Opinions on tire pressure
04-01-2001, 01:14 PM
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Opinions on tire pressure
After picking up my new 225QC yesterday, I went out and purchased a digital tire gauge. All tires were different. RF = 48, LF = 41, RR = 36, LR = 38. Dealer prep a little lacking! I adjusted all to the specs on the fuel cover. 36 front, 33 rear. What is the general consensus on the best pressure settings.
04-01-2001, 01:35 PM
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Not trying to argue, but wouldn't you want to take the air pressure...(more)
at what ever the operating temp/conditions are?
If you take pressure readings when the tire is cold, and inflate to the recommended pressure, wouldn't the heat buildup in the tire, from driving, increase the air pressure in the tire?
I have no idea what the change would be, and I suspect under street driving it would be minimal, but for track conditions it could be substantial.
Haven't tested this out, but this is what I recall from a thrermodynamics class - increase in heat equals increase in pressure.
Just a thought.
If you take pressure readings when the tire is cold, and inflate to the recommended pressure, wouldn't the heat buildup in the tire, from driving, increase the air pressure in the tire?
I have no idea what the change would be, and I suspect under street driving it would be minimal, but for track conditions it could be substantial.
Haven't tested this out, but this is what I recall from a thrermodynamics class - increase in heat equals increase in pressure.
Just a thought.
04-01-2001, 01:54 PM
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Yes, temps increases when operating, but...
the recommended tire pressures take that into account.
I assume the philosophy is that it's pretty easy to arrange to take the
tire pressure when you KNOW they're "cold" (at least, at ambient temp),
and from there, you can predict what pressures the typical high temps
will produce. Also, it's convenient - when the car has been sitting in the
yard/garage and you're about ready to go somewhere, the tires are still
"cold", so you are starting from a known point.
(disclaimer: if part of the car has been sitting in direct sunlight for a while,
that CAN affect temp/pressure a bit; best to avoid such situations if possible)
It's a lot harder to decide after the car was been driven a bit where the
tires are located on the temperature/pressure spectrum. Are they at the
top, or somewhere in the middle? And given the actual temp/pressure at
the time, is it correct, or how much does it need to be adjusted?
It's a lot harder to come up with a simple rule for that case.
Not impossible, but a lot harder to put into the owner's manual,
along with that new "tire thermometer" that you'll need!
I assume the philosophy is that it's pretty easy to arrange to take the
tire pressure when you KNOW they're "cold" (at least, at ambient temp),
and from there, you can predict what pressures the typical high temps
will produce. Also, it's convenient - when the car has been sitting in the
yard/garage and you're about ready to go somewhere, the tires are still
"cold", so you are starting from a known point.
(disclaimer: if part of the car has been sitting in direct sunlight for a while,
that CAN affect temp/pressure a bit; best to avoid such situations if possible)
It's a lot harder to decide after the car was been driven a bit where the
tires are located on the temperature/pressure spectrum. Are they at the
top, or somewhere in the middle? And given the actual temp/pressure at
the time, is it correct, or how much does it need to be adjusted?
It's a lot harder to come up with a simple rule for that case.
Not impossible, but a lot harder to put into the owner's manual,
along with that new "tire thermometer" that you'll need!
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04-01-2001, 01:56 PM
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From what I've learned...
about tire pressure, why would you want to check it when its cold? well thats the only time when the pressure in all 4 wheels have settled down. (for example checking it in the morning while the car has been rested for the entire night) Because as it heats up under normal driving conditions, the pressure in 4 wheels are not equal, the left tires may not have the identical pressure as the right tires, and vice-versa, there for while checking up on the pressure at that time wouldn't be accurate. Yes you would expect the air to expand under heat, thats what you want. This is only from what I have learned and been told, it makes sense to me, so thats what I believe in 
04-01-2001, 07:18 PM
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In other words, tires heat irregularly depending on road grade, number of right vs.
left turns. So that is why we test them cold. They are all exposed to the same external factors at once.
Or did he just say that?
Or did he just say that?
04-01-2001, 07:20 PM
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Which tires? I run different pressures on my RE730's than I did on my Bubbletenzas...
since the sidewall is harder on the RE730 it changes ride quality.
My guidelines: check em cold, keep rears 3 lb lower than fronts, trial and error to what feels good to your bum and don't exceed the rated max pressure written on the sidewall, even when hot! I am running 38/32 right now.
My guidelines: check em cold, keep rears 3 lb lower than fronts, trial and error to what feels good to your bum and don't exceed the rated max pressure written on the sidewall, even when hot! I am running 38/32 right now.