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Anything wrong w/ this logic? Setting tire pressure using a warm tire with TPMS
- Thread starter ncpbmw1953
- Start date
Kevin......there are nitrogen aspects to be resolved yet.Never before have I wished so badly for a good old fashioned oil thread to get started.
OM
Realshelby
Addicted to windshields
I think I am not doing myself any good here. I'll take my tire gauge, set my tire pressures in the garage ( temp is usually 73 in summer, 68 in winter ) and be happy. Because when I look at my tpm readout, it is almost always 1, 2, or 3 pounds lower than my normal 37/42. I have seen it higher once or twice as well, but usually much lower. And that changes as the day goes. Something isn't accurate. I know my gauge is.
Yes, I imagine the tpm is plenty accurate for safeties sake. I just won't be adjusting tire pressures on a trip to try to get the readings to match 37/42 or whatever I choose to run. Now if it has been reading 35/40 most of the time, or whatever value it displays and suddenly goes to 35/33 I will be glad I have tpm! I am glad, I just don't use it to adjust tire pressure......
Yes, I imagine the tpm is plenty accurate for safeties sake. I just won't be adjusting tire pressures on a trip to try to get the readings to match 37/42 or whatever I choose to run. Now if it has been reading 35/40 most of the time, or whatever value it displays and suddenly goes to 35/33 I will be glad I have tpm! I am glad, I just don't use it to adjust tire pressure......
ncpbmw1953
Member
Absolutely--clearly that is its most important value. I don't use TPM to adjust tire pressure either, but I'm clearly convinced I can, and all will remain well. I just thought it was interesting that BMW thought you should adjust to their numbers, which apparently is contrary to popular belief.
ncpbmw1953
Member
Never before have I wished so badly for a good old fashioned oil thread to get started.
Don't bang your head Kevin--you wouldn't be in the thread if you weren't interested, right? Sure. Enjoy the discussion for what it brings--other ways to look at things.
danfinazzo
New member
What abputthat temperature
Slightly off subject - I have a Smartire (no longer made) set of sensors (yes it is over 10 years old and still runs) on my 2009 LT and it does "not" give me temperature compensated pressure like my 2016 R1200GSA.
It gives me both real tire pressure and temperature - so running down the highway in Kansas fully loaded @75 mph on a hot summer day the cold setting was 48 PSIG on the rear when I took off - confirmed by a gage and the TPM - the pressure rises to 58 PSIG with the tires are bumping 180 degrees F.
The sensor is strapped to the wheel in the valley and I think some of the temp is from the brakes / drive but in any case I will assume that the wheel and tire after a long time running are all the same temp.
I slow down the temp drops and the pressure drops. Talked to Bridgestone Tire Expert - TJ Tennent - says slow down to keep them below 200 degrees F.
The system flashes if there is a sudden 10% change in either pressure or temperature. Drove over the Mackinac Bridge one summer and got the flashes due to fast temperature drop due to temperature on the bridge surface. Also happens in summer rain storms.
Would be nice if they could relay the temperature along with the temperature compensated pressure - I agree with others would be nice to see the real pressure . . . this of course is coming from someone who likes to see and evaluate technical information while driving.
My 2 cents
Slightly off subject - I have a Smartire (no longer made) set of sensors (yes it is over 10 years old and still runs) on my 2009 LT and it does "not" give me temperature compensated pressure like my 2016 R1200GSA.
It gives me both real tire pressure and temperature - so running down the highway in Kansas fully loaded @75 mph on a hot summer day the cold setting was 48 PSIG on the rear when I took off - confirmed by a gage and the TPM - the pressure rises to 58 PSIG with the tires are bumping 180 degrees F.
The sensor is strapped to the wheel in the valley and I think some of the temp is from the brakes / drive but in any case I will assume that the wheel and tire after a long time running are all the same temp.
I slow down the temp drops and the pressure drops. Talked to Bridgestone Tire Expert - TJ Tennent - says slow down to keep them below 200 degrees F.
The system flashes if there is a sudden 10% change in either pressure or temperature. Drove over the Mackinac Bridge one summer and got the flashes due to fast temperature drop due to temperature on the bridge surface. Also happens in summer rain storms.
Would be nice if they could relay the temperature along with the temperature compensated pressure - I agree with others would be nice to see the real pressure . . . this of course is coming from someone who likes to see and evaluate technical information while driving.
My 2 cents
pglaves
#13338
Slightly off subject - I have a Smartire (no longer made) set of sensors (yes it is over 10 years old and still runs) on my 2009 LT and it does "not" give me temperature compensated pressure like my 2016 R1200GSA.
