sg530

Loss of air pressure in a tire is automaticly sensed on E60. If the tire gets a leak, you get a warning before you can feel the problem if you are driving at the time. If the leak is a slow one, with the warning alarm, you will have a chance to stop at your convenience, assuming you can feel the change in handling enough to gage the rate of loss of air before the tire is damaged. After driving on a soft tire for a time, the high temperatures from internal friction and flexing can make it 'blow out' suddenly.
Now, to my question. Assume you have a low tire but not enough to set off the alarm. Driving at high speed on the highway heats it up and the pressure increases. Will this increase in pressure trigger the alarm the same as a reduction in pressure?

chicosy

Are we talking about RFT or normal ones?

AFAIK, the way the tyre sensor works is that it doesn't detect pressure per se. If measures wheelspin per wheel and a significant difference in one tyre, meaning one wheel spinning faster allows it to tell that one tyre is low on pressure.

So I doubt that it will detect the increase in pressure you're mentioning.

On the other hand though, I've not heard of RFT having a "blow out". I think they're heaps stronger than a normal wheel and should allow enough time for the system to detect the situation and inform you of the situation. Not sure though on normal tyres.

kscarrol

I doubt it also, as the heating will take place on all tires, thus raising the pressure in all. The real unknown is say (not that you ever would!) you let the attendant at a gas station put air in your tire and he puts way too much, would the sensor detect that difference, where maybe that wheel is spinning slower than the rest? That is when you need to worry about the increasing pressure from heating while driving causing a blowout (on regular tires).

JDN

I just had an interesting issue with my tires. Even with a compressor and a 50' hose extension, it has been quite a while since I checked my tires. Today I was giving the outside a good rinse and wipe down and decided to check the tires since it was such a beautiful day.

Much to my surprise instead of 32 psi each of the fronts was 27 and instead of 35 psi on the rear, each was 30. That was an even 5 psi down on each tire. This was my same old trusty gauge that was used on the last check. Our FTM friend has never so much as hiccupped, so it appears that as long as they all spin the same, theoretically one could deflate to zero without FTM mentioning the fact that a problem was about.

Now, I need advice. Should I air five over to even the wear -- none visible?

530E60NL

I would even them. You should always drive around with correct tirepressures. Safes a lot of gas too. I would also initialize the RFT in the I-Drive.

JDN

Maybe you misunderstood. I aired them to specs. Question is should I air over specs. I really don't think I will, but asked the rhetorical question anyway.

I will get around to the FTM initialization when I head for the airport in the am. Thanks.

530E60NL

Sorry, my english can be bad some times.. I always give my tires 0.1 or 0.2 bars over pressure.. I don't know how much it is in PSI. A tireguy once told me that it is better to drive around with a little overpressure then a little underpessure so that's the reason why I do it.

Iceman

Dennis, the tireguy was telling you BS.
In the past a lot of ppl recommended to have 0.2 more to save fuel, but that is absolute BS.
Just think about how much of your tires actually is in contact with the street. Four wheels are having a total contact with the street equivalent to about one DIN-A-4 piece of paper. Inflating the tires more or less then on the car manufacturers recommendation will lead to less grip/contact.
There is only the right or the wrong pressure for tires, nothing else.

Jimbo

Hate to disagree with Iceman, but softer tires give you more contact. Ask any drag racer. My run flats are 29 front/36 rear as per the manual. The dealer tech stated that I should run 36 all around because the tires will last longer and the lower pressure is better only when high speed cornering regularly.

Iceman

You don't disagree with me, you disagree with experts and race drivers!
That is not my opinion, it's a pro opinion.

What you need for racing is indeed softer tires, but not less pressure, softer rubber!



When you check the internet on this topic or (better!) speak with pro's they all will tell you, that raceing tires are different, and you better don't drive your tires with more or less than the recommended tire pressure!

You have less grip and the tires don't last very long. They also get louder...