[yian77]

I am running on Conti Sport CS2 Run flat on a 320d coupe. In the wet you have to be extremely careful but in the dry, which is like 300 days a year in Cyprus, are actually very good.

A very good friend of mine was running the same set-up on a 320i coupe and decided to move to a non run flat configuration. He opted for Michelin PS2 non run flats. Although he confirms that daily driving is better as far as going over potholes etc he complains for softer handling when driving spiritedly especially on cornering and round abouts. His complain is that the car leans more than it used to when cornering.

I know that the 320d coupe is heavier (especially the engine) than the 320i coupe so if I change to non run flats I may face the same or even worst problem.

So the question to all of you that changed tyres from run flats to non run flats is, do you experience the same problem? Is it a specific problem with the Michelin PS2.

I saw that a lot manufactures have reinforced sidewall tyres which are actually non run flat. Is that an option, does anyone know anything more about this.

Thanks

[creepy coupe]

I have changed to regular Falken 452's and the ride is both quieter, smoother and no problems with being to soft, although I have heard of some owner with non M Sport suspension complaining of this.

Also spring rates may vary from Country to Country

[Masterplan]

I too looked at the non run flat option, as mines is a 320i.

When I spoke to the guy at BMW, he said that from a BMW perspective they would reccoment runflats as the car is configured for them. However, from a BMW Mechanics point of view, he said that non RFT's are not a problem. Many of the cars now come with non run flat tyres as an option.

I guess it depends what setup you have. I have RFT's and SE suspension, and I still get bodyroll when driving hard. This would be reduced with the sport suspension I would imagine. it also depends on road quality. Scotland is utterly hellish when it comes to pot holes!

[yian77]

Thanks for the commends. I have an SE suspension and my friend’s 320i is with an SE suspension. Maybe those with the sport suspension are happier when they change to Non run flat.

Anybody knows anything about the reinforced tyres?

[HighlandPete]

Originally Posted by yian77

Thanks for the commends. I have an SE suspension and my friend’s 320i is with an SE suspension. Maybe those with the sport suspension are happier when they change to Non run flat.

Anybody knows anything about the reinforced tyres?

Long answer, but hard to say it all in less.

At first comparison reinforced, XL or 'extra load' tyres have the same load carrying capacity, but at an increased pressure. The maximum load for XL tyres is calculated @ 42 psi within the ISO Metric (ETRTO) standard. Rather than 36 psi for standard tyres.

But in reality we usually see a higher LI (Load Index) for the reinforced, RD/XL tyre.

An example would be: 225/50R16 95V vs. 225/50R16 99V RD (Reinforced), where the load/pressure graph is the same until 36 psi, the RD continues to increase the load/pressure capacity to a maximum loading @ 42 psi.

Normally the rating moves up 4 points when moving to RD/XL for a direct comparison for running at lower than the maximum load capacity pressure.

I run Falken FK 452 XL of a LI rating of 94(Y), on the front of my car. The normal tyre would be a 91(Y) (1356 lbs/615 kgs @ 36 psi). The 94 is rated @ 1356 lbs/615kgs @ 38 psi*, but as it is an XL tyre, its rating (LI) is 1477 lbs/670 kgs @ 42 psi.

(* NOTE: 2 psi higher than the normal 91 LI @ the ISO Metric (ETRTO) standard’s 36 psi rating.)

The reinforced tyre is a stiffer tyre, so will perform slightly different, but it is about load ratings and pressures required to achieve that rating.

A bit of math confirms whether the tyre is rated high enough for the axle load rating of the car in question. The 94Y XL used in my own case, can carry the maximum axle load at less than the maximum rating. It performs well within capacity of the 91 LI standard tyre, at the pressure which the standard (91 LI) tyre uses. BUT only by having a 94 Load Index as a XL rated tyre.

Hope this helps.

HighlandPete

EDIT: Corrected The 94 is rated @ 1356 lbs/615 kgs @ 38 psi* (not 670 kgs)

[yian77]

Excellent, thanks HighlandPete

[dxb335d]

I find the car is far more pliant with Non runflats. The car is fantastic at speed and does not skip and is not unpredictable like it was on Runflats.

[YvesD]

Originally Posted by HighlandPete

Normally the rating moves up 4 points when moving to RD/XL for a direct comparison for running at lower than the maximum load capacity pressure.

I run Falken FK 452 XL of a LI rating of 94(Y), on the front of my car. The normal tyre would be a 91(Y) (1356 lbs/615 kgs @ 36 psi). The 94 is rated @ 1356 lbs/670kgs @ 38 psi*, but as it is an XL tyre, its rating (LI) is 1477 lbs/670 kgs @ 42 psi.

(* NOTE: 2 psi higher than the normal 91 LI @ the ISO Metric (ETRTO) standard’s 36 psi rating.)
HighlandPete

Totally confused.

Why does the M3 fitment 98Y rear tyre only run at 36psi then?

Need to know cos thats what I have on my 335i... ( 91Y front )

Yves

[HighlandPete]

Originally Posted by YvesD

Totally confused.

Why does the M3 fitment 98Y rear tyre only run at 36psi then?

Need to know cos thats what I have on my 335i... ( 91Y front )

Yves

That's the 'black art' of tyre LI and pressure recommendations by the car manufacturer. There is much more to selecting a car's tyre than just choosing the load index, although that must be of a high enough value, or we could be running an overloaded tyre. Because a tyre is a high LI or even XL rated it doesn't mean we run at the pressure for the maximum load rating. Often we run at much higher pressures than a standard tyre's maximum load/pressure rating, but not to increase the load rating. It is done for all the other reasons tyre pressure is selected, handling, ride, heat at speed, wear, etc.

Also, we could be running lower pressures than appears correct, if the LI is of a high value.

HighlandPete

[HighlandPete]

Originally Posted by dxb335d

I find the car is far more pliant with Non runflats. The car is fantastic at speed and does not skip and is not unpredictable like it was on Runflats.

I'll second that, predictability and a fluid drive, mean a lot more to me, than a 'feeling of roll' some mention.

I'm not sure how much more roll a non run-flat high performance tyre will give, over the RFT, if pressures are correct, as we are only talking a few millimetres of extra deformation, not any huge figures that would make a car roll significantly more. The confidence the non run-flat inspires, may allow us faster cornering speeds, that could generate more roll from the suspension as a whole.

HighlandPete