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Greenninja

Tyres and Non Runflat

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So after much deliberation and time spent investigating, my Pending MOT has forced me to buy new Tyres all round.... I may have got away with only doing the rears but figured for the price I will do all 4.

 

So what I have gone fore is Khumo Ecsta PS91 which according to the blurb are perfect for BMWs M sports cars!!

 

SO to put a final Nail in the coffin of Run flat vs Non run flat I will update this thread with my own personal views once they are on.. of course this will be personal and no doubt everyone is different, however i`m sick of the whole thing and should I or should i not tell insurance... so its being done and im just gonna drive the thing!!

 

On that note too its cost me £370 for tyres and £60 to have fitted!!

 

Edited by Greenninja

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22 hours ago, Mijmap said:

Is there any update on the Khumo Ecsta PS91’s? 

 

Not got round to having them fitted yet fella, still got a bit to go on my run flats but going to time it all when i get my alloys refurbed in march then have them swap my tyres out at the same time

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2 minutes ago, Greenninja said:

Not got round to having them fitted yet fella, still got a bit to go on my run flats but going to time it all when i get my alloys refurbed in march then have them swap my tyres out at the same time

 

I might beat you to it although only the rears due hopefully be fitted by next week.

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Question guys i am going for uniroyal rainsport 3s on my current tyres are 97 for load rating but obviously runflats, i have two options on uni royals i can either go for 97 on those or go for 101 XL. I was going go for the latter as i didnt want 97s to be too soft and change the handling but what are your thoughts on it? 

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What size are your tyres @Erhan?

 

Load rating of 97 is correct for 17" tyres, the bigger diameter tyre sizes have a lower load rating on them which you will see by looking at the pressure chart on your drivers door cill.

 

101XL on the rear if you tow perhaps but you shouldn't need anything with a higher load rating.

 

Some of the runflats only come in higher load ratings than is required. My Michelin Primacy 3 19" rfts are 98 which is higher than 94Y specification. They don't make them at lower than that in 245/40/19 flavour.

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I'm going for a higher load rating on my wife's F45 this week 91 - 95 and can't imagine they'll make much difference at all. I'd suggest you'll be fine. but will let you know once they're on the car on Saturday morning.

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21 minutes ago, Enzo503 said:

The difference in load ratings is primarily down to what air pressure the tyre can hold.

 

 

ok i will start with xl given the wear rate they would be gone in 6 months for me. I also asked to the insurance (direct line) they said they would note it on policy but that would be it as its not something they would class as change to the policy and they are fine with it. Hope this helps to people.  I will also update the topic once fitted (hopefully next week)

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34 minutes ago, Enzo503 said:

The difference in load ratings is primarily down to what air pressure the tyre can hold.

 

 

 

This is not the case, the load index is the maximum load the tyre can carry.

 

Tyre Load Ratings

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Indeed your chart is correct.  

 

The more weight you carry though, the more air pressure you should have in your tyres.    An xl version of a tyre will have a higher air pressure capacity then a standard version of the same make/brand.

 

My point being in response to Erhans post is that this does not mean that an XL version of a tyre will have thicker sidewalls then the standard version.  Both tyres will ride the same with the same air pressure.   

Edited by Enzo503

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21 hours ago, 535i Andrew said:

What size are your tyres @Erhan?

 

Load rating of 97 is correct for 17" tyres, the bigger diameter tyre sizes have a lower load rating on them which you will see by looking at the pressure chart on your drivers door cill.

 

101XL on the rear if you tow perhaps but you shouldn't need anything with a higher load rating.

 

Some of the runflats only come in higher load ratings than is required. My Michelin Primacy 3 19" rfts are 98 which is higher than 94Y specification. They don't make them at lower than that in 245/40/19 flavour.

Sorry just saw yours i dont know i missed it. Mine are 225 55 17 with it being se i thought with conventional tyres being softer having hihger load rating might not have as much adverse effect on handling. I am positive i read in one of the topics that it makes the ride cushiony.

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I had 17" winter tyres on mine and it did make the ride a bit more wallowy in the bends as the side wall can flex more as it's physically longer so there can be more flexing. They were also more forgiving on the potholes, something which I'm regretting by getting rid of them for 18" winter tyres.

