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#41
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Does a tyre change its CIRCUMFERENCE when underinflated?
On 23/06/2018 17:04, The Natural Philosopher wrote:
On 23/06/18 14:28, John Rumm wrote: On 23/06/2018 06:56, The Natural Philosopher wrote: https://www.youtube.com/watch?v=_2l5bOhHNxU Answer. not by very much, if at all. So the short answer to your question is "yes". This seems to be a perpetual urban myth. Which you have just agreed with by claiming there is a small change. No the urban myth says that since there is say a 10% change in what peooplle think is 'the radius', therefore the RPM will be 10% slower. Make up your own myths if you like... The 1% seems plausible enough for me. Can't see that being too difficult in itself - especially as you probably have input from other sensors and know the steering angle input Â*Â*and so can assess when you are driving straight and not under high acceleration etc. Why would there be monitors on steering angle? Stability control programs, collision avoidance system, traction control and various other systems will use it. Type pressure monitoring will need to be more sensitive to rate of change than absolute difference since unequal tyre wear would otherwise be flagged. Well teh way it aseems to work is that one wheel will overotate with respect to its diagonalÂ* consisetntly. Splembib! But not by very much. We like that. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#42
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
On 23/06/2018 17:07, The Natural Philosopher wrote:
On 23/06/18 14:50, Huge wrote: On 2018-06-23, John Rumm wrote: On 23/06/2018 06:56, The Natural Philosopher wrote: https://www.youtube.com/watch?v=_2l5bOhHNxU Answer. not by very much, if at all. So the short answer to your question is "yes". This seems to be a perpetual urban myth. I just love watching Turnip arguing that a system that exists, is in production and works is an "urban myth". What next, Flat Earth? Oh dear. What I was arguing was that the reason the systemn works is not what people here believe. If you told me that essence of angel was what was in antibiotics and they fought the demons in the pus, it doesnt mean that I disagree that antibiotics cure infections, when I tell you you are talking ********. But basic logic is another thing that has passed you by it seems. Well you were the one to introduce circumference into this, a value which is irrelevant to the relationship between the 2 things measured (the vehicles speed and the angular velocity of the wheel) and what relates them (the rolling radius). The irrelevance of the circumference can be seen by looking at caterpillar tracks. Ignoring slippage etc a 20m track goes round once when the vehicle moves 20m. But that's true whether it is attached to wheels with a radius of 0.5m or 0.25m. So the circumference tells you nothing about the relationship between speed and the RPM of the wheels. On the other hand, the (effective) radius of the wheels does. -- Robin reply-to address is (intended to be) valid |
#43
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
On 23/06/2018 18:33, Tim Streater wrote:
In article , Robin wrote: Well you were the one to introduce circumference into this, a value which is irrelevant to the relationship between the 2 things measured (the vehicles speed and the angular velocity of the wheel) and what relates them (the rolling radius). The irrelevance of the circumference can be seen by looking at caterpillar tracks.Â* Ignoring slippage etc a 20m track goes round once when the vehicle moves 20m.Â* But that's true whether it is attached to wheels with a radius of 0.5m or 0.25m.Â* So the circumference tells you nothing about the relationship between speed and the RPM of the wheels. On the other hand, the (effective) radius of the wheels does. Aren't you overlooking that, with a track, the wheel is only in contact with a part of the track. Whereas with a flat tire, even though the shape of the tire changes, the wheel is still in touch with the tire all the way round (the entire tire, IOW (phew!)). Thus TNP is right to say that, inflated or not, for one revolution of the wheel, the whole circumference of the tire rotates once. Or, to put it another way, any spot on the tire circumfernce will touch the road just once. (ignoring slippage on the road, or slippage between the tire itself and the wheel). Yep. But that's just another way of saying that with a tyre on a wheel the fact that the rolling radius changes with pressure means the "rolling circumference"[1] also changes with pressure. As TNP admitted. So I was and am still unclear why he asked about the circumference. I thought at first it might be because he thought that the steel cords/belts in tyres are like caterpillar tracks. But it can't be that when he volunteered there is an effect. Of course I may well be missing something. But I _know_ I'm - hic - missing the bottle downstairs, so ... [1] TM TNP? -- Robin reply-to address is (intended to be) valid |
#44
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
GB wrote
Robin wrote That ruling in 2001 was in the context of what could and couldn't meet a statutory requirement in the USA for pressure monitoring in new cars that also alerted if more than one tyre - including all 4 tyres equally - are 25% or more below pressure. It's no surprise that indirect methods couldn't meet that requirement. If the car has sat nav installed and available to the car's computer, as many do now, the speed across the ground could be compared to the wheel rotation. That could detect all 4 wheels being equally underinflated. Maybe. gps speed isnt that accurate in the short distances. And if you get 4 new tyres at a time, as many do, and the tyre place underinflates all of them by the same amount, and the tyres are a bit different profile wise to the previous set, its going to be hard for the system to work out that they are all underinflated. And thats the main situation where all 4 would be equally under inflated. But, that's 2018, not 2001. |
#45
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
