W205 pre-facelift - switch tyre pressure units from Kpa to PSI - how?

[cws196]

as per title, anyone know how to do this without STAR or accessing engineering menu?

 

[Farmer boy]

I have tried to do this without success. There are no settings in the car that will do this. In another thread on the forum it was suggested that you could change the settings via Mercedes Me; changing the units this way only changes how they are shown on Mercedes Me and does not change the units on the in car display.

 

[cws196]

I think changing the settings via MercedesMe for the actual car only works on MBUX.

 

[st13phil]

As a guess, it would be tied to other units - probably temperature - if it can be done at all, so you may be able to code it to display PSI, but you may also get temperatures in Fahrenheit instead of Centigrade.

 

[Bobby Dazzler]

I’ve never found a way to change the units either. I set and check the pressures (with a gauge) in PSI or Bar, and then reset the TPMS in the car. Then between checks I use TPMS to make sure that they’re the same (or very similar) across the axle, and that they’re roughly the same as on my last journey.

To be fair I would probably do that even if it was displayed in PSI, as I’d never remember the the right pressures across multiple cars in different Summer/Winter and light/heavy load scenarios. Fortunately, I never have to remember the variations for high speed running as I never drive above 155 MPH on the road.

One quirk that I’ve found is that even though tyre pressures are the same across the axle when measure in PSI or Bar when set and checked using my hand held gauges, but the car displays slightly different pressures using TPMS. Naturally the pressures vary whilst in use, but they’re usually different on first “display”, and when cruising in a straight line.

 

[ShaunB]

You can change it to PSI in the Mercedes me app, but its just the app that changes.

 

[23 Romeo Tango]

I brought this up with my dealership over 2 years ago. I was told that it isn’t possible to change the reading on my dash to PSI, but they could provide a printed conversion table that I could stick to my windscreen as a guide

 

[GeeJayW]

I’ve never found a way to change the units either. I set and check the pressures (with a gauge) in PSI or Bar, and then reset the TPMS in the car. Then between checks I use TPMS to make sure that they’re the same (or very similar) across the axle, and that they’re roughly the same as on my last journey.

To be fair I would probably do that even if it was displayed in PSI, as I’d never remember the the right pressures across multiple cars in different Summer/Winter and light/heavy load scenarios. Fortunately, I never have to remember the variations for high speed running as I never drive above 155 MPH on the road.

One quirk that I’ve found is that even though tyre pressures are the same across the axle when measure in PSI or Bar when set and checked using my hand held gauges, but the car displays slightly different pressures using TPMS. Naturally the pressures vary whilst in use, but they’re usually different on first “display”, and when cruising in a straight line.

I'm not convinced that the TPMS sensors are particularly well calibrated. I've tried several times to inflate the tyres uniformly, but have yet to see uniform type pressure displayed on the dash.

Spent most of my working life working with kPa, mBar, psi, mmHg and (too much lesser extent) inHg, so just live with it as is.

We are an odd bunch. We buy fuel in litres, the engine consumes fuel and air by the kilogram, we discuss miles per gallon, have adjusted to using Celsius for ambient temperature, but the still talk about it being 90 in the shade. We buy litres of milk, pints of beer. Engine performance has for decades been measured in kW and Nm, yet we discuss horse-power and lbs.ft or even horse-power and Nm. Tyres are described as being xxx mm wide whilst rims are y inches in diameter and n inches wide with z mm of offset. Etc..

I find it quite astonishing that even after many decades, the SI system of measurement has not been broadly adopted. On the other hand, there are many many other examples where particular language and behaviour have very long legacies in society.

 

[Bobby Dazzler]

I'm not convinced that the TPMS sensors are particularly well calibrated. I've tried several times to inflate the tyres uniformly, but have yet to see uniform type pressure displayed on the dash.

I’m glad it’s not just me!

 

[190]

kPa may be the scientifically correct preferred unit of pressure measurement but it's a particular inappropriate unit to apply to the pressures used in tyres. The decision to use kPa's can only have been made by men in white coats remote from the real world where kPa's are not common currency.

This is not about imperial vs metric. We don't have to look backwards and use PSI when the perfectly sensible unit of Bars is available and what are kPa's but Bars with some noughts added. Except for very low pressure measurements, using Pascals is the scientific equivalent of political correctness and just as stupid.

 

[GeeJayW]

kPa may be the scientifically correct preferred unit of pressure measurement but it's a particular inappropriate unit to apply to the pressures used in tyres. The decision to use kPa's can only have been made by men in white coats remote from the real world where kPa's are not common currency.

This is not about imperial vs metric. We don't have to look backwards and use PSI when the perfectly sensible unit of Bars is available and what are kPa's but Bars with some noughts added. Except for very low pressure measurements, using Pascals is the scientific equivalent of political correctness and just as stupid.

So 2.55 Bar is preferable to 255 kPa?

 

[SW18]

I still think in PSI when inflating tyres, so my way around the in-car TPMS display showing only in Bars is to test my mental arithmetic! The TPMS reads in Bars so I multiply by 14 to get PSI. Whiles away time on long journeys...

 

[GeeJayW]

I still think in PSI when inflating tyres, so my way around the in-car TPMS display showing only in Bars is to test my mental arithmetic! The TPMS reads in Bars so I multiply by 14 to get PSI. Whiles away time on long journeys...

2 Bar = 29 psi

 

[SW18]

2 Bar = 29 psi

I'd better adjust my arithmetic to 14.5 then!

 

[190]

So 2.55 Bar is preferable to 255 kPa?

Much preferable, if only because it's more easily multiplied by 14.5 to get to real units

 

[Mickyh7]

29.4 to be exact
1 Bar = 14.7 psi at Sea Level !