Tyre Pressure (M3, 19")

Hi,

I've just had 2 new rear tyres fitted to my M3 with factory fitted 19" 's on
it. I had a nail in one so the pressure warning light came on.

Since having them fitted the pressure warning light keeps coming on, I keep
resetting it and checking the pressures which seem to be ok.

On the inside of the door it states the 19" wheels should have between 2.4
and 3.3 BAR in them, that sounds like a lot when converted to PSI?

Google says...
2.4 bar = 34.8 pounds per square inch
3.3 bar = 47.8 pounds per square inch

I'm usually in the car alone and don't carry anything heavy, but at BMW
they've put 33psi in the rear and the front have 30? Sounds like if the
door sticker is right I should have them all running at about 36?

Is the warning coming on because the pressures are too low in the 1st place?

I've also notice the car seems a bit "light" on the road, as though it's not
really as connected as before, is this just because I've got a lot more grip
and am not driving with slicks on or is it because I've got new tyres on the
back and 17,000 on the fronts?

Thanks

Daz

new tires on back and used on front, especially if wider in rear will make
the car a little less responsive.
I run 33/38 on my 17" and size is not important when it comes to pressure,
17 or 19" gets the same psi. The door sticker says 38/41 I believe.
the sticker is right, I have the tire shop always putting about 32psi in,
because they don't know to put the proper amount, BMW does seem to take more
air

"SharkmanBMW" wrote
> size is not important when it comes to pressure, 17 or 19" gets the same
> psi.

Well, it kind of is important, but mostly to do with load rating. If a tire
has lower load rating, you might want to increase the PSI a little because
at higher pressure, it can handle more load.

Also, people sometimes put in slightly higher pressure in very low profile
tires to reduce the risk of pothole rim damage, but of course that doesn't
have much to do with proper tire inflation for handling purposes.

Regards,

Pete

"Daz" <daz@home> wrote
> I've just had 2 new rear tyres fitted to my M3 with factory fitted 19" 's
> on it. I had a nail in one so the pressure warning light came on.
>
> Since having them fitted the pressure warning light keeps coming on, I
> keep resetting it and checking the pressures which seem to be ok.

I don't know which method that BMW is using for tire pressure warnings:
1) in-wheel sensors/transponders, or
2) comparison inside the ABS/DSC system of tire rotations.

Our Toyota Highlander uses the latter: the system works by comparing
the rotational speeds of the wheels. If the steering wheel is straight
ahead
and one tire is slower than the others, it's low. It's *possible* that the
system is detecting a rotational speed difference between front/rear
tires due to the wear on the fronts.

FloydR

The light comes on because the tires are not turning at the same speeds.

The Low Air warning is an offshoot of the ABS/Traction Control (DSC?)
system. When the tires are not turning at the same speeds in ABS or DSC,
then it means that the tires are about to lock, or break away. But while
cruising and the tires are going the same speeds, then it means that one or
more is low on air, and the warning turns on.

I haven't a clue how much air there should be in a 19, but if you put 35 psi
(about 2.4 BAR) in all four tires, then the Low Pressure indicator should go
out. This won't be the correct pressure, but it will test the theory, then
you can figure out what the correct pressure should be later.






"Daz" <daz@home> wrote in message
...
> Hi,
>
> I've just had 2 new rear tyres fitted to my M3 with factory fitted 19" 's
> on it. I had a nail in one so the pressure warning light came on.
>
> Since having them fitted the pressure warning light keeps coming on, I
> keep resetting it and checking the pressures which seem to be ok.
>
> On the inside of the door it states the 19" wheels should have between 2.4
> and 3.3 BAR in them, that sounds like a lot when converted to PSI?
>
> Google says...
> 2.4 bar = 34.8 pounds per square inch
> 3.3 bar = 47.8 pounds per square inch
>
> I'm usually in the car alone and don't carry anything heavy, but at BMW
> they've put 33psi in the rear and the front have 30? Sounds like if the
> door sticker is right I should have them all running at about 36?
>
> Is the warning coming on because the pressures are too low in the 1st
> place?
>
> I've also notice the car seems a bit "light" on the road, as though it's
> not really as connected as before, is this just because I've got a lot
> more grip and am not driving with slicks on or is it because I've got new
> tyres on the back and 17,000 on the fronts?
>
> Thanks
>
> Daz
>

Daz wrote:
> Hi,
>
> I've just had 2 new rear tyres fitted to my M3 with factory fitted 19" 's on
> it. I had a nail in one so the pressure warning light came on.

I run 2.7bar front, 3.0 bar rear on my B10;

235/40 R 18 front, 265/35 R18 rear

33psi seems low.