"Chris Hogg" wrote in message news On Sat, 23 Jun 2018 17:04:38 +1000, "Jeff" wrote: "Chris Hogg" wrote in message . .. On Sat, 23 Jun 2018 16:08:44 +1000, "Jeff" wrote: "The Natural Philosopher" wrote in message news https://www.youtube.com/watch?v=_2l5bOhHNxU Answer. not by very much, if at all. But the radius clearly does vary significantly. Does it? It clearly does with the distance between the axle and the ground. I think we're at cross-purposes here. Obviously, as you say, when a tyre is flat, the axle is nearer the ground. But is it reasonable to regard that as the radius of the tyre? It is the only distance that matters with the rotation speed of the wheel. The distance between the axle and the top of the tyre is irrelevant to that. If you simplify the shape and call it an ellipse, then you have two radii; quite how many radii would be needed to describe a tyre with a flat on one side, I wouldn't like to speculate. But those distances are irrelevant to the rotation speed of the wheel. But the circumference, perhaps perimeter would be a better word, won't have changed significantly. It'll just become distorted, i.e. no longer circular. Yes, but that isnt what determines the rotation rate of the wheel. But that assumes there is a weight pressing down on the tyre, which I grant you, would be the case for a loaded tyre on a vehicle. But I was thinking of an unloaded tyre; Its irrelevant when deciding if the tyre is under inflated. does the circumference change between under-inflated and fully- or even over-inflated? Not by much at all with steel belted radials and any system that detects under inflated tyres has to work with those. When I were a lad in the days when tyres had inner tubes, we used to go to our local garage and get old tubes that were no longer serviceable, patch them where necessary, inflate then and use them as super-sized rubber rings for taking down to the beach (and probably getting blown out to sea!). As they were inflated, the radius and circumference most certainly did increase; they blew up like a balloon. But put them into a tyre and there'd be no significant change in the circumference as they inflated and deflated. The structure of the tyre wouldn't allow that to happen. Likewise, I suggest that the circumference (perimeter if you prefer) of a modern tubeless tyre doesn't change significantly as it inflates or deflates. Yes, but the circumference isnt what determines the rotation rate of the tyre on a moving car. Every full rotation of the hub must correspond to a full rotation of the perimeter, regardless of the state of inflation of the tyre, otherwise serious slippage will be occurring between the tyre and the rim, which would result in friction heating and fairly rapid failure. Yes, but the circumference doesn't determine the rotation rate of the tyre. So as far as speedometers and odometers are concerned, state of inflation won't make a significant difference. That's arguable with the very small variations being discussed. (What amounts to 'significant' as I've used it here, I'm not sure; it depends on the pressure difference being considered between under and fully inflated, and the elasticity of the structures within the treaded surface of the tyre, amongst other things, but others in this thread have mentioned figures of around 1% for the stretching of the perimeter as the tyre is inflated. In this context, I would regard that as not significant). But someone must have checked that the ABS rotation rate does change with under inflated tyres otherwise that wouldn't be used to detect under inflated tyres. |
#46
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
On Sun, 24 Jun 2018 04:55:50 +1000, cantankerous geezer Rot Speed blabbered,
again: If the car has sat nav installed and available to the car's computer, as many do now, the speed across the ground could be compared to the wheel rotation. That could detect all 4 wheels being equally underinflated. Maybe. gps speed isnt that accurate in the short distances. And if you get 4 new tyres at a time, as many do, and the tyre place underinflates all of them by the same amount, and the tyres are a bit different profile wise to the previous set, its going to be hard for the system to work out that they are all underinflated. And that¢s the main situation where all 4 would be equally under inflated. Darn, Mr Know-it-all has it all worked out, yet again! LOL -- Archibald Tarquin Blenkinsopp addressing Rot Speed: "You really are a clueless pillock." MID: |
#47
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
"harry" wrote in message ... On Saturday, 23 June 2018 06:56:49 UTC+1, The Natural Philosopher wrote: https://www.youtube.com/watch?v=_2l5bOhHNxU Answer. not by very much, if at all. This seems to be a perpetual urban myth. It tyre pressure sensors are using this, it has to be a very very complicated bit of software to detect - say - less than 1% change in RPM relative to the other wheels. https://en.wikipedia.org/wiki/Centra...flation_system Bit weird with the retrofitted stuff https://www.dropbox.com/s/yj56jztegr...93fa6.jpg?dl=0 Cant see that surviving too long off road here. |
#48
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
"The Natural Philosopher" wrote in message news On 23/06/18 08:09, Jeff wrote: "The Natural Philosopher" wrote in message news On 23/06/18 07:08, Jeff wrote: "The Natural Philosopher" wrote in message news https://www.youtube.com/watch?v=_2l5bOhHNxU Answer. not by very much, if at all. But the radius clearly does vary significantly. This seems to be a perpetual urban myth. It can't be given that Andy and others have had a number of warnings that have turned out to be accurate every time. It tyre pressure sensors are using this, it has to be a very very complicated bit of software to detect - say - less than 1% change in RPM relative to the other wheels. Yes, but that isn't hard to measure when its relative to other wheels. A piece of online research [https://one.nhtsa.gov/cars/rules/rul...prmonsys.html] showed that relative wheel rotation was pretty crap at detecting low tyre pressures especially in all 4 wheels or 2 wheels on the same side (= I am going round and round in circles!) Hence the move to in wheel sensors. I am notr syoing it doesn't work, just that it relies on some pretty iffy interpreation of very small differences in road speed. Tyre tread belts do strech under inflation, but not by much. The radius is completely irrelevant as a road weheel is not, in use, round and does not have a 'radius.' Of course it does at the only place that matters, between the axle and the road. Oh dear. Oh dear oh dear. You just dont get it, do you? It is you that doesnt. That distance is the only thing that matters, it is what determines the rotation rate of the wheel, exactly the same way the diameter of the wheel determines the rotation rate of the wheel, but in this case that radius clearly does vary with the pressure in the tyre. What happens with the rest of the tyre is completely irrelevant. |
