tire pressure

[leokaplin]

is the 42 tire pressure that is written inside my door for the model X 90d COLD or HOT?

currently i'm at 37 in the AM, but get to 40-41 when driving...

If I pump to 42 for each tire COLD, when its hot it might be close to 45,46,47.. is that OK?

 

[gearchruncher]

Door stickers are for "cold" temperatures. But even that is fuzzy, since cold is a standard day which is about 72F.

 

[leokaplin]

Yeah, that is the average HIGH here in NY

 

[bikeandsail]

Tire pressures should be adjusted in the am before the sun hits the tires and the car has been driven. They also need to be adjusted seasonally.

The tires should be 42 psi on a 80 degree summer day in the am. They should also be 42 psig on a 20 degree winter day in the am. Each of these conditions requires a significantly different amount of air in the tires. The main reason you should check your tires monthly is not because they loose air but so you can adjust for seasonally differences.

 

[leokaplin]

excellent info and very precise. thank you.

so on a 20 degree day the pressure might hit 48-50 after highway driving at high speeds.. no issues there?

 

[RobertSeattle]

OT, but are their any consumer vehicles out there that will actually maintain/adjust the tire pressure instead of just monitoring it? Just curious.

 

[jerry33]

is the 42 tire pressure that is written inside my door for the model X 90d COLD or HOT?

Tire pressure recommendations are always cold, first thing in the morning, before you have driven one mile slowly.

The ambient temperature at which the recommendations are made is always 18C (65F). If it's hotter, you need to adjust the pressure upwards to compensate. If it's lower and you inflate indoors where it's warmer (we're mainly taking below freezing here where the compressor inside the garage is much closer to room temperature) you need to adjust the pressure upwards to compensate.

When going on a trip with the family, be sure to add a bit to compensate.

The vehicle placard pressure is a starting point only and needs to be adjusted for the actual conditions you drive in--and your driving style.

Heat is what kills tires, not pressure. Also the air pressure in the tires is your main defense against pothole damage.

 

[jerry33]

OT, but are their any consumer vehicles out there that will actually maintain/adjust the tire pressure instead of just monitoring it? Just curious.

The Hummer H1 (the original before GM bought Hummer and turned it into a kit car) you were able to adjust the pressure from inside the car. Note however, that you never ever want to lower the pressure in a warm tire in normal use. (Off road at low speeds is a different story). Here's what happens:

The tire is set to some pressure. As you drive the tire heats up from flexing, the sun, and the ambient temperature change. This increases the pressure and reduces the flexing. Eventually, the amount of heat going into the tire is equal to the amount of heat leaving the tire. This state is called thermal equilibrium.

Consider two tires, one inflated to 30 psi and the other inflated to 40 psi. Both tires will eventually arrive at close to the same pressure, but the tire that started at 30 psi will be far hotter than the tire that started at 40 psi. Looking from a different direction, if you keep lowering the pressure to the starting pressure, the tire will never reach thermal equilibrium and will get hotter and hotter as the day goes on. In the worst case it will catch on fire (never a fun happening).

 

[ptsagcy]

excellent info and very precise. thank you.

so on a 20 degree day the pressure might hit 48-50 after highway driving at high speeds.. no issues there?

I keep mine at 42 cold and they haven't gone above 45 when completely warmed up.