Does a tyre change its CIRCUMFERENCE when underinflated?

Dear oh dear, such bollocks. Explain how the circumference can "vary", would you.

Imagine this: take some white paint and paint a line from within the wheel's nuts out to the edge of the wheel, onto the inflated tire and out to where the tread starts. Repeat at angles of say 30 deg so you have 12 segments all the way round the wheel.

Now rotate the wheel once. All the lines will stay intact and the car will move along a distance equal to the circumference. Now it's been said here that the steel belts are not quite circumferential, so if we now deflate the tire, its circumference will reduce a small amount. I am not considering that since arguments here seem to focus on other reasons for reducing the circumference.

If we now again rotate the wheel once, then assuming no slip along the rim between the wheel and the tire, after one turn the lines on the wheel/tire will be intact and the car has moved the same distance.

Now, what *might* happen, is that because the side wall can flex, the painted lines will spiral a small amount on the tire wall and the first turn of the wheel doesn't move the car as far as it should. But the spiralling will cease to have a further effect once the tire wall has spiralled as much as it can. After that, the car will move the same distance for one wheel turn, flat or inflated.

You can also imagine that if you could get hold of a tire of the same overall diameter but to go on a much smaller wheel, that the spiralling effect when flat would be much more pronounced as the tire wall would be bigger. But, once spiralled up, one turn of the wheel would send the car the same distance, flat or not.

The problem we have on this ng is too many unimaginative dimwits unable to think clearly about the problem.

Yeah, better that we have some whose imagination is so powerful, they can dream up ways to say that a device that plainly does work, cannot possibly work ...

It seems the self confessed 'know it all's' are tripping over themselves to disprove reality on this one Andy. ;-)

They all seem so very keen to deny the *facts* put forward by the experts in the field (and those of us who can understand them) but completely fail to come up with an alternative explanation themselves (well, not that a 5yr old couldn't see though, like Streaters last droolings). ;-)

Cheers, T i m

This could be interesting ... the fine arts dropout trying to explain mechanics ...

Here we go ... we had to get back to painting didn't we ...

Yes ...

No!?

They are not *at all* 'circumferential and in fact criss cross at nearly 90 Degrees to each other.

No it won't. The 'effective circumference' will though (as the only time the two are equal is where there is no load on the tyre at all).

Go on ...

Why would you even have to write that? When was the last time you were aware of any such slip, outside of a trials bike and they have rim locks to prevent that very thing?

OOI, how many tyres of any type have you ever dismounted in your life?

The same distance as the first time based on the effective circumference yes.

That would be transitional so irrelevant to any of this.

Duh.

Yes, and 'winding up' of the sidewall is transitory in any case dimwit.

WTF are you drooling on about now!?

Bwhahahaha ... go back to painting lines on yer car wheels you fine artist! ;-)

Why are you and your kind in so much denial re what are obviously the facts and why do you continue to put up fascicle and bogus BS in the way of some alternative explanation?

It's exactly the same thing re Brexit where you seem to have this special insight but it fails every RW test anyone throws at it. ;-(

Cheers, T i m

I can't see why people can't see that a tyre has knobbly bits on them. these move so the actual circumference changes when these bits, also known as the tread, moves. Then there are the flexible side walls.

That was never claimed.

Only the means by which it worked.

Dont be such a 'flat tyre denier'

I've been thinking about this a lot trying to make it simple enough for even a remoaner to understand.

The fallacy is in Huge's basic premise that because the axle is a given height above te ground, that represents the 'effective/rolling radius*' of the tyre.

It does not.

The 'effective/rolling radius' is /always/ the circumference divided by

How can this be? Quite simply because the tyre is attached to the wheel all round, and the tyre is dragged along by the sidewall such that the tread is moving faster (angular velocity) than the rim at the point of 'flatness'.

So Huge's assumption that the tyre tread speed is actually it's distance from the axis of rotation, times the speed of rotation of the wheel, is simply a mistake. It is in fact *greater*, at that point, and its the sidewall flexure that takes up the strain, and the attachment of the tyre at other points of the rim that creates that strain.