#49
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
"The Natural Philosopher" wrote in message news On 23/06/18 09:34, Jeff wrote: "Tim Lamb" wrote in message ... In message , Jeff writes "The Natural Philosopher" wrote in message news On 23/06/18 07:08, Jeff wrote: "The Natural Philosopher" wrote in message news https://www.youtube.com/watch?v=_2l5bOhHNxU Answer. not by very much, if at all. But the radius clearly does vary significantly. This seems to be a perpetual urban myth. It can't be given that Andy and others have had a number of warnings that have turned out to be accurate every time. It tyre pressure sensors are using this, it has to be a very very complicated bit of software to detect - say - less than 1% change in RPM relative to the other wheels. Yes, but that isn't hard to measure when its relative to other wheels. A piece of online research [https://one.nhtsa.gov/cars/rules/rul...prmonsys.html] showed that relative wheel rotation was pretty crap at detecting low tyre pressures especially in all 4 wheels or 2 wheels on the same side (= I am going round and round in circles!) Hence the move to in wheel sensors. I am notr syoing it doesn't work, just that it relies on some pretty iffy interpreation of very small differences in road speed. Tyre tread belts do strech under inflation, but not by much. The radius is completely irrelevant as a road weheel is not, in use, round and does not have a 'radius.' Of course it does at the only place that matters, between the axle and the road. I've been thinking that but... unless the effective circumference is changed, the tread in contact with the road surface will not alter. Steel bracing etc. as mentioned above. I'm not convinced that it is the circumference that determines the rotation rate of the wheel. Well unless the tyre is slipping on the rim or in the road, there is no way anyuthing else can. And those who actually measured it talk about the rolling radius, for a reason and must have done the most basic tests of watching the rotation rate as the tyre pressure varies, and see that it does vary by enough to measure. No, the world is full of stupid people pretending to be clever. The 'effective rolling radius' is the circumference divided by 2 PI. Not when the wheel and tyre isnt a perfect circle and it never is with a vehicle wheel and inflated tyre. Trying to make a squashed dougnut into a circle doesnt really fit though. Maybe there is some perceptible scrubbing going on. Why should there be any significant scrubbing with say a 20% lower pressure in the tyre ? Excatly. And yet those that say that the radius has altered by 20% and yet the circumferemce hasn't altered at all, have only one way to make the RPM rise by the amount they say the radius has rteduced. Introduce tyre scrub. No need for any tyre scrub, just the reduced radius under the axle. That is what determines the rotation rate of the wheel. |
#50
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
"The Natural Philosopher" wrote in message news On 23/06/18 14:28, John Rumm wrote: On 23/06/2018 06:56, The Natural Philosopher wrote: https://www.youtube.com/watch?v=_2l5bOhHNxU Answer. not by very much, if at all. So the short answer to your question is "yes". This seems to be a perpetual urban myth. Which you have just agreed with by claiming there is a small change. No the urban myth says that since there is say a 10% change in what peooplle think is 'the radius', therefore the RPM will be 10% slower. No one said that the change will be the same percentage, just that when the distance between the axle and the ground changes, that the rotation rate will change and that change can be measured. It tyre pressure sensors are using this, it has to be a very very complicated bit of software to detect - say - less than 1% change in RPM relative to the other wheels. Can't see that being too difficult in itself - especially as you probably have input from other sensors and know the steering angle input and so can assess when you are driving straight and not under high acceleration etc. Why would there be monitors on steering angle? Type pressure monitoring will need to be more sensitive to rate of change than absolute difference since unequal tyre wear would otherwise be flagged. Well teh way it aseems to work is that one wheel will overotate with respect to its diagonal consisetntly. But not by very much. But enough to measure with RPM so easy to measure differentially. |
#51
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
"pamela" wrote in message ... On 17:01 23 Jun 2018, The Natural Philosopher wrote: On 23/06/18 13:42, Chris Hogg wrote: On Sat, 23 Jun 2018 17:04:38 +1000, "Jeff" wrote: "Chris Hogg" wrote in message ... On Sat, 23 Jun 2018 16:08:44 +1000, "Jeff" wrote: "The Natural Philosopher" wrote in message news https://www.youtube.com/watch?v=_2l5bOhHNxU Answer. not by very much, if at all. But the radius clearly does vary significantly. Does it? It clearly does with the distance between the axle and the ground. I think we're at cross-purposes here. Obviously, as you say, when a tyre is flat, the axle is nearer the ground. But is it reasonable to regard that as the radius of the tyre? Not if you have any understanding of mechanics. The whole tread, up to and including a caterpillar track, goes round once per revolution of the track or tyre. Surely the circumference changes because the area in contact with the road is a chord and not an arc. Nope, not when the circumference doesn’t stretch and it doesn’t with steel belted radials. The length of the chord increases when the tyre is underinflated on account of compression of more of the former arc in contact with the road. The circumference is reduced. Not with steel belted radials. Only if all the compression of the former arc occurs at the leading edge of contact would the speed be unaffected. The circumference is irrelevant. What determines the rotation rate of the wheel is the distance between the axle and the road. THAT is what determines the RPM/speed relations ship. What happens with tyre pressures is quite clear. The tread stretches slightly under higher pressures. How much will be a function of the tyre construction. And this is what the sensors rely on. Since no wheel is circular using radius as a concept is plain wrong. At best you can calcualate a '*radius it would be if it were round*,' from the actual circumference. For it to be any other way the tyre must slip on the rim or on the road, substantially. |
