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      03-24-2014, 10:20 AM   #1
halfmoonclip
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How is tire pressure measured for FTM?

While perusing the 'Quick Reference Guide' this morning, I found the following quote on page 29:
"Flat Tire Monitor The system identifies a loss of pressure by comparing the speeds of rotation of the individual wheels as the car is traveling."

I would welcome this as a fact, because I plan to buy winter tires on rims for next season, and avoiding the electronic tire valves is a time and money saver. My bride's Audi uses the 'tire rotation' method, and it has worked very well.

Any more info? I presume the factory brochure should be right, but I thought I had read elsewhere that electronic stems were involved.
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      03-24-2014, 03:15 PM   #2
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U.S. spec has the tpms as part of the valve stem or whatever.
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      03-24-2014, 04:31 PM   #3
halfmoonclip
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Quote:
Originally Posted by Twix View Post
U.S. spec has the tpms as part of the valve stem or whatever.
Not meaning to argue Twix, as I have heard this elsewhere...but I don't understand why the 'guide' would say what it does.
Thnx,
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ETA- The car is a '14.
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      03-24-2014, 05:59 PM   #4
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Do you have metal valve stems? If so you have TPMS.
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      03-24-2014, 07:08 PM   #5
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I am a little curious as to how sensitive this system is because there is a 6 psi difference (32 front, 38 rear) in air pressure based on the recommended tire pressures. How much off does the tire pressure have to be before the system picks it up.

As far as sticking more money into more TPMS sensors for winter tires why bother. I just pull the fuse on the TPMS system and bingo, no issues. Granted there is a little yellow icon that stays lit but it is not annoying, it is small and out of the way in the dash readout. And how long does one really leave the winter tires on...3 months, maybe 4 during a bad winter. It isn't worth it in my estimate.
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      03-24-2014, 08:02 PM   #6
halfmoonclip
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Quote:
Originally Posted by Red Bread View Post
Do you have metal valve stems? If so you have TPMS.
The stems appear to be threaded metal.
Do you mean the sensors are then in the stems?
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      03-24-2014, 08:06 PM   #7
halfmoonclip
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Quote:
Originally Posted by forteatwo View Post

As far as sticking more money into more TPMS sensors for winter tires why bother. I just pull the fuse on the TPMS system and bingo, no issues. Granted there is a little yellow icon that stays lit but it is not annoying, it is small and out of the way in the dash readout. And how long does one really leave the winter tires on...3 months, maybe 4 during a bad winter. It isn't worth it in my estimate.
This had been my practice with a Ford Focus that I have since given to my daughter. She occasionally grouses about the light, but she's gotten in the habit of checking her tire pressures.
What is the reason for pulling the fuse if the light remains lit? Please don't tell me there's a relentless chime...
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      03-24-2014, 08:55 PM   #8
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My '13 has sensors and I ordered additional sensors when I bought my "winter" wheels/tires.
I wouldn't disable the TPMS under any circumstances. It has warned me of a low tire on two occasions where I'm certain that I would have damaged/destroyed the affected tire(on a rather long interstate trip) had I driven on it for a prolonged period of time...once with runflats, once without. Not to mention the danger to myself and others had the tire become hot and come apart.
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      03-24-2014, 09:52 PM   #9
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The reason the guide says differently is because it's written for the entire world, not just Murica. All U.S. spec cars have the tpms built into the stems. Period.

Also, if you remove the fuse to disable the system I can only imagine the legal ramifications which would come about if you ever happened to injure somebody in a collision caused by a loss in tire pressure. Murica is in love with suing people.
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      03-24-2014, 10:53 PM   #10
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Quote:
Originally Posted by Twix View Post
The reason the guide says differently is because it's written for the entire world, not just Murica. All U.S. spec cars have the tpms built into the stems. Period.

Also, if you remove the fuse to disable the system I can only imagine the legal ramifications which would come about if you ever happened to injure somebody in a collision caused by a loss in tire pressure. Murica is in love with suing people.
Twix,

You've been watching too many American movies. Get a grip.
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      03-25-2014, 09:39 AM   #11
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I bought a new 07 RX8 with nicer lighter Enkei GF-1 wheels modded by the dealer.

Nobody tried to put sensors in the wheel and I've always had the light which I don't mind.

I also take it to sports car tracks and run high performance tires.

Those kind of tires have thicker carcass.

I've never had a flat in that kind of tire, but have found worn out nails when replacing worn tire.

Tires not speed rated like All season get punctured easier.
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      03-25-2014, 10:44 AM   #12
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Quote:
Originally Posted by 0w40X1 View Post
Those kind of tires have thicker carcass.

I've never had a flat in that kind of tire, but have found worn out nails when replacing worn tire.

