**Tire Pressure/TPM Sensors and Tire Wear** - BMW K1600 Forum : BMW K1600 GT and GTL Forums
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post #1 of 88 Old 06-29-2012, 09:55 AM Thread Starter
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**Tire Pressure/TPM Sensors and Tire Wear**

I did a search and it doesn't appear that this subject has been discussed in this context. I have rear of terrible wear on the factory Metzler's and how the center wears out much faster than we think it should.

Tire wear is a direct result of driving style and tire pressure. Over-inflation will reduce your contact patch and cause pre-mature wear on the center of the tire.

I believe that we can all agree on the above statements, pleaes feel free to support any arguments to the contrary if needed.

A recent overservation has caused me to call into questions the veracity of the BMW Tire Pressure Monitoring system. When i initially purchased my bike, the dealer had replaced the "air" with N2 (Nitrogen). Blah Blah Blah, we could go for days on that discussion, but what I will say from my Chemical Engineering days is that N2 is more stable than "air". The technician used his pocket-protector tire pressure guage to set the pressures and the BMW TPM stated that the front was 47 and the rear was 43. Being picky I complained and they got the tires to 42/42.

I was pre-flighting my bike this morning and while I have been relying on the TPM I decided to check the pressure manually. Cold pressure with a caliberated guage that I used on my race-cars showed that the tires were at 47/47... Hmmmmm.... Scary.....

Maybe my guage is out of caliberation...... I tried my digital tire pressure guage... 47/47.... ok that is 2 that are showing the same... not good.....

So I decided that it was best if I used somethnig that I know without a doubt is accurate. Working for an analytical instrument company, we have pressure guages that are accurate to .001 pounds... With a quick adaptaion of the guage to work with a tire the exact pressures were 47.249/46.831... Definitely not good...........

I have adjusted them to 42.064/42.027 (ok.. I got them as close as I could... The reading on the TPM display is now 37/37....

What if..... all the tire-wear threads were a direct result of over-inflation????

Would love to get some input from others on this one.

Cheers......
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post #2 of 88 Old 06-29-2012, 10:00 AM
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What we have discussed in the past is to use a quality pressure gauge to adjust the pressure. To compensate for cold pressure when ambient is different than 70 degrees. Then, when you start to ride, note what the dash says. That is the number which represents the right tire pressure.

The TPM is in reality a warning system, not an accurate pressure system.

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post #3 of 88 Old 06-29-2012, 11:49 AM
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Originally Posted by RL Lemke View Post

The TPM is in reality a warning system, not an accurate pressure system.

And it works really well for that. If you have a drop in air pressure, it'll display the TPM warning symbol and automatically change the display over to the tire pressure and highlight the offending tire and pressure in red. It's pretty hard to miss. Otherwise, I've learned to ignore it and generally leave that part of the display on the ambient air temp or fuel range.
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post #4 of 88 Old 06-29-2012, 12:23 PM
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The issue with tire wear is interesting because of the different views we have seen here, and elsewhere. Everything from the Avon representative saying 50 psi in the rear, to others saying a pressure below the recommended 42 psi.

Can we get a volunteer to conduct a study for us? Ride the same roads, with the same tires, at different pressures, and report back on tire life?

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post #5 of 88 Old 06-29-2012, 01:09 PM
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There is another thread in here talking about the same issue and here is my take...

The recommended cold tire inflation pressure is 42 psi. "Cold" is defined to be 68F. So you should inflate your tires to 42 psi when the tempurature inside the tire is 68F.

During operation the bike will get the pressure and tempurature readings from the sensor inside the tire and adjust the display to compensate for any tempurature variation from that 68F standard. In the real world we normally can't control the tempurature but the reading you see on display is the pressure the tire would have at 68F, which should be 42 psi.

What that means is our gauge readings probably will not match up with the display unless the tempurature inside the tire happens to be 68F.

