For some reason this is starting to remind me of that diagrammatic representation in a circle which Clive George kindly showed me of the complex roots of a polynomial. You too helped my understanding of complex roots in that discussion.
I hope we don't end up with similarly abstract stuff before this speedo and wheel thing gets sorted out but it could be heading that way. Oh well.
Plenty models share the same look speedo - but it is individual to the actual model. If they can decide which size wheels to fit surely they can pick the correct speedo from the bins? And models with a choice of engine sizes etc in the same body will likely also have different final drive ratios.
Can they? I've not actually seen speedo programming being part of software choices. Not to say it isn't.
Fitting the incorrect wheels and tyres could alter the way the speedo reads either way. So is no reason for not to have it reasonably accurate in the first place. An up to 1% error on new tyres would be easy to achieve.
why would they when it adds cost?
Winter tyres and wheels are not incorrect.
I have created an animated gif to show how the wheel and tyre both rotate together, but the tyre distorts so that only the distance between the axle and the road is important.
See
Now I believe the tread part is generally made of steel or some other inelastic material.
Therefore, while the tread may be slightly compressed longitudinally, to a quite accurate first approximation the circumference remains unchanged irrespective of wall distortion. That is up to the point where it may be possible for the tread to 'bell up' towards the centre of the tyre, assuming of course anything like that happens.
What you seem to be saying is, if by way of example, where I have a loop of wire with some compressible spokes attached to a central disk, then the circumference will be dependent on the radius of the wire loop which in contact with the road?
I would have thought the distance travelled by one rotation of this 'central disk' would be the circumference of the loop, and not dependent on the radius in contact with the road at any one time.
Why do you think this assertion only holds for a solid wheel?
My van's adaptive cruise control and steering just undertakes them........
Its made of steel because it is elastic. It wouldn't be much of a tyre if it wasn't.
Bosch ABS systems (can) have it built in, not necessarily enabled unless you pay extra for it, the system is measuring the rotational speed of all the wheels all the time, so it looks out for one wheel running at a different speed over the course of a few minutes, if the car has a steering angle sensor that (or data from the air-bag accelerometer) could provide information to it to prevent false alarms while cornering.
Mine has never given a false positive, and it has given several true positive alerts where it's spotted a slow flat before I'd noticed any sign of the car getting "wallow".
If anything I find it tends to trigger (correctly) at the point you stick your foot down, rather than when cornering.
The only reason for knowing your speed to any degree of accuracy is because of speed limits which are pretty arbitrary. Otherwise who gives a shit about whether you are doing 33 or 30mph?
Bit late on this but my car gives me actual pressure in each tyre and the relevant temperature. How does it manage that ?
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You have what is known is known as a Direct Tyre Pressure Monitoring system as opposed to the indirect type I referenced earlier which the TNP had never heard of though he hasn't come back to deny the existence of such a thing and argue endlessly that because he hadn't heard of it can't exist so he hasn't quite turned in to his mate Harry yet.
Your vehicle will have sensors in each wheel usually built into the valve base which send information to the onboard computer system about pressure and in your case the temperature as well. The link from wheel to the fixed wiring is a radio signal from each sensor/transponder. They are far more sophisticated than the indirect system that I have. Like anything more sophisticated it may be more expensive to maintain if it plays up. The sensors have a battery in each one which after 5 or six years is getting on for replacement and the whole unit has to replaced with the price being near 3 figures for some OEM ones, you can get generics but they will have to be programmed for the vehicle.
G.Harman
Agreed, but some here are suggesting the 'steel' circumference would change for some reason they haven't explained.
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