Run Flat Tyres

[duotone]

A space saver wheel in a UX load area, just to give an idea how much room it takes up.                                                                                              Personally I don’t carry the space saver, I prefer to put my trust in run flats.

 

 

[GMB]

I had a 1976 Rover P6 V8 with dunlop denovo runflats. They were very expensive, a bugger to balance and cost a fortune. If you got a puncture and run it flat then the canisters inside the rim were trashed and the whole thing had to be replaced except the actual rim of course.

Having said that they actually looked good and had quite a low profile for the 70's era.

Tech note: The Rover rotted away and became an orange pile of ferrous ( or is it ferric? ) oxide on the road and the engine was prone to overheating but it was good for 120mph - just keep an eye on the temp gauge.

[GMB]

Just now, GMB said:

I had a 1976 Rover P6 V8 with dunlop denovo runflats. They were very expensive, a bugger to balance and cost a fortune. If you got a puncture and run it flat then the canisters inside the rim were trashed and the whole thing had to be replaced except the actual rim of course.

Having said that they actually looked good and had quite a low profile for the 70's era.

Tech note: The Rover rotted away and became an orange pile of ferrous ( or is it ferric? ) oxide on the road and the engine was prone to overheating but it was good for 120mph - just keep an eye on the temp gauge.

picture-

[Nelsthebass]

Having just come back to the fold with a Lexus UX from a Kia Stinger GTS which had “normal” tyres, the Dunlop RF on the UX are way quieter than ultra low profile sport tyres as fitted to the Kia - I had two punctures in 14 months with the Kia and the inconvenience of not having a spare would have been outweighed by run flats if they had been fitted!

[Gorb]

Interesting that on the Blackcircles website the Bridgestone Turanza 005A runflat tyres fitted to my Lexus from new are rated as D, C 71B at £190 whilst Hankook tyres rated as C, B 67A are £165. The Goodyear website states that a 3 db difference doubles the amount of external noise the tyre produces.

[Harrier Man]

Another thought (and I'm no expert). Generally speaking, a lower profile tyre is noisier than one with a higher profile. The manufacturer, 'rubber' compound and tyre construction all make a difference but in a like-for-like comparison, more noise will be transmitted to the cabin with a low profile tyre. So my thought for those who don't want the extra noise but who like the benefits of run-flats is, could you change to a tyre with a different profile?

The NX F-Sport comes with 20" 235/50 tyres whereas the basic NX comes with 18" 235/60 tyres. Despite the 2" difference in wheel diameter, both have a very similar circumference, just 13mm (half inch) difference, which equates to a difference of about 3 wheel revolutions over a mile (sorry for mixing my units up!). At some point it is necessary to change the gearing when different wheels and tyres are fitted to remain legal because the speedometer reading would become out of its design limits. In the old days, the feed for the speedo came from a cable taken off the gearbox so it was quite easy to change the gear to ensure the speedo read correctly. Digital speedometers will be operated differently but the same principle applies.

Hence 40 years ago, it was not common to improve a car's handling by fitting wider, lower profile tyres that had a sharper turn-in. Some of my friends at the time changed the gearing others did not (naughty!) However, then, as now, manufacturers offered different models with different wheel tyre combinations but, in many cases, the options had/have similar tyre circumferences so that the manufacturer didn't/doesn't need to change the gearing for every model.

The bit I don't know is whether the 2 different options available on the NX are similar enough to ensure that the speedo doesn't get you into trouble. My gut feeling is that it wouldn't because the normal differences in operating pressures and temperatures would create a similar small difference in circumference.

Is this an option worth considering? You would need new wheels and that wouldn't be cheap. What wheel tyre combination do you have already? Is it even feasible for you to swap within the manufacturer' range of options? Are you prepared to lose the sharper turn-in? Most SUVs subjectively look better with a larger wheel, would you be prepared to accept the change in look? Only you can decide. For me, I'll stick with what the car comes with and when the tyres wear out, I'll look at what's on the market and decide which way to go - or buy a new car (I wish!).

[Gorb]

Easier to get "normal" tyres or a different car😀

[Las Palmas]

Last time I had to use a spare-wheel (full size) was in 1985 I think, In Africa somewhere. Then space savers and sealants were as far as I knew then non-existing.

