Porsche’s Tire Pressure Monitor (TPM)

Most Porsches from the last decade come equipped with a Tire Pressure Monitor (TPM). While it used to be an optional feature, it has gradually become standard equipment, and now every model includes it.

This warning appears when you get a flat tire

When inflating, check the ‘difference’ reading

The TPM displays tire pressure in real time while driving and alerts you if the pressure drops beyond a certain point. What’s great about Porsche’s TPM is that it tells you exactly how much air to add or release, based on the current tire temperature.

Some Porsche owners with TPM sometimes mistakenly tell gas station attendants to inflate their tires to a fixed number like “2.8,” based on the displayed pressure. This is incorrect. The correct way is to use the difference display and say something like “add 0.2 more,” so the pressure is accurately adjusted considering the tire temperature.

I’ve written a detailed article on this topic before, so please refer to it:

ポルシェの正しいタイヤの空気圧の入れ方について（TPMつき車種の場合）

Aftermarket Tire Pressure Monitors on Air-Cooled Porsches

While Porsches from 997 onward often come with TPM, air-cooled Porsches from before that era do not have this feature. However, having gotten used to always knowing the tire pressure on modern Porsches, I find it unsettling not to have that info, so I installed an aftermarket tire pressure monitor.

The aftermarket units replace the valve caps. I didn’t notice any wheel balance issues on either the 964 or the NISMO. The button battery lasts about two years.

The one I use is an inexpensive Chinese-made tire pressure monitor bought on Amazon. It measures tire temperature and pressure with almost no deviation compared to a proper gauge. It runs on a solar panel, so no wiring is needed, and it even alerts you when the pressure reaches the preset level.

It worked so well that I installed it not only on my air-cooled Porsche 911 (964) but also on my Nissan Note e-Power NISMO S.

Air-Cooled Porsche Gets a Flat: What Did the Tire Pressure Monitor Do?

Recently, while driving my air-cooled Porsche on the highway, a loud alarm suddenly went off.

The left rear tire pressure dropped to 1.9

Checking the monitor in a panic, I saw the left rear tire pressure had dropped to 1.9 bar. For a stock 16-inch 964, normal pressure is around 3.0 bar, so this was a significant difference from the right rear tire. It was clearly a flat.

I carefully drove to my destination, and after finishing work, I inspected the car in the parking lot. Sure enough, a small nail was stuck in the tire. Since the pressure was still around 1.9 bar, I slowly pulled into a nearby gas station.

I had the flat repaired on the spot without issue, but thinking about what could have happened if I hadn’t noticed and had driven on the highway until a blowout occurred is truly frightening. Especially since it’s rear-wheel drive—losing control could have been disastrous.

That experience made me truly grateful to have the tire pressure monitor installed. Nowadays, high-quality monitors are available at very affordable prices, so I highly recommend installing one if you prioritize safety.