Nope.
I say its insiginicant in terms of ordinary measurements. You beed veruy careful speed monitoring to detecte it - a simple exoeriment wont.
My thesis has always been to try and illustrate the erroneous thinking of those who think in terms of radius rather than circmference.
Because its an intersting engineering problem and has highlighted a very intersteing psychological and educational issue.
well I think he got 0.8% which triggered his warning system
What he didn get was 5% which is what you might expect from the 'radius' change
Aww bless. I best she's made fewer online typos in her life than you made in this one post!
So, when are you going to concede that many of us had it right and you are still in left brainer denial?
Do you now accept the answer to your question is 'yes', 'an underinflated tyre does change it's circumference' ... for the purposes of iTPMS specifically (even if you still can't understand how)?
Cheers, T i m
centre of wheel vertically to ground, 320mm vs 315mm
Wodney seems to have really excelled himself this time around.
He's even got people changing the air pressure in their tyres and doing measurements.
michael adams
...
Surprisingly low. But greater than the % RPM change you measured isn't it?
1.5% instead of what you measured...0.4%.
Yes, my 50mph test was pretty crude, hardly controlled conditions, I choose a road that is pretty straight, but it isn't entirely level, runs were in different directions, there's other traffic on the road, the software takes a fraction of a second to readout the speed of each wheel in turn, etc.
It might be fun to paint lines all over my tyres, have an outrigger slow-mo camera pointing at them and sneak into the test track up the A5, but I don't think MIRA would be too impressed.
Nobody is saying it's the real radius, or the real circumference, but if you've got a known rate of rotation over a known distance travelled that does let you derive an "effective radius" or "rolling circumference"
They use those terms because they *know* it's not real, it's a nod towards the lies of O-Level physics with granite wheels on a granite road, rather than steel and rubber on tarmac, which we all realise will deform and slip and squirm as they rotate, even if only a little, and they'll do that more when underinflated.
If you mean me, it was 0.4% speed change (I haven't seen actual numbers from anyone else, but my killfile does hide whole sub-threads once certain people contribute to them).
My radius change was 1.5%
As I hinted just now, certain people (and any responses to them) don't get seen here ...
For the purposes of detecting speed changes, I'm not discounting it at all, as I've made clear before. What I'm discounting is a *big* change in circumference because the axle is "closer to the road" or because somehow circumference "disappears".
255/35R19 tyres, so not very "tall" to start with.
Yep.
But you didn't completely flatten the tire IIRC (not that I blame you for that :-)
Various people here have talked about that, with a flat, the axle is much closer to the road. Well, so it is, by almost the whole distance from where the tread starts down to the tire rim. That's prolly about a third, say 30%, and consequently, people have been trying to imply that
30% of the circumference must disappear too. Well it would need to, otherwise the wheel and tire would rotate at a different rates and the tire would disintegrate.And since as Den so helpfully points out, this is what actually happens, we conclude that the circumference does not "shrink".
Well, my axle is 5mm closer to the road (when stationary, who know how much centrifugal [let's not have *that* discussion] force negates that when moving?)
With the crossed diagonals of the steel belts
when the pressure is lowered, the sidewalls will bulge more, which will pull on the circumference because the steel strands are only contained in rubber ...
Oh they are. They define that as minimum axle to road distance.
or the real circumference,
Yes, I am.
Circvmference is putting a tape measure round the loaded tyre. It has a definite meaning
but if
Which is the tape measure circumference.
But they dont change their circumference by anthying more than elasticity accounts for.
You know what, I almost did that myself out of pure curiosity. I know that iTPMS works because I had it trigger when I had a leaky, corroded wheel rim, and I was *almost* curious enough to break out VCDS :-)
I'll inject facts into the handwaving fest:-)
A diagonally belted tire has 5% more travel per rotation at 180km/h than at
60km/h, a radially belted tire 1% more.This from the German Wiki page on the subject "Abrollumfang".
The article also contains the words "the dynamic rolling radius under load is greater than the distance from the wheel middle to the road r sub(s)." and a formula I can't be arsed to transcribe, but I'll toss in
r sub(0): unloaded wheel radius r sub(s): static radius r sub(D): dynamic radius
Thomas Prufer
Still twisting what I said I see. You can't be trusted with anything you say.
You get a lot of it wrong and lie about most of the rest AFAICS.
TNP is still stuck in his closed mind.. it is not the tape measure distance where you said you can put a tape measure around and measure it. It changes with speed to start with and other things that cars do when driving.
Elasticity in which bit?
TNP won't answer because he knows I am right so he will maintain his killfile. Someone else that you can't trust on this newsgroup.
It negates it quite a lot.. I had a puncture and my front tyre went flat over a couple of hundred yards in the roadworks on the M6. Rather than stop I continued to drive for three miles to the end of the road works so I could get on the hard shoulder. When I got the tyre replaced there was no wear on the inside to show it had been rubbing but the hole couldn't be fixed. The car drove fine. The only reason I knew it had gone was the TPMS (with pressure sensors) told me. I might have noticed if there had been a big bang and I had braked by mistake. Not that I recommend doing 50 mph on a flat tyre.
The other flat I had on the M6 was in the rear tyre when I ran over something in the dark, that split the tyre and dented the rim. After I pulled up on the hard shoulder there were about another 6 cars pull up near me all with one or more flats.
I haven't had a flat since but there is always the chance. There is no spare on the latest car nor anywhere to put one so the AA can fix it next time.
It might be but unless you can measure it under the dynamic conditions it is just a guess. I think it would be hard to get an accurate measurement while driving and a rolling road isn't going to help either.
I don't suppose you have a laser you can exactly centre on the wheel and suspend a measure down from the wheel arch with a slow mo camera to record what actually happens? Not serious BTW.
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