from the axle to the ground is changing with internal pressure - the answer is obviously yes, this measure is growing with increasing pressure from 0 bar to nominal or an even higher pressure.

This is by the way how modern Tire Pressure Monitoring Systems are detecting with the inverse method an air loosing wheel:
Revolution of each wheel is compared among all wheels, and if one has higher revolution it is losing air.

As you can see, the difference is significant...


Regards
Toni




tooseevee

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Reply #5 on: September 07, 2020, 06:42:28 pm

This is by the way how modern Tire Pressure Monitoring Systems are detecting with the inverse method an air loosing wheel:
Revolution of each wheel is compared among all wheels, and if one has higher revolution it is losing air.

As you can see, the difference is significant...


Regards
Toni

           Would you expand on that a bit?

           

            "higher revolution"?
 
              Do you mean: 'RPM of each wheel is compared among all wheels and if one has a higher RPM it is LOSing air"?
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Toni59

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Reply #6 on: September 07, 2020, 08:31:12 pm
Exactly.

I mean the wheel rotations. May be I have used a wrong expression, sorry for that.

There is a sensor at every wheel measuring the rotations and comparing them with all the other wheels.

This is the reason, why you also have to tell the system when you have the correct pressure in the tires.

Lower pressure means „smaller“ diameter means more rotations to reach a certain velocity...

Regards
Toni


DavidGraves

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Reply #7 on: September 16, 2020, 01:07:43 am
And I always thought the special tire valve stems had little radios in them transmitting a pressure reading....are you saying they are only transmitting a signal for tire rotation?

Where is the sensor for that signal ? in the fender or some fixed point adjacent to the wheel/tire ?


Tooseevee...Why did you want to know ?  When one inflates a tire from this pressure to that higher pressure one can see the increase in diameter.
« Last Edit: September 16, 2020, 01:10:35 am by DavidGraves »


Richard230

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Reply #8 on: September 16, 2020, 02:07:25 pm
And I always thought the special tire valve stems had little radios in them transmitting a pressure reading....are you saying they are only transmitting a signal for tire rotation?

Where is the sensor for that signal ? in the fender or some fixed point adjacent to the wheel/tire ?


Tooseevee...Why did you want to know ?  When one inflates a tire from this pressure to that higher pressure one can see the increase in diameter.

On my BMW RS the air pressure sensor is contained in a sealed box located in the center of the drop rim below the air valve, which is installed in one of the cast aluminum spokes, facing outward. The box contains a battery and transmitter, which activates when the wheel starts to rotate. Naturally, the battery is not replaceable and the entire device must be replaced as a unit for big BMW Bucks when the battery dies. And then it must be programmed and linked to the CPU of your bike by a franchised BMW dealer, using a computer link to BMW's factory service computer system. More big BMW Bucks. Fortunately, the battery seems to be quite long-lasting and I haven't heard of very many people needing to replace the device. On my bike they got it adjusted very well at the factory and it reports pressure that is within one PSI of what I measure in my garage with an accurate gauge. Plus, it compensates for changes in tire/wheel temperature as the tire and atmosphere warms up and of course alerts the rider via the instrument display if the tire's air pressure drops below a certain point while you are riding. (It is one more thing that you have to deal with when changing and balancing the tire.)
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Bilgemaster

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Reply #9 on: September 16, 2020, 02:34:45 pm
           Would you expand on that a bit?         

            "higher revolution"?
 
              Do you mean: 'RPM of each wheel is compared among all wheels and if one has a higher RPM it is LOSing air"?

Circumference of circle = π x diameter of circle. This is typically written as C = πd. Lesser diameter (lower "d") means lesser circumference, and hence more revolutions to roll a given distance.
« Last Edit: September 16, 2020, 04:11:15 pm by Bilgemaster »
So badass my Enfield's actually illegal  in India.

Legal enough to pass muster if they don't look too closely in Woodbridge, Virginia, where the buses don't run at night, holidays or weekends


Toni59

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Reply #10 on: September 16, 2020, 05:47:27 pm
The sensor for counting rotations can just be the already existing ABS sensors.

Just let them count the rotation of each wheel, and if the figures are in a certain, defined and allowed window at a  given speed all wheels must have same conditions.

You don‘t even need additional hardware - it is just a software feature....

Regards
Toni


tooseevee

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Reply #11 on: September 17, 2020, 12:54:33 am
Circumference of circle = π x diameter of circle. This is typically written as C = πd. Lesser diameter (lower "d") means lesser circumference, and hence more revolutions to roll a given distance.

           I understand all the math involved. My question was not about the math. It was about the semantics.
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tooseevee

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Reply #12 on: September 17, 2020, 01:06:31 am

Tooseevee...Why did you want to know ?  When one inflates a tire from this pressure to that higher pressure one can see the increase in diameter.

        Mostly because I just wanted to see what all the answers would be.

        But what I was thinking one morning about 3:30 is that if you had one of those digital Hall-effect bye-cycle computers*, the speedo-meter would only be accurate at the tire pressure you had when you laid out your measurement of tire circumference. Plus, in theory, the tire would increase in circumference with the increase in RPM.

         You can only enter ONE number for circumference and that number is derived with the tire at rest and at a given air pressure and temperature. And elevation.

         I know. I know. The difference is microscopic and it doesn't matter!  :) :)

         * Which I have had on 2 motorcycles.
« Last Edit: September 17, 2020, 01:12:35 am by tooseevee »
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DavidGraves

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Reply #13 on: September 17, 2020, 02:03:54 am
Thanks for that...eh, I guess...wait !... MY Brain hurts again !!

Somehow I thought you were just asking whether a tire got taller with more air pressure......

Nevermind.... 


tooseevee

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Reply #14 on: September 17, 2020, 03:20:25 am
Thanks for that...eh, I guess...wait !... MY Brain hurts again !!

Somehow I thought you were just asking whether a tire got taller with more air pressure......

Nevermind....


          Well, yeah. I was  :) I guess  ;)

           
'08 Black AVL Classic.ACEhead 9.8:1/manifold/canister. TM32/Open short bottle/hot tube removed. Pertronix Coil. Fed mandates removed. Gr.TCI. Bobber seat. Battery in right side case. Decomp&all doodads removed. '30s Lucas taillight/7" visored headlight. Much blackout & wire/electrical upgrades