tire pressure

[VirginiaJim]

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

I did not say it was a DUMB question.  You are the one that inferred that from the response.  I could have said it's so easy a caveman could do it but I didn't.   Put the gauge on, check the pressure, make an adjustment by adding or decreasing said pressure with either the air gauge, sharp pointy thing,  or compressed air source.  I don't worry about it again until the next ride or trip.  I've been checking air in tires for well over 40 years and haven't worried about air temperature vs air pressure vs what's supposed to be in there vs what's not.  I consistently get good mileage and performance with all my tires/vehicles without stressing about it.

Oh, I'm not a rocket scientist, but if i need one I can go across the street and get one.  Cavemen are harder to find....

[jimmymac]

I fill mine to 42 LBS after mounting them, and usually wear them out before they need adjustment.

[VirginiaJim]

My kind of guy....   

[Jeremy Mitchell]

I fill mine to 42 LBS after mounting them, and usually wear them out before they need adjustment.

If I could get you sponsored by Michelin you would have enough money left over to buy Cap'n Bob the first non KiPass equipped C14.   

[B.D.F.]

Great method. Another thing that would work would to to guesstimate how much air the tire will lose over its lifespan and put in enough extra air to 'split the difference'. For example, think it will lose 20 PSI and you want the actual pressure to be 42 PSI? No problem, just fill the tire to 52 PSI initially and 1/2 way through the time you have it the pressure will be exactly 42 PSI. When it hits 32 PSI throw the tire away and start again.

Brian

I fill mine to 42 LBS after mounting them, and usually wear them out before they need adjustment.

[VirginiaJim]

You see, Brian, you're just over thinking the whole thing.  In your case, you could have checked the air pressures (42lbs) before your marathon trip, go to the West coast and back (assuming no punctures), and return without checking it again.  I know I went to Reno and back (from the East coast) and only checked pressures once (when I left) and that was a 10 or 11 day trip.  I broke it up a bit with civilized (no cavemen) hotel stays at night, unlike yourself where you wanted to do it in one fell swoop...

[B.D.F.]

I can tell you something funny about that very thing Jim, and it is absolutely true:

I rode to the other coast with my tires filled to about 42 PSI, and they read between 44 and 45 PSI for most of the trip. The tires were in great shape when I left but they showed a pretty nasty center flat from all that highway riding. When I got to the coast the tires were down maybe a lb. or so but they dropped another pound before I started back and I did not add any air on purpose to try to reduce the flatting of the rear tire. Got home with the on board sensors reading about 41 PSI and the rear tire looked a little better (more worn but also a bit closer to round).

Besides, I didn't want to mix any of that nasty west coast air in the east coast air in my tires.... 

I have found my C-14 to be very sensitive to tire pressure as it relates to rear tire wear. Just a couple of PSI below the ideal pressure and the rear tires will wear badly just outside the hard center of a two- compound tire (Michelin and Pirelli that I have tried). A couple of pounds over and they wear badly directly in the center (flatting). Just a guess but the compounds used in sport- touring tires are probably on the soft side for such a heavy bike as the C-14, especially when the bike is even slightly loaded with gear, passenger, etc.

Brian

You see, Brian, you're just over thinking the whole thing.  In your case, you could have checked the air pressures (42lbs) before your marathon trip, go to the West coast and back (assuming no punctures), and return without checking it again.  I know I went to Reno and back (from the East coast) and only checked pressures once (when I left) and that was a 10 or 11 day trip.  I broke it up a bit with civilized (no cavemen) hotel stays at night, unlike yourself where you wanted to do it in one fell swoop...

[VirginiaJim]

I just put 42 in mine and fahgetabout until the next ride for the most part.  But my 42 may not be your 42 due to gauge discrepancies in accuracy.  I had a good flat spot on mine after the trip but it was basically straight riding, unfortunately.  Only twisties were the the ramps  .    All I keep in the tires is 42.  I haven't much played with pressures.

[NDCUNIONGUY]

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.

