RXVIII

Tyre Pressure Monitoring System

Does anyone have any experience with these “Tyre Pressure Monitoring Systems” (good or bad) particularly on the RX8?

xxup

Hmmm... I wonder if a group buy could get the price down? $600 seems expensive... I like the idea...

takahashi

If it is not going increase the weight of each wheel by much I would love to have them

RXVIII

FEATURES

[Weighs only 32 grams
5 year battery
Unique ID code for each sensor
Pressure measurement accuracy +/- 1.5 Psi
Able to detect the slightest pressure loss
Durability and Reliability in any climate
Operating temperature -40 to 125 degrees Centigrade
Helical transmitting technology
Alerts driver of under-inflation or over-inflation
Resetable sensors
Spare tyre monitoring (optional)


Thought it would be good for track days as well!

takahashi

Look good - so it is the valve thing that sensing it hmmm...

Where do you mount the dash thingy... look enormus?

RXVIII

Thanks to d00nson's link. Batteries not replacable! Only upto 5 years

http://www.carbibles.com/


TPMS - Tyre (Tire) Pressure Monitor Systems.

Indirect TPMS
Indirect TPMS works without actually changing anything in the wheel or tyre. It relies on a component of the ABS system on some cars - the wheel speed sensors.

Current / First / Second generation Direct TPMS.
The current generation of direct tyre pressure monitoring systems all work on the same basic principle, but have two distinctly different designs. The idea is that a small sensor/transmitter unit is placed in each wheel, in the airspace inside the tyre. The unit monitors tyre pressure and air temperature, and sends information back to some sort of central console for the driver to see.

Strap-on sensors.
The first type of sensor is a strap-on type. It's about the size of your thumb and it clamped to the inside of the wheel rim with a steel radial belt. Normal wheel-balancing procedures can compensate for these devices. The downside is that you have the potential for the steel strap to fail and start flailing about inside your tyre, and if you do get a flat, the location of the sensor means it will be crushed and destroyed within the first wheel rotation of your tyre going flat.

Valve-stem sensors.
The second type of sensor is a small block which forms part of the inside of the tyre valve stem.These sensors are lighter and weigh about 28g (an ounce). Because they are smaller and are part of the valve stem itself, they are mounted to one side of the wheel rim. Again, regular wheel-balancing can account for this weight. The disadvantage of this system is that because of its proximity to the side of the wheel, a ham-fisted tyre-changer can easily destroy the sensor with the machine that is used to take tyres off the rims. Also, when re-fitting the tyres, the tyre bead itself, if not correctly located, can crush the sensor.


The limits of what TPMS can do.
All TPMS systems have limits. These are usually around ±1.5 PSI/.1 BAR in pressure accuracy, and ±5.4°F/3°C temperature accuracy. They cannot warn you of an impending blowout. Tyre blowouts are caused by instantaneous failure of the tyre. However they can tell you about the symptoms that lead to blowouts, and that is the primary reason for having TPMS. Tyre failures are usually preceded by long periods of running at lower-than-acceptable pressures - TPMS would warn you about that. When the tyre pressure is low, the sidewall flexes a lot more, generating more heat - TPMS can tell you about that too.
Typically, tyre pressure is transmitted as soon as your vehicle starts moving. Pressure data is then transmitted every 4-6 minutes randomly, although the sensors read tire pressure every 7 seconds. If the new pressure reading differs from the last transmitted pressure by more than 3 PSI/.21 BAR, then the data is transmitted immediately to alert you of a problem.
Tyre temperature is also normally transmitted as soon as the vehicle starts moving. As with pressure data, temperature data is then transmitted every 4-6 minutes randomly. Again the sensors will read the temperature more frequently, however the system will only alert you if the temperature exceeds 80°C/176°F.
One thing to note is that if you rotate the tyres on your vehicle, you MUST re-program the receiver unit inside otherwise it will think the sensor is on a different wheel.

The hidden down-side of current TPMS.
TPMS sensors need power to work. All the current sensors use batteries. Whilst these are rated for about 5 years use, or 250,000 miles, the batteries are not replaceable in any system. The manufacturers don't want a battery cover to come loose and start zipping around inside your tyre. For one it is dangerous to the inside of the tyre and for another, if the battery compartment opened, the battery would come out and you'd lose all sensor data for that wheel. As a result, the batteries are built-in to the sealed unit during manufacture. If you get a dead sensor, you need to buy a whole new one. Also, you know what batteries are like in extreme cold and extreme hot - bear that in mind if you regularly park in snow and ice....
Currently, there are no laws mandating manufacture dates to be put on these third-party systems. So if you buy one from a store, it could be brand new, or it could have been sitting on the shelf for a year. You've been warned.

Next-generation TPMS.
Several companies are working on the battery problem for the sensor modules. As I mentioned above, the basic pitfall of all existing systems is that at some point, the battery will wear out, and you'll need a new sensor. There are a few competing, emerging technologies right now trying to tackle the problem of perfecting transmitter-sensors that don't require a battery..
The Pera Piezotag system relies on the inherent properties of piezoelectric materials - that is a material which generates current when pressure is applied to it. The inside of a tyre is constantly at pressure so it seems reasonable that a correctly-manufactured piezoelectric wafer could generate enough current to operate the sensor just from the pressure inside the tyre.
The ALPS Batteryless TPMS system (licenced from IQ Mobil, a small German R&D company) is similar to an RFID chip in that it gets its power from the radio signal which interrogates it. Current systems, (including the Pera proposal) are classified as "active" transmitter / receiver systems. The sensors transmit signals of their own accord and the in-car receiver picks them up. The ALPS system is a "passive" RFID transceiver system. The sensors remain dormant and un-powered until the in-car transceiver sends a high-power short-range radio signal out which basically carries a "tell me your status" command. The RF power in the radio signal is enough to cause the RFID unit in the sensor to power up, take a reading, transmit it and power down. Clever eh? The downside of this system is that it's likely to be pricey compared to others coming to the market. There are 9 pcbs in their system; one in each wheel, one in each wheel arch and one in the console.
Transense Technologies in England are licensing their technology to SmarTire, Michelin and Honeywell. Unlike the Alps system, Transense's system has only one PCB and employs passive surface acoustic wave sensors (piezo-based again) at the inner end of each tyre valve. Their sensors monitor both pressure and temperature. It's worth noting that Transense hold the patent for resonant SAW technology which expires in 2019. Pera were exposed to this technology in the early 90's and have since come out with their own Piezotag system (see above). Coincidence?


Drivers are lazy. That is the very simple reason that all these companies are burning off millions in R&D budgets, sales and marketing. If we all checked our tyre pressures once a week using one of the tyre pressure gauges mentioned above, we'd know if there was a problem brewing. That is the ultra-low-tech approach.