#52
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
On 23/06/2018 21:47, Tim Streater wrote:
snip Dunno what "rolling circumference" means, but the circumference can't change, as it is fixed by the loops of steel belts in the tire (may stretch a bit but not much). *That* is the point. Three points: a. you seem to be assuming the steel is perfectly inelastic. When it usually is made up of thin steel wires woven into cords and then into belts I'd like to know it's actual modulus; b. I posted a link to a paper which modelled tyres and reproduced observed pressure effects. It noted that "the belt structure strongly influences the effective rolling radius". But it also pointed to the effects of pressure on the deformation of the tread - ie the stuff between the belts and road. It seems to me credible that behaves differently with changes in pressu eg just look at the sidewall when pressure is low; c. I introduced the term "rolling circumference" because how iTPMS works can be discussed perfectly well without any reference to circumference. So ISTM it behoves those who introduce "circumference" into it to define what they mean. The circumference of the static, unloaded tyre? Or the distance travelled for one rotation of the wheel - which all the evidence shows does vary with pressure? -- Robin reply-to address is (intended to be) valid |
#53
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
On Sun, 24 Jun 2018 07:12:45 +1000, cantankerous geezer Rot Speed blabbered,
again: Not if you have any understanding of mechanics. The whole tread, up to and including a caterpillar track, goes round once per revolution of the track or tyre. Surely the circumference changes because the area in contact with the road is a chord and not an arc. Nope, I KNEW it! LMAO -- Sqwertz to Rot Speed: "This is just a hunch, but I'm betting you're kinda an argumentative asshole. MID: |
#54
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
On Sun, 24 Jun 2018 06:33:28 +1000, cantankerous geezer Rot Speed blabbered,
again: https://en.wikipedia.org/wiki/Centra...flation_system Bit weird with the retrofitted stuff https://www.dropbox.com/s/yj56jztegr...93fa6.jpg?dl=0 Cant see that surviving too long off road here. Let's hope you won't survive long here, Rot! Just keep bull****ting your way into your grave! There's nothing else left for you to do. BG -- Cursitor Doom about Rot Speed: "The man is a conspicuous and unashamed ignoramus." MID: |
#55
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
On Sat, 23 Jun 2018 21:47:33 +0100, Tim Streater
wrote: snip Dunno what "rolling circumference" means, but the circumference can't change, as it is fixed by the loops of steel belts in the tire (may stretch a bit but not much). But the 'belt's' are parallel loops around the circumference of the tyre but woven diagonally and so form a parallelogram. This parallelogram can change it's shape slightly and therefore allow the tyre to become bigger or smaller due to pressure or whilst carrying a load. *That* is the point. You wouldn't get the point unless it was stuck in you by someone else. ;-) Cheers, T i m |
#56
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
On 23/06/18 17:17, The Natural Philosopher wrote:
On 23/06/18 17:13, Andy Burns wrote: The Natural Philosopher wrote: Why would there be monitors on steering angle? For the stability control system. But once they're a standard part of the car you can use feed the data to other systems, such as overlaying the curves on the reversing camera display, or knowing when you're travelling straight and therefore the TPMS doesn't have to worry about different wheel speeds caused by the action of a differential. All to modern for me. Never seen steering angle sensed yet on any car I've driven. https://www.knowyourparts.com/techni...r-diagnostics/ |
#57
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
On 23/06/18 17:40, John Rumm wrote:
On 23/06/2018 17:04, The Natural Philosopher wrote: On 23/06/18 14:28, John Rumm wrote: On 23/06/2018 06:56, The Natural Philosopher wrote: https://www.youtube.com/watch?v=_2l5bOhHNxU Answer. not by very much, if at all. So the short answer to your question is "yes". This seems to be a perpetual urban myth. Which you have just agreed with by claiming there is a small change. No the urban myth says that since there is say a 10% change in what peooplle think is 'the radius', therefore the RPM will be 10% slower. Make up your own myths if you like... The 1% seems plausible enough for me. Can't see that being too difficult in itself - especially as you probably have input from other sensors and know the steering angle input Â*Â*and so can assess when you are driving straight and not under high acceleration etc. Why would there be monitors on steering angle? Stability control programs, collision avoidance system, traction control and various other systems will use it. Type pressure monitoring will need to be more sensitive to rate of change than absolute difference since unequal tyre wear would otherwise be flagged. Well teh way it aseems to work is that one wheel will overotate with respect to its diagonalÂ* consisetntly. Splembib! But not by very much. We like that. |
#58
Posted to uk.d-i-y
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Does a tyre change its CIRCUMFERENCE when underinflated?
