Tire pressures

[Alwayssunny]

A simple question as it just sprung to mind, tire pressures should be taken cold as this is what it says in the manual, if the pressure is say 33psi cold the pressure will be 35psi when hot, so should the pressure really be adjusted when the tire is hot as this is what they are 99% of the time here?

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[wantan]

No, you should take your bike in a room with aircon for at least 1 hour before adjusting tire pressure. Alternatively you can cool down the tire with ice from 7eleven, but this is not a very accurate method. This only applies to very hot summer days, not needed in thai winter

Edited May 28, 2014 by wantan

[Alwayssunny]

No, you should take your bike in a room with aircon for at least 1 hour before adjusting tire pressure. Alternatively you can cool down the tire with ice from 7eleven, but this is not a very accurate method. This only applies to very hot summer days, not needed in thai winter

I'll pass on taking the bike into my room with air con as the gf would not be impressed, I'll also pass on the 7/11 idea as that's just ridiculous, maybe I'll wait for a better more sensible reply but cheers for your input!!

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[wantan]

Cold means you should not ride the bike before measuring. And you should not park the bike it in the sun too. If you stick to this you should be fine imo

[Alwayssunny]

I'm asking for an opinion on whether to actually adjust the tire pressure when cold knowing that the pressure will increase above what is recommended by the manual, if you take the pressure when cold it will be correct according to the manual but incorrect when the tire is hot, in other words a recommended pressure of 33psi will be approx 35psi when hot which is above what is recommended!

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[ThaidDown]

If the recommended pressure is 33 psi COLD in the manual then that is what you should fill to. The manufacturer has already allowed for the fact that HOT will be a higher pressure.

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[Alwayssunny]

If the recommended pressure is 33 psi COLD in the manual then that is what you should fill to. The manufacturer has already allowed for the fact that HOT will be a higher pressure.

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Cheers makes sense!!

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[macknife]

But if your tire is hot and your psi is currently too low, say 20, how much more above the recommended psi(lets say 30) should one put it?

[ll2]

do what is said in the manual apart from tire air pressures.

manuals always state a higher air pressure i guess for making the tires last longer ad let the bike accelerate easier.

But, i think it is better and more grip if you set the air pressure one or two PSI down that what is recommended.

Of course, at your own risk!

[wantan]

But if your tire is hot and your psi is currently too low, say 20, how much more above the recommended psi(lets say 30) should one put it?

How far above sea level? In winter or summer?

[RubberSideDown]

Ideally you should check your tire pressure in the morning or evening, or at least when the bike has been out of direct sunlight for a while during the day. While high ambient temperatures can have a small effect on tire pressure, even the heat of Thailand can't heat your tires to road or track temperatures and your tires are considered 'cold' if the bike hasn't been ridden for an hour or so, regardless of how hot the weather might be.

What hot weather can do is affect the ultimate temperature of your tires once the friction of the road surface has brought them up to full temp- if you're really concerned with setting your tire pressure properly, you have to measure it in both 'cold' and 'hot' conditions and see the degree to which it's changed, and then fill them (when 'cold') accordingly- you might find filling them to 33* when cold brings them up to, say, 37* when hot instead of the ideal 35*, in which case filling them a bit less would be the better move- obviously this would change in a more seasonal climate depending on the time of year you're riding.

[Alwayssunny]

Good and clear explanation, I set my pressures to 33psi cold and hot they increase to 35psi I'm happy with that!

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[ktm jeff]

If you check the pressures when the tires are "hot" , as you have ridden to the garage , as macknife asks , then setting them 3 / 4 / or 5 PSI over the "cold" recommended pressure will result in them being the correct pressure when cold.

[elgordo38]

I notice the tire pressure on our push bikes drops over a couple week period after putting air in them. Does the heat affect tire pressure?

[ktm jeff]

Pressure loss is normally poor quality inner tubes and /or tires or tire not seated. Or puncture !.

[papa al]

(Pressure x volume)/temp = k

if Boyle is to be believed.

[taotoo]

Did Boyle happen to mention what K is?

[Kwasaki]

Did Boyle happen to mention what K is?

' K ' = 4 fingers each side of tyre and press with both thumbs.

[papa al]

K=constant

[papa al]

(Pressure x volume)/temp = k

if Boyle is to be believed.

PV/T=k is the ideal gas law experimentally confirmed by Boyle.

So if temp goes up pressure and/or volume must go up also, as we see with our tires.

[Pinot]

I don't believe there is a rule of thumb for what the tires should be when they're hot. Take the tire pressure in the morning before riding the bike.