Not that it is that hard to change a wheel, but the convenience and efficiency of sealants is much underrated. I believe that more than 99% of flats can be fixed enough with sealants to get to a place where the tyre can be repaired or replaced. Las time I had a flat tyre (2012 maybe) was on a rented car and the sealant in the car got me to the rental company where they gave me another car.

Have only once been driving a car with run-flat tyres (long time ago) and they were OK (did not have any flats). If they were noisy did not matter as cars were noisy then. If comfortable I do not remember and being younger was comfort not one of the priorities. But paying extra to get a run-flat is not for me.

[PPD]

On a related note, does anybody know why the 300e comes with 'normal' tyres, whereas the 250h is on run flats? The Lexus dealership I sourced my 300e with were adamant the tyres were run flats, so I do think there is a bit of confusion around this issue. I wonder if the weight of the electric car precludes run flats?

[Roger Bill]

18 minutes ago, PPD said:

On a related note, does anybody know why the 300e comes with 'normal' tyres, whereas the 250h is on run flats? The Lexus dealership I sourced my 300e with were adamant the tyres were run flats, so I do think there is a bit of confusion around this issue. I wonder if the weight of the electric car precludes run flats?

I wondered the same. Could be weight or could be Lexus wanted quieter tyres. I've read that the 300e has more sound proofing than the 250h because road noise is more noticeable with less power train noise.

[GMB]

On 6/19/2022 at 11:12 AM, Gorb said:

Interesting that on the Blackcircles website the Bridgestone Turanza 005A runflat tyres fitted to my Lexus from new are rated as D, C 71B at £190 whilst Hankook tyres rated as C, B 67A are £165. The Goodyear website states that a 3 db difference doubles the amount of external noise the tyre produces.

Hi   FYI  SVP

3db increase is a doubling of the sound level ( logarithmic relationship ).  Google the 3db law. Fortunately the human ear can tolerate vast changes in sound levels - up to a point. 

[Bill Dawes]

After a couple of days with my UX Takumi I am relieved to say tyre noise from my run flats is not a problem as far as I can tell at the moment.

Bill D.

[rayaans]

On 6/20/2022 at 5:35 PM, PPD said:

On a related note, does anybody know why the 300e comes with 'normal' tyres, whereas the 250h is on run flats? The Lexus dealership I sourced my 300e with were adamant the tyres were run flats, so I do think there is a bit of confusion around this issue. I wonder if the weight of the electric car precludes run flats?

To reduce tyre noise inside the cabin. As there is no engine as such, there's a lot less noise in the cabin than the 250h which means that ears naturally focus on the next noisiest thing, which is usually tyres. 

I recently drove a BMW 540i M-Sport. Different class of vehicle I know but amazingly quiet even with the 20" wheels and run flats. However, you do feel cats eyes on the motorway a lot more when changing lanes. I personally would remove them. I dont think they're worth the loss in handling and driving feel.

[David Claridge]

On the subject of run flat tyres. This happened to my son after driving 7 miles at 25mph. Not a Lexus I know but it’s making me think about buying a skinny spare and a jack. It stayed partially inflated for a couple of miles then slowly collapsed.

[Harrier Man]

36 minutes ago, David Claridge said:

On the subject of run flat tyres. This happened to my son after driving 7 miles at 25mph. Not a Lexus I know but it’s making me think about buying a skinny spare and a jack. It stayed partially inflated for a couple of miles then slowly collapsed.

That's scary! No wonder garages won't repair run-flats.

[Las Palmas]

More unsprung weight (the wheels) is reducing the efficiency of the suspension. The heavier the wheels the worse handling. A heavy wheel is in contact with the road less than a light wheel.

Today where most of us have mobile phones so we easily can contact assistance run flat tyres are not of any use in countries where most of us live.

 

[LenT]

36 minutes ago, David Claridge said:

On the subject of run flat tyres. This happened to my son after driving 7 miles at 25mph. Not a Lexus I know but it’s making me think about buying a skinny spare and a jack. It stayed partially inflated for a couple of miles then slowly collapsed.

Just for clarification, David, you’re saying that this was a run flat.  If so, then that damage is surely extraordinary as they are supposedly designed to withstand running on the rim.  Which brand was it?

