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My 2018 Clarity factory OEM tires (Michelin green LRR) at 36,000 miles is not looking good for longevity.

Even with rotations every 10K, I am not happy with the treadwear.
Also unhappy that I had to wait for a tow truck when one tire blew (mobility compressor was useless) last year.
Although I had the tire protection and had it replaced which paid for the insurance - the inconvenience was the big factor.

Now I am looking at getting run flat tires (RFT) to replace the OEM tires.
The reason for run flats is that you can drive for up to 50 miles at 50MPH on a flat tire without worrying about wheel damage.
I have had RFT on all my BMWs for the past 20 years so I know how helpful that can be if you had to drive on a flat tire to a shop.

Using the factory OEM size of 235-45x18 I only find one RFT: Bridgestone DriveGuard at $220 each - which by the way, is the same exact brand I use on my current BMW 5 sedan....

Then going up a size to 245-45-18 (.5" taller and .5" wider) I can find tons of RFT options - over 20 options.
Looking at the Pirelli Winter Sottozero they are priced a bit better ($190 ea).

Although I live in a dry, hot climate - the appeal of a winter RFT harkens my memory to the days I used to go winter skiing and the high silica content tires gripped the snow and ice very well...

I don't know which to choose: AS factory sized RFT or Winter +1 sized RFT....

Any ideas / suggestions / comments ?
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Would these sizes mess with the TPMS that reads tire size instead of PSI? Or does the recalculate feature handle this?
The Clarity TPMS reads wheel rotation speed. When you calibrate it measures the rotation speed of all four wheels, then later if one wheel is rotating differently it interprets that as being due to low tire pressure.

With runflats I suspect that the Clarity TPMS would not recognize that a tire has lost pressure because the rotation speed probably won't change much. Probably would need an add-on tire pressure monitor. I got one because of false alarms on the TPMS, and also because Clarity TPMS doesn't tell you which tire is low. They make ones that sit on top of the dash, but I wanted something less obtrusive, the one I got is made by Tymate and plugs into the 12V.

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The Clarity TPMS reads wheel rotation speed. When you calibrate it measures the rotation speed of all four wheels, then later if one wheel is rotating differently it interprets that as being due to low tire pressure.

With runflats I suspect that the Clarity TPMS would not recognize that a tire has lost pressure because the rotation speed probably won't change much. Probably would need an add-on tire pressure monitor. I got one because of false alarms on the TPMS, and also because Clarity TPMS doesn't tell you which tire is low. They make ones that sit on top of the dash, but I wanted something less obtrusive, the one I got is made by Tymate and plugs into the 12V.

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I'm surprised that the "rotation-delta-method" for tire pressure can be used in the presence of other systems that also use comparative rotation speeds as triggers, like ABS, traction control and stability programs. Perhaps the pressure-sensing software looks for long-term differences, while the others are looking for more transient effects? (That's probably a question more for the engineers that implement these systems, but I like to speculate and problem-solve.)
 

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The Clarity TPMS reads wheel rotation speed. When you calibrate it measures the rotation speed of all four wheels, then later if one wheel is rotating differently it interprets that as being due to low tire pressure.

With runflats I suspect that the Clarity TPMS would not recognize that a tire has lost pressure because the rotation speed probably won't change much. Probably would need an add-on tire pressure monitor. I got one because of false alarms on the TPMS, and also because Clarity TPMS doesn't tell you which tire is low. They make ones that sit on top of the dash, but I wanted something less obtrusive, the one I got is made by Tymate and plugs into the 12V.

View attachment 780

View attachment 781
I just ordered one of these from Amazon. The reviews on this one are hit and miss, but I took a chance anyway, wanting to see battery voltage and temperatures that aren't on the other branded, round ones. I'll follow up with results when it arrives.

Thanks for sharing!
 

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I'm surprised that the "rotation-delta-method" for tire pressure can be used in the presence of other systems that also use comparative rotation speeds as triggers, like ABS, traction control and stability programs. Perhaps the pressure-sensing software looks for long-term differences, while the others are looking for more transient effects? (That's probably a question more for the engineers that implement these systems, but I like to speculate and problem-solve.)
Yeah, it’s either gotta be a long term thing or it takes into account other variables like turning a corner. Roughly, if a car is in a 50-foot radius turn (100-foot diameter circle) and the distance from the inside tire to the outside tire is about six feet, then the outside tire is making a 50-foot radius arc while the inside tire is making a 44-foot radius arc. That means one wheel is turning about 15% faster than the other.
 

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Yeah, it’s either gotta be a long term thing or it takes into account other variables like turning a corner. Roughly, if a car is in a 50-foot radius turn (100-foot diameter circle) and the distance from the inside tire to the outside tire is about six feet, then the outside tire is making a 50-foot radius arc while the inside tire is making a 44-foot radius arc. That means one wheel is turning about 15% faster than the other.
And it's going to be a slightly different delta for the fronts (which turn) as it will for the rears (which don't). I bet that's a fun problem to solve. (Not being sarcastic. I'm an engineer, too.)
 