As for wear in the middle...
Riding straight up and down on a properly inflated tire is going to do that no matter what. It's a sure bet most of us ride these bikes with some vigor, more than say a typical HD or GW rider, and it is going to eat those tires up. Every start, stop, upshift, downshift wears the tire a little more. At 800 lbs with the power of these bikes it's going to take a toll.

To complicate things more, if the tire is underinflated it's going to flex more and therefore heat up more so you you will see a bigger difference between the gauge reading while 'cold' vs hot. If it's overinflated it won't flex as much and therefore won't heat up as much resulting in a smaller difference. At the track the effects of under/over inflation can be seen as what is called cold or hot tearing of the tire. Either of those can greatly reduce tire life. The goal is to hit the sweet spot where the tire pressure helps keep the tire at the correct tempurature for the best grip and durability.

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post #6 of 88 Old 07-02-2012, 11:25 AM Thread Starter
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OK... I will take your whole "The recommended cold tire inflation pressure is 42 psi. "Cold" is defined to be 68F." and put it to the test.

Being the boss here, thus I get to do what I want I have pulled my K1600GTL into my lab at work and have set the AC on the lab to be 68F. I'll give the bike about 6 hours to acclimate to its new environment and then adjust the tire pressure to 42psi. If what you are saying is correct, then when i take the bike outside the reading on the display should be 42psi as "During operation the bike will get the pressure and tempurature readings from the sensor inside the tire and adjust the display to compensate for any tempurature variation from that 68F standard. In the real world we normally can't control the tempurature but the reading you see on display is the pressure the tire would have at 68F, which should be 42 psi."
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post #7 of 88 Old 07-02-2012, 12:10 PM
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Originally Posted by SVTWEB View Post
OK... I will take your whole "The recommended cold tire inflation pressure is 42 psi. "Cold" is defined to be 68F." and put it to the test.

Being the boss here, thus I get to do what I want I have pulled my K1600GTL into my lab at work and have set the AC on the lab to be 68F. I'll give the bike about 6 hours to acclimate to its new environment and then adjust the tire pressure to 42psi. If what you are saying is correct, then when i take the bike outside the reading on the display should be 42psi as "During operation the bike will get the pressure and tempurature readings from the sensor inside the tire and adjust the display to compensate for any tempurature variation from that 68F standard. In the real world we normally can't control the tempurature but the reading you see on display is the pressure the tire would have at 68F, which should be 42 psi."
Awesome. Please post your results. My money says the the bike display will, at times, be significantly off. It varies so much for me, I don't use it.


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post #8 of 88 Old 07-02-2012, 12:17 PM
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While I think the test will be informative, the point of the TPM is the same as the oil level warning.

The bigger issue for me is what is the best pressure to set the tires at for tire life and road holding. I will then set that pressure at home with my accurate gauge, plus one pound, then head out on my long ride, confident that unless there is a problem, the tire pressure is "in the hunt".

For the manual to indicate that 42 psi is the be all, and end all, for all conditions, seems like lawyer speak to me. We each need to determine the pressure that we like best for our riding style, motorcycle loads, and tire model. What would be nice is if we share our favorite pressures with the forum.

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post #9 of 88 Old 07-02-2012, 12:28 PM
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I check mine with my good gauge. I periodically sanity check that with another gauge.

I know that the display will never show exactly what the gauge says. The display temperature always goes up a couple of pounds after I start riding.

I use the display as another sanity check. If it's way off, I need to check with my gauge. If while I'm riding, it starts dropping, or if the two tire pressures start changing relative to each other, then I need to see if I've picked up a nail or something.

The TPM is great to be able to watch the pressure deltas while riding. I do not use it as an indicator of the exact tire pressure. I seriously doubt that its specs justify placing faith in it as absolute truth. It provides an indicator of change while riding, nothing more.

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post #10 of 88 Old 07-02-2012, 12:28 PM
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If your tires are supposed to be inflated to 42 pounds at 68 degrees and if for every 10 degrees change in temperature there is a 1 pound change cannot one just check the temperature and adjust the pressure accordingly?
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