Low tyre pressure indicator

[b0rk]

The TPWS function of the standard ABS/ESP brake control module is not validated by the manufacturer for compatibility with 19" alloys hence VW not offering it as an option. R's have different brake control module by the same manufacturer that does have the TPWS function validated for 19" alloys.

The validation is more about ensuring the system always triggers on a low pressure / loss of pressure event.

[RW1]

Maybe a clue? There are two!

TPMS Byte Bits.JPG

C.

[lugano]

So if its not validated by the manufacturer then how come its still possible to retro fit it?

[RW1]

Because you can switch it on and it thinks the wheels are valid..... Just may not work properly.

C.

[lugano]

So is it a gamble retro fitting it since it may not work properly. Are there guys out there who have retro fitted & does it work ok for them? or was it a waste of time

[b0rk]

The system doesn't actually know how large the wheel is or even the tyre pressure, it works by calculating the rotational diameter.. An underinflated tyre has a smaller rotational diameter than a properly inflated tyre on the other wheels. However the smaller the sidewall the less the diameter changes with loss/reduction of pressure.

The system will work with larger wheels than validated you'll just find it will not trigger until the tyre has lost a lot more pressure... due to the lower profile tyre being inherently stiffer.

[lugano]

So if it will work with larger wheels then will it let a person know in good time before it becomes that much deflated that it would render it unrepairable?

[RW1]

The key is in this post (Link).

During learning the system can only detect changes in tyre pressure of about 10psi. On maturity of the learning process this improves to detecting about 4 - 5 psi drop before the speedo dial tyre warning symbol comes on.

Now thats based on actuals using 17 inch wheels with 45% profile tyre. When compared to a bigger wheel at 19 & above with lower profile tyres to get to that radius & therefore speed change in the algorithm.......

So with a 19 inch/35% profile the characteristic will be less pronounced, so the TPMS will be more delayed in reacting as the code is not programmed for that adjustment of wheel size in the ABS-Brakes controller as I showed in the graphic above.

Plus bear in mind, the TPMS is not the end all, be it of all...... If a tyre is going down fairly quickly, you'll have flat tyre before you can stop from speed with very little or no warning. Its really a system to say a tyre is running under inflated, check inflation soon......
Even when I let a tyre down by 6psi with the system fully learnt during testing, it took nearly 0.5 mile to react.

And the learning process may take 60 miles at 70mph but in urban driving with a daily average of 20mph, it took 900 miles to maturity, ie. 4 - 5psi detection level. Seems its how you drive in the first 50 - 100 miles after resetting influences how long to maturity as does how well balanced the tyres are.

The system can detect a rebalanced/repaired tyre and the more the balance is out, the longer it takes to mature (There is a vibration component in the calculation). So you can assume the TPMS after pressing the button/resetting with VCDS is operating for quite some distance where a deflation can go undetected on a particular tyre at as much as -10psi for the wheel configuration which the system is validated for.

Bottom line is you switch it on or you don't. If you do, at least its going to alert the best it can and thats better than nothing while on the move. If you want bricks & mortar, fit soild rubber tyres!

C.

[lugano]

Nice detailed explanation, thanks

[1 6 D]

I have activated this in my Rocco, and I found that in adaptation of brake electronics there is new channel active. It's number 1. I can set there from 0 to 7 or 8. With not activated TPMS this channel is not available. Can somebody with stock TPMS check what setting he have and what wheels/tires are when car was new?

Older brake electronics MK60 in Golf 5 have in this channel wheel size setting(0=15 inch, 1=16 inch or similiar). In MK60EC1 there is no description for this channel.