Tire pressure monitor system

My system kicks in after a short ride and reads out cold pressures. But those pressures don't change as I ride. An after ride check with my own gauge showed the expected increase in hot pressures. Is this normal for the BMW system? My KTM measured in real time and read out the hot pressures.

That is normal. The way I understand it, the system corrects to 68 Deg. F in all conditions. Detailed in your owners manual. I sometimes see a rise of a pound or two during a ride and can't explain that.

Frank

As explained above, the BMW system compensates for temperature. In other words, the readings tell you what the pressure would be at a nominal 20C/68F. Let's say the recommended pressure for the rear tire on your bike is 42 PSI. Halfway through a day-long ride, your TPMS reading for the rear tire shows 39 PSI. That's telling you that you're down 3 PSI. It does not mean that, if you put a tire gauge on that tire, it would read 39 PSI. Let's say your gauge read 41 PSI at that moment. You should then add 3 PSI, and bring it up to 44 PSI.

A few times, I have left a thermometer in my garage, and was able to check my tire pressures with a gauge when the ambient temperature in the garage was bang on 68F (and the bike and car had been there overnight, and the outside temperature was also at 68F). I corrected my pressures to the recommended 36/42. When I rode later that day, the TPMS readings showed 36/42, even with a higher ambient air temperature, and after having ridden for a couple of hours. This demonstrated to me that the system was operating as BMW described. I don't use TPMS as a tire gauge, but I do find it easy to determine if I need to add air, and how much.

The temperature compensation may not always be perfect so during a ride you may see a 1 or 2 psi change in the readout. Watch it to see if it goes down indicating a leak, but otherwise understand that the algorithm may not be perfect. The highest value is the alarm function, not single digit accuracy at all temperatures.

51797 said:

That is normal. The way I understand it, the system corrects to 68 Deg. F in all conditions. Detailed in your owners manual. I sometimes see a rise of a pound or two during a ride and can't explain that.

Frank

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I have sometimes seen a pressure rise of up to 4 PSI during a ride. Cannot explain it either, but i don't worry about it.

PGlaves said:

The highest value is the alarm function, not single digit accuracy at all temperatures.

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And my system alerted me to a leak (nail) just as I was heading out of town into 50+ miles of great road, but little else. I was able to turn around and go back to a truck stop/mega service station I had passed a mile or so before. I'm a believer!

Frank

51797 said:

And my system alerted me to a leak (nail) just as I was heading out of town into 50+ miles of great road, but little else. I was able to turn around and go back to a truck stop/mega service station I had passed a mile or so before. I'm a believer!

Frank

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I agree with @PGlaves about the alarm function having the greatest value. I had a similar experience as @51797 on my commute last year, and was able to safely make it home while monitoring the deflation.

marcopolo said:

When I rode later that day, the TPMS readings showed 36/42, even with a higher ambient air temperature, and after having ridden for a couple of hours. This demonstrated to me that the system was operating as BMW described. I don't use TPMS as a tire gauge, but I do find it easy to determine if I need to add air, and how much.

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I use it as a tire gauge and the argument can be made that BMW even expects you to be able to rely on it. At least that is how I interpret some of the language in the rider manual for my '16 RT. Quite frankly, it's just another electronic sensing system and te mperature-compensated at that, which adds value in my mind. I see no reason why an electronic digital hand-held tire pressure gauge should be any more accurate really. Since all electronic and mechanical gizmos can fail I do cross check it a few times a year with a good old-fashioned analog mechanical pressure gauge from Flaig. When TPMS indicates the warmed tire pressure is below where I like it, I'll add enough air to get it back to spot on again. An acid test for its temperature-compensating prowess occured when we left Big Pine, CA early morning of June 4, 2016 heading east on the fabulous 168 then down past Las Vegas and up to St George UT. When we left Big Pine I want to say it was 52F or something, but by the time we were an hour north of Vegas we were at 110F, and from there on to St George it was up to 112.9F: tire pressure never budged off of 36F/42R! It really works!

Thanks for the replies. I'll have another look at the OM. I evaluate starting pressures using the 10% rule -- a rise of 10% means the cold pressures were correct, less and I started too high, more and I started too low. If the TPMS read out actual increases, it would be useful to evaluate pressures for different loads. Alas, not so much.

I learned something I should have already known the other day. Girlfriend and I had gone for a ride / picnic lunch, about 150 mile loop, had a nice day and a good ride. About 10 miles from her house we got hit with wood chips from someone mowing their lawn. A few minutes later I notice the rear tire pressure dropping. I absolutely love TPMS, and keep an eye on it every ride.

The drop was slow enough that I felt OK getting getting home. We pulled into the driveway with about 32 lbs in the leaking tire. OK, up on the center stand, break out the sticky strings and 12 volt tire pump, get to work. This set of tires has >8,000 miles, so, going to be time for some new ones anyway. Wrestle the sticky string into place, pull the pump from its box, go to plug it into the power outlet on the fairing of my RT, here's where the new information revealed itself.

I had never really paid attention to the nature of the outlet. It's not the classic "cigarette lighter" outlet. The pump cannot plug into it. Once again, what do you get when you assume? You'd think that in my mid 60's I'd know better.

The good news, Touratech offers an adapter for about $12. Oh, and we'd made it home and were able to pull her car up close enough to use the pump.

Live and learn.

Stebe said:

The good news, Touratech offers an adapter for about $12. Oh, and we'd made it home and were able to pull her car up close enough to use the pump.

