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Cold weather - Tire pressure Q

ecka00

Tuned and Synch'ed
Joined
Aug 13, 2011
Messages
32
Location
USA
It's the high 30's/low 40's this morning and I checked my tire pressure; Front 30 / Rear 38. So I pumped them up to 34/40 (manufacture recommends 36/42). My question is this--I know that when the tires warm up the PSI changes so I was concerned if I filled them to the recommended 36/42 when this cold they would be over recommended PSI when brought up to running temp. Am I over thinking this? What does everyone else do?
 
The recommended PSI is always cold pressures.

So I assume you are worried about the tires being over inflated do to the large ambient temperature swings (ie 30+ swings) between morning and afternoon this time of year in OH.
ie. If you set the PSI correct in the morning on your way to work. They will be overinflated coming home from work.

At times I've been really anal; by setting my PSI correctly in the morning, carrying a tire pressure gauge with me, and re-setting my PSI in the afternoon before leaving work.
BUT that tends to get annoying after a couple days.

So with the rule of thumb being a 1 PSI change for every 10° Fahrenheit change in air temperature.
Even with a 30° Fahrenheit rise in temperature. There won't be too much of a PSI change.
I usually set the PSI correct for the mornings and let the tires be slightly over inflated in the afternoon.

The trickier part of setting cold tire pressures this time of year.
Is the large temperatures swings combined with the temperature of the place where you keep your motorcycle (aka garge) usually being much warmer than the outside temperatures.
 
As ET said, recommended pressures are when the tires are cold - cold as in not warm from being run, not cold as in outside temperatures. It doesn't matter when during the day you check and adjust, as long as you're doing it regularly (2-4 times a month for me).

Don't worry about the outside temperature change during the day; if that was an issue, we'd be airing up every morning and letting air out every afternoon. Set your pressures to recommended and go. You are trying to avoid being 5-10 psi low - a couple of psi due to ambient changes is not a big deal.

My $.02.

Tom
 
You are over thinking this in my opinion.
What is key is that the air pressure is right at operating temp. The tires getting colder will lower the air pressure reading if you check it when they are colder (although not by much). But the tires will still be at the correct air pressure once they warm up to operating pressure.
Aside from keeping track of the pressures to make sure they do not drop beyond the amount expected from changes in temp I would not adjust the pressures in response to changes caused by ambient temperature changes.
Again, it is the final pressure when at operating temperature that matters.
 
Actually, what really matters is the temperature of the tire. The hotter the tire (up to a core temperature of 100 degrees centigrade), the more traction is available. The lower the tire pressure, the more a tire flexes. The more a tire flexes, the more heat is generated. The hotter the tire more traction is available but there is more wear. Recommended tire pressures are developed to give a balanced trade off between tire stick, and tire life. However if the tire pressure is too low, handling is compromised. If pressure is too high, there isn't as much traction available as the tire stays cool.
 
"Again, it is the final pressure when at operating temperature that matters."

It is both. The tire needs to be in the right temperature range for the rubber of the tire to offer the best grip.
The tires are built so that the correct air pressure should result in the tire reaching that temperature. The air pressure also plays a part in the tire being able to carry the load as well as the shape and size of the contact patch.
The end result is that once the tire is at the correct cold pressure to achieve those goals a reduction in ambient temperature resulting in a slight reduction in cold pressure does not affect things. It would still be the correct cold pressure to reach the correct hot pressure. Adjustments to cold tire pressure due to ambient temperature changes are not required and if performed may result in the tire not reaching the correct hot pressure/temperature.
When it becomes cold out the measure cold pressure of the tire will be lower. If you add air at that point to bring the cold pressure back up you are reducing the amount of heat the tire will generate and thus the amount the pressure will rise during use. That may result in the tire never reaching the prescribed operating temperature and/or pressure. That would result in a reduction of grip, and if it is cold out it is exactly the wrong time to be reducing the amount of heat and grip the tire generates.
 
+1 We ain't running MotoGP machines which tie pressures are usually much lower than what we run. My book says 36.3 psi is the recommended. Do you think you can keep it at 36.3 psi? Are they talking about after a ride or before a ride? Are they talking a hot day or a cold day, or is the pavement cool or hot? My personal thing is +/- 10% and it works for me. I usually check mine every couple of weeks depending on how much I've been riding. To try to keep it closer than that is really being anal. Tread is a lot for important that air pressure. Go romping around a corner an a cool damp road as you pull out of the garage may not be the best decision you made that day! Give the tires a few miles to get some temp in the tread and you'll still want to take it easy as the road isn't going to warm them up much.
Bare

"Again, it is the final pressure when at operating temperature that matters."

It is both. The tire needs to be in the right temperature range for the rubber of the tire to offer the best grip.
The tires are built so that the correct air pressure should result in the tire reaching that temperature. The air pressure also plays a part in the tire being able to carry the load as well as the shape and size of the contact patch.
The end result is that once the tire is at the correct cold pressure to achieve those goals a reduction in ambient temperature resulting in a slight reduction in cold pressure does not affect things. It would still be the correct cold pressure to reach the correct hot pressure. Adjustments to cold tire pressure due to ambient temperature changes are not required and if performed may result in the tire not reaching the correct hot pressure/temperature.
When it becomes cold out the measure cold pressure of the tire will be lower. If you add air at that point to bring the cold pressure back up you are reducing the amount of heat the tire will generate and thus the amount the pressure will rise during use. That may result in the tire never reaching the prescribed operating temperature and/or pressure. That would result in a reduction of grip, and if it is cold out it is exactly the wrong time to be reducing the amount of heat and grip the tire generates.
 
The funny thing to me is how, in the road racing world, they have switched from setting air pressure cold to setting air pressure hot. This may in part be driven by the use of tire warmers, but it is still odd to me. Yet it is what they do and clearly they make it work.
I am still old school and subscribe to the 10 - 15% increase in pressure cold to hot. We tend to use 15% when you are working the tires hard and 10 would be for more sedate riding, I don't use 10% much.
 
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