It gives me both real tire pressure and temperature - so running down the highway in Kansas fully loaded @75 mph on a hot summer day the cold setting was 48 PSIG on the rear when I took off - confirmed by a gage and the TPM - the pressure rises to 58 PSIG with the tires are bumping 180 degrees F.
The sensor is strapped to the wheel in the valley and I think some of the temp is from the brakes / drive but in any case I will assume that the wheel and tire after a long time running are all the same temp.
I slow down the temp drops and the pressure drops. Talked to Bridgestone Tire Expert - TJ Tennent - says slow down to keep them below 200 degrees F.
The system flashes if there is a sudden 10% change in either pressure or temperature. Drove over the Mackinac Bridge one summer and got the flashes due to fast temperature drop due to temperature on the bridge surface. Also happens in summer rain storms.
Would be nice if they could relay the temperature along with the temperature compensated pressure - I agree with others would be nice to see the real pressure . . . this of course is coming from someone who likes to see and evaluate technical information while driving.
My 2 cents
The other KEY thing to note is the 3rd readout for each wheel. Pressure - temperature - and deviation with deviation being a plus or minus number reflecting temperature compensation as revealing pressures above or below the target pressure. I ignore +1 or -1 but would recheck with a guage cold at the next opportunity.
chewbacca
New member
Do you guys actually read posts?
In post #2 I state " I attached my GS911 and connected my laptop to get the tire temp and pressure from the sensors. " You could log tire data for hours if you want. When one of our inmates states that we only have " ANECDOTAL input to this thread I must say someone should compare the meaning of anecdotal and experimental. I will restate. You can attach a GS911 to your bike and to a laptop which will collect both the internal temp and pressure of both the front and the rear tires. Please note that is internal tire pressure and temp, NOT ambient temp. I also logged display readings of tire pressure and ambient temp. I also stopped and measured pressure at the tire at various intervals. That is EXPERIMENTAL data although it is only one bike and to be truly valid one should have data from several bikes.
In post #2 I state " I attached my GS911 and connected my laptop to get the tire temp and pressure from the sensors. " You could log tire data for hours if you want. When one of our inmates states that we only have " ANECDOTAL input to this thread I must say someone should compare the meaning of anecdotal and experimental. I will restate. You can attach a GS911 to your bike and to a laptop which will collect both the internal temp and pressure of both the front and the rear tires. Please note that is internal tire pressure and temp, NOT ambient temp. I also logged display readings of tire pressure and ambient temp. I also stopped and measured pressure at the tire at various intervals. That is EXPERIMENTAL data although it is only one bike and to be truly valid one should have data from several bikes.
Realshelby
Addicted to windshields
I sure did read your post. No need to belittle anyone that might not see things as you do. When I read your post, quoted above, I was still under the assumption that pressure was the only thing the tpm sensor transmitted. TEMPERATURE was, I thought, taken from the bikes ambient temperature sensor. Your post does say you got tire temp and pressure from the sensors. So you are correct, and I was wrong to think that internal tire temperature was calculated by the ambient air temp sensor.
From my point of view the GS911 could have been reading the ambient sensor, your post does not clarify that to me. I now know, after noelcp posted and I looked it up in my service manual, that the GS911 is using the tire tpm sensors for temperature. So I apologize for upsetting anyone.
That said, all this stuff about "setting" tire pressure using the bikes TPM still does not sit well with me. WAY TOO MUCH CALCULATING/EXPERIMENTING to arrive at what I can get by using a high quality tire gauge. Using that gauge on a cold ( at rest ) tire. Just like manufacturers recommend.
Too much calculating?? As you say, set the tire pressure with an accurate gauge when the tire is "cold" at about 68F. Start the bike, ride a block and look at the TMPS readout. That is your base pressure to use. When it varies from that more that a couple of psi, then look for an issue. That is what the manufacturer recommends.
Sent from my iPad using Tapatalk
Realshelby
Addicted to windshields
That is exactly what I don't get with this debate. Why would I want to check my tires in the garage, with an accurate tire gauge, then get the bike to 19 mph to then read the readout on the tpm display? I have looked at that before, and it is not the same as my gauge reading. What if the outside air temp is 100 degrees? Which it has hit here lately. Just one lap around the block would influence the tpm measurements at that temp. Even if I depended on the tpm display to adjust/maintain air pressure in my tires, why would I want to ride it around the block then come back and put air into the tire hoping I have it right then ride around the block again and come back to adjust? My air compressor and hose are right beside where the bike is parked. Don't tell me using an accurate tire gauge in a climate controlled garage on tires that have sat overnight to cool isn't the very most accurate way to maintain correct pressure! IF, and that is not proven yet, I trusted the tpm to be as accurate as my gauge I could look at the display at any given time and remember to add/subtract that exact amount when I could get to it. But how would I know if I added/subtracted the exact amount needed?