Should the wheel deflate completely, then the strain in the sidewall and the friction between the tread and the rim as the two models compete...leads to rapid separation of tread and wheel.

You then end up then with a wheel rim and tyre tread rotating at completely different angular velocity. The triumph of 'Huge's model' is to rip the tyre sidewall apart to allow that to happen.

If you follow F1 you can see this regularly - you end up with the sidewall disintegrating and a more or less intact tread separating from the car wheel entirely.

This leads to the conclusions that what affects wheel RPM - in a non slip case - apart from car speed, is change in *circumference* alone, and that will be a function of tyre tread elasticity, tyre pressure and tyre RPM only, due to 'centrifugal force'.

Loading won't affect it at all.

And whoever dreamt up 'effective' or 'rolling' radius deserves to be strapped to a centrifuge.

A little knowledge is a dangerous thing.

So is relying on 'experts' who are equally ignorant.

A lot of engineering is highly counter intuitive.

I think even the thickest of them may know that but may not be able to go from that to the concept the a tyre is a very dynamic thing.

I think it all takes too much of a leap of the imagination for people who are very likely to be left brainers.

They will find it very difficult to accept something they don't or can't understand, no matter how many people try to explain it to them or the facts that it's working all around them.

It's all down to the construction of the structure within the tyre and how it does what it does.

Many people have seen a pantograph, even if they haven't consciously considered what it does when it's working but if you were to imagine the mechanism of a pop rivet gun, wrapped round on the flat into a circle, then that's what a steel belted tyre construction is.

Where the flat of the tyre (cord) is on the road, the tread would be flattened out and spread wider and when these things get bigger in one dimension they *have* to get smaller in the other?

Hence, where the tyre sits flat on the road the carcase of the tyre will have shrunk longitudinally and hence reducing the 'effective circumference'.

Most of the rest of the tyre would still be 'normal' because unlike the rivet gun, the steel belts are reasonably flexible (or we would see the flat bit at the bottom spread round the entire tyre).

Cheers, T i m

It does when considering the distance that determines the rotation rate of the wheel.

Not when it is the distance between the axle and the road that determines the rotation rate of the wheel.

But it is very easy to measure both a fully inflated tyre and one that is say 20% under inflated and see if the rotation rate of the wheel is in fact determined by the distance between the axle and the road or the very minimal change in the circumference of the tyre and that must have been done when designing the ABS system for detecting under inflated tyres.

Doesn?t matter when it is so easy measure.

The only way you will be able to do that (Brexsh1tter) is by first understanding it yourself.

There is such a thing but I'm not saying that it is any mechanically measurable.

Nope. The effective rolling radius is the effective rolling circumference divided by 2 Pi.

It can't so it isn't.

No such thing. The whole process of a tyre moving is far from 'quite simple' (if it was, even you would understand it).

So where is your 'the circumference is always the circumference' now?

It's nearer the truth than any waffle you have come up with so far.

All distraction waffle. Where is your constant circumference in all this now?

You got that be right at least but has nothing whatsoever to do with this topic. The front of the car will also deform when you hit a wall.

Nope, Unless the bead has separated from the rim, everything will still be rotating at the same speed (as we have now jumped from low pressure to no pressure and most of the previous rules go out the window as the tyre isn't moving 'as designed'.

Nope. Still very wrong.

I love the way you announce such things so authoritively where it's patently obvious to most (right brainers) that you are way out of your depth.

The *reason* most F1 tyres disintegrate that way is because the sidewalls have been weakened / damaged in some way, either because they have been pushed too hard for too long or (and most commonly), because they have made contact with another car, the barriers or debris.

What else can it be? What else is related to rpm and distance traveled?

Correct (for this topic).

See above.

So, an iTPMS wouldn't trigger at high speed because centripetal force was making the tyre expand and so rotate *slower* for the same mph?

Of course it will.

Typical left brainer response to something they don't understand. Everone else who does actually know are just 'talking heads' to be ignored.

As you perfectly demonstrate here.

Bwhahahaha.

Obviously.

To you, not those who actually understand what's going on.

So, once again you have attempted to disprove both what is going on with millions of cars ITRW whilst not offering a counter argument to actually explain what's going on.

