Tyre pressure through wheel rotation and odb2?

cy80rg · 24th May 2017, 11:14

Hi guys,
Looking at how OEM tyre sensors work, seems they work on revolution timing of the wheels to calculate tyre pressure, rather than actually taking and sending tyre pressures.

Bit beyond me, but this would seem to be a function of calculation, rather thank hardware?

Could this be exposed via odb2, then calculated on one of the many odb2 apps?

Rover 75...

T-Cut · 24th May 2017, 12:30

Quote:

Originally Posted by cy80rg

Looking at how OEM tyre sensors work

Have you a link to this info?

TC

cy80rg · 24th May 2017, 14:07

Nothing specific to the 75, but here... Indirect....

https://en.m.wikipedia.org/wiki/Tire...itoring_system

Only doubtfully hopeful myself, but seems possible in theory, depending what sensors are available via odb2?

Sector-9 · 24th May 2017, 15:56

It's possible, and individual wheel rotation speeds are available from the ABS ECU (though not to a generic EOBD reader I don't think, you'll most likely need T4 or TOAF to get at that live data), however I don't think this system of calculation is as accurate as measuring - there are other factors that can cause variance in rotational speed even when the pressures are identical!

T-Cut · 24th May 2017, 16:11

The two sensor sytems used monitor completely different things. Only one measures the actual air pressure in the tyre (and its temperature in some cases). In effect, there's a miniature pressure meter (and thermometer in some) which transmits their data by wifi to a receiver. This displays the air pressure (and temperature) from each tyre individually on a screen.

The other type doesn't measure (nor calculate) anything about air pressure. The ABS system is used to compare the rotation speeds of the wheels. A tyre that's low on pressure runs more and more 'flat'. This reduces the rolling radius, so that wheel turns slightly faster than the others. At some preset difference, a warning will pop up that this particular tyre has a low pressure. It doesn't say what that pressure is, just that it's lower than the others.

The 75/ZT models were not available with the ABS based monitoring system, though an aftermarket kit of the first type could be installed.

TC

cy80rg · 24th May 2017, 17:13

Thanks guys,

Have seen the after market ones, but always look a bit cheap ... Ie ineffective.

Anyone got any experience with these?

Personally, i cant see how sensor, WiFi and battery can be crammed into a tyre valve cap, and last more than 5 minutes on power?

Happy to be proved wrong, i really want one!
Used to have per-wheel pressure on my Chrysler 300c (original, hard core version

) and i miss it! Plus, also good to keep an eye on for fuel economy etc.

geofftl1000r · 24th May 2017, 23:19

My Bike has a Garmin satnav which you can connect TPMS to. The front works well and lasts about 6 months on a tiny battery.
The rear lasts maybe 3 weeks on a battery. Very poor. Stopped worrying about the rear now. Need a repeater I think to boost the signal from the rear sensor.

Sector-9 · 25th May 2017, 00:02

Quote:

Originally Posted by cy80rg

Personally, i cant see how sensor, WiFi and battery can be crammed into a tyre valve cap, and last more than 5 minutes on power?

It's possible but the battery would be so small it'd not last 2 minutes (OEM systems have all the electrickery inside the wheel at the base of the valve where there's much more room) and I suspect the extra weight would throw the wheel out of balance.

T-Cut · 25th May 2017, 08:42

Some TPMS systems don't use a battery and are powered inductively by the wheel rotation. Presumably you get what you pay for.

TC

berkshirelad · 25th May 2017, 08:45

Quote:

Originally Posted by T-Cut

Some TPMS systems don't use a battery and are powered inductively by the wheel rotation. Presumably you get what you pay for.

TC

Exactly so.

On the Rangie, the antenna is powered and at operates in the same way as an RFID chip in a credit card. So no battery required.

All of this is built into the wheel valve body ( at £75 each from JLR!).

Many after-market systems that replace the valve cap, constantly keep the tyre valve open

24th May 2017, 11:14	#1
cy80rg Regular poster Rover 75 Saloon Join Date: Jan 2012 Location: Huddersfield Posts: 54 Thanks: 2 Thanked 2 Times in 2 Posts	Tyre pressure through wheel rotation and odb2? Hi guys, Looking at how OEM tyre sensors work, seems they work on revolution timing of the wheels to calculate tyre pressure, rather than actually taking and sending tyre pressures. Bit beyond me, but this would seem to be a function of calculation, rather thank hardware? Could this be exposed via odb2, then calculated on one of the many odb2 apps? Rover 75...

