TPM Sensors

[MichiganBob]

Good Evening All. My 2018 1200RT has tire pressure monitors. Never had them before on a motorcycle but the ones on my car have never been correct. I have two dead on calibrated air gauges and set the tires to them. The front sensor reads 4 pounds less and the rear sensor 3 pounds less. In addition, they tend to not vary as the tires heat up or cool down according to the instrument panel readout . Still plenty of warranty left, Can they be calibrated by the dealer? Should I request replacements? Or are these devices prone to error? Any feedback will be appreciated.

[Rinkydink]

Just got back from my annual Springfield Mile trip. I of course set air pressure to 38/44 as usual. TPS Read 34/41 the whole trip with a one psi variance due to 90+ degree temps. Checked a couple of hours after I arrived home and still 38/44. 

[MichiganBob]

Now we have two data points. Anyone else?  

 

(I was at Springfield too. Damn shame about the Sunday rain out but Saturday racing was top shelf)

 

 

 

[Kerry in Mpls]

The displayed pressure values are temperature compensated. Ideally they should read nearly the same values from cold to hot and back to cold.

Regarding accuracy, I am not aware of a way to calibrate them.

[Rinkydink]

3 minutes ago, MichiganBob said:

Now we have two data points. Anyone else?  

 

(I was at Springfield too. Damn shame about the Sunday rain out but Saturday racing was top shelf)

 

 

 

I watched the Mile II final on Fanschoice. What a race!!!

[Red]

I use a less that $10 pressure gage on my vehicles.  It is consistent with the data displayed in my automotive TPM's by + or - 1 lb. 

When I fill the bike to 36 and 42 (using my gage) as per manual, the bike TPM can be spot on one day and + or - 2 lbs the next.  I can't say which device is off.  BMW says the bike instruments are supposed to correct for temp.  So, if you fill your tyres on a day when the temp is 50  or 90 degrees and  use your hand held gage, then you will certainly be inconsistent with the bike TPM because the bike corrects the pressure read out to a standard temp of 68 - 70 degrees.

[Clievma]

I understand the display to be temperature compensated for 20 deg. So when cool, it will display pressure it calculates for when the tyre is at 20 deg.

 

mike

[dirtrider]

10 hours ago, MichiganBob said:

Good Evening All. My 2018 1200RT has tire pressure monitors. Never had them before on a motorcycle but the ones on my car have never been correct. I have two dead on calibrated air gauges and set the tires to them. The front sensor reads 4 pounds less and the rear sensor 3 pounds less. In addition, they tend to not vary as the tires heat up or cool down according to the instrument panel readout . Still plenty of warranty left, Can they be calibrated by the dealer? Should I request replacements? Or are these devices prone to error? Any feedback will be appreciated.

 

 

Morning Bob

 

As suggested above your BMW TPMS system automatically compensates for TIRE temperatures. The dash gauge always shows what the tire pressures "would be" at 68°f (20°c).

 

If you fill your tires using a precision air gauge & the motorcycle is in the SHADE, & has been sitting unridden at 68°f for a decent amount of time then the dash readout should be close or match your tire gauge. (both dash readout & your precision tire gauge showing tire pressures at 68°f)

 

Then if move your motorcycle into the sun (sun shining on a tire), or ride the bike,  as the tire heats up then your dash TPMS gauge should still show about same pressure as it did when the tire was 68°f (temp compensated) but if you check the tire pressure with your precision gauge it will show the 'true'  higher pressure of a heated tire.

 

The secret for this to work is to know the tire temperature at tire check/fill time then manually compensate for that temperature. (something a rider should do even if the bike doesn't have a TPMS system).

 

If your tires are at 68°f, no direct sun on the tire & bike hasn't been ridden in a few hours then just fill & check as usual. (lets say the tire requires 34psi per the manual).  You precision gauge should read 34 psi & your dash readout should read 34psi.

 

Now if your bike (tires)  are  sitting in a ambient temperature of 88°f long enough to be at that 88°f temperature (like in a hot garage overnight) then when you check/fill them using your precision gauge  you need to set them to 36°f. Your precision gauge will show 36°f but your dash readout should show close to the (68°f corrected) 34 psi.

 

It is difficult to figure tire temperatures after riding or with the motorcycle in the hot sun so never set or check the tire pressures in those conditions. 