On 23/06/18 17:01, The Natural Philosopher wrote:
On 23/06/18 13:42, Chris Hogg wrote: On Sat, 23 Jun 2018 17:04:38 +1000, "Jeff" wrote: "Chris Hogg" wrote in message ... On Sat, 23 Jun 2018 16:08:44 +1000, "Jeff" wrote: "The Natural Philosopher" wrote in message news https://www.youtube.com/watch?v=_2l5bOhHNxU Answer. not by very much, if at all. But the radius clearly does vary significantly. Does it? It clearly does with the distance between the axle and the ground. I think we're at cross-purposes here. Obviously, as you say, when a tyre is flat, the axle is nearer the ground. But is it reasonable to regard that as the radius of the tyre? Not if you have any understanding of mechanics.Â* The whole tread, up to and including a caterpillar track, goes round once per revolution of the track or tyre. THAT is what determines the RPM/speed relations ship. A revolution is the movement of one object (*point* on circumference) around a centre (hub). Your caterpillar track is supported by wheels, each of which will do many revolutions for one revolution of the track. The circumference of the track is many times the circumference of each wheel. What happens with tyre pressures is quite clear. The tread stretches slightly under higher pressures. How much will be a function of the tyre construction. And this is what the sensors rely on. No. Since no wheel is circular using radious as a concept is plain wrong. At best you can calcualate a '*radius it would be if it were round*,' from the actual circumference. The use of radius is completely right. The circumference doesn't change. The centre of the instantaneous circle moves closer to the radius. The tyre is a three dimensional structure and this debate is being conducted in a two dimensional manner. For it to be any other way the tyre must slip on the rim or on the road, substantially. |
#59
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Does a tyre change its CIRCUMFERENCE when underinflated?
On Sat, 23 Jun 2018 16:51:02 +0100, The Natural Philosopher
wrote: snip No, the world is full of stupid people pretending to be clever. Oh the irony! The 'effective rolling radius' is the circumference divided by 2 PI. Trying to make a squashed dougnut into a circle doesnt really fit though. Quite. Try measuring the circumference of something that isn't circular. Maybe there is some perceptible scrubbing going on. Why should there be any significant scrubbing with say a 20% lower pressure in the tyre ? Excatly. Exactly, there isn't. And yet those that say that the radius has altered by 20% and yet the circumferemce hasn't altered at all, have only one way to make the RPM rise by the amount they say the radius has rteduced. Yup. Introduce tyre scrub.] Nope. It's like climate change all over again. Facts dont fit the theory, so introduce 'feeedback' Bwhahaha. Look into how the steel wire is laid in a steel belted radial tyre and check out 'pantographing'. Cheers, T i m |
#60
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Does a tyre change its CIRCUMFERENCE when underinflated?
On Sun, 24 Jun 2018 06:43:16 +1000, "Jeff" wrote:
snip No, the world is full of stupid people pretending to be clever. snip Excatly. And yet those that say that the radius has altered by 20% and yet the circumferemce hasn't altered at all, have only one way to make the RPM rise by the amount they say the radius has rteduced. Introduce tyre scrub. No need for any tyre scrub, just the reduced radius under the axle. I wonder if Turnip actually climbed out of his basement once in a while he's see all these things in action ITRW and realise just how stupid *he* is being? That is what determines the rotation rate of the wheel. Quite. I believe the regs for these tyre pressure sensors are that they should react before the pressure has changed by no more than 25%. Many tyres are run at that sort of reduced pressure (slow punctures, no TPMS) and would have to be 'scrubbed away' in no time. They aren't, so it's something else, something Turnip doesn't understand so it doesn't exist. ;-( Cheers, T i m |
#61
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Does a tyre change its CIRCUMFERENCE when underinflated?
The hight of the axle is reduced - therefore the effective radius is
reduced and therefore its effective circumference. The part of the tire not in contact with the ground is irrelevant. |
#62
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Does a tyre change its CIRCUMFERENCE when underinflated?
