tire pressure

[So Cal Joe]

I always check my tire pressure before I ride my bike, a short time back someone posted a different way to check them. Something about checking them cold and then running them for 15 minutes and checking them again, if they were over  so many pounds you added air or if they were over a greater amount   you let a pound or two out. Anyone have a link to this post, I want to try it.

[ZG]

Isn't it just supposed to be 42 cold?? 

[maxtog]

Isn't it just supposed to be 42 cold?? 

That is my understanding, also.  When I do check pressures, I always use a quality, dial-indicator type meter.  Life is too short to waste money on crappy meters (and there are a LOT of them out there).

I am not pleased that the TPS "temperature adjusts" because I can't remember what it is doing.  I would prefer it told me what the actual pressure was.  I am not stupid, I know the pressure will go up as the tires get hot.  It is just like yesterday, I had been riding 30 min and looked at the pressures and it said "40".  So I have to think "hmmm... is that 40 for real or some pseudo-40?  It should be something like 45 or 46 now."  Either way, it is low... will check with the real meter before next ride.

[B.D.F.]

Kind of.... the problem is what is 'cold'? I believe that the nominal cold is 20C or 68F. If you fill a tire to, say, 42 PSI when it is 90F outside and the tire 'cold' from sitting overnight, you will put less air into that tire than you would if you had filled it at 68F. It is actually a complex issue as to how much air we should be putting in a tire but a good 'rule of thumb' is to add or subtract one PSI for each 10 degree change from 68F (I use 70 'cause I can do it in my head). So if it is 90F outside and I am shooting for 42 PSI, I put fill the tire to 44 PSI. If it is 20F out and you are the only motorcycle that will be out riding, and we are still shooting for the nominal 42 PSI, then I would fill the tire to 37 PSI.

The goal is basically to get the same amount of air in the tire at any ambient temperature.

Either that or just put air into the tire until the bottom is about the same shape as the top. 

Brian

Isn't it just supposed to be 42 cold?? 

[curly]

I have a digital roadgear gauge. I just put 42 psi cold no matter what the temp is and hit the road

[ZG]

Kind of.... the problem is what is 'cold'? I believe that the nominal cold is 20C or 68F. If you fill a tire to, say, 42 PSI when it is 90F outside and the tire 'cold' from sitting overnight, you will put less air into that tire than you would if you had filled it at 68F. It is actually a complex issue as to how much air we should be putting in a tire but a good 'rule of thumb' is to add or subtract one PSI for each 10 degree change from 68F (I use 70 'cause I can do it in my head). So if it is 90F outside and I am shooting for 42 PSI, I put fill the tire to 44 PSI. If it is 20F out and you are the only motorcycle that will be out riding, and we are still shooting for the nominal 42 PSI, then I would fill the tire to 37 PSI.

The goal is basically to get the same amount of air in the tire at any ambient temperature.

Either that or just put air into the tire until the bottom is about the same shape as the top. 

Brian

Well lucky for me I live in the PNW, we haven't broke low 80's at all this year... 

[VirginiaJim]

I have a digital roadgear gauge. I just put 42 psi cold no matter what the temp is and hit the road

+1  It ain't rocket science.

[Mister Tee]

Street tire pressure ratings are always cold.  They only time when you would adjust pressures for hot tires (other than outside ambient air corrections) is when you are using race tires that are intended to be heat cycled - there is a significant difference between hot and cold temperatures and they are intentionally kept hot for grip.

[mkorn]

On my 09 the pressure goes up as i ride and if i run through a set of twisties the pressure goes up and then goes back down on a straight section ... according to the dash read out.
are you sayin that the computer compensates for the tire warming up?

[Mister Tee]

Of course the temperature will go up when you ride aggressively and down when you straighten out.  I'm not sure why the TPS would adjust itself for temperature, other than for internal calibration.

[fmwhit]

I usually run my Road Pilot 2's at abt 41 lbs. when the tires are warm according to the Tire Pressuse Sensors which by the way agree with my digital read out tire pressure guage.   I find if I fill them to abt 39 lbs in the morning after a few miles of riding they come right up to abt 41 when the tires warm up and the bike seems to handle fine.