Tires not speed rated like All season get punctured easier.
Do you really believe this? Performance tires have stiffer sidewalls, but typically lighter belting and of course much stickier compounds. This makes them flat magnets. I have had countless flats in track tires and higher performance tires like PS2's and PSS's than with my daily which is currently on Pilot A/S3's or my wife's X1 on the P7 A/S's.

I had a rear blowout with a Toyo T1R that I caught quickly and didn't shred the rear fender or eat a guardrail, but to think that good tires save you from flats or other issues is just bunk, akin to thinking that a more expensive car should be safer than a cheaper car, or not get flats.

Buy some TPMS sensors folks, TireRack sells them for $40/ea. If you're buying good tires, a BMW, premium fuel and paying your insurance, why not maintain a simple safety device that costs you very little and provides a small amount of safety? You can also move them between wheels if you really don't want to buy a second set.
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      03-25-2014, 11:17 AM   #13
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Red Bread,

Maybe my article seemed a little fluffy to you, but I used to sell and adjust tires so I do know a little about tire failures.

Speed rated radiaL tires usually have soft sidewalls , but tougher belts.

Why do you think that some tires are rated to 168+ mph for tread separation?

I've had cheap tires that would separate when I tried to run 40 psi.

I also had a H rated 130mph tire go soft into a turn once at 100 mph because of bad tire stem. Stems fixed, tire reused for a few years and worn out.

There is a wide variation in tire quality, and wide variation in how people drive cars.

TPMS is a great safety device, and I wouldn't defeat it myself, but I track my cars and can feel something off with the tires or suspension.
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      03-25-2014, 11:24 AM   #14
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Agreed, I just replaced an awful set of H rater Kumhos on my daily with V rated Michelins. Using better tires is great, but I get so sick of hearing how all season tires are the devil. Maybe I overreacted to that, apologies if so.

I track quite a bit too and have a good sense of what my tires are up to, but my wife panics if the TPMS light comes on and waits until I "fix" it. I'm okay with that.
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      03-25-2014, 11:43 AM   #15
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Quote:
Originally Posted by Red Bread View Post

I track quite a bit too and have a good sense of what my tires are up to, but my wife panics if the TPMS light comes on and waits until I "fix" it. I'm okay with that.
Yeah, so where do you track? I started with Lambo Days April 2008 at MSR Cresson which is a very good track. I'm a member of BMWCCA Lone Star Region, but they put on 2 day driver schools.

I've been autoxing since 1973 and just want to drive at HPDE without the "minder" in the car for about 4 20 minute sessions.

That first day I had a Lambo in my mirror every 30 seconds and had no problem.

I want to drive without the hand wringing.

I did just get back from Arroyo Seco Raceway in Deming NM where they let us go and timed us as a super lap.

Sorry to OP for the hijack.
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      03-25-2014, 01:01 PM   #16
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Quote:
Originally Posted by halfmoonclip View Post
Any more info? I presume the factory brochure should be right, but I thought I had read elsewhere that electronic stems were involved.
Moon
Quote:
Originally Posted by halfmoonclip View Post
The stems appear to be threaded metal.
Do you mean the sensors are then in the stems?
Moon
shows what the tpms transmitters in the wheels look like
http://www.oewheelsllc.com/Home_3?se...1#.UzHEB-Mo6M8
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      03-25-2014, 01:30 PM   #17
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Can you install real tpms sensors on the Canadian version that comes without it?
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      03-25-2014, 02:46 PM   #18
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Quote:
Originally Posted by Njerts View Post
Can you install real tpms sensors on the Canadian version that comes without it?
the dealer would be the best to answer your question.
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      03-25-2014, 07:21 PM   #19
halfmoonclip
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If the sensors are down to $40@, I may well go with them. Last time I was making this decision, they were more like $90.
What must you do when you change sets of tires to enable the system?
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      03-26-2014, 08:12 AM   #20
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Quote:
Originally Posted by halfmoonclip View Post
If the sensors are down to $40@, I may well go with them. Last time I was making this decision, they were more like $90.
What must you do when you change sets of tires to enable the system?
Moon
I'm just tossing this out, others may have first hand experience.
If the TPMS transmitter in the tire is the same 433 MHz frequency the receiver is on the X1, then when you swap tires, you go to the TPMS screen and reset the sensors.

Last edited by fjrmann; 03-26-2014 at 11:58 AM..
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      03-26-2014, 10:48 AM   #21
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Quote:
Originally Posted by Red Bread View Post

You can also move them between wheels if you really don't want to buy a second set.
Would you have to remove the tire from the rim to remove the sensor? I guess I thought the sensor was in the valve stem.
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      03-26-2014, 11:20 AM   #22
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Quote:
Originally Posted by forteatwo View Post
Would you have to remove the tire from the rim to remove the sensor? I guess I thought the sensor was in the valve stem.
Yeah, you'll have to pull each tire to deal with the way they're mounted.
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