A

"Floyd Rogers" > wrote in message
...
> "Daz" <daz@home> wrote
>> I've just had 2 new rear tyres fitted to my M3 with factory fitted 19" 's
>> on it. I had a nail in one so the pressure warning light came on.
>>
>> Since having them fitted the pressure warning light keeps coming on, I
>> keep resetting it and checking the pressures which seem to be ok.
>
> I don't know which method that BMW is using for tire pressure warnings:
> 1) in-wheel sensors/transponders, or
> 2) comparison inside the ABS/DSC system of tire rotations.
>
> Our Toyota Highlander uses the latter: the system works by comparing
> the rotational speeds of the wheels. If the steering wheel is straight
> ahead
> and one tire is slower than the others, it's low. It's *possible* that
> the
> system is detecting a rotational speed difference between front/rear
> tires due to the wear on the fronts.
>
> FloydR

Does anybody know which system BMW use? If it's the ABS/DSC system then it
could explain things?

I have inflated the tyres to 40psi rear and 37psi front, I'll see how it
goes over the weekend but have booked the car into BMW on Monday morning so
they can check it out.

Thanks

Jeff Strickland wrote:
> The light comes on because the tires are not turning at the same speeds.
>
> The Low Air warning is an offshoot of the ABS/Traction Control (DSC?)
> system. When the tires are not turning at the same speeds in ABS or DSC,
> then it means that the tires are about to lock, or break away. But while
> cruising and the tires are going the same speeds, then it means that one
> or more is low on air, and the warning turns on.
>
> I haven't a clue how much air there should be in a 19, but if you put 35
> psi (about 2.4 BAR) in all four tires, then the Low Pressure indicator
> should go out. This won't be the correct pressure, but it will test the
> theory, then you can figure out what the correct pressure should be later.

I don't get it. How would that cause the light to come on if all the
tires are the same pressure (and low)? What is it comparing the wheel
rotation to to determine the tire pressure is low?

I see how it would work if one tire was low, but what about if all of
them are?


--
-Fred W

"Malt_Hound" <""Malt_Hound\"@*spam-me not*yahoo.com"> wrote
> Jeff Strickland wrote:
>> The light comes on because the tires are not turning at the same speeds.
>>
>> The Low Air warning is an offshoot of the ABS/Traction Control (DSC?)
>> system. When the tires are not turning at the same speeds in ABS or DSC,
>> then it means that the tires are about to lock, or break away. But while
>> cruising and the tires are going the same speeds, then it means that one
>> or more is low on air, and the warning turns on.
>>
>> I haven't a clue how much air there should be in a 19, but if you put 35
>> psi (about 2.4 BAR) in all four tires, then the Low Pressure indicator
>> should go out. This won't be the correct pressure, but it will test the
>> theory, then you can figure out what the correct pressure should be
>> later.
>
> I don't get it. How would that cause the light to come on if all the
> tires are the same pressure (and low)? What is it comparing the wheel
> rotation to to determine the tire pressure is low?
>
> I see how it would work if one tire was low, but what about if all of them
> are?

Well, yes, this system's design won't allow it to find low tires if all
of them are low - it assumes that they start out correct. But in this
guy's situation that might not be good enough, since the fronts are
worn but rears new - the radii are possibly incompatible.

Floyd

"Daz" <daz@home> wrote in message
...
> Hi,
>
> I've just had 2 new rear tyres fitted to my M3 with factory fitted 19" 's
> on it. I had a nail in one so the pressure warning light came on.
>
> Since having them fitted the pressure warning light keeps coming on, I
> keep resetting it and checking the pressures which seem to be ok.
>
> On the inside of the door it states the 19" wheels should have between 2.4
> and 3.3 BAR in them, that sounds like a lot when converted to PSI?
>
> Google says...
> 2.4 bar = 34.8 pounds per square inch
> 3.3 bar = 47.8 pounds per square inch
>
> I'm usually in the car alone and don't carry anything heavy, but at BMW
> they've put 33psi in the rear and the front have 30? Sounds like if the
> door sticker is right I should have them all running at about 36?
>
> Is the warning coming on because the pressures are too low in the 1st
> place?
>
> I've also notice the car seems a bit "light" on the road, as though it's
> not really as connected as before, is this just because I've got a lot
> more grip and am not driving with slicks on or is it because I've got new
> tyres on the back and 17,000 on the fronts?
>
> Thanks
>
> Daz

I no longer have my M3, but I had an identical problem when the
tyre-pressure monitor kept going off after a puncture was repaired on on of
my 19's.
In the end I took it back to the dealer and they reset it. It can be very
tempremental.