Sponsored by The Tire Rack

[fdriller9]

So every time I go on a long trip, I check my tire pressures. Im going home today (about a 2 hour drive) so while I was filling up, I checked the tire pressure on all 4 wheels and they were all within 2 psi (of spec) but the front, passenger side wheel. It was at around 20 psi....my fronts are suppose to be 32psi.

Anyway, my car didn't tell me I had a "flat." I know FTM is not as accurate as TPMS but 12psi is a pretty big drop. FTM should have picked this up and warned me, no?

I always reset the FTM when I check the tire pressures and I did today after making sure my tires were properly inflated.

Does anyone know exactly how the FTM system works? I know it monitors the rotational diameter of the tire or something....less air, smaller diameter, more air, larger diameter.

But which sensors are used? ABS?

I want to clean them as I think the winter salt/road grime has hindered their ability to read proper values.

Thanks.

[ceb]

Originally Posted by *********

So every time I go on a long trip, I check my tire pressures. Im going home today (about a 2 hour drive) so while I was filling up, I checked the tire pressure on all 4 wheels and they were all within 2 psi (of spec) but the front, passenger side wheel. It was at around 20 psi....my fronts are suppose to be 32psi.

Anyway, my car didn't tell me I had a "flat." I know FTM is not as accurate as TPMS but 12psi is a pretty big drop. FTM should have picked this up and warned me, no?

I always reset the FTM when I check the tire pressures and I did today after making sure my tires were properly inflated.

Does anyone know exactly how the FTM system works? I know it monitors the rotational diameter of the tire or something....less air, smaller diameter, more air, larger diameter.

But which sensors are used? ABS?

I want to clean them as I think the winter salt/road grime has hindered their ability to read proper values.

Thanks.

Yep, primarily the ABS sensors. The system determines overall rolling diameter using inputs from various sensors and comares it to the other tires - but - it really is only as good as the the person pushing the reset button.

Let's say that your front left was at 30 and your front right at 20. The system will think that is OK and you'll be able to lose several pounds before it alerts you.

Try this

Inflate all tires to the same amount (or front two the same, the rear two the same)
Drive for a week
Check pressure

If the tires held pressure then

Deflate 1 tire to 20psi and start driving. You should get a warning. If not, then your system needs repair.

[alex2364]

I don't know anything about FTM, but you should check tire pressures when cold. Best way is doing it early morning when the car has been sitting overnight. Checking pressures during the middle of trip won't give you accurate readings.

[SpmnE9zero]

When I read your title I thought you were referring to the E90postwhore Midget!
he sucks!

back on topic sorry.

[SpmnE9zero]

Originally Posted by alex2364

I don't know anything about FTM, but you should check tire pressures when cold. Best way is doing it early morning when the car has been sitting overnight. Checking pressures during the middle of trip won't give you accurate readings.

this is true, as temps rise so does pressure.

[Lenaxia]

Originally Posted by *********

So every time I go on a long trip, I check my tire pressures. Im going home today (about a 2 hour drive) so while I was filling up, I checked the tire pressure on all 4 wheels and they were all within 2 psi (of spec) but the front, passenger side wheel. It was at around 20 psi....my fronts are suppose to be 32psi.

Anyway, my car didn't tell me I had a "flat." I know FTM is not as accurate as TPMS but 12psi is a pretty big drop. FTM should have picked this up and warned me, no?

I always reset the FTM when I check the tire pressures and I did today after making sure my tires were properly inflated.

Does anyone know exactly how the FTM system works? I know it monitors the rotational diameter of the tire or something....less air, smaller diameter, more air, larger diameter.

But which sensors are used? ABS?

I want to clean them as I think the winter salt/road grime has hindered their ability to read proper values.

Thanks.

FTM monitors the rolling radius differential between the left and right wheels.

When you initialize it, it is checking the difference between the two. Meaning if both the left and right tires lose air at the same rate FTM will NOT activate.

I agree with you it's retarded. My tires werent holding air for some reason and my pressures in both fronts got down to 15 only 2 days after I filled them up and FTM never activated. I only noticed because I scraped my bottom going over a speed bump.

I check my tires religiously now.

[fdriller9]

Thanks for the responses guys....I'll have to try deflating one side to see it it trips.

I usually check my pressure at the beginning of the trip so it shouldn't be warm (expanded) especially in this weather.

[stressdoc]

Curious, the FTM works great on my 335. Some times it seems more sensitive than at other times. Not sure how it is able to deal with measurement when there is tons of snow, I guess it is able to detect differences that are consistent over a long period.

[fdriller9]

Originally Posted by stressdoc

Curious, the FTM works great on my 335. Some times it seems more sensitive than at other times. Not sure how it is able to deal with measurement when there is tons of snow, I guess it is able to detect differences that are consistent over a long period.

I think my sensors are dirty....I haven't washed my car for some time because it's too cold and I do not go to car washes. Always hand washed by me.

But washing the car shouldn't affect the sensors.

I mean I haven't had problems with it until this winter.....the car is about to turn 5 years old in May though.

[username604]

what? my idrive says tpm?
This whole time i thought my tires were up to spec, but its just been measuring the tire diameter difference?
Can anyone confirm that i have a FTM and not a TPMS?
What about tirerack, it says that my car requires tpms sensors?

Edit: would FTM even work with RFTs?

[DJKhan85]

The older system that used the ABS system is DIFFERENT than newer cars with TPMS. TPMS has a sensor in the tire that reports tire pressure changes to the car. FTM uses the abs sensor to determine rolling diameter. I do not think there is a sensor in the wheel when you have FTM.

[fdriller9]

Originally Posted by davidkneiber

what? my idrive says tpm?
This whole time i thought my tires were up to spec, but its just been measuring the tire diameter difference?
Can anyone confirm that i have a FTM and not a TPMS?
What about tirerack, it says that my car requires tpms sensors?

Edit: would FTM even work with RFTs?

You have TPMS. It was mandated in early '07.

FTM works with RFTs. All pre-March '07 (I think it was March) models have FTM and all E9xs come with RFTs.

[MPR]

How do you check tire status on non idrive vehicles? (sorry im a bmw newb)

[fdriller9]

Not sure. Maybe through your turn signal stalk?

Procedure should be in your manual. If you don't have one, there is one on the bmwusa.com website.

[ceb]

Originally Posted by davidkneiber

what? my idrive says tpm?
This whole time i thought my tires were up to spec, but its just been measuring the tire diameter difference?
Can anyone confirm that i have a FTM and not a TPMS?
What about tirerack, it says that my car requires tpms sensors?

Edit: would FTM even work with RFTs?

Anything newer than '07 in the US will have TPMS

[John 070]

Are the systems different on the 330 v. 335? I do find it funny, that when I switch to my snows, which do not have TPMS, it takes about 4 miles for the system to light up. Likewise when I put the OEM's back on.

[fdriller9]

Originally Posted by John 070

Are the systems different on the 330 v. 335? I do find it funny, that when I switch to my snows, which do not have TPMS, it takes about 4 miles for the system to light up. Likewise when I put the OEM's back on.

330s in the US will have ftm. Post March '07 e9x in the US have TPMS. That's why it takes a few miles to tell you it's flat....ftm measures the rotational diameter of the tire.

[Bartman619]

One way you can tell if you have FTM is to look at the valve stems. If they are rubber, then you have FTM. Metal valve stems means you have TPMS.

[Byermecham]

I believe ftm go off the rotation of the tire like if your rear left is spinning faster than your rear right due to the tire loosing pressure it will send the code as a flat tire