Yes.Jed wrote:Don,deilenberger wrote: Also note - the pressure is specified with the tire temperature at 68F (20C?).. add or subtract ~1 to 1.3 PSI per 10 degrees F tire temperature difference from that (lower when colder, higher when hotter.) That's based on what I observe on my TPMS - which gives me both tire air temperature and pressure. It's rough, but close enough to get you into the ballpark. IE - if it's 38F you can expect to see 29-30PSI in the front and 32-33PSI in the back. If it's 98F - figure on 35-36 PSI front and 39-40 PSI rear. It is slightly non-linear, but - again - close enough to get you into the ball park of correct pressure for the tire temperature.
Can you clarify this statement above? Are you saying that the recommended tire inflation pressures from BMW are defined to a specific temperature?
That's actually wrong. If you have a BMW TPMS from the factory, it corrects for the actual tire temperature (which once the tire is rolling WILL be different from ambient) to show what the pressure would be at 20C (68F).Jed wrote:While I agree that changes in ambient temperature will affect air pressures in tires, inflation pressures are based on ambient temps. So if it's 40° F outside when we check our "cold" tires, the inflation pressure should be (your pressure) XX psi. If the ambient temp is 90· F outside when we check our "cold" tires, the inflation pressure should be the same (your pressure) XX psi. In other words, there is no temperature correction that is applied to inflation pressures for "cold" tires. In this case a "cold" tire is defined as a tire at ambient temperature, ie not warmed up from having been ridden.
No - it isn't. Your tire heats up as it rolls. On a 40F day, with stock tire pressure I can see 100F on my TPMS after some serious highway riding. That's all caused by the tire heating up. I'll also see tire pressure well in excess of what it was at 40F. If I had set the pressure to 32 PSI at 40F, by the time the tire fully warmed up (say 100F) - I'd see in excess of 40PSI. Should I then lower the pressure to the 32 PSI that's spec'd at 68F? If I then slowed down and the tire pressure dropped, should I again stop and adjust it (adding air this time?) Nope. Set it correctly at 68F and forget it.Jed wrote:Drastic variations in ambient temps during the day (very cold mornings giving way to warm afternoons) can lead to higher than desired inflation pressures as the temperatures rise over +40° F. But this is a different issue.
It is normalized on motorcycle tire pressure specs. At least that's how BMW sees it. All the TPMS systems I've used that have a warning feature for high or low pressure also use a compensation curve for temperature as to when they trigger the warning. On the ZADI one I used to use they even provided a nice chart showing the curve they used. And their suggestion was to set the tires to the manufacturer's spec'd pressure at 20C.Jed wrote: Pressures also vary depending on how hard the tires are worked, with more aggressive riding warming the tires (and hence the air inside them) more due to heat generating effects of tire flex. It's also well known that slightly lower inflation pressures will allow a tire to warm-up more quickly while slightly higher inflation pressures will tend to slow and, to some extent limit, tire warming.
There are lot's of interesting games to play relative to variations in inflation pressures to modify how the tires behave and perform at various operating pressures and temperatures, but none of these variations are normalized to a particular temperature. That's not how inflation pressures (or compressed gasses) work.
cheers,
From the BMW R1200R manual http://www.ascycles.com/pdf/RiderManuals2012/R1200R.pdf:
Page 24:
Page 38 has what the TPMS will warn about, and another mention of the "Engineering Details"BMW R12R Manual wrote: Tyre-pressure readout
(48)
The figures shown in the tyre-pressure readings are temperature-compensated (see the section entitled "Engineering details")
Page 59 has the pressure spec's with "tire cold"
Starting on page 82 is more on the TPMS system, and on page 83 is:
(Emphasis added..)BMW R12R Manual wrote: Temperature compensation
Tyre pressure is a temperature sensitive variable: pressure increases as tyre temperature rises and decreases as tyre temperature drops. Tyre temperature depends on ambient temperature, on the style of riding and the duration of the ride.
The tyre-pressure readings shown by the multifunction display are temperature compensated; the reference tyre temperature for these readings is always 20 °C. The air lines available to the public in petrol stations and motorway service areas have gauges that do not compensate for temperature; the reading shown by a gauge of this nature is the temperature dependent tyre pressure. In most instances, therefore, these gauge readings will not tally with the pressures shown by the multifunction display
Note the reference to 20C.. and the temperature compensating TPMS display.
Best,
02R1100S,05R1100S(BCR), 
(2)-S1000XR 
