TPMS activation points
 

Does anyone know how low does the tire pressure have to go, before the TPMS (Tire Pressure Monitor System) warning lights up on the dashboard?

Did you check the manual?

I had asked the dealer and they said 25%, so - 32psi +- 25% = 24psi to 40 psi

http://www.finishlineperformance.com.../docs/0018.pdf
There, I found it... 26psi on the low side, and 49 on the high side. Hm, thought the stock tires state 42PSI max, wonder how much the 49PSI limit helps?

I'd test it if I had a good compressor or air source laying around.

42PSI would be the cold pressure. The TPMS probably has to allow for the tires heating up and raising the pressure.

My sensor light came on at 26 psi last week when the temp dropped in NOLA. I inflated all 4 to 30 psi to allow room for ithe pressure to increase once the car was driven and temp rose.

Just for another data point, mine came on this morning, one tire was at 24.5, all others at 31... damn slow leaks.

You don't need to allow room
 

Set it to the recommended temp. That's the recommended COLD temp. They already consider that it will increase with temperature when driving. Although 30 is probably fine, if you prefer that, but I'm just saying 32 cold is "right" and will probably get you slightly better gas mileage.