TPMS inaccurate.
- Thread starter exavid
- Start date
justscootin
Member
Is your bike still under warranty, see what your dealer has to say, has it always been inaccurate from day one
JaimeC
New member
I never use the TPMS as a gauge of ACTUAL tire pressure. I remember when I first used it and it was showing pressure much lower than what was recommended. I hooked up my airpump (it's a manual, floor pump with a built-in pressure gauge) and saw the pressure was exactly what BMW recommended in the under-seat sticker. So, I took out my trusty pressure gauge and checked it and sure enough, the pressure was correct and the TPMS was reading too low.
From what others here have posted, that appears to be what everyone experiences. The TPMS sensors are entirely encased within the tire/wheel. Tire pressure is measured by the difference of the air pressure INSIDE the tire vs atmospheric pressure on the outside. I don't know what kind of external sensor the TPMS has; if it doesn't have any then all the engineers can do is "guess" at the outside pressure. If this thing was calibrated in the Bavarian Alps, then I can understand why it is showing low where I live (which is practically at sea level).
I just use the TPMS as a gauge as to whether or not I'm losing air. Other than that, I trust an old-fashioned tire pressure gauge.
From what others here have posted, that appears to be what everyone experiences. The TPMS sensors are entirely encased within the tire/wheel. Tire pressure is measured by the difference of the air pressure INSIDE the tire vs atmospheric pressure on the outside. I don't know what kind of external sensor the TPMS has; if it doesn't have any then all the engineers can do is "guess" at the outside pressure. If this thing was calibrated in the Bavarian Alps, then I can understand why it is showing low where I live (which is practically at sea level).
I just use the TPMS as a gauge as to whether or not I'm losing air. Other than that, I trust an old-fashioned tire pressure gauge.
This. I don't rely on it at all.
exavid
Member
That's pretty much what I'm using it for since it varies over ten percent at times from the pressure measured with a separate gauge. It did lead me to a slowly leaking rear tire today, a small nail hole. Unfortunately the dealer has had the rear tires on backorder for some time. I browsed the internet and found much the same thing, 160/60ZR-15 tires on backorder with several vendors. This is really a bummer, I did need a new front tire, it's down to the wear bars but the rear could have done a couple thousand more. At the moment I don't know how long my scooter will sit on the bike lift. I could patch the rear tire, the hole is small but wouldn't trust the thing. I tend to ride this scooter like a sports bike and wouldn't want a patch to give way in the twisties.
I'll wait a couple weeks but if I can't get a new rear tire I'll patch this one and ride on. The front tires are easy to find, I suspect the tires for the GT and 600s are used only for those bikes or at least very few other models.
I'll wait a couple weeks but if I can't get a new rear tire I'll patch this one and ride on. The front tires are easy to find, I suspect the tires for the GT and 600s are used only for those bikes or at least very few other models.
JaimeC
New member
I've never had an issue ordering the correct size FeelFrees from BikeBandit.com.
Except I just checked and the rear tire is backordered from them, too. By the way, our scooter have H-rated tires, NOT Z-rated. Having a tire that can run at sustained speeds above 150 mph makes no sense. H-rated tires are good for sustained speeds up to 130 mph and is more than enough for our needs. We probably don't need anything more than an S-rated tire (sustained speeds up to 110 mph) but nobody makes them as far as I can tell.
Except I just checked and the rear tire is backordered from them, too. By the way, our scooter have H-rated tires, NOT Z-rated. Having a tire that can run at sustained speeds above 150 mph makes no sense. H-rated tires are good for sustained speeds up to 130 mph and is more than enough for our needs. We probably don't need anything more than an S-rated tire (sustained speeds up to 110 mph) but nobody makes them as far as I can tell.
exavid
Member
The Michelins I just ordered from Bike Bandit are H-rated which are certainly good enough for a bike that tops out around 105mph. At least that's where mine does according to my GPS. I like the look of the tread on the Michelin Power Pure tires. On my Goldwing, tires that didn't have a continuous groove in the center of the tread tended to ignore tar snakes and bridge gratings better.
exavid
Member
I'm not sure the TPMS is measuring outside air vs. inside the tire air. It could be a diaphragm deal that's working against a spring or even a piezo crystal chip setup. I'm a little disappointed in the system on the bike, the one on our Chevy Equinox agrees within 1psi with my digital and mechanical tire gauges.