 

The 17" tyres I had were 97 load rating. 

 

You will be fine with them.

 

The reason some manufacturers offer "XL" is that to make the tyre a run flat it needs stiffer sidewalls. This has the effect on allowing the tyre carry more load hence why a rft tends to have a higher load rating than a non rft version of the same size and spec of tyre.  I was told this form a Michelin rep when I was asking why the Primacy tyres are offered at  higher load ratings than required by BMW.

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OK so the XLs would have the same wallowy effect too  then? I mean price difference between them is about 70 pence per tyre so thought might be better ti have the XLs.

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You need to check what pressure you are running the tyres at when it comes to XL tyres. They have a higher load rating but normally that higher load is at a higher pressure. If the car doesn't require those pressures then you may find a normal tyre at the lower pressure will have a higher load rating than an XL at the same pressure.

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40 minutes ago, dandle said:

You need to check what pressure you are running the tyres at when it comes to XL tyres. They have a higher load rating but normally that higher load is at a higher pressure. If the car doesn't require those pressures then you may find a normal tyre at the lower pressure will have a higher load rating than an XL at the same pressure.

 

Tyre pressures are the same on both my cars whether XL rated or not.

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You'd think if the only difference between tyre and tyre XL is the sidewall thickness, then the air chamber volume would be the same. Same air pressure but you gain better load rating from the thicker sidewalls.

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This was what i was getting at. The two tyre ratings below show the difference between an XL tyre and normal. Both tyres rated at 98 for example can carry 750kg, the standard tyre at 2.5 bar but the XL tyre requires 2.9 bar to carry the same load. The XL tyre which is still 98 but only inflated to 2.5 bar is only rated at 665kg. Its not as simple as saying the XL tyre will be stiffer it has to be run at the right pressure in the first place.

 

To be fair though I would think most tyres on our cars would be XL rated, mine are as standard and when towing if i remember right the tyre pressure are 3.3 bar on the rear and 2.9 on the front.

 

Standard car tyre.jpg

XL car tyre.jpg

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1 hour ago, Erhan said:

OK so the XLs would have the same wallowy effect too  then? I mean price difference between them is about 70 pence per tyre so thought might be better ti have the XLs.

Going from runflat to non runflat will improve the ride.  It did for me.   If however you find that the non runflat standard/xl tyres are rolling over or are too cushioned for your liking, you can raise the pressures up which will bring back some of the stiffness.   I run mine around 40psi   and my wear thus far has been even.

 

Side note: Run flat tyres work on the basis of having really thick and stiff sidewalls so if the tyre goes flat.  The side walls of the tyre keep the car from running on the rims and you are able to trundle home at slow steady speed.  BMW have specially designed alloys so when this does happen, the side walls do not pop off the beeds and go into the wells.    Caravanners and police vehicles will be aware of this with the use of their tyreon bands. (a reason why police use bmw)

For this reason, putting a runflat tyre on a non designed rim is pointless.  

 

Edited by Enzo503

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20 minutes ago, HandyAndy_UK said:

You'd think if the only difference between tyre and tyre XL is the sidewall thickness, then the air chamber volume would be the same. Same air pressure but you gain better load rating from the thicker sidewalls.

 

I don't think it is only, if any, sidewall thickness variation. From what I've read the ply on the face is of a more durable material which could lead to longer tyre life but sacrificing comfort and allowing greater load. 

 

I think the changes are subtle though and negligible for we mere mortals. I've just done about 100 miles on the XLs I had fitted to the F45 2 Series (replaced 2 91Ws with 2 95W XLs as the 91Ws are not available for 2 months) and there is no noticeable difference in comfort nor handling.

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Agreed with Mattew, you will not notice a difference between the tyres (xl/std).   Wear rates will be the same, ride quality will be the same.    The whole thing is actually do to with heat but its quite a lengthy conversation to go into.

Edited by Enzo503

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4 hours ago, Erhan said:

OK so the XLs would have the same wallowy effect too  then? I mean price difference between them is about 70 pence per tyre so thought might be better ti have the XLs.

 

There is your answer.

 

As you can see from the posts above, tyre choice is very subjective and can generate lengthy discussions. 

 

Go with what you are happy with.

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