On Sunday, 24 June 2018 16:16:29 UTC+1, DerbyBorn wrote:
The hight of the axle is reduced - therefore the effective radius is reduced and therefore its effective circumference. The part of the tire not in contact with the ground is irrelevant. I DO get what TNP is saying. Consider a fully inflated tyre with a mark on the tread area. That mark will always be at the same relative angle to the wheel, otherwise the tyre would be sliding on the wheel rim. The wheel rotates one revolution. Measure the distance between the first and second points where the mark touches the road. Now partially deflate the tyre so that the distance between the axle and the road is much less. Repeat the measurement. The distance along the road will be almost exactly the same as before because the circumference of the tyre has not changed significantly due to all the steel wire in it and the tyre is not scrubbing against the road surface. In both cases the wheel rotates exactly one revolution - the tyre is not slipping on the wheel rim - and the distance traversed in that rotation has hardly changed. So the "effective radius" has hardly changed, even though the radial distance from axle to road has changed considerably. It really is the circumference (or perimeter) of the tyre that matters, not how much the axle has dropped relative to the road. John |
#63
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Does a tyre change its CIRCUMFERENCE when underinflated?
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#64
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Does a tyre change its CIRCUMFERENCE when underinflated?
On Sunday, 24 June 2018 18:16:52 UTC+1, T i m wrote:
True ... so, it's either witchcraft, or your assumption that the *effective* circumference (how far the vehicles travels per revolution) must be wrong? Because of the way the steel wire is laid up in the tyre they tend to cross and form a parallelogram. As the tyre deflects the shape of the tyre changes and therefore causes an effective change in circumference (more accurately, how far the vehicle travels per wheel revolution (down to pantographing)). The smaller the distance the smaller the effective circumference (or effective rolling or load radius as it's known) and to the faster the wheel will spin for a fixed ground speed of the vehicle. Everyone seems very fixed in their ideas about this. However, a simple experiment should be informative. Take a spare tyre. Wrap a tape measure around the circumference along the centre of the tread area. Measure the circumference. Place a plank through the tyre and stand on the ends. The tyre will deform in a similar way to a deflated tyre on a wheel. Re-measure the circumference. The air pressure will not have changed, so if "pantographing" has taken place the circumference will be significantly reduced and that change will be attributable purely to such shape factors. If on the other hand the circumference is not significantly altered then "pantographing" is not an important factor. Does that experiment seem valid? John |
#65
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Does a tyre change its CIRCUMFERENCE when underinflated?
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#66
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Does a tyre change its CIRCUMFERENCE when underinflated?
wrote in message ... On Sunday, 24 June 2018 16:16:29 UTC+1, DerbyBorn wrote: The hight of the axle is reduced - therefore the effective radius is reduced and therefore its effective circumference. The part of the tire not in contact with the ground is irrelevant. I DO get what TNP is saying. Consider a fully inflated tyre with a mark on the tread area. That mark will always be at the same relative angle to the wheel, otherwise the tyre would be sliding on the wheel rim. The wheel rotates one revolution. Measure the distance between the first and second points where the mark touches the road. Now partially deflate the tyre so that the distance between the axle and the road is much less. Repeat the measurement. The distance along the road will be almost exactly the same as before because the circumference of the tyre has not changed significantly due to all the steel wire in it and the tyre is not scrubbing against the road surface. In both cases the wheel rotates exactly one revolution - the tyre is not slipping on the wheel rim - and the distance traversed in that rotation has hardly changed. So the "effective radius" has hardly changed, even though the radial distance from axle to road has changed considerably. It really is the circumference (or perimeter) of the tyre that matters, not how much the axle has dropped relative to the road. And yet if you consider a solid wheel, no tyre, it is the distance between the axle and the road that determines the rate at which it rotates at the same speed of the car over the ground. So when a wheel with tyre sees a reduction in the distance between the axle and the road due to a lower pressure in the tyre, you get the same change in the rotation rate of the wheel which is easy to measure with the ABS sensor on that wheel. |
#67
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Does a tyre change its CIRCUMFERENCE when underinflated?
On Sun, 24 Jun 2018 21:04:49 +0100, Andy Burns
wrote: wrote: Everyone seems very fixed in their ideas about this I think it all comes down to the distortion of the tyre and the reduced length of the flat chord BA vs the arc BPA that would exist if it wasn't loaded at all. http://the-contact-patch.com/book/road/c2020-the-contact-patch#figure-ERr the more heavily loaded, or the less pressure it's inflated with, the greater z will be, and the smaller the effective rolling radius, reading through to the end of that page gives chapter and verse formulae ... In short the flatter the tyre, the smaller the effective radius and the faster the wheel needs to rotate to keep up, which is what the sensors detect. Bingo. ;-) Pretty sure Turnip will still argue the case ... he's still arguing the that the world is flat. ;-) Cheers, T i m |
#68
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Does a tyre change its CIRCUMFERENCE when underinflated?
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#69
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Does a tyre change its CIRCUMFERENCE when underinflated?
On 24/06/18 22:18, Jeff wrote:
So when a wheel with tyre sees a reduction in the distance between the axle and the road due to a lower pressure in the tyre, you get the same change in the rotation rate of the wheel which is easy to measure with the ABS sensor on that wheel. No, you don't. a tyre and wheel is not a sun and planet reduction gear, the tyre is not rotating relative to the wheel, ergo every revolution of the wheel one circumference of tyre must move along the road. The ABS sensors do not detect a massive change in radius, but a small change in circumference due to the tread shrinking very slightly. |
#70
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Does a tyre change its CIRCUMFERENCE when underinflated?