Live and learn.

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When you get the adapter you may learn the outlet will not run the pump if your bike has canbus.
If you have canbus you need to wire a harness direct to the battery.

Lee said:

When you get the adapter you may learn the outlet will not run the pump if your bike has canbus.
If you have canbus you need to wire a harness direct to the battery.

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"May learn", yes, if you have a pump that exceeds about 6amps, but there are pumps that stay under that and work fine. Mini Inflator Pro is one of those and worked flawlessly on my F800GT and RTW's aux power outlets w/ the requisite adaptor. I don't think that pump is available any more but I'm sure there will be others.

Stebe said:

I absolutely love TPMS, and keep an eye on it every ride.

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U n me both. My first example happened when I departed from Casa De Fruita, a tourist trap albeit nice place to stop for food and drink, when upon entry to the freeway onramp there w/ ample high speed traffic TPMS let me know well before I was halfway down the ramp that I was losing air fairly fast. That could have been tense entering a freeway while a flat tire was evolving. I've had two other instance where I was able to repair the tire way before it lost significant air. I always leave the TPMS values displayed while riding it's comforting to know before attacking curves etc all's well. I would not want a bike w/o TPMS. Plus, despite the common belief in forums that somehow relying on their $29 tire gauge is somehow superior to this built-in, temperature-compensating wonder is, to me, ludicrous.

ncpbmw1953 said:

"May learn", yes, if you have a pump that exceeds about 6amps, but there are pumps that stay under that and work fine. Mini Inflator Pro is one of those and worked flawlessly on my F800GT and RTW's aux power outlets w/ the requisite adaptor. I don't think that pump is available any more but I'm sure there will be others.

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Hmm. Good to know. I have a Battery Tender input wired directly to the battery, should the adapter not be able to adapt I will splice the output cable from one of my old Battery Tender's to the adapter and run it that way. Thanks for the info, I may not have thought about the canbus system not allowing it to work.

Stebe said:

Hmm. Good to know. I have a Battery Tender input wired directly to the battery, should the adapter not be able to adapt I will splice the output cable from one of my old Battery Tender's to the adapter and run it that way. Thanks for the info, I may not have thought about the canbus system not allowing it to work.

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If the accessory port cannot handle the pump it is not because the bike uses a CANBUS to communicate between processors, it's because it draws more current than the wiring was designed to handle. The accessory port is not even on the CANBUS. The ZFE monitors the current and if the draw is too high it will shut down the circuit until the next restart. The ZFE just serves as a circuit breaker or fuse to protect the wiring. The benefit in using a dedicated lead to the battery is that you can select properly sized wiring and circuit protection for your intended load.

Incorrect usage of the term "CANbus" is rampant. Vendors contribute to this by using the term when they should be explaining the role of the ZFE in controlling chassis electrics and the impact it has when planning the installation of accessories.

Sent from my SM-T813 using Tapatalk

RadioFlyer said:

Incorrect usage of the term "CANbus" is rampant.

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I slapped myself on the wrist and said five Hail Marys

Lee said:

I slapped myself on the wrist and said five Hail Marys

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We need to establish new terminology: I nominate the acronym CCOES. That stands for Computer Control Of Everything System. (Pronounced Seek Hose) So instead of saying the CANBUS turns off the accessory outlet if it draws too much amperage, we say the CCOES turns off the accessory outlet.

That way we don't actually need to know the name, or last year's name, or the new name for each of the several microprocessors BMW is stuffing into their motorcycles. Airhead and Classic K bike owners do not need to use the CCOES terminology.

PGlaves said:

We need to establish new terminology: I nominate the acronym CCOES. That stands for Computer Control Of Everything System. (Pronounced Seek Hose) So instead of saying the CANBUS turns off the accessory outlet if it draws too much amperage, we say the CCOES turns off the accessory outlet.

That way we don't actually need to know the name, or last year's name, or the new name for each of the several microprocessors BMW is stuffing into their motorcycles. Airhead and Classic K bike owners do not need to use the CCOES terminology.

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I like that, mostly because if anyone had made the mistake of asking me what a "canbus" was, I'd have said: "It's the gizmo that allows the computer control of everything".

LFarling said:

I have ALWAYS seen a rise in my tire pressure during riding, and especially loaded or when I used to haul a passenger.

I really does not matter what temp something is calibrated to, if something gets hot, it expands, causes a pressure rise and should register.

I have seen 1 to 2 PSI on the front and 1-4 PSI on the rear loaded Depending on road and temp, how hard I am running and braking, and if I am loaded for a rally or trip. As a rule just me, no bags top case I see 1 in the front and 1-2 in the rear. And that is a cold check set 40/42 before the ride. It is a predictable and there is math to show you what % of rise one should see and not be concerned with if you want to look it up.

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Yeah I know what you mean but BMW is serious about this 68 degree compensation thing.

Manual says to use the TPMS as a relative reading. So if even after a long ride rear reads 40 it means add 2 pounds no matter what pressure the tire is at that moment. If it's 44 add air to 46.

It took me the longest time to wrap my head around this coming from years of setting my tires (car and bike) to recommended pressure no matter the ambient temp.

So if it is 90. Set your cold pressure to 44 and your tpms will read 42 all day long assuming no leaks. (Assuming about 1 lb per 10 degrees)

Reverse in cold weather. At ambient 48 set cold pressure to 40 and tpms will read 42 all day long.

Try it!