Huh?  Did I miss something?  Is the wheel sensor measuring the temperature of air inside of the tire or is this a larger programming feature to factor in outside ambient temps?  Next question is how and why would this be necessary when the sensor merely needs to measure and report the pressure that exists inside of the tire in real time?

As I said, I may have missed something. 

As far as accurate guages go, I've had a good dial guage for twenty odd years and it disagrees with my on-board readout.  I also have a cheesier dial guage that is about 3 psi off (low) at 40psi, but it agrees with my on-board so I just use that one.  I go with 42-44 with all of this in mind.

[maxtog]

Huh?  Did I miss something?  Is the wheel sensor measuring the temperature of air inside of the tire or is this a larger programming feature to factor in outside ambient temps?

Not sure

  Next question is how and why would this be necessary when the sensor merely needs to measure and report the pressure that exists inside of the tire in real time?

Exactly.  That was my problem with the whole concept.  Don't try to "help" me, which means I now don't know what it is doing.  Just show me the actual damn pressure in the tire!!!!

[VirginiaJim]

Right...I could care less about temp compensation.  Show me the 'real' pressure.

[Steve D]

Temperature compensation is an industrial standard for electronic pressure transducers.  It’s all about making the sensor read more accurately in the world it lives in…one of changing temperatures.  Without this they would only read accurate at one temperature. I suspect it is the same with our sensors and I don’t think it’s about compensating for the temperature of the tire or the air in the tire.   

[wally_games]

Has anyone mentioned differences in altitude and barometric pressure (the pressure OUTSIDE the tire)?

And nobody has even mentioned that the tire (being rubber) expands and increases in available volume as it heats up. Thermal expansion of rubber is about six times that of steel, so... ...

Wait a minute. Now it IS sounding like rocket science. 

Just make sure that a good guage shows 42 psi in each tire at the start of your ride, note the pressure shown by the TPS for future reference just in case a tire begins to go flat, and get out there and ride your a$$ off.

[AirplaneTim]

Exactly.  That was my problem with the whole concept.  Don't try to "help" me, which means I now don't know what it is doing.  Just show me the actual damn pressure in the tire!!!!

I suspect the reason they run compensation calculations is the same reason there are so many "driving assistance features" in new luxury cars now.  It's not for the avid cyclist who knows what they are doing, it's for the least common denominator (idiots).  I guarantee that there are a significant number of people out there who would fill their tires to the 41 psi cold, then when their tires warm up and the gauge starts reading higher they would freak out and stop for fear of bursting their tires and let air out.  Then they can't figure out why it's low the next time they ride, or they leave it low because "it always seems to come back to where it's supposed to be after I ride for awhile."

[B.D.F.]

Exactly right in my opinion. If the TPS read "65 PSI" when the tire was warm, the first thing that everyone who wants the raw data displayed would want to know is the tire temperature. More data and then they would need a chart to see if the new pressure aligns properly with the new, elevated temperature. I think Infineon (the folks who make the sensor's controller) made a wise decision to display a compensated pressure, and I do not think any controller manufactuerer will be foolish enough to supply one that displays the raw data.

Back in the early days there were a lot of people who were quite concerned about 0.10 volt changes in the voltage display. I can just imagine the panic that would set in if the voltage was displayed in real- time, starting voltage depressions, charging spikes and all.

In the words of Jack Nicholson- 'You want the truth? You can't handle the truth'

 

Brian

I suspect the reason they run compensation calculations is the same reason there are so many "driving assistance features" in new luxury cars now.  It's not for the avid cyclist who knows what they are doing, it's for the least common denominator (idiots).  I guarantee that there are a significant number of people out there who would fill their tires to the 41 psi cold, then when their tires warm up and the gauge starts reading higher they would freak out and stop for fear of bursting their tires and let air out.  Then they can't figure out why it's low the next time they ride, or they leave it low because "it always seems to come back to where it's supposed to be after I ride for awhile."