"Tjoepstil" wrote in message news On 24/06/18 22:18, Jeff wrote: So when a wheel with tyre sees a reduction in the distance between the axle and the road due to a lower pressure in the tyre, you get the same change in the rotation rate of the wheel which is easy to measure with the ABS sensor on that wheel. No, you don't. Yes you do, as you should be able to see with a rim with no tyre at all. As the rim diameter changes, the rotation rate will obviously change. a tyre and wheel is not a sun and planet reduction gear, It is a rack and pinion tho. the tyre is not rotating relative to the wheel, Correct. ergo every revolution of the wheel one circumference of tyre must move along the road. Yes, but it is the distance between the axle and the road that determines the rotation rate. The ABS sensors do not detect a massive change in radius, but a small change in circumference due to the tread shrinking very slightly. They actually detect the substantial change in the rotation rate the is due to the substantial change in the distance between the axle and the road. |
#71
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Does a tyre change its CIRCUMFERENCE when underinflated?
On Mon, 25 Jun 2018 07:50:42 +0100, Chris Hogg wrote:
On Mon, 25 Jun 2018 15:50:06 +1000, "Jeff" wrote: Yes, but it is the distance between the axle and the road that determines the rotation rate. If the length of the perimeter of the tyre is say 1.5 metres, At what state of inflation? and the vehicle is travelling at 150 km/hr, that means the tyre rotates 100000 times per hour, or 1666.6 rpm, At what state of inflation? assuming no slippage between tyre and road or tyre and rim. Ok. There's no getting around that, See above. ;-) and there's no mention of state of inflation, But there should be as that's a key variable that affects the effective 'perimeter length. ;-) shape of the tyre or axle to road distance. No, but there should be as the shape of the tyre is instrumental in the calculation. On a solid tyre it wouldn't be because you have removed that variable. Do you also deny the change in tyre diameter on a dragster (and therefore rpm / mph)? https://www.youtube.com/watch?v=YViiNxnQTr8 What about this. Imagine some lunar rover module where the 'tyre' is made up of many completely independent segments. With the vehicle up on jacks you might measure the effective circumference of the wheel as the measurement made with a tape drawn around it. But put it under load and with it standing on one (sprung) segment. the RW radius of that segment at that time under that load will be less. Imagine that reduction in radius being passed round the wheel segment by segment and you could then see (hopefully) that the effective circumference would be calculable from the loaded radius and it *would* be very different from the unloaded one. Join those segments together on the outside by something plastic, like say thin balloon rubber and nothing really changes. Join them with something heavier but with the similar ability to 'give' and you have a pneumatic car tyre. ;-) Cheers, T i m |
#72
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Does a tyre change its CIRCUMFERENCE when underinflated?
"Chris Hogg" wrote in message ... On Mon, 25 Jun 2018 15:50:06 +1000, "Jeff" wrote: Yes, but it is the distance between the axle and the road that determines the rotation rate. If the length of the perimeter of the tyre is say 1.5 metres, and the vehicle is travelling at 150 km/hr, that means the tyre rotates 100000 times per hour, or 1666.6 rpm, assuming no slippage between tyre and road or tyre and rim. There's no getting around that, and there's no mention of state of inflation, shape of the tyre or axle to road distance. Yes, but it is the distance between the axle and the road that determines the rotation rate. |
#73
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Does a tyre change its CIRCUMFERENCE when underinflated?
In message , Jeff
writes "Chris Hogg" wrote in message .. . On Mon, 25 Jun 2018 15:50:06 +1000, "Jeff" wrote: Yes, but it is the distance between the axle and the road that determines the rotation rate. If the length of the perimeter of the tyre is say 1.5 metres, and the vehicle is travelling at 150 km/hr, that means the tyre rotates 100000 times per hour, or 1666.6 rpm, assuming no slippage between tyre and road or tyre and rim. There's no getting around that, and there's no mention of state of inflation, shape of the tyre or axle to road distance. Yes, but it is the distance between the axle and the road that determines the rotation rate. Why? Long time since 'O' level maths but I suspect the relationship between the radius and the perimeter only works for a perfect circle. -- Tim Lamb |
#74
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Does a tyre change its CIRCUMFERENCE when underinflated?
On Mon, 25 Jun 2018 18:47:14 +1000, "Jeff" wrote:
"Chris Hogg" wrote in message .. . On Mon, 25 Jun 2018 15:50:06 +1000, "Jeff" wrote: Yes, but it is the distance between the axle and the road that determines the rotation rate. If the length of the perimeter of the tyre is say 1.5 metres, and the vehicle is travelling at 150 km/hr, that means the tyre rotates 100000 times per hour, or 1666.6 rpm, assuming no slippage between tyre and road or tyre and rim. There's no getting around that, and there's no mention of state of inflation, shape of the tyre or axle to road distance. Yes, but it is the distance between the axle and the road that determines the rotation rate. When considering this sort of thing I first consider the real world facts. iTPMS systems obviously work. I believe the regs for such systems state that they must warn the driver of a pressure lost *before* it passes 25% of the pre-set pressure. This means that it must be accurately measurable so when a 32 psi tyre drops it's pressure to 24 psi (23?), it should raise the alarm. The instructions for calibrating cycle speedos require you to measure the *loaded* rolling circumference of the wheel bearing the speed sensor (when it would be easier just to put a tape round the wheel). So, a right brainer would take these sorts of things and then try to look for a scientific / mathematic solution as to why this is. A left brainer would jump to a conclusion based on their lack of understanding and then look for information to support their denial (from other left brainers typically). ;-) Cheers, T i m |
#75
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Does a tyre change its CIRCUMFERENCE when underinflated?
