Run-Flat Tyres : All you need to know

[akshay1234]

This video gives you quite a bit of information on run flat technology, for those who are not familiar with it yet.

BMW Run Flat Tires - YouTube

Run Flats are most widely used by BMW, standard on all their cars besides the M cars. The have many benefits over normal tubeless tyres, but also are worse off in a way or two. Other manufacturers also use run flats on some models.

Run flat tyres can be repaired
For a normal puncture, run flats can be repaired just like a normal tubeless tyre. They will work just fine after that. Even the way of fixing a puncture is the same. BMW owners note that if you go to a dealership they will ask you to replace, since that is their policy. We don't do autobahn speeds all the time so even fixing the puncture may suffice.

When Can run flats NOT be repaired
Run flats can not be repaired if they are driven on zero air for some distance. They are designed to be driven only a certain distance on zero air, and since the sidewall is supporting the car weight, it weakens. In this case the tyre will have to be replaced.

Also if the sidewall is torn, or there is a huge puncture, or the tyre is shredded, and in other situations where a normal tubeless tyre would have to be changed. These are the situations where a run flat will have to be replaced.

Run flats can also puncture slowly
Again like normal tubeless tyres, you may just get a small puncture, in which case the air will leak slowly, maybe reduce just a few psi over a couple of days. A common misconception is that run flats have to be changed as soon as they are punctured since they get damaged. Like I mentioned above, the puncture is fixable, and you can continue using the tyre as long as it doesn't run on ZERO air for any distance.

What if you are driving long distance?
Run flats are always at the back of any car owners mind on a long distance trip, since there is no spare to change to. Since run flats can only run a maximum of 150-200km (would probably be less with Indian roads) at 80kph people wonder what they would do if they are in between Mumbai and Goa, since there are no dealers in between.

Every car with run flats would have a tyre pressure loss indicator, which would tell you some tyre has lost pressure if it senses a pressure loss of more than approx 5psi in any of the tyres. So this is like an early warning.

Now as soon as the tyre pressure loss light/sound comes on, you pull into the nearest petrol pump (there would be enough on any major highway) and check the air pressure, note which tyre has lost air, fill in more air and continue. Depending on the loss in air you can stop accordingly along the way again to top up air/fix the puncture.

BUT if the tyre gets torn, bursts, or any other such thing you will be running it on no air, and that will be a problem.

Run flats can be good for you too
If at a high speed, for any reason which would cause a tubeless tyre to burst or lose air totally, the runflat would still have its sidewall and help to a certain extent to keep the car in control. This is also shown in the video above.

What are disadvantages of run flats
Run flat tyres give a car a much stiffer ride because of the strengthened sidewall, which absorbs less shocks. They also weigh upto 40% more than tubeless tyres in some cases and lower the fuel economy because of more rolling resistance. Some also say the grip on these tyres is not as good because of the stiff sidewall.


Hope I managed to clear a few things up.

[VeyronSuperSprt]

Originally Posted by akshay1234

Run flat tyres give a car a much stiffer ride because of the strengthened sidewall, which absorbs less shocks.

This was the case with the earlier run flats.The latest run flats actually help to improve ride. Talk about the way technology improves.

[akshay1234]

Originally Posted by VeyronSuperSprt

This was the case with the earlier run flats.The latest run flats actually help to improve ride. Talk about the way technology improves.

The runflats you speak of are the 3G (3rd generation) run flats by Bridgestone. While the ride is improved it is still 5-10% worse than normal tubeless tyres. Also I don't think you get them anywhere in India. They can also apparently only run 80kms now on zero air.

[rajeshchand]

Nice write up and it is way long reassuring for those using run flats especially on beemers where there s no option for a spare wheel. Filling up nitrogen instead of air also smoothens the ride to a lot extent on run flats.

[pganapathy]

My biggest fear with run flats is if the tyre gets shredded or unusable when you are driving, because BMW specially refuses you even a biscuit spare tyre

[VeyronSuperSprt]

Originally Posted by akshay1234

The runflats you speak of are the 3G (3rd generation) run flats by Bridgestone. While the ride is improved it is still 5-10% worse than normal tubeless tyres. Also I don't think you get them anywhere in India. They can also apparently only run 80kms now on zero air.

Bridgestone released the 3G sometime in 2009. The new F30 has been released with Pirelli Cinturato P7 run flat tires abroad partly because of the feedback of the harsh ride of the Bridgestones. Dunlop have already released the 4G run flats which give as good if not better ride than normal tyres. Feedback on the the Pirelli run flats is that they are on the softer side.

[akshay1234]

Originally Posted by VeyronSuperSprt

Bridgestone released the 3G sometime in 2009. The new F30 has been released with Pirelli Cinturato P7 run flat tires abroad partly because of the feedback of the harsh ride of the Bridgestones. Dunlop have already released the 4G run flats which give as good if not better ride than normal tyres. Feedback on the the Pirelli run flats is that they are on the softer side.