[marku8a]

Temperature compensation is an industrial standard for electronic pressure transducers.  It’s all about making the sensor read more accurately in the world it lives in…one of changing temperatures.  Without this they would only read accurate at one temperature. I suspect it is the same with our sensors and I don’t think it’s about compensating for the temperature of the tire or the air in the tire.

I wondered about this. I couldn't believe that the display didn't show 1 psi difference regardless of ambient temperature or riding conditions.

Mark

[VirginiaJim]

In the words of Jack Nicholson- 'You want the truth? You can't handle the truth'

 

Brian

You're probably right...

[maxtog]

Interesting.  All this talk about pressure and I have been noticing on the display that both tires seem to have lost pressure a little more each week since my last (first) service.  When I took it from service two months ago, it said "41" or "42" on both.

Yesterday they were reading 38 while cold OR hot.  Figured it was time to check/fill for the first time on the new bike.  Got out my gauge and portable inflator...   wouldn't you know.... unlike my last bikes, THIS bike has wheel orientations that deny access to the valve at certain places.  And with my luck, BOTH wheels were like that, while it was on the cover stand, locked, and just starting to rain.  I managed to get to the rear one.  It is EXACTLY 42.  Hmm.  I had to abort before the front tire.

Very odd.  My gauge is notoriously VERY accurate.  Not sure what to think about the situation now.

[CrashGordon]

So in a really hot climate (like here in Texas), I guess I should be compensating for the temperature. When my gauge reads 42psi, the TPM says about 38psi ("cold" here now is about 85 degrees in the morning or 105 in the afternoon). I want the best gas mileage and the longest tire wear, but I don't want to over-inflate my tires. Should I trust the TPM or should I break out the thermometer and slide-rule and figure out what pressure I should be running?

[B.D.F.]

Slide rule? Do they even make batteries for those things anymore? 

You cannot really use the on- board tire pressure system to measure tire pressure because it already is temperature compensated. Unless you allow the system to do the compensation and always set the tire pressure so it reads the desired number on the dash display. That would be difficult with the bike stopped though. You only need to compensate if using a non temperature compensated pressure gauge such as a manual, hand- held gauge.

Again, just a rule of thumb that we can all do in our heads: for every 10F or so above or below the 'normal' temp. (68F) add or subtract one PSI when the tire is cold (when the tire has been sitting overnight without the vehicle being used). So you go out to get the bike and the temp. is 100F..... that is about 30 degrees above the setting temperature (70F is really close to 68F and makes it easy- remember, this is a rule of thumb, not an exacting scientific calculation) and you want to fill the tires to 42 PSI.... just add three (3) PSI and fill them to 45 PSI. 'Gallagher, is it just that easy? Yes, it is just that easy!' (before he smashes the apples between the pie plates with the patented "Sledge-o-matic").

Of course we can always make it more complex. A very quick search turned up this jewel by Toyota: http://www.toyotapart.com/TIRE_INFLATION_PRESSURE_COMPENSATION_AND_ADJUSTMENT_T-SB-0345-08.pdf

That document reads like a US tax worksheet. If you follow those directions carefully enough, you may not end up with any pressure in the tire and a headache.

Now that this subject has gone on for three pages it is time to inject some really useful information:

'Rule of thumb' is often claimed to originate in old English law and states roughly that 'you cannot beat your wife with a stick bigger than the diameter of your thumb.' In actual fact that claimed origin is without foundation and almost certainly false, and the expression itself seems to melt into antiquity. Still, it is more interesting than reading about the best way to calculate the mass of air that should be inserted into a given tire based entirely on pressure and temperature measurements alone. 

Brian

So in a really hot climate (like here in Texas), I guess I should be compensating for the temperature. When my gauge reads 42psi, the TPM says about 38psi ("cold" here now is about 85 degrees in the morning or 105 in the afternoon). I want the best gas mileage and the longest tire wear, but I don't want to over-inflate my tires. Should I trust the TPM or should I break out the thermometer and slide-rule and figure out what pressure I should be running?