Tyre Pressure Monitors

[BuRP]

How do you determine the actual?

Try a tyre pressure gauge?

[TheBear]

How do you determine the actual?

Try a tyre pressure gauge?

Which you know is 100% accurate, I assume?

[BuRP]

Which you know is 100% accurate, I assume?

Your point is?
If you want 100% accuracy keep on dreaming.
If you want 95+% accuracy have it calibrated at your local SANS Laboratory - and know it may only be that accurate for the duration of the testing there, never mind a validity duration specified on the Certificate you'll be handed.
If however you only want all sensors to display the exact same value on the dash as the exact same tyre pressure gauge's value then refer my 100% accurate above.

If on the other hand you want to use them for the purpose they were intended for, i.e monitors if not indicators, then I'm sure you know how to do that.
If after RTFM the literature describes them as 'accurate measuring instruments' then I'm wrong, my apologies in advance 

[Jughead]

I'm with @BuRP here.

They are intended as monitors, ie. to give a warning should there be a sudden downward change in pressure, or when their own lowest assumed safe pressure is exceeded.

To be quite honest, however, setting tyre pressures is blown way out of proportion.  You are not going to feel the difference between 2.2 bar and 2.4 bar.  Yes, you will feel a difference between 1.8 bar and 2.6 bar, especially when riding gravel.  So, really, whether the TPM (Tyre Pressure MONITOR) indicates 2.2 bar or 2.3 bar is irrelevant.  It is there to warn you if it's own reading changes drastically.

[BuRP]

give a warning should there be a .... change in pressure

I'm not one for gadgets, and I do consider these things just that.
But, when I rode the (rented) thing on day 6 it suddenly warned me, rather unmissable by a huuuuge warning on the display, that the rear was too low.
With about zero trust in this - battery low, glitch etc - I carried on, and only at the next town put really minimal air in - et presto, billboard gone!
Less than 10km on it reappeared though, so I searched for a petrol station again, bit more urgent this time..... when I found a slow leak, a screw in the rear.
Screwed by a screw, and luck had it that nobody could help me there, an AA towtruck was called.
I learned that these things can give an early warning, and that is nice to have!

Who cares what value they display as long as they do the job hmm?   

[Jughead]

Who cares what value they display as long as they do the job hmm?   

Precisely!

[n0b0dy]

Replace both front and rear, twice allready.
Problem is the correct battery that came with the TPMS is bigger ( 2x)  so they ( 2032) don't last as long.
The biggest Battery i can get here in SA is a 2032.
the battery required is a CR2050

I have imported some from Japan-land but they are costly. if anyone in SA have a supplier for this please let me know.

Thanks a stack

[Jughead]

Replace both front and rear, twice allready.
Problem is the correct battery that came with the TPMS is bigger ( 2x)  so they ( 2032) don't last as long.
The biggest Battery i can get here in SA is a 2032.
the battery required is a CR2050

I have imported some from Japan-land but they are costly. if anyone in SA have a supplier for this please let me know.

Thanks a stack

The "2032" and "2050" numbers refer to the physical size ie. 20mm diameter and 3.2mm thick for the 2032 and 20mm diameter and 5.0mm thick for the 2050. 

Capacity difference is 210mA for the 2032 and 290Ma for the 2050.

The important part is to get the tagged batteries as applying any heat to the actual battery destroys it.

[TheBear]

I'm with @BuRP here.

They are intended as monitors, ie. to give a warning should there be a sudden downward change in pressure, or when their own lowest assumed safe pressure is exceeded.

To be quite honest, however, setting tyre pressures is blown way out of proportion.  You are not going to feel the difference between 2.2 bar and 2.4 bar.  Yes, you will feel a difference between 1.8 bar and 2.6 bar, especially when riding gravel.  So, really, whether the TPM (Tyre Pressure MONITOR) indicates 2.2 bar or 2.3 bar is irrelevant.  It is there to warn you if it's own reading changes drastically.

I fully agree with you Jughead and that is why I wonder why anyone would trust an over the counter tyre pressure gauge and not trust the one already on the bike.  To me (personal feeling), it makes no sense.  The TPM on the bike is more than accurate enough for our purposes and your chance of buying a gauge that will be more accurate is slim.

@BuRP :  If you care to check, you will notice my question, that woke your sarcasm brain cell, was directed at someone who was comparing a bought tyre pressure gauge to his bike's TPM and believing one over the other.  It is okay, you can apologize later.