Motoring Discussion > Run flats - another downside ? Miscellaneous
Thread Author: henry k Replies: 12
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New Sat 20 Jun 15 10:11 
 Run flats - another downside ? - henry k
Son managed to " nudge" a kerb at low speed and damaged the side wall of an expensive low profile rear tyre
( plus a scrape on the wheel ).
It happened just a few hundred yards from chez mois so simple to drive it to here.
During the mile or so to the local BMW glass palace something was hitting the ground on " flat" roads.
Shirley BMW would have tested things with a deflated tyre ?
We await any response from BMW.
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New Sat 20 Jun 15 11:58 
 Run flats - another downside ? - ....
Does the car have TPMS ? Could the something have been a sensor inside the wheel ? If so, another £100 on the bill.
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New Sat 20 Jun 15 15:14 
 Run flats - another downside ? - Armel Coussine
Happens to us all sometimes. On the way to London yesterday slipped off a kerb with the n/s front wheel and felt and heard a slightly nasty graunch. Later, on the way back, started to feel a front wheel oscillation at 60-plus. But going even faster made the shudder disappear and it stayed OK all the way home.

I think the wheel lost a balance weight though, because it used to have one and hasn't now. It's going to need rebalancing and of course the tracking and toe will have to be checked too. At least all the wheels except the o/s rear are holding tyre pressure to within a pound or two of optimum for a week or so. Even that one only loses six or eight pounds.
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New Sat 20 Jun 15 23:25 
 Run flats - another downside ? - WillDeBeest
Does the car have TPMS?

Shouldn't have run-flats without it, should it? Otherwise how does the driver know a tyre has lost pressure?

I think the answer, as with all driver aids - auto lights, radar cruise control, park assist - is to treat run-flat and TPMS as a complement to human awareness, not a replacement for it. Pick up a screw you might not otherwise notice and TPMS lets you know while run-flat lets you get to somewhere safe to have it checked. But clout a kerb and you still need to understand that you might have a problem beyond the technology's ability to help, so stop and look.
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New Sat 20 Jun 15 23:50 
 Run flats - another downside ? - Londoner
TPMS is great.

Run flat tyres were invented by Satan

We put BMW run-flat tires to the test and give them a thumbs-down
www.torquenews.com/1083/we-put-bmw-run-flat-tires-test-what-you-need-know

Run-Flat Tires Letting Air Out of Customer Satisfaction
autos.jdpower.com/content/blog-post/LLBEeIR/run-flat-tires-letting-air-out-of-customer-satisfaction.htm

Tire study: Replacement rate runs higher for run-flats
www.autonews.com/article/20130329/RETAIL05/130329837/tire-study:-replacement-rate-runs-higher-for-run-flats

I can't find the reference for now, but ISTR that about 30% of runflat tyre failures left you stranded, i.e the damage was so great that you couldn't use them to limp to the nearest garage.

Even a space saver is better than a runflat IMO.
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New Sun 21 Jun 15 00:40 
 Run flats - another downside ? - henry k
>> Does the car have TPMS?
>>
>> Shouldn't have run-flats without it, should it? Otherwise how does the driver know a tyre
>> has lost pressure?
>>
It all happened at low speed In a 30mph zone.
The car was immediately stopped and it was obvious the tyre wall was damaged.

No Idea if it has TPMS. I suspect not.

The only minor compensation was that the tyres were close to replacement.
Four new tyres no fitted at considerable expense.
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New Sun 21 Jun 15 13:29 
 Run flats - another downside ? - WillDeBeest
I don't think the car would be legal with run-flats but without TPMS. But the key fact about run-flats is that they use a strengthened sidewall to take most of the load if the tyre loses its air, so an incident that causes major damage to that sidewall is going to reduce or even eliminate its capacity to do that.

I admit I have some personal interest here, now that I'm tootling about on 18-inch Bridgestone run-flats. The manual explains that TPMS works by comparing rotation rates - as with ABS and probably using the same sensors - so I don't think you need worry about Gmac's suggestion of a pressure sensor on the wheel rim. The section about what to do when a tyre goes flat doesn't make a distinction between a simple puncture and sidewall damage, which surprises me.
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New Sun 21 Jun 15 14:11 
 Run flats - another downside ? - jc2
Rotation type TPMS are not very good-the vehicle must be moving for them to work and this can cause damage to the tyre/wheel and the cannot be very sensitive otherwise they would report a loss of pressure whenever you corner! Most manufacturers who fitted this type are now changing to pressure sensors.
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New Sun 21 Jun 15 14:18 
 Run flats - another downside ? - Zero
Most manufacturers who fitted this
>> type are now changing to pressure sensors.

I thought it was the other way round.
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New Sun 21 Jun 15 15:21 
 Run flats - another downside ? - jc2
The latest pressure sensors are not part of the valve.
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New Mon 22 Jun 15 18:07 
 Run flats - another downside ? - WillDeBeest
Hmm, that may be true, but Bridgestone, whose runflats are on my BMW, mentions only 'indirect' (i.e. rotational) and 'direct', which appears to rely on sensors built into an enlarged valve unit. Wouldn't anything else require special mounting points on the wheel rim - or even an entirely special wheel?
m.bridgestonetire.com/tread-and-trend/drivers-ed/tire-pressure-monitoring-system-how-tpms-works

A bit of googling suggests that the direct type is an option for some MBs, although I think mine has the indirect system. The direct sensors are still integrated with the valve assembly, though. What I didn't know is that there's a legal requirement in Europe and North America for new cars to have one or other form of tyre pressure warning system.
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New Mon 22 Jun 15 20:14 
 Run flats - another downside ? - rtj70
My Passat CC had tyre pressure monitoring valves (a low cost extra) and so I could see the current pressures in the 4 tyres (the CC didn't monitor the spare unlike the Phaeton). The A3 I now have only has the pressures monitored using the ABS sensors.

The main reason I opted for the TPMS on the CC (it did the ABS sensor monitoring without this) was the self-sealing tyres on it by default... So for less than £2/month I elected to have peace of mind.

I also liked the fact the Passat's have a full size (alloy) spare... I've only got a space saver on the A3. Better than nothing.
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New Mon 22 Jun 15 22:32 
 Run flats - another downside ? - Ted
Pressure monitors on the Grand Vitara are instantly removable. Found on the end of my leg and constructed of black leather.

Just kidding....I do check them now and again !
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