Falling MPG any ideas?

BeenThroughItAll

Norman_Castle wrote: »

It will use the circumference of the tyres when new as a median diameter. The reduction of this diameter over hundreds or thousands of miles is measured by the onboard computer which shows the amount of wear.. When new tyres are fitted the computer recognises the sudden increase in diameter and re-calibrates.

I'd love to believe this is true but I've never seen any evidence of it to date. Have you got a source example I can research or do you have some sort of inside knowledge?

Norman_Castle

BeenThroughItAll wrote: »

I'd love to believe this is true but I've never seen any evidence of it to date. Have you got a source example I can research or do you have some sort of inside knowledge?

Its an extension of the use of the information given from the abs sensors. They're used to spot punctures based on comparative wheel speed. With the increase in computer power now cheaply available more information can be processed increasing fuel computer accuracy.

mcpitman

Norman_Castle wrote: »

Its an extension of the use of the information given from the abs sensors. They're used to spot punctures based on comparative wheel speed. With the increase in computer power now cheaply available more information can be processed increasing fuel computer accuracy.

Whilst I would hate to question you sir.....:o

What cars is this technology used on? AFAIK it isn't Ford's/Vauxhall's or anything french.

My car has no idea when a puncture occurs or if wheels/tyres have been changed, unless this is part of TPMS (Tyre pressure monitoring systems)

Norman_Castle

Its a development of indirect TPMS. Its unlikely to be advertised. Its just part of the fuel computers programming.

mcpitman

Norman_Castle wrote: »

Its a development of indirect TPMS. Its unlikely to be advertised. Its just part of the fuel computers programming.

What cars is this used on?

The parameters on my car from the ABS sensor, have nothing to do with the TPMS system, they are independant from each other.

Equally I am failing to understand how an ABS sensor based at the hub of the wheel, can calculate the variances of rolling radius within that wheel.

Unless of course it is calculating the speed of each road wheel independantly to achieve the accuracy you mention. (using the "travelling ion an arc" example.

From reading the codes and interacting with OE software on my car, I cannot see any live data fields that would portray this data.

Again, not questioning (or maybe I am), just interested in this stuff...

AdrianC

mcpitman wrote: »

The parameters on my car from the ABS sensor, have nothing to do with the TPMS system, they are independant from each other.

Equally I am failing to understand how an ABS sensor based at the hub of the wheel, can calculate the variances of rolling radius within that wheel.

There certainly are TPMS that use ABS wheel speed data, instead of sensors on the wheel rim or in the valve. (They're probably more reliable, too, but that's a side issue.) They do so by watching for one wheel which is rotating at a different speed from the other three, due to reduced tyre pressure.

It's far from impossible that tyre diameter could be correlated to GPS-calculated distance, and the overall diameter taken from that, but - really - it'd be easier just to use the GPS distance compared with the odometer distance and/or GPS speed with speedo to recalibrate the odometer/speedometer directly. After all, apart from that, the tyre diameter isn't actually that relevant.

Limey

OP mentioned an ECU reprogram and subsequent change, were you told why they did this?

Also is the car an auto?

Herzlos

Norman_Castle wrote: »

It will use the circumference of the tyres when new as a median diameter. The reduction of this diameter over hundreds or thousands of miles is measured by the onboard computer which shows the amount of wear.. When new tyres are fitted the computer recognises the sudden increase in diameter and re-calibrates.

It can't detect the sudden increase in diameter; it only knows how fast it is spinning. It might notice that one has changed in relation to the others but that means it's only work if you replaced tyres one at a time.

All I can do is identify that suddenly one of the wheels has spinning faster, which indicates that it's radius has reduced and is likely punctured.

It's not capable of wear monitoring without some additional input on distance travelled, and that'd either need some ground facing camera calculating how fast the ground is passing, or super accurate GPS.

Herzlos

AdrianC wrote: »

There certainly are TPMS that use ABS wheel speed data, instead of sensors on the wheel rim or in the valve. (They're probably more reliable, too, but that's a side issue.) They do so by watching for one wheel which is rotating at a different speed from the other three, due to reduced tyre pressure.

It's far from impossible that tyre diameter could be correlated to GPS-calculated distance, and the overall diameter taken from that, but - really - it'd be easier just to use the GPS distance compared with the odometer distance and/or GPS speed with speedo to recalibrate the odometer/speedometer directly. After all, apart from that, the tyre diameter isn't actually that relevant.

It'd likely be more accurate to use something like a laser to measure how far away the ground is from the axle, assuming it can handle potholes (maybe aim it a mm in front of the contact point and average it out over about a foot of travel). If that suddenly drops then you've got a flat. It could probably also be calibrated to identify when you've lost $x mm of tread.

alastairq

Whatever happened to a good old boot with a steel toecap?