Lee
New member
I wanted to revisit this post. I seem to have the same false low tire pressure readings from the on-board TPMS display on my 2016 C650GT. I am now using both the BMW digital tire gauge as well as the Motion Pro analog tire pressure gauge to validate the tire pressures. However, besides that, it seems as if over time, that both tires are slowly losing pressure. I mean nothing has gone flat, but I'm a little concerned about this before I go on a 3 day road trip. I don't carry a "spare" tire with me!! 
Both tires have no obvious punctures to them......?
Both tires have no obvious punctures to them......?
SteveADV
Active member
Dude....errr, I mean Lee (sorry I know I've done that before, but it* just was on the other night, so...),
In as much as you aren't new to this PTW gig, and with "both" tires slowly losing pressure, whaaaaat?
*The Big Lebowski. One of the greatest movies of all time. It was a crime that it didn't win the Academy Award for Best Picture. (I am only half kidding.)
In as much as you aren't new to this PTW gig, and with "both" tires slowly losing pressure, whaaaaat?
*The Big Lebowski. One of the greatest movies of all time. It was a crime that it didn't win the Academy Award for Best Picture.
(I am only half kidding.)
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Sparkrn
Member
I wanted to revisit this post. I seem to have the same false low tire pressure readings from the on-board TPMS display on my 2016 C650GT. I am now using both the BMW digital tire gauge as well as the Motion Pro analog tire pressure gauge to validate the tire pressures. However, besides that, it seems as if over time, that both tires are slowly losing pressure. I mean nothing has gone flat, but I'm a little concerned about this before I go on a 3 day road trip. I don't carry a "spare" tire with me!!
Don't sweat it dude, losing air seems normal. I put 2-4psi in every other week. Have a good trip.
Saw my TPMS yesterday. Bolted to the inside center of the wheel - not an integral part of the valve stem. I wondered why my rims seemed to have an inordinate amount of wheel weights. The TPMS is huge and is the reason the wheel is so out of balance. And a replacement TPMS is $165 each. Hope I can just remove them when the batteries take a dump.
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JaimeC
New member
Yeah, usually when you mount a tire, you line up the little red dots (demarking the lightest part of the tire) with the valve stem to minimize the amount of wheel weights you'll need. We discovered that thanks to those HUGE honking sensors, you should line those dots up OPPOSITE the valve stems and inline with the sensors instead.
exavid
Member
All tires lose air over time, whether it's seeping molecule by molecule through the tire itself or seeping through the somewhat porous cast wheels. It's important to have a good valve cap with a rubber seal too. These small leaks don't affect big tires much since with their volume it takes longer to lose enough to show up much. Scooter tires being smaller tend to drop pressure faster than larger motorcycle tires. I've owned two Silverwing scooters, a Burgman 650 and now my GT. All of them lost tire pressure faster than my Goldwing. It's a shame there's not a way to use the bike's computer to calibrate the TPMS. The means are on the bike for someone with some savvy it ought to be possible to adjust the TPMS to the actual value. On my bike the differential between actual and TPMS pressure seems pretty close when I first add pressure to the
tire but begins to diverge over time. Temperature of the tire vs. ambient temperature doesn't seem to make much difference
to the TPMS error.
tire but begins to diverge over time. Temperature of the tire vs. ambient temperature doesn't seem to make much difference
to the TPMS error.
To prevent the Feel Free Tire from cupping (as Much), I set my tires to 37 and 40. The TPMS will indicate 34 and 35. The TPMS must be calibrated to a standard day of 59 degrees and 29.92, everything is reading what it would be on a standard day. Living in southeastern Arizona at 100+ 40 PSI would be 34 at 59 degrees. The only thing I use the TPMS for is to see if I am getting a flat, then it takes 15 PSI loss of pressure to set off the warning.
MatteOrange
New member
You do know that the TPM that is used by BMW is temperature compensated, the pressure gauges most use are not.
To correctly set the pressure follow the manual, your TPM will then read correctly.
To correctly set the pressure follow the manual, your TPM will then read correctly.