Recent experience of fitting Run Flat Tyres anybody?

  1. My model of MX-5 is: __3.75
  2. I’m based near: Preston
  3. I’m looking for technical help or recommendations on: fitting run flat tyres

About to change the tyres on my 2012 Mk 3.75 Coupe. I believe the run flats have improved over the last few years but no recent posts re experience of using. Can anybody advise?
Regards Glenn

Hmm, one of my more distant friends dumped them less than half worn from his new BMW Mini because they were noisy and uncomfortable and had very poor grip in winter.

This was only a couple of years ago, and while he still has the car he has no intention of ever returning to the “expensive heavy” (his words) run-flats.

This is only hearsay. But I then also read the wiki article which seems to agree with him to some extent.

I brought a z4 with them on they were terrible noisey , hard poor handling, and if you went round a bend and caught the edge of a drain it bounced the rear end out…dint even wait for them to wear out to replace even the tyre guy said he did not like changing them as hard to get off the rim…

Don’t bother, terrible idea as someone else has said noisy, no grip and a harder ride, plus you can get leakage around the rims if the rims are not in good condition and you push to hard.

I had a BMW with them 15 years ago. Horrific noise and a shudder thru the chassis on choppy surfaces. But old car suspension wasn’t designed for them. MX5 suspension isn’t designed for them either. I ditched them and it transformed the car but be aware insurance companies are within their right to class it as a modification, and in the event of a collision you can be prosecuted for changing the cars type approval without certification for it. If their is a significant injury expect prison food then. Ironically it held the road far better without them but I wouldn’t want to try to explain that to a judge.
My BMW M140 that I get Thursday has them. They are fine. The car is designed with them in mind so they are quiet and comfortable. A few friends have newer BMs with them and all are fine too.

I have had exponentially (word of the moment) more people requesting and having non runflat tyres fitted to their run flat rims than the other way around. You should also have TPS monitoring if you have run flats too.
I am about to fit a pair of 205 40 18’s to a Mini that has taken the sidewall out of one of the existing. I am not suppsised the ride is harsh, the amount of movement in the sidewall is tiny.

What about the latest foam filled tyres? Not sure they are in use on public roads yet. A closed cell foam with semi permeable wall structures. Operates a bit like a foam filled fuel tank to baffle fluid movement, allowing low movement during light load events, but as load rises fluid transfers increases exponentially with defamation. Side wall flexion is still considerably higher than run flat rubber but with the same net results. The main claim they make is a reduction in road noise from an average 70dB to more like 55dB. And as noise is a logarithmic expression that’s HUGE. It acts like any noise suppression system, reduce drumming, isolate and isolate again lol.

Forgot to mention, some of the cells are none permeable allowing them to act as run flat tires.

Frequently owners change to normal tyres from run-flats for reasons given in previous replies (harsh ride, noise,etc.), and the actual fitting of normal tyres onto run-flat rims is not a problem. However, I understand run-flats have to be fitted to rims which are specifically designed for them, with additional inboard ribs to hold the tyre in position while being driven if it loses pressure. Your rims probably don’t have this feature so may not be compatible to take run-flats. I’m sure someone more qualified can clarify this.
The harsh ride obviously comes from the almost solid-feeling tyre wall, which has to fully support the corner of the vehicle when there’s no air pressure left to do the job.

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They have such stiff side walls that the ride is harsh and noisy and grip is poor. OK if the suspension etc is designed to run with them.
Personally I would never buy another car fitted with them.

Widely hated on BMW forums, known as RunCraps .

Personally, had them on a BM a few years ago, and thought they were fine… but when I did have a puncture, it fell to bits within 15 miles of driving slowly. So I would not consider them a ‘get you home’ benefit, more of a ‘get you to a safe place to stop’ benefit.

As mentioned above, you must get a TPMS system with them, very dangerous to have a puncture and not know about it.

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Yes monitoring is a must. Standard fit on most cars now tho. Even the crude but effective way Mazda monitor rolling circumference on an MX5 would pick it up tho.

My BMW with ‘designed to work with run flat suspension’ is quiet and grips very well and is very comfortable. I have heard reports of replacing them with standard tyres makes the ride squidgy and bouncy and lowers the available grip levels. The tyre is an integral part of the suspension. A tyre will react instantly to a shock event, on light weight cars you simply can not do that with shocks and dampers alone. That’s why F1 cars still run high profile rubber. As with everything in life there’s always trade offs both ways. Or as a famous man once said, every action has an equal and opposite reaction.

Thanks everybody for your input. Definitely a no no!

I will post another post re current favourite tyre.

Regards Glenn

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Right I have to eat a little humble pie here. After having larger heavier cars with run flats and standard rubber all was equal, the softer suspension and more curb weight hid any harshness perfectly. So on softer fatter cars I wouldn’t worry about it. An MX5 isn’t a fatter heavier car tho is it.

I have recently swapped the run flats for MPS4’s on the M140i after a friend gave me a 50% off voucher, on top of a Black Friday deal they almost paid me to take them, who wouldn’t? That was November 27th, so after 9 days I have to say these tyres are more fuel efficient, SIGNIFICANTLY quieter and more comfortable when set at any pressure, but at my favoured 31psi when cold it’s like a different car. It’s not even close, a friend who didn’t know they had been changed commented that the car felt smoother and quieter, I kid you not. And the grip!!! I can get it off the line full throttle in the rain with very limited wheel spin, the Bridgestone Potenza 001s would just give up and slide around like a lame duck. I can power out of a bend in the wet confidently now where as I used to slide out on the Bridgestones. Very impressed.

Called my insurance who said it was but wasn’t a modification and charged me £18 for the privilege. They did say had I not informed them they could back end load any claims by a percentage tho so I’m pleased they are informed for a few bob.

So, ultimately, run flats on fat cars don’t matter but sports cars do. That’s my 2p anyway.

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I bought my current NC3 in the summer. The garage it came from replaced the rears with new tyres as they were worn.

A few weeks ago while checking pressures I noticed a little two letter mark on the sidewall - RF. Reading round the sidewall, there it was; RUN-FLAT.

I needed new fronts anyway, so ended up with new Kumho PS71s all round and it’s a totally different car as a result. The twitchiness has gone, it’s quieter, the ride is less harsh and it’s far more like my previous NC1. Fuel economy remains to be seen!

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I sold a new car after a very short ownership because of run flats. The side walls are just too stiff and don’t allow the tread to remain flat on the road, the handling and ride were atrocious. Would have seen me in a field if I had kept it.
I will NEVER buy a car with runflats.

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