[Prime]

Okay, this shouldn't be overly hard to figure out, but I want to get a second opinion...

I check the tire pressure on my Wee maybe once every two-three weeks or so. I usually do this in the mornings while bike is warming up and while I'm putting on my jacket and whatnot. My Wee is always garage kept and the outside temp lately is not overly hot or cold. Not really enough to distort tire pressure readings.

I try and keep my tires at 37 psi front, and 40 psi rear. If a check of the tires indicate they need some air I have to ride to my local gas station and use their air pump. Now this is a nice pump BTW, not your stereotypical crappy one. I use two gauges to verify accuracy. Anyways, by the time I get there the tires have greatly warmed up and what was just an under inflated tire is now warmed up to normal psi.

My question is: If my cold rear tire was, say, 3 psi low, do I simply add 3 psi to the warmed up tire? This would mean putting 43 psi in my rear tire. Is this cool?

 

[EC90T]

No. The reason why you check air pressures when the tire is cold is a underinflated tire will heat up more than a properly inflated one, thus raising the pressure in the tire. The results you're seeing is the product of an underinflated tire. This is why in the cooler,wet, times of the year I'll run my tires with slightly less pressure to build up more heat. This will allow the tire to stick better and work more efficiently.

Go out and invest in a small compressor or air tank so that you can adjust your tire pressures when the tires are cool.

 

[LordSmoke]

Don't have an answer to your original question, but a simple hand pump eliminates the issue for me. I ave a 12v, but don't bother getting it out for a top off.

 

[realshelby]

While it would be hard to get a tire/bike manufacturer to quote this to you, many "tire experts" will tell you the point of a "cold" tire pressure is a starting point that will net you about a 10% increase in pressure when the tire is up to operating temperature. Obviously when riding different rodes, surfaces, and temperatures this will vary. This procedure works very well when riding on asphalt. You might be surprised at how close this technique will come to mirroring your factory recommended pressure on tires your bike comes with!

Back to the point of the thread, if you add 3 pounds after it is hot you are probably just fine. What you then need to do is check it that evening or next morning while it is cold and see if the pressures are exactly what you want them to be. A little trial and error and you will be able to get it just right!

( you can always bleed a little off if you are a pound or two over )

 

[dl1busa0]

37-41 here checked in the shed the night before a ride and don't check again till next trip.

 

[Stalky Tracker]

... Back to the point of the thread, if you add 3 pounds after it is hot you are probably just fine. What you then need to do is check it that evening or next morning while it is cold and see if the pressures are exactly what you want them to be. A little trial and error and you will be able to get it just right!

That's what I would do in your situation. Fortunately, I have a compressor and check and air up periodically. I am not overly anal about tire pressure, and have noticed no difference between a pound or two either way.

YMMV

 

[johnnail]

"local gas station"....how local? If you're only riding a couple miles, pressure won't be off much.

Tire pressure is very misunderstood--you are allowed 7-10% pressure rise between hot/cold. For example, a 40psi cold tire is OK at 44psi after an hour's hard ride. If it's higher than that, you need more pressure.

 

[Ahnold Stromzenegger]

Tire Pressure

I go with the 10% rule that RealShelby mentioned. I run my tires 33 lbs in the front, 36 lbs in the rear cold. At full operating temperature, that would be plus 3.3 lbs (36.3 lbs) in the front and plus 3.6 lbs (39.6 lbs) in the the rear. I don't get that worried about it though. If I checked warm tires I'd look for 36 and 40 and/or bring the tires up to that pressure. You would have to be really anal to worry about it any more than that.

 

[juddspaintballs]

I picked up a bicycle pump with the T handle at a swap meet to keep in my garage to top off tires (before I finally ran electric out there). It said it was good to 50 psi, so it worked fine for inflating both of my bike's tires. Definitely worth the $5 investment and a whole lot quicker than waiting for my air compressor to build pressure.

 

[johnnail]

I picked up a bicycle pump with the T handle at a swap meet to keep in my garage to top off tires (before I finally ran electric out there). It said it was good to 50 psi, so it worked fine for inflating both of my bike's tires. Definitely worth the $5 investment and a whole lot quicker than waiting for my air compressor to build pressure.

A wise man would carry a plug kit and slime pump under the seat. Just sayin'

 

[bwringer]

I picked up a bicycle pump with the T handle at a swap meet to keep in my garage to top off tires (before I finally ran electric out there). It said it was good to 50 psi, so it worked fine for inflating both of my bike's tires. Definitely worth the $5 investment and a whole lot quicker than waiting for my air compressor to build pressure.

Yes, this.

Even if you have an air compressor, a bicycle pump is often faster for topping up motorcycle tires. Even a pretty nice floor pump is cheap, small, nearly silent, and will add a few PSI with just a couple of strokes.

 

[OydnaR]

My question is: If my cold rear tire was, say, 3 psi low, do I simply add 3 psi to the warmed up tire? This would mean putting 43 psi in my rear tire. Is this cool?

the question should BE

:yikes: I'm 3psi low why, do I have a slow leak ? did the temperature drop 50° overnite

to answer your question, how far is it to the air pump ? a short ride moderate pace, NO STOP AND GO, 5 or 6 miles, sure, add 3psi, if that ain't close enuf, yer to anal

or is it 318 turns in 11 miles, if so, let all the air out of your tires and reinflate with fresh air to your warmed up tire pressure I just posted that in the internet, so its gotta be true, right

the reason I emphasize STOP AND GO, is cause brake application and acceleration is what exersizes the tires carcass and heats it up quicker, waging side to side does very little to heat up a radial tire (and looks kinda dorkey when ya see someone doing it :green_lol:



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[Dino M]

I was on my way back from vacation towing my boat with my truck. I felt something odd after about two hours on the highway so I pulled into the next rest area to have a look-see. Everything looked fine including the temperature of the trailer hubs. Simply out of curiosity I check the tire pressure on the truck. The tire pressure cold was set to 35psi. The hot temp was 58psi. I'm not sure if this relates but the tires were fairly new, aligned and inflated correctly so the added psi was caused by high speed and high load. The odd sensation was I suspect caused by the newly paved road but I think the increased tire pressure was normal. I think under the right conditions, tire pressure can get quite a bit higher than we suspect.

 

[LordSmoke]

I think the following might be relevant...

Gay-Lussac's law: P=kT, P=pressure, T=temperature, k=constant

P1 = 37 psi
P2 = pressure at pump - ?

dP1 = 3 (what you want to add cold)
dP2 = what you need to add at the pump - ?

Given you know the psi at the pump, the constants and temps cancel out, so:

dP2 = (P2/P1)dP1

If your pressure when you get to the pump is, say, 45, then you would add:

(45/37)*3 = 3.65 psi

This assumes an ideal gas and that the tire volume remains constant. Also, the temperature of the air from the pump is not likely to be the same as that in the tire, and its addition will change the temperature of the air in the tire, so this could become a more complicated problem. If the tires don't heat up too much, just add three psi.

DISCLAIMER: I am not a physicist, nor have I ever played one on TV.