The Dunlop 4g were also released in 09. The Pirellis on the f30 would be soft, like all Pirellis, but these too can only travel upto 80kms on zero air, similar to the Bridgestone 3g run flats. So basically by improving the ride run flats seem to have lost the distance they can do on zero air.

[VeyronSuperSprt]

Originally Posted by akshay1234

So basically by improving the ride run flats seem to have lost the distance they can do on zero air.

4G tyres are softer and do about 2.3 times the zero air distance of 3G tyres.

[akshay1234]

Originally Posted by VeyronSuperSprt

4G tyres are softer and do about 2.3 times the zero air distance of 3G tyres.

You might as well mention the source -
Dunlop?s 4th Generation Runflat Tires Thermal Control Technology Enhances Ride Comfort to Be Same as or Better than Standard Tires

And I don't see anywhere that the Dunlops can do any more than 80kms on zero air. If you can find some info please post it.

Seems to me Dunlops 4G are the same are Bridgestones 3G in terms of tech.

[honeybee]

Nice video there, Akshay.

A couple of queries: In the video if you are watching the slow motion replay of how the run-flat tyre supports the vehicle even after losing air, the tyre seems to go off the rim for a brief moment (2:42/3:45) and then moves back to its place. So what is the chance the tyre would just slide off the rim?

Also what happens in case of a blowout? Will the run flat still remain on the rim?

[VeyronSuperSprt]

Originally Posted by akshay1234

You might as well mention the source -
Dunlop?s 4th Generation Runflat Tires Thermal Control Technology Enhances Ride Comfort to Be Same as or Better than Standard Tires

And I don't see anywhere that the Dunlops can do any more than 80kms on zero air. If you can find some info please post it.

Seems to me Dunlops 4G are the same are Bridgestones 3G in terms of tech.

There are several sources - here's another:

asahi.com¡ÊÄ«Æü¿·Ê¹¼Ò¡Ë¡§Sumitomo Rubber Receives "Tire Technology of the Year" for 4th Generation Runflat Tire Technology at Tire Technology Expo 2010 - English

And here's another which says that the new Pirelli's can also do 150 kms on zero air:

Run Flat Tyres Test

[akshay1234]

Originally Posted by VeyronSuperSprt

There are several sources - here's another:

asahi.com¡ÊÄ«Æü¿·Ê¹¼Ò¡Ë¡§Sumitomo Rubber Receives "Tire Technology of the Year" for 4th Generation Runflat Tire Technology at Tire Technology Expo 2010 - English

And here's another which says that the new Pirelli's can also do 150 kms on zero air:

Run Flat Tyres Test

The first link says pretty much the same thing as the earlier one, that the Dunlops do 2.3 times the distance. But that is all they've said with no mention of distance exactly. From whatever I read about Dunlop RFTs on tire rack their newer tires do 80km only on zero air. I think when they said 2.3 times it was in comparison to their own older run flats.

The Pirelli Eufori is not new, that article itself says 2001. And 150kms/miles is what most of the slightly older run flats can do. Its only the newest gen run flats which say 80kms, hence my statement that with increased comfort the distance on zero air has gone down.

[VeyronSuperSprt]

Originally Posted by akshay1234

From whatever I read about Dunlop RFTs on tire rack their newer tires do 80km only on zero air. I think when they said 2.3 times it was in comparison to their own older run flats.

The Pirelli Eufori is not new, that article itself says 2001. And 150kms/miles is what most of the slightly older run flats can do. Its only the newest gen run flats which say 80kms, hence my statement that with increased comfort the distance on zero air has gone down.

The advantage of Tire rack is that they have a lot of information (read about all brands); however not all of that is accurate. It is better to use Tire Rack as a general guideline and not an absolute one as they do not update all content accurately.

Even if it were in comparison with Dunlop's earlier run flats, it would mean that the earlier run flats did only about 34kms which was not the case.

The article on Eufori says that the tire has been available "since" 2001 - it is not dated 2001 - it is dated 2009 (refer the bottom of the page). Tire Rack in respect of the Eufori does not give the 150km figure but instead repeats the same 50 miles @ 55 mph as it does on all their write ups on run flats.

OT - should this thread be in the Tyres & Wheels section?

[smartcat]

Akshay, can the run flats be repaired at the local tyre shop? I'm wondering if the machines available at such shops will have trouble separate the tyre from the alloy - because of hard compound of the run flat tyre.

I've seen some tyre shops having trouble installing 17 inch tyres on alloys because the side profile of such tryes are quite hard.

[Nikhilb2008]

Originally Posted by smartcat

Akshay, can the run flats be repaired at the local tyre shop? I'm wondering if the machines available at such shops will have trouble separate the tyre from the alloy - because of hard compound of the run flat tyre.

I've seen some tyre shops having trouble installing 17 inch tyres on alloys because the side profile of such tryes are quite hard.

That is a whole different issue!

SOme tyre changers are certified for RFTs. If you try mounting or demounting an RFT on a standard tyre changer, you are going to end up with a badly scratched rim or a cut tyre.

And repairing an RFT is impossible unless yo uare talking about just patching a puncture.