On 25/06/2018 10:12, T i m wrote:
snip So, a right brainer would take these sorts of things and then try to look for a scientific / mathematic solution as to why this is. A left brainer would jump to a conclusion based on their lack of understanding and then look for information to support their denial (from other left brainers typically). ;-) I don't think it helps to introduce another myth[1] - let alone a mirror image of the usual one [1] http://www.oecd.org/education/ceri/neuromyth6.htm -- Robin reply-to address is (intended to be) valid |
#76
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Does a tyre change its CIRCUMFERENCE when underinflated?
In article ,
Tjoepstil wrote: The ABS sensors do not detect a massive change in radius, but a small change in circumference due to the tread shrinking very slightly. What they detect is a change in speed of the wheel. -- *Why were the Indians here first? They had reservations.* Dave Plowman London SW To e-mail, change noise into sound. |
#77
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Does a tyre change its CIRCUMFERENCE when underinflated?
In article ,
Jeff wrote: "Chris Hogg" wrote in message ... On Mon, 25 Jun 2018 15:50:06 +1000, "Jeff" wrote: Yes, but it is the distance between the axle and the road that determines the rotation rate. If the length of the perimeter of the tyre is say 1.5 metres, and the vehicle is travelling at 150 km/hr, that means the tyre rotates 100000 times per hour, or 1666.6 rpm, assuming no slippage between tyre and road or tyre and rim. There's no getting around that, and there's no mention of state of inflation, shape of the tyre or axle to road distance. Yes, but it is the distance between the axle and the road that determines the rotation rate. Seems lots on here can't understand the concept of one wheel running at different RPM from the others. Perhaps they only ever drive in a straight line. -- *CAN VEGETARIANS EAT ANIMAL CRACKERS? Dave Plowman London SW To e-mail, change noise into sound. |
#78
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Does a tyre change its CIRCUMFERENCE when underinflated?
In article ,
Huge wrote: I'll type this slowly for the hard of thinking. The - Bits - Of - The - Tyre - Not - In - Contact - With - The - Road - Are - Irrelevant. The - Only - Thing - That - Matters - Is - The - Diameter - Of - The - Circle - Whose - Radius - Is - The - Distance - From - The - Axle - To. The - Road. You should have used caps, Huge. For those whose physics are still at kindergarten level. -- *(over a sketch of the titanic) "The boat sank - get over it Dave Plowman London SW To e-mail, change noise into sound. |
#79
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Does a tyre change its CIRCUMFERENCE when underinflated?
Dave Plowman wrote:
Huge wrote: The - Bits - Of - The - Tyre - Not - In - Contact - With - The - Road - Are - Irrelevant. The - Only - Thing - That - Matters - Is - The - Diameter - Of - The - Circle - Whose - Radius - Is - The - Distance - From - The - Axle - To. The - Road. You should have used caps, Huge. For those whose physics are still at kindergarten level. Except there isn't a single distance from the centre of the axle to all parts of the tyre in contact with the road ... the average distance perhaps? |
#80
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Does a tyre change its CIRCUMFERENCE when underinflated?
"T i m" wrote in message
news This means that it must be accurately measurable so when a 32 psi tyre drops it's pressure to 24 psi (23?), it should raise the alarm. I've found that it triggers the alarm at a much smaller reduction than 25%. Our Honda developed a very slow puncture and when I checked the tyres, one was about 0.2 bar (3 psi) lower than it should have been. The instructions for calibrating cycle speedos require you to measure the *loaded* rolling circumference of the wheel bearing the speed sensor (when it would be easier just to put a tape round the wheel). How much does the radius of a bike tyre (at the point of contact) decrease when you sit on the bike. It's difficult to tell when I'm the one sitting on the bike so I don't get a side-on view. I think my speedo actually recommends measuring the (unloaded) circumference by marking a point on the tyre that is in contact with the ground and rolling the wheel along the ground until the point is next in contact. But I agree that *if possible* you should try to measure the radius under load and *assume* that the whole tyre is that radius. I've heard is suggested that there is *significant* error between a brand new tyre and one with a worn tread, though I'd have thought that it was negligible. https://www.halfordsautocentres.com/...pth-and-safety says that a new tyre has about 8 mm tread. If you use it until the tread is 2 mm, and assuming the same pressure in both cases, then the radius has reduced by 6 mm in a total radius of 635 (for my car's 215/65/15 tyres) so about 1%. I wonder how much the effective radius varies for an under-inflated tyre, assuming the trigger level for a sensor is 25% loss of pressure. Any sensor has to be able to distinguish between expected change in radius due to tyre wear and unexpected due to loss of pressure. |
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