 

A good rule to live by when it comes to tire pressures (within reason as there are outliers) is to just back figure to 68°f (or as close as possible).

 

In the mean operating range of most tires at most riding conditions (normal riders & normal riding conditions anyhow) you get about 1psi change for every 10°f change in TIRE TEMPERATURE. So if are checking/setting your tire pressures at  normalized 48°f just subtract 2 psi from the needed pressure (34psi -2 psi = 32psi). Or if you are checking/setting your tire pressures at normalized 88°f just add 2 psi to the needed pressure(34psi +2 psi = 36psi).

 

You need to do it manually when using a tire gauge, your dash readout does it automatically for you.

 

Some automobiles have automatic TPMS  compensation & some don't, some need it to have an accurate dash readout low tire pressure warning system.

 

Or just do what you have always done then just know that your dash readout is showing temperature-corrected-pressures corrected to 68°f (20°c).

 

 

 

 

[Dave_in_TX]

4 hours ago, Clievma said:

I understand the display to be temperature compensated for 20 deg. So when cool, it will display pressure it calculates for when the tyre is at 20 deg.

 

mike

That 20 degrees is Celsius, not Fahrenheit so in Fahrenheit, it would be 68 degrees.

[MichiganBob]

Good Morning,

 

Garage temp is 62 degrees. TPM is 33 front and 38 rear. My calibrated Tiretek guage measures 35 front and 40 rear. The specs call for 36 front and 42 rear. Using the TPM calls for motion to work so my guess is that I need to figure the correct pressure stationary in the cool garage. What would you folks do to get the correct tire pressure?

 

Thanks.

 

Bob

 

 

[dirtrider]

17 minutes ago, MichiganBob said:

Good Morning,

 

Garage temp is 62 degrees. TPM is 33 front and 38 rear. My calibrated Tiretek guage measures 35 front and 40 rear. The specs call for 36 front and 42 rear. Using the TPM calls for motion to work so my guess is that I need to figure the correct pressure stationary in the cool garage. What would you folks do to get the correct tire pressure?

 

Thanks.

 

Bob

 

 

 

Afternoon Bob

 

If you are positive that your calibrated gauge is accurate (how long ago was it calibrated?) then that 62°f is close enough to the 68°f nominal to just use your gauge to set the tires to  36 front and 42 rear. Or set to 35.5 psi & 41.5 psi if you have the gauge resolution & accuracy.

 

As you ride the bike a short distance the TPMS system should wake up, then catch up, & show the 'corrected to 68°f' tire pressures.

 

If all is working OK then your dash reading should always be fairly close to the 36 front and 42 rear (some are closer than others).

 

Where I work we calibrate our tire pressure gauges weekly as they must be accurate for most vehicle testing.

 

 

[MichiganBob]

Good Morning DR. The gauge was calibrated about two months ago. It was sent back to Tiretek. If I wanted it to be calibrated around town, what kind of place would I go to for a calibration? Who does it?

 

Thanks.

 

Bob

[dirtrider]

21 minutes ago, MichiganBob said:

Good Morning DR. The gauge was calibrated about two months ago. It was sent back to Tiretek. If I wanted it to be calibrated around town, what kind of place would I go to for a calibration? Who does it?

 

Thanks.

 

Bob

 

Afternoons Bob

 

Depends on the town.

 

You need to find a place that has a master gauge (usually a place that does vehicle test &  certification work)  or  has a need to have calibrated gauges.

 

You might call some tire stores or repair facilities to ask if they have a master gauge to check your calibration against.

 

If you verify your present  gauge against other tire gauges be sure to use a larger tire like a car tire as motorcycle tires have a rather small air volume so can lose a bit of pressure at each gauge use. (the larger the gauge air chamber or longer the hose on the gauge then the more air that the tire will lose at each test)     

[marcopolo]

I won't repeat what's been explained above in detail.  I'll just add that, on a couple of occasions, I have set my tires to the recommended cold-tire inflation pressures (36/42) in my garage, after the bike had sat there overnight, and with the ambient temperature in the garage in the morning measuring bang on 68F (having put a digital thermometer in the garage overnight).  I measured the tire pressures with two gauges, and both read 36/42.  Once out on the road for fifteen, or so, minutes, the TPMS pressures displayed were also 36/42, just like the readings on my manual gauges at 68F.  I'm assuming, of course, that the tire temperatures were also at 68F, after the bike had been sitting in the garage overnight.