This all comes down to accuracy and repeatability. Which the bikes TPM system has not shown to have an advantage in either case. If you choose to look only at your TPM system to maintain your air pressure I don't doubt you will be safe doing that. I have full confidence in my TPM system when on a trip to tell me that I have a tire going down. I have confidence that when I look at my TPM readout when doing 75 mph down the road on a high mile day that it will read something close to what I think it should, giving me confidence again that I don't have a slow leak. I very much value this on my RT.
But when I can adjust my front tire pressure by 1 pound and feel the difference, I do NOT trust the TPM to give me that accuracy. I overfill my tire by a couple pounds, then slowly release the air to get to the EXACT amount ( even down to 1/10 lb if you want that ). There is simply NO WAY to do that with the TPM. BTW, that stands for Tire Pressure Monitoring. Not maintenance.
chewbacca
New member
I actually agree with EVERYTHING you say above. The thing that bothered me most was you can only do one data dump at a time with GS911 out of two possibilities. If you go for the tire sensors you get internal pressure, internal temp and time. Ambient temp is in the other data dump. IMO that degrades your ability to compare the environment temp with the tire temp. There is a lag between what the sensors send and the corrected reading too. So, my conclusion, this data collection process of timing and accuracy is leads to "good enough for government work" readings from the TPS.
What is the temp in your garage? Mine was 60 at 6am, it's in the low 70's now, and will be near 80 in about an hour. Please tell us how you determine what is cold? I would like to know how BMW defines that in the service manual too. When I ride my cold bike to 19mph the TPS readings show, and stick at that temp for 5 to 10 minutes. They are close to what I set the valve stem pressure to but NOT exactly the same. They also vary so it is not something you can calibrate your pressure gauge with. Within half and hour I usually have a pressure of 36/42 because I make a guess at what I put in as cold depending on garage temp. Normally I set it to show a bit high, 37/38 front, 43/44 rear after that half hour. If it is 37/43 I leave it alone, if significantly higher I let air out. I make it read high so I don't have to break out my air pump. I don't burn up a single synapse doing it this way. When you say "When it varies from that more that a couple of psi, then look for an issue" why bother with RDC/TPS? Just have an idiot light that comes on if the pressure goes below a defined value.
greenwald
New member
Excellent summary of an over-complicated hypothesis.
Check cool tires before a road trip, and let the TPMS do it's job - monitor tire pressure and notify you if loss is significant or progressing towards failure. That's all you should rely on it for.
The pressure in our tires change every so many minutes, with short, medium or long rides, altitude, ambient temps, riding on hot pavement, loads, cornering, braking, etc., etc., etc.
Obsessing with that 'ideal' pressure makes a dog chasing its tail look like intelligent.
Proper pressure at the beginning of the day - then go ride - check next morning if you feel the need.
TPMS is a 'smoke detector' - not a pacemaker.
akbeemer
SURVIVOR
Excellent summary of an over-complicated hypothesis.
Check cool tires before a road trip, and let the TPMS do it's job - monitor tire pressure and notify you if loss is significant or progressing towards failure. That's all you should rely on it for.
The pressure in our tires change every so many minutes, with short, medium or long rides, altitude, ambient temps, riding on hot pavement, loads, cornering, braking, etc., etc., etc.
Obsessing with that 'ideal' pressure makes a dog chasing its tail look like intelligent.
Proper pressure at the beginning of the day - then go ride - check next morning if you feel the need.
TPMS is a 'smoke detector' - not a pacemaker.
Exactly!!!! Time spent fretting over the TPMS should be better spent chasing the oil level up and down the sight glass.
pglaves
#13338
The answer to that is very simple: 20 degrees celsius is the standard for "cold" used by BMW and all of the tire makers I know of. That is 68 degrees F. Rounding to 70 makes little difference.
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greenwald
New member
Exactly!!!! Time spent fretting over the TPMS should be better spent chasing the oil level up and down the sight glass.
kinterridge
Member
I've wondered the same, I just use my tire pressure guage, as I've done for my 40+ years of riding.
pglaves
#13338
I kick the tires every time I get on the bike, and check with a guage every few days. That makes me a slacker of course but after you kick a tire a few hundred times you begin to get a feel for this approach.
greenwald
New member
I'm sure BMW is feverishly working, as we speak, on a module to report back to us handgrip pressure, number of times we squirm in the saddle and how often we open and close panniers in 100% humidity.
And the 'Uber-faithful' will cry out "How ever did we get by without this software up until now?"