24th May 2017, 15:56	#4
Sector-9 Gets stuck in Rover 75 CDT manual Tourer Join Date: Aug 2014 Location: nr. Mansfield Posts: 767 Thanks: 24 Thanked 182 Times in 137 Posts	It's possible, and individual wheel rotation speeds are available from the ABS ECU (though not to a generic EOBD reader I don't think, you'll most likely need T4 or TOAF to get at that live data), however I don't think this system of calculation is as accurate as measuring - there are other factors that can cause variance in rotational speed even when the pressures are identical! __________________ Free fault codes scan/clear (TOAF) - M1 J27 area

24th May 2017, 16:11	#5
T-Cut This is my second home Rover75 and Mreg Corsa. Join Date: Nov 2006 Location: Sumweer onat mote o'dust (Sagin) Posts: 21,753 Thanks: 341 Thanked 3,660 Times in 2,924 Posts	The two sensor sytems used monitor completely different things. Only one measures the actual air pressure in the tyre (and its temperature in some cases). In effect, there's a miniature pressure meter (and thermometer in some) which transmits their data by wifi to a receiver. This displays the air pressure (and temperature) from each tyre individually on a screen. The other type doesn't measure (nor calculate) anything about air pressure. The ABS system is used to compare the rotation speeds of the wheels. A tyre that's low on pressure runs more and more 'flat'. This reduces the rolling radius, so that wheel turns slightly faster than the others. At some preset difference, a warning will pop up that this particular tyre has a low pressure. It doesn't say what that pressure is, just that it's lower than the others. The 75/ZT models were not available with the ABS based monitoring system, though an aftermarket kit of the first type could be installed. TC Last edited by T-Cut; 24th May 2017 at 16:14..

24th May 2017, 23:19	#7
geofftl1000r Gets stuck in Rover 75 Saloon in Moonstone Green Join Date: Jan 2010 Location: Salfords, Redhill Posts: 525 Thanks: 17 Thanked 16 Times in 14 Posts	My Bike has a Garmin satnav which you can connect TPMS to. The front works well and lasts about 6 months on a tiny battery. The rear lasts maybe 3 weeks on a battery. Very poor. Stopped worrying about the rear now. Need a repeater I think to boost the signal from the rear sensor. __________________ Rover 75 2.0L V6 Auto Connie in Moonstone "I started out with nothin' and I still got most of it left"

24th May 2017, 14:07	#3
cy80rg Regular poster Rover 75 Saloon Join Date: Jan 2012 Location: Huddersfield Posts: 54 Thanks: 2 Thanked 2 Times in 2 Posts	Nothing specific to the 75, but here... Indirect.... https://en.m.wikipedia.org/wiki/Tire...itoring_system Only doubtfully hopeful myself, but seems possible in theory, depending what sensors are available via odb2?

24th May 2017, 17:13	#6
cy80rg Regular poster Rover 75 Saloon Join Date: Jan 2012 Location: Huddersfield Posts: 54 Thanks: 2 Thanked 2 Times in 2 Posts	Thanks guys, Have seen the after market ones, but always look a bit cheap ... Ie ineffective. Anyone got any experience with these? Personally, i cant see how sensor, WiFi and battery can be crammed into a tyre valve cap, and last more than 5 minutes on power? Happy to be proved wrong, i really want one! Used to have per-wheel pressure on my Chrysler 300c (original, hard core version ) and i miss it! Plus, also good to keep an eye on for fuel economy etc.

25th May 2017, 08:42	#9
T-Cut This is my second home Rover75 and Mreg Corsa. Join Date: Nov 2006 Location: Sumweer onat mote o'dust (Sagin) Posts: 21,753 Thanks: 341 Thanked 3,660 Times in 2,924 Posts	Some TPMS systems don't use a battery and are powered inductively by the wheel rotation. Presumably you get what you pay for. TC