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I'm surprised that the "rotation-delta-method" for tire pressure can be used in the presence of other systems that also use comparative rotation speeds as triggers, like ABS, traction control and stability programs.
My guess is that the same sensor is providing the same rotational data to all of these systems, and each system uses the data whenever and however often it needs it.
And it's going to be a slightly different delta for the fronts (which turn) as it will for the rears (which don't).
Assuming it can tell from other sensors when the car is going straight as opposed to being in a turn, I would think the TPMS system only looks at rotational data during those periods.
 

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I just ordered one of these from Amazon. The reviews on this one are hit and miss, but I took a chance anyway, wanting to see battery voltage and temperatures that aren't on the other branded, round ones. I'll follow up with results when it arrives.

Thanks for sharing!
Had it a few months and seems to be working well. Being the first time I have used one of these the installation took longer than I thought. Getting it to synchronize for the first time was a little confusing, but reading the manual combined with trial and error, as well as giving it enough time to synchronize, it eventually got sorted out. Also the installation of the sensors onto the valve stems is a bit tricky the first time you do it, mainly related to the rubber sleeve that covers the gap between the sensors and the valve stems. The rubber sleeve seemed to get in the way during installation, but with some practice I finally got used to it by the time I did the fourth tire LOL. Some people say they don't even use the rubber sleeves, but I think they serve a purpose so it's worth the effort to figure out how to get them installed with the sleeves.

Next time I rotate my tires I have to decide whether to reprogram the sensors to their new location, or remove each sensor and reinstall it at the location where it was previously. Reprogramming isn't that hard to do so I will probably go that route.

The disconcerting thing about all of the systems that I looked into is they all seem to say that they may not immediately report a drop in pressure, it may show up only over time. Not great if you hit a nail and have fairly rapid pressure loss. I suspect they are just covering their tracks by saying that and it may respond quicker than they make it sound, but no real way to know. But presumably the built in TPMS system will give you a warning about a sudden pressure loss.
 

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Discussion Starter · #10 ·
The Clarity TPMS reads wheel rotation speed. When you calibrate it measures the rotation speed of all four wheels, then later if one wheel is rotating differently it interprets that as being due to low tire pressure.

With runflats I suspect that the Clarity TPMS would not recognize that a tire has lost pressure because the rotation speed probably won't change much. Probably would need an add-on tire pressure monitor. I got one because of false alarms on the TPMS, and also because Clarity TPMS doesn't tell you which tire is low. They make ones that sit on top of the dash, but I wanted something less obtrusive, the one I got is made by Tymate and plugs into the 12V.

View attachment 780

View attachment 781
Very cool!

On my BMWs, the run flat tires do show a "sag" or slight flat looking profile when the air is gone, but the sidewalls are stiff enough to hold up the car to drive a limited distance which is what I really wanted.

Will report back on which RFT I decide to get...
 

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Had it a few months and seems to be working well. Being the first time I have used one of these the installation took longer than I thought. Getting it to synchronize for the first time was a little confusing, but reading the manual combined with trial and error, as well as giving it enough time to synchronize, it eventually got sorted out. Also the installation of the sensors onto the valve stems is a bit tricky the first time you do it, mainly related to the rubber sleeve that covers the gap between the sensors and the valve stems. The rubber sleeve seemed to get in the way during installation, but with some practice I finally got used to it by the time I did the fourth tire LOL. Some people say they don't even use the rubber sleeves, but I think they serve a purpose so it's worth the effort to figure out how to get them installed with the sleeves.

Next time I rotate my tires I have to decide whether to reprogram the sensors to their new location, or remove each sensor and reinstall it at the location where it was previously. Reprogramming isn't that hard to do so I will probably go that route.

The disconcerting thing about all of the systems that I looked into is they all seem to say that they may not immediately report a drop in pressure, it may show up only over time. Not great if you hit a nail and have fairly rapid pressure loss. I suspect they are just covering their tracks by saying that and it may respond quicker than they make it sound, but no real way to know. But presumably the built in TPMS system will give you a warning about a sudden pressure loss.
Installed mine, and it worked without any extraordinary interventions on my part. I left the default settings for alarms, because my usual pressure is 38psi, which is close to the center of the default range. I am disappointed that I can't change temperature units to F, and it's difficult to see the display. It needs to be much brighter.
 

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Installed mine, and it worked without any extraordinary interventions on my part. I left the default settings for alarms, because my usual pressure is 38psi, which is close to the center of the default range. I am disappointed that I can't change temperature units to F, and it's difficult to see the display. It needs to be much brighter.
I don't remember if there is a brightness setting but I don't think so. For me the brightness is okay since it's in the shade. I knew the visibility would be a little awkward, I have to tilt my head down a little to see it, but I prefer having it out of the way rather than having one sitting on my dashboard. I suppose a 12V extension cord would enable moving it closer, but so far I am okay with it where it is. Yeah a common complaint is not being able to set the temperature to Fahrenheit. Maybe I'll actually use it as a reason to start thinking in Celsius. But probably not LOL.
 
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