Tolerance of flat tyre indicator.
Discussion
A week ago had to replace one of my back wheels ( non run flat) which only had 2k on it as had a nice shiny screw embedded in the corner, typical.
Garage bloke said he inflated it to 31 psi so took his word for it.
This morning on the same road the flat tyre indicator came on checked the pressure and noticed the one that had been changed was showing 28.5 psi.
I have inflated it and am keeping an eye out for it, my question is how much psi would it have to lose before the indicator comes on ? Am curious as I am not the type who checks the pressure very often so if the tolerance is low I might have to start doing so regularly as do not like getting that nasty beep if it can be helped.
On a different subject as found this very surprising drove to Sheffield all the way from Newcastle and back early in the week, the cost on the e92 330i was £55 and that was at a decent speed.
Had to do the journey again today and had to use my Berlingo hdi because of the problem above.
Yes as you might have guessed it cost the same amount in fuel and driving considerably slower.
Was quite chuffed as always thought the car was a guzzler.
Garage bloke said he inflated it to 31 psi so took his word for it.
This morning on the same road the flat tyre indicator came on checked the pressure and noticed the one that had been changed was showing 28.5 psi.
I have inflated it and am keeping an eye out for it, my question is how much psi would it have to lose before the indicator comes on ? Am curious as I am not the type who checks the pressure very often so if the tolerance is low I might have to start doing so regularly as do not like getting that nasty beep if it can be helped.
On a different subject as found this very surprising drove to Sheffield all the way from Newcastle and back early in the week, the cost on the e92 330i was £55 and that was at a decent speed.
Had to do the journey again today and had to use my Berlingo hdi because of the problem above.
Yes as you might have guessed it cost the same amount in fuel and driving considerably slower.
Was quite chuffed as always thought the car was a guzzler.
Edited by TX1 on Saturday 16th April 16:31
You can't check tyre pressure often enough really. Once a week is pretty good but keeping an eye on them daily for obvious punctures is a good idea.
Have you reset set the monitor once you've reinflated them?
On my M5 which was an earlier, yet system that works on the same principle - so in essence the same, it would lose about 1.0 bar before it flagged up on the dash.
Have you reset set the monitor once you've reinflated them?
On my M5 which was an earlier, yet system that works on the same principle - so in essence the same, it would lose about 1.0 bar before it flagged up on the dash.
They can be fickle and appear to defy logic. Last summer I had a puncture warning and all 4 tyres were within a few psi of what I normally run them at. So just reset the indicator and it was fine. Changed to winter wheels and tyres in December and the car never noticed. Changed back to the summer wheels and tyres and 60 miles later got a puncture warning. Pressures were exactly were I had set them. Go figure. The lesson to me in all of this is that nothing beats a proper check with a gauge.
i'd get the tyre you had fitted rechecked. It sounds like the tyre may need sealing onto the rim. I assume its an alloy wheel - if so did the tyre company clean the rim before installing the tyre. Alloy wheel rims can be terrible for sealing prpoperly - the slightest bit of dirt or a pit mark in the rims edge where the tyres bead seals will be enough to cause an slow deflation. As previously said i'd get it rechecked & ask for tyre to be sealed on using specialist tyre sealing compound all tyre companies should have.
The tyre pressure monitor just checks for differences between the tyres not overall drops in pressure, so you need to check them still.
Did he warning come on from cold, so less than 2 odd miles from home?
I had it come on a few times when the car was sat half in the sun and half in the shade, probably 25ºc on one side and still pretty cold on the other, suddenly 2-3psi extra from being heated can set it off as you pull away.
If they are non run flats you need more than 31psi as well, if it is 31psi for run flats you need around 34psi for regular tyres.
Did he warning come on from cold, so less than 2 odd miles from home?
I had it come on a few times when the car was sat half in the sun and half in the shade, probably 25ºc on one side and still pretty cold on the other, suddenly 2-3psi extra from being heated can set it off as you pull away.
If they are non run flats you need more than 31psi as well, if it is 31psi for run flats you need around 34psi for regular tyres.
Yup, I agree, you do now need to be keeping a regular check on all 4 tyre pressures until the situation stabilises again.
Dont' forget that the "BMW Run Flat Indicator RPA does not measure the tyre pressures as such.
"The system detects a pressure loss on the basis of a comparison between the speeds at which the individual wheels rotate while the vehicle is in motion.
In the event of a pressure drop, the diameter and therefore the rotational speed of the wheel in question change. This is detected and reported as a flat tyre.
The system has to be reinitialised every time the tyre pressures are corrected"...
Source: Owner's Handbook
This system design (which does not actually measure the pressures) has its limitations and its benefits. Limitations are that you can get false alarms. Benefits are that it is very robust (no delicate spinning guages) and presumably very low additional costs (car already has ABS sensors and steering wheel angle sensor).
Better have a few false alarms than have people running around on one half-flat tyre, shirley?
Dont' forget that the "BMW Run Flat Indicator RPA does not measure the tyre pressures as such.
"The system detects a pressure loss on the basis of a comparison between the speeds at which the individual wheels rotate while the vehicle is in motion.
In the event of a pressure drop, the diameter and therefore the rotational speed of the wheel in question change. This is detected and reported as a flat tyre.
The system has to be reinitialised every time the tyre pressures are corrected"...
Source: Owner's Handbook
This system design (which does not actually measure the pressures) has its limitations and its benefits. Limitations are that you can get false alarms. Benefits are that it is very robust (no delicate spinning guages) and presumably very low additional costs (car already has ABS sensors and steering wheel angle sensor).
Better have a few false alarms than have people running around on one half-flat tyre, shirley?
Thanks for all your help.
Yes the tyre alarm comes on just a couple of miles away from when I set off.
I have rechecked the pressures and funnily enough the 4 tyres seem to have lost 1 to 1.5 psi, I am putting this to ambient temperature change and measuring pressures when tyres are warm.
I am pretty positive there is no puncture and this morning I drove it and all was fine.
Not sure if this is a good idea however the tyres were showing 29 - 30 psi when cold so I reset the computer and put a couple more psi in each wheel after so it gives me a bit of leeway.
Yes the tyre alarm comes on just a couple of miles away from when I set off.
I have rechecked the pressures and funnily enough the 4 tyres seem to have lost 1 to 1.5 psi, I am putting this to ambient temperature change and measuring pressures when tyres are warm.
I am pretty positive there is no puncture and this morning I drove it and all was fine.
Not sure if this is a good idea however the tyres were showing 29 - 30 psi when cold so I reset the computer and put a couple more psi in each wheel after so it gives me a bit of leeway.
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