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940 After market tyre pressure sensors dissapointing.

Just installed an after market kit which, being obsessive about my tyre pressures, thought this would be ideal. While it does work (on 3 wheels anyway) it is rather dissapointing.

System: Tyre Alert from Richard Grant Mouldings in the UK (no manufacturer declared).

  1. Valves were difficult to fit and wern't long enough for the wheels to properly tighten the retaining bolt, I think this was the reason the fitter broke one! (alloys: 15" multispoke 1995)

  1. 2/5 valves wouldn't seal completely, even with the retaining bolt on the outside well tightened. They've sent me different valves that don't have nuts and seem to pop in from the inside. They are prettier with chrome sleeves, so seems protected as long as its real chome and sealed.

  2. The original valves were bare aluminium, this is bound to corrode.

  1. The accuracy seems abismal. I was slightly concerned when I read the brochure with 1.5psi tolerance (5C tolerance for temperature), but thought it that would be a maximum, however my digital pressure gauge which I thought reads a little high, reads 28.5 when the remote system is reading

  1. So its at the limit or more. They all read the same offset.

  1. The update is rather slow (from No. 5), and it read 3C for 10 mins when the others read 10-15C after a bit of driving and braking. Measurement update is by pressure change apparently.

Perhaps I'm expecting too much and I'm sure these will get better, but seem to need a bit of development.

-- Tony Stanley ++Always Learning+

Reply to
Tony Stanley
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Just explain this kit a bit more:

These replace the valves in the wheel rims, and you can read off the pressure and temperature from them? Where do you read it from - the valves themselves (I've seen something that replaced the valve cap and showed red if the pressure dropped low)? Does it affect inflating the tyre? Batteries? Cost? Can they get nicked? I wonder how prolonged high speed use will affect them. Or rain and salt.

Reply to
Stewart Hargrave

Following up my own post - I just found a website:

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Feck me, that's expensive for a tyre gauge.

Aren't cars with ABS able to warn of low tyre pressure? Something to do with the wheels having different average angular velocity across an axle.

Reply to
Stewart Hargrave

manufacturer

Technically it'd be possible to measure relative difference so you could tell if one tire was lower than the other, I'm not aware of any cars actually doing this though.

Reply to
James Sweet

From

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"General Motors Corp. uses a system that will compare the speed of wheels on the same axle and determine if a tire has insufficient air pressure. This is not the same system used earlier to actually measure tire pressure using a monitor ring mounted in the tire. This system would operate by observing a faster wheel speed, which would indicate low tire pressure. This system would also look at other inputs, such as a steering wheel angle sensor, before determining a low tire pressure situation. "

Reply to
Mike F

message

You probably could do this but it would be very insensitive, and would really just detect severe punctures.

Sorry for the lack of info, thought these things were all the rage, especially when there is talk about fitting them to new cars. The tyre fitter tells me the Renault Lagunas with it have continual problems with the alarm going off too often, apparently problems with sensor accuracy and very tight and unadjustable alarm limits. You can program your own limits with these aftermarket units.

Anyway technology: The new valve is just something to bolt the transmitter to, some systems use a big clamp that goes round the entire rim.. probably more desirable than messing about wth unstandard valves that won't seal. They work by transmitting a RF signal with data on sensor number, battery voltage, pressure and temperature. Apparently this system triggers a transmission when pressure varies by 0.2psi so it doesn't transmit all the time. The RF signals are received and logged by a unit on the dash/stuck on window. This is powered by a battery line and ignition on/off. It always receives, so if your tyre goes flat when the engine is off it warns you when you switch on otherwise it cycles round each tyre displaying the last reading logged.

The wheel electronics are sealed and not subject to the elements anyway, other than temperature and whatever is inside the wheel. Batteries are reported to last 5 to 7 years, I've no idea what the plan is for replacement, but the back of the modules are silicone filled so you could probably remove that.

-- Tony Stanley ++Always Learning++

Reply to
Tony Stanley

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