Fred

[wally_games]

Well lucky for me I live in the PNW, we haven't broke low 80's at all this year... 

 
I live in North Texas and today is the 31st day in a row over 100! Supposed to hit at least 108 later this week. Needless to say, I'm limiting my riding to before 10:00 am.

I put 42 in my tires "cold", but with the nightly temp only getting down to about 84, that's not exactly the correct way to describe it. My onboard sensors read about 2-3 psi lower than my gauges (quality digital).

[lt1]

I live in North Texas and today is the 31st day in a row over 100! Supposed to hit at least 108 later this week. Needless to say, I'm limiting my riding to before 10:00 am.

I put 42 in my tires "cold", but with the nightly temp only getting down to about 84, that's not exactly the correct way to describe it. My onboard sensors read about 2-3 psi lower than my gauges (quality digital).

This is a good example of what BDF was explaining.  Since you are filling the tires at about 20F above the "cold standard", you would need to put approximately 44psi in the tires to have the same amount of air in the tire as 42psi at 65F (or 68F - I've seen both used as the stated "cold" temp).

Air expands as it is heated.  More expansion = more psi.  More air mass (volume? I regularly misuse the words) = more psi.  The TPS in essence calculates the air mass by comparing psi & temp, and reports it as a compensated psi figure.  If the air in the tires was perfectly dry and the display resolved 10ths of a psi, the display would be pretty constant.  As with any electromechanical device, it is possible to have an inaccurate unit, but the tech is pretty accurate for the most part.  The more moisture in the air in the tires, the more the pressure rise curve is affected as the tires warm up.  IE, if your TPS moves a lot between hot and cold, you probably have a lot of moisture in your tires.

It may not be rocket science, but it is science & physics.  A lot of riders seem to struggle with the concept.  Since I have confirmed that my TPS matches my gauges at 65F, I set the pressure cold to target a 42 readout on the TPS.

[stevewfl]

tire and oil threads are always epic

[stevewfl]

42 cold front, 42 cold rear.

want to know what they are at various "operating" temps, pop on a set of chicken hawk racing warmers.  but who cares?  42 cold 42 cold for the street.

tire warmers:

[So Cal Joe]

Thanks for the replies, I always run 42 front & rear cold. I know that it changes when the tire temp goes up  but the post I was talking was a good read and I just wanted to reread it, I guess no one has a copy of it.
Could of went all day with out hearing
It ain't rocket science.
Makes one think they asked a  DUMB question

[lather]

Does any other bike have front tire spec'd for 42 psi? Every other bike I have owned was spec's for 36 psi front or at least a few pounds lower than the rear spec. I don't run 42 front because I feel its wrong to run same psi front and rear. And I feel my results have been good as far as mileage and handling.

[B.D.F.]

It did not strike me as a dumb question. As to the comment about it not being rocket science, neither is rocket science if you choose to look at it in a simplistic manner. ‘Fire on the bottom make rocket go up’ is a true statement as long as one is not trying to actually design a rocket. The physics going on in the gasses inside a tire can be quite complex but of course it is not practical to do scientific studies and collect endless data to fill a vehicle’s tire. On the other side of the coin, just about all of us use some type of gauge to try to put some known 'amount' of air into our tires; this is science all by itself and proves that most people do care how ‘full’ their tires really are.

Whatever works for the owner of the bike works for me.     I find it easy enough to add or subtract a few pounds based on the outside, ambient temperature to at least get within reason of the correct tire pressure and posted the method I use in an earlier post. For those who choose not to do that, great. For those who do not believe it makes any difference, also great.

Brian

Thanks for the replies, I always run 42 front & rear cold. I know that it changes when the tire temp goes up  but the post I was talking was a good read and I just wanted to reread it, I guess no one has a copy of it.
Could of went all day with out hearing
It ain't rocket science.
Makes one think they asked a  DUMB question

[Flathead]

Reminds me of this 

http://youtu.be/THNPmhBl-8I

[ZG]

Reminds me of this