A star tyres , myth or fact

[Spandex]

The trouble is, information on BMWs website is clearly just marketing nonsense. For example, they say that the star mark ensures "that they are made specifically for your BMW model", yet clearly this cannot be true because certain tyres can be used across a number of different models. So, we know that the tyres definitely aren't made for our specific model. What are we left with? Lots of claims of 'optimum' grip, comfort, safety, etc. Nice to know, but not really relevant to discussions about rolling radius or transfer boxes.

It seems clear though that the star mark program is a set of quality requirements and a testing process. Given that the staggered setup for the E70 should (if the sidewall specs are followed accurately) result in identical diameters, and assuming that part of the BMW quality requirements covers accuracy of sidewall specs, it's likely that the star mark can be taken to demonstrate that the tyres will be the same diameter when new across a staggered setup. Nothing to do with being designed for that car or that specific wheel configuration - just a simple design tolerance and testing program.

But the problems arise when people use that information to make unsupported assumptions about non-star marked tyres. For example, a particular tyre might meet every single one of BMWs quality requirements, but won't be eligible for a star mark because it's not runflat. It's even possible that there are tyres out there that exceed all of BMWs specs, but for commercial reasons the tyre manufacturer has simply decided not to submit it for testing. Perhaps the testing process is expensive (you can be sure BMW don't pay for it). Perhaps it's not cost effective if you know that tyre design isn't likely to sell in large volumes in that particular size/load rating.

There is so much information we're missing here, so it's disappointing when people come on forums asking for advice and receive what is basically a proclamation - "thou shalt not fit non-approved tyres, lest thy transfer box doth expire!"

[X5Sport]

A while back someone got a figure of less than 1.5mm difference in depth front to rear mattered.  There was a %figure too but I haven’t found it.

The weight one is interesting though.  That has to be inertia when starting off perhaps?  ‘Load’ on the transmission down the various shafts to get the unsprung wheels rotating (inertia being the resistance to that in that case).  Slowing the rotation down again is mainly on the brakes.  If it matters that much, then as an engineer that worries me a little.

Generally the whole thing points at suspect engineering and materials choices - driven by bean counters or a desire to hit emissions limits by making things lighter?

[kkx5]

Weight of the tyre?  "*" tyres are made so rear rolling is same as front. Thats it. In fact, the rears can be "smoller" then the fronts, if you do a lot motorway miles and all of you will be fine,  but if the rears are higher then fronts (non "*" tyres) you will damage transfer box. Transfer case can not compensate if the fronts are spinning faster. That's how the system is design.

[Chrispy]

Rolling? Weight or radius?

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[kkx5]

Whats your question? Radius/ rolling always comes together. You can not change rolling without changing radius.

[Chrispy]

Ah your post has changed since I read it. Not sure if it's my app.
This actually raises the question I was curious about when someone said weight would match on a staggerered setup. Not sure how it can as the RR might be the same but the width is not - it's wider. So therefore the tyre at the back simply has to weigh more than the fronts as its bigger.
So if "weight" is the thing then the logic doesn't make sense to me unless we're talking tolerances where the weight difference needs to be within X percent.

Either way it all feels like nonsense to me. A cop out for warranty claims when the crummy balsa wood transmission components implode. Something they wouldn't get away with in the states as the legal system would eat them alive.

The number of mates I've had running around on Audi quattros with whatever tyres they felt like and had zero problems, this whole "Xdrive is made of chocolate so therefore you need tyres made of reclaimed moon dust" thing would otherwise be unknown to me unless it was for forums such as this. And if that's the basis for BMW refusing warranty claims when things go south then they need to face the small claims court.

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[kkx5]

Sorry, it was me still writing and pressed post by mistake. Weight is nonsense for me. The difference to Audi system: its all about the programming: xdrive software is much "tighter" then Audi, acts faster for road condition changes. Quattrro is just so slow compared to xdrive. Not on the firs gen of the xdrive system but on the second and third i can change the values/classification/clutch setting so the transfer box will last 400.000 miles, not a problem but is just very slow, not like ultimate driving machine:)

[Spandex]

You can’t really compare the different systems used by other manufacturers because, well, they’re different. I used to have a Tuareg, and that was also sensitive to differences in tyre diameter, although I don’t believe a staggered setup was offered on that car, so the issue was only of concern to people replacing the tyres on one axle, or fitting different tyre models on each axle.

All 4wd systems can handle a speed difference front to back - otherwise you couldn’t drive them round corners - but the design of the system will govern how long it can handle that difference for. Cornering alone won’t introduce too much heat into the system, but significantly different tyre sizes probably will, as it will be a constant effect.

[ommis]

So after all the answers
I still dare not buy non run flat tyres
Even if I got the guy to stand the tyres next to the old ones . So they match in size .not by the tyre wall sizes
I put 4 continentals on run flats just under a £1000

[asoni]

Well I’ve had my non run flat latitude sport 3s on for about a month now and best decision I made, ride is so much better especially as slower speeds. Also no unusual noises or issues from transfer box etc.

[Icicles]

[quote="asoni"]
Well I’ve had my non run flat latitude sport 3s on for about a month now and best decision I made, ride is so much better especially as slower speeds. Also no unusual noises or issues from transfer box etc.
[/quote]I agree 100%
They have been fantastic

Chris

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[Mob17]

Read every post of this thread and still confused.

I’m about to buy a 40d that has dunlops and bridgestones. Is this something to worry about? The car is perfect has everything i want but im worried after reading all of this.

[Reusch]

Get the seller to put 4 new tyres on or negotiate the price to do it yourself.

[Chrispy]

In terms of getting answers, yeah this thread really hasn't cleared it up much unfortunately and the evidence either way is fairly anecdotal with some claiming that they've seen failures as a result of not using the * tyres, and some having failures even with the * tyres installed. 

IMO BMW themselves would have you use * marked tyres :

1. As leverage to get out of warranty claims should your car fail and you not use them.  Warranty claims cost them a fortune and any opportunity to reduce these overheads will be taken.  Would love to see this challenged in the small claims court as choice of tyres, providing they adhere to the size, speed and load ratings from the factory (which is what insurance companies also want, although they are only concerned with safety) should be the consumers choice.
Adding the * marked thing into the mix is likely not to wash, and in territories like the US I bet they can't get away with telling people "no, we're not going to fix your car sir as you aren't using Bridgestone Dueller HP's all round that were replaced at the same time to guarantee they all have the same wear levels etc".  They'd be on Judge Judy in a heartbeat.

2. To keep the tyre manufacturers happy as no doubt there are deals and / or golf course agreements between them that these tyres will be promoted.

One thing that I've wondered with all of this is the BMW approved used program, where they sell X drive cars with an extended warranty and with whatever tyres happen to be fitted to the car at the time, assuming they have sufficient tread depth.  My 2010 3 series (bought in 2013) was from a BMW dealer and had all random tyres on it (all decent brands but not matching all round) but they said as they all had decent tread on them they wouldn't fit new ones when I queried it.  Admittedly I had lost some bartering power as I was trading in my Civic Type S at the time but still, if an XdDrive equipped car leaves their premises clad with whatever rubber happens to be on there, they'd have a hard time denying a warranty claim should there be a problem.....

Personally, my choice when my 19" Dueller HP's wear out will be to put non RFT's on and that's a decision I've made.  All 4 will be replaced at the same time, with Hankook Ventus tyres (the only ones that have the correct size, speed and load rating as mine is the 7 seater) and I'll relish the expected vast improvement in the ride quality as a result, in addition to the reduced unsprung weight and the benefits that brings.

[Mob17]

Thanks chrispy