If not ROF, then it’s the expected result.  Like you, I prefer the option of a SpaceSaver and associated tools.  But then I can still change a wheel.

However, on a motorway I can see a good argument for calling for roadside assistance purely on safety grounds.  Having been an AA member since 1967, I think I’ve already paid for the odd recovery!

 

[David Claridge]

It was definitely a run flat. I can’t tell you the make as it’s not my car. He had to call the AA who put a universal skinny wheel on and followed him to the tyre fitters. The AA man said he regularly attends to people with this problem, that’s why he and his colleagues carry skinny spare wheels.

[Roger Bill]

Reviving an old thread as I think this video presents some good info on newer runflats: 

 

[ColinBarber]

Certainly impressive compared to the rubbish Lexus fitted as standard to my UX. Will definitely look to see if Seal tyres are available when I need to replace mine.

[Brian R]

Hmmm, I have a very poor practical experiences of run flats on both a BMW and now my Lexus. I really do not like their tendency to "solidify" all four corners of the car. I appreciate the reviewer has tested current rf's but I'm afraid my dire experiences with Bridgestone rf's leaves me uncertain, whereas the seal tyres seem to provide much of what one would wish for but by the looks of it with a more conventional feel. Regardless, my rf's will eventually be replaced either with standard tyres or just maybe these seal units.

[Malcolm Kemp]

The run-flat v normal tyre debate mainly concerns road noise, ride comfort, convenience and price issues. With my previous four cars (all BMW's) two had run-flats and two had normal tyres, and having had the misfortune to have had punctures with both types my views are as follows:

Road noise is more to do with with the road surface than the type of tyre. Run-flats may be a little noisier but the difference is negligible when compared with the noise levels from different road surfaces.

My last SUV had normal tyres with sports suspension, and when I first took my wife for a drive in my Lexus UX with run-flat tyres the first thing she commented on was how much smoother the ride was.

Regarding convenience, I prefer not to carry tools or a spare wheel as they take up a lot of otherwise usable space, and having experienced punctures with both types of tyre and suffered the inconvenience of using the compressor and goo remedy on a cold wet winter's night, I think this is a no-brainer in favour of run-flats.

Although run-flats are more expensive and usually require a new tyre in the event of a puncture, I think the benefits far out weigh the disadvantages.

 

 

 

[Barry14UK]

BMW have fitted Run Flats for many years, may have been first or thereabouts to fit them and this subject has come up many times on BMW forums.  Certainly RF's have improved over the years and there are a fairly small number of BMW owners that find them acceptable.  But most owners on forums at least, either change to normal tyres when replacement is called for or change before then as a friend of mine did.  (Fortunately my E39 has a full size spare). 

So down to personal choice, although having driven a UX with it's miniscule boot, I can understand greater acceptance of RF tyres for this model.

[rayaans]

On 7/13/2022 at 10:31 PM, LenT said:

Just for clarification, David, you’re saying that this was a run flat.  If so, then that damage is surely extraordinary as they are supposedly designed to withstand running on the rim.  Which brand was it?

If not ROF, then it’s the expected result.  Like you, I prefer the option of a SpaceSaver and associated tools.  But then I can still change a wheel.

However, on a motorway I can see a good argument for calling for roadside assistance purely on safety grounds.  Having been an AA member since 1967, I think I’ve already paid for the odd recovery!

 

Its definitely a runflat. The car in question looks like a Mercedes C-Class which is fitted with runflats from the factory. I should know, I have one of the same generation.

I removed the runflats from the C-Class and it absolutely transformed it. It was harsh on the bumps, made a right old racket when changing lanes on the motorway going over cats eyes. All that has disappeared, not to mention it no longer skips on tight turns. 

[Bill Dawes]

My new UX has of course got run flat and I was a bit worried reading this thread a while ago, having now had a few months running I am quite relieved they do not seem any worse than other tyres, only two runs up the same length of road with identical cars other than fitted with conventional v run flat would conclusively prove this but on a run up the M5 recently the rough surfaced parts were noisy as you would expect, smoother tarmac a pleasant drive.

Tyre and road surface noise is the dominate noise on modern cars with their fat tyres and better body insulation, apart from noisy tuned cars of course.

Bill D.