I think the stress of being a fanatical Brexiteer (along with Streater et al) has burnt what is left of your brain out ... that and / or desperately trying to defend the indefensible. ;-(

Cheers, T i m

The thing is one is a function of the other (cause and effect).

eg, If you have a solid wheel then the arbitrary circumference is the same as the rolling circumference (so wouldn't work with an iTPMS system). ;-)

Once a tyre can deflect under load and especially when it does so as per of it's design, you no longer have a linear circumference (or even a circumference in the true sense) but you do have something that relates to the original circumference by some factor. The *exact* same applies to the real radius (solid wheel) and an effective / loaded / rolling radius when you don't have a real circumference.

Now, I haven't stated the RW relationship between the distance between the axle and the ground on a loaded pneumatic tyre / wheel and the 'effective circumference' other than there is likely to be a link between the two.

The key factor here is *how* does the speed of a deflating tyre change for an iTPMS system to work (and they do work obviously). Now, we don't need to define the situation by saying 'assuming no slip between the tyre and the rim' as anyone who has tried to remove a tyre will attest, nor do you have to state 'with no slip between the tyre and the road' because if there was it would nearly be impossible to predict anything. We certainly wouldn't need to mention anything about the sidewall winding up because that will simply unwind again as the torque (acceleration / braking) is removed.

So, we are down to *something* happening to effectively shorten the effective circumference and about the only think logical (to any right brainer that is) that at the point of the cord where the tyre flattens out and the sidewall bulges where the tyre sits on the road, there is a shortening of the tread length across this cord and hence a produce a shorter 'effective rolling circumference'.

So, the left brainers deny this being even likely but without offering any better solution themselves (and Turnip never will now of course, not now he's backed himself into a very dark corner. Or he might, but it will be that he has now come up with the answer all by himself). ;-)

Cheers, T i m

Indeed. I see that my efforts are watsed and you havent understood a word I said, nor even looked at the video I posted way back where someone did precusely this and showed that within the limits of te technique, flattening te tyre made no measureable difference - ceraiunly not as much as the 'loss of radius' would account for. Nor yet te p[aper I likned to that showed taht te differemnce with 30% deflation was of the order of a percent or so. WAY less than would be accounted for by the 'loss of radius'

Why don't you measure it then?

I see that other people have, and that confirms my thesis.

What I wouuld ask you is how a tyre, rotating at a differentent rate from a wheel, so that its circumference does in fact get covered on the ground by that rotaion, stays on the wheel without ripping the tread off?

Yes, but the change in the circumference is much smaller than the change in the distance between the axle and the road with an under inflated tyre and it would be obvious which is controlling the measured rotation rate of the wheel.

True?

Except it can only be the circumference that impacts the distance traveled per revolution can't it? Anything else is consequential?

Cheers, T i m

And yet we know that the TMPS system that uses the ABS sensors does work to detect under inflated tyres very reliably.

- ceraiunly

My car does have ABS, but doesn?t show the instantaneous rotation rate of each wheel on the OBD2 data.

IF youy watch te video ytou will see that 'no measurable difference in that video is less than 5% or so.

If you read the article I linked to it showed that 30% defltion was less than 1% difference. This is detecatable by good software.

You just have to put a chalk mark on the tyre and put another chaklkmark on te ground, roll it forward a few revolutions, then flatten it by 30% and roll it back to where it started. If you are correct the chalk marks will be out by 10% or more. If I am right they will be damned near lined up perfectly.

This threaad is not about the abilituy of software to detect a 1% change, its about the claim by Huge and others that the tyre rotation rate will cahnge by 10% or more depending in pressuer AND LOADING

What matters is the rotation rate of the wheel, because that is what the ABS sensors are measuring.

ABS sensors have multiple teeth. If all you needed to do is measure the speed of the wheel per revolution, one tooth would do just fine.

Except that multiple teeth allow a quicker reading of any change, without having to wait (potentially) a full wheel revolution before noticing that something had changed. For ABS, there are big advantages in reducing the time between the change occurring (ie one wheel spinning faster than all the others) and being able to detect this so you can do something about it.