Tyre Comfort Calculator

[SAC1]

Thanks Steve. Is the Good to Know App already in the car's PCM unit? If so, how is it accessed?

Yes it should be. If not download the app to your smartphone and pick your specific year and model from the list

[FirstSeaLord]

Steve's the expert, but this might also help

[DJMCUK]

Start off by leaving the pressures as now. Then go for a reasonably long drive- at least 15 minutes at above 50 mph. Bring the car to a halt. On the thumb wheel, scroll to tyre pressures (TPM). Press the thumb wheel and it will show how much air to add / remove from each tyre.

Steve, is that how much air to add/remove in relation to what I HAVE SET or to what the car already knows the pressures should be?

If the former, I'm no further forward as I don't know what pressures to set for other than 70F ambient temp... being anal, as I so often am.

If the latter, how does the car know how many occupants, luggage?

[dlgis]

I put this chart together to make life easier. All settings from cold:

tempC Front Rear
20-21 33 36
18 32.5 35.5
13 32 34.5
7 31 33.5
0 30 32.5

[DJMCUK]

Steve's the expert, but this might also help

Thanks. From 68F to 32F is around 8% reduction, so for example the usual 2.5 BAR rear at 70F would come down to 2.3 at 35F, which is where I started with the tyres warm.

[SAC1]

Start off by leaving the pressures as now. Then go for a reasonably long drive- at least 15 minutes at above 50 mph. Bring the car to a halt. On the thumb wheel, scroll to tyre pressures (TPM). Press the thumb wheel and it will show how much air to add / remove from each tyre.

Steve, is that how much air to add/remove in relation to what I HAVE SET or to what the car already knows the pressures should be?

If the former, I'm no further forward as I don't know what pressures to set for other than 70F ambient temp... being anal, as I so often am.

If the latter, how does the car know how many occupants, luggage?

As long as you have correctly set the Load, Type - summer. all season or winter tyre options and tyre Diameter in the PCM, then it will tell you the relevant pressure adjustment needed. Take a look in the relevant GTK app page for full details.

[Nuclear Nick]

It’s extraordinary how often this question is asked and answered isn’t it Steve?

For those who may not have seen the previous many posts on this:

The tyre pressures should only be adjusted by consulting the ‘Fill info’ page in the TPM section of the Multi-function Display (MFD). After a short drive this will tell you the difference in pressure that is in your tyres compared to the recommended pressure. If the number is negative then you need to add that amount to that tyre or if positive then let that much out. Bear in mind that this fill info is corrected for tyre temperature so will be correct whatever the ambient temperature. This is why it is better to do it this way than by using a hand held pressure gauge. Of course the TPMS needs to have the correct tyre information already entered in the car’s settings.

[SAC1]

It’s extraordinary how often this question is asked and answered isn’t it Steve?

For those who may not have seen the previous many posts on this:

The tyre pressures should only be adjusted by consulting the ‘Fill info’ page in the TPM section of the Multi-function Display (MFD). After a short drive this will tell you the difference in pressure that is in your tyres compared to the recommended pressure. If the number is negative then you need to add that amount to that tyre or if positive then let that much out. Bear in mind that this fill info is corrected for tyre temperature so will be correct whatever the ambient temperature. This is why it is better to do it this way than by using a hand held pressure gauge. Of course the TPMS needs to have the correct tyre information already entered in the car’s settings.

I agree Nick. The more so when how to check levels for the coolant, screen wash, brake fluid and oil is hardly ever asked about.

[Neil1911]

It’s extraordinary how often this question is asked and answered isn’t it Steve?

For those who may not have seen the previous many posts on this:

The tyre pressures should only be adjusted by consulting the ‘Fill info’ page in the TPM section of the Multi-function Display (MFD). After a short drive this will tell you the difference in pressure that is in your tyres compared to the recommended pressure. If the number is negative then you need to add that amount to that tyre or if positive then let that much out. Bear in mind that this fill info is corrected for tyre temperature so will be correct whatever the ambient temperature. This is why it is better to do it this way than by using a hand held pressure gauge. Of course the TPMS needs to have the correct tyre information already entered in the car’s settings.

I agree Nick. The more so when how to check levels for the coolant, screen wash, brake fluid and oil is hardly ever asked about.

I recall at some point since I got my first S (1 Sept 2019) a thread that got deeply into the physics/thermodynamics of this. At that point the "look at and follow the TPMS>Fill info" nugget wasn't raised, that came later. Worth its weight in gold too! I'm -1 all round at the moment but it'll have to wait for a rise in temperature before it gets any attention.

[On-Track]

It’s extraordinary how often this question is asked and answered isn’t it Steve?

For those who may not have seen the previous many posts on this:

The tyre pressures should only be adjusted by consulting the ‘Fill info’ page in the TPM section of the Multi-function Display (MFD). After a short drive this will tell you the difference in pressure that is in your tyres compared to the recommended pressure. If the number is negative then you need to add that amount to that tyre or if positive then let that much out. Bear in mind that this fill info is corrected for tyre temperature so will be correct whatever the ambient temperature. This is why it is better to do it this way than by using a hand held pressure gauge. Of course the TPMS needs to have the correct tyre information already entered in the car’s settings.

I've followed this practice since owning my SD but somehow it always seems counter intuitive. For many years with whatever car I happened to own at the time I would add air in the midst of winter and release it at the height of summer so that the pressures were "correct" at the average temperature for that time of year. As digis' chart shows, tyre pressures at zero degrees centigrade are around 10% lower than at 20 degrees. Porsche seem happy with that and, presumably, so are their preferred tyre manufacturers so who am I to argue.