„During a test drive consisting of two equally long laps – 7.7 kilometers from the Schwentinental district of Raisdorf via the L 52 to Klausdorf and back – the fuel-saving training actually proved effective. Pfeiffer’s first tip: „Check your tire pressure regularly!“ If it’s just 0.3 bar too low, fuel consumption increases by 25 percent.“ http://www.kn-online.de/lokales/ploen/229237-Kosten-fuer-Benzin-sparen.html
This doesn't just work during ADAC test drives; it works with your own vehicle too. If you want to monitor your tire pressure while driving, if you don't want to waste valuable time at gas stations checking the pressure – only to find it was correct after all – if you want to drive smart, then a tire pressure monitoring system is worthwhile. TireMoni

