Run-flat tyres have been derided for their poor ride quality, but new tech from Bridgestone aims to address that. We sample it first hand
1 October 2016

Bridgestone revealed more details of its new DriveGuard tyre technology at an event in the UK recently.

The DriveGuard is a self-supporting run-flat tyre that can be fitted to conventional wheel rims and driven at speeds of up to 50mph for a maximum distance of 50 miles. The tyre can be fitted to any car equipped with a tyre pressure monitoring system (TPMS) and is compatible with standard rims.

When a conventional tyre deflates, the sidewalls collapse and fold, becoming trapped between the wheel rim and the road. If the car carries on driving, a combination of the pressure exerted by the rim on the trapped carcass and the heat generated in the folded sidewall leads to the rapid destruction of the tyre.

Self-supporting run-flat tyres have thick sidewall inserts with enough strength to keep the rim suspended above the ground when the tyre is deflated. The downside is that the thicker section and increased rigidity of the sidewalls impairs ride quality compared with conventional tyres.

The DriveGuard is constructed using Bridgestone’s proprietary Nano Pro-Tech technology, which evens out the distribution of sulphur bonds between the carbon molecules in the compound. This chemistry reduces internal friction within the material and inhibits heat generation in the sidewalls. Heat build-up is further reduced as the tyre rolls along by a cooling fin design moulded into the sidewall.

The combination of these factors allows a thinner sidewall construction and this, combined with a new crown structure to better absorb bumps and lumps in the road surface, is claimed to deliver comfort levels comparable with those of standard tyres.

An advanced polyester carcass body ply design reduces heat generation and helps the tyre to hold its shape when deflated. The thinner sidewalls also help to keep weight down, an important factor when manufacturers are struggling to remove every gram of weight to save fuel and reduce CO2 emissions.

We haven’t had the chance to test the claims of improved ride quality from behind the wheel yet, but we did have a demonstration ride in the passenger seat of a Vauxhall Astra with a front tyre completely deflated. The car steered around a low-speed handling course without drama and rode well enough that the flat wasn’t immediately obvious without TPMS.

The Astra was fitted with the more accurate type of TPMS, which displays an absolute tyre pressure in the instrument display via wireless pressure sensors in the wheels. The test runs started with zero pressure showing for the deflated tyre, but after a couple of laps the heat generated in the tyre was enough to expand residual air and raise the pressure to 1psi. Tyres generate some heat whether deflated or not, and this suggests the integrity of the tyre remained intact, allowing it to reinflate slightly, whereas a conventional tyre would have been damaged beyond repair.

Bridgestone says a punctured DriveGuard can be repaired by authorised dealers, as long as the sidewall or the structure of the tyre hasn’t been compromised in any way. A tyre inflation system can be used, but Bridgestone warns against reinflating a tyre that has been run flat without expert inspection first.

The DriveGuard scores well under the EU tyre labelling scheme with ‘A’ for wet performance and ‘C’ for rolling resistance. According to a Bridgestone technician, achieving high scores in all of these areas with a run-flat tyre is a challenge because of the stiffer sidewalls.

The DriveGuard is on sale in the UK now in 19 summer and 11 winter sizes, ranging from 185/65 R15 to 245/40 R18. The cost is 10-12% higher than that of a Bridgestone Turanza, or about £365, fitted, for a set of four in 225/45 R17 size.

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Comments
9

1 October 2016
I get the safety angle, but what do you do if you are driving on a road at night ,maybe to catch a flight and you get a puncture ,no spare I assume and these runflats can't be repaired ,at least that is what I am informed and is the tyre finished after up to 50 miles ,so with the amount of punctures I appear to get every year would be expensive and inconveniant.Would you be stranded and try to get a tyre fitted at 4am in the morning in the middle of nowhere and get thoroughly ripped off ,even if you could get a replacement.Doe snot sound like a good idea to me.

1 October 2016
Ski Kid wrote:

I get the safety angle, but what do you do if you are driving on a road at night ,maybe to catch a flight and you get a puncture ,no spare I assume and these runflats can't be repaired ,at least that is what I am informed and is the tyre finished after up to 50 miles ,so with the amount of punctures I appear to get every year would be expensive and inconveniant.Would you be stranded and try to get a tyre fitted at 4am in the morning in the middle of nowhere and get thoroughly ripped off ,even if you could get a replacement.Doe snot sound like a good idea to me.

You clearly didnt read the whole article then and missed the bit about these tyres can be repaired.

And having a spare is no good if you cant shift the wheel bolts.

1 October 2016
In practice the probability is that the sidewalls will be damaged is it 10 miles, 20 miles or 50 which always appears the maximum figure quoted,before the tyre wall is damaged beyond repair.Alsi, I am going off low profile tyres due to the tendency to damage the alloys and these runflats appear to be quite low profile.

3 October 2016
How the hell can low profile tyres damage alloys ? Tyres cant damage alloys . . . unless you mean that you dont bother to use your mirrors when reversing and therefore drive into the kerb and YOU damage the alloys ? If so, take a bit more care, use your mirrors and hey presto, no kerbing ! Its much cheaper than buying new tyres.

1 October 2016
Not sure doe snot will fix a tyre SK, badger's phlegm probably better and easier to vulcanise...

1 October 2016
How do you limit speed to 50mph, and ensure the driver stops after 50 miles ? Does the car automatically call the cops and tell them the driver is being a naughty boy ? ( He's NOT the Messiah)
I know someone with a 7-Series with 20 inch runflats.When he got the tyre pressure warning he carried on driving, knowing that the tyres were run-flat. But the flat was caused by the broken wires in the carcass puncturing the tyre (20 inch wheels + potholes = bad tracking and shoulder wear) so eventually the tread band separated from the sidewall.....

1 October 2016
Whilst these Bridgestones allow you to continue driving, their thinner sidewalls mean you're more likely to damage your alloy while they're deflated. So you'll not only be looking at a new tyre but a new wheel too. The best compromise in my view is a space saver. Lighter than a full size spare and fewer compromises than run flats or a can of tyre sealant.

2 October 2016
255/35,18 rim...?

Peter Cavellini.

3 October 2016
A few people commented on low-profile tyres increasing the risk of damaged alloys. Ironically, "old-style" run-flats with their rigid sidewalls seem to do a great job of protecting wheels, and seem to be less prone to sidewall damage from potholes, etc! As for ride-quality issues, I've owned 3 cars with run-flats: 2 generations of Corvette and a BMW Z4. The Z4's ride-quality was dreadful, but both of the Corvettes have been fine - seems to show manufacturers can get decent ride-quality if they know what they're doing :)

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