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Author Topic: A star tyres , myth or fact  (Read 1517 times)

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April 17, 2018, 12:23:17 AM
Reply #45

asoni

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Re: A star tyres , myth or fact
« Reply #45 on: April 17, 2018, 12:23:17 AM »
https://www.pistonheads.com/gassing/topic.asp?h=0&f=72&t=1059084

Interesting. It’s the first thread I’ve found where people have actually given believable and good technical info on the star marked system and now it makes a lot more sense to the point where I’m considering sticking with star marked tyres.

April 17, 2018, 12:26:21 AM
Reply #46

asoni

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Re: A star tyres , myth or fact
« Reply #46 on: April 17, 2018, 12:26:21 AM »
For example:

A response from Dunlop on another forum gavce the info that the star marked tyres are made to a specific rolling weight AND radius (which works out the same no matter what size is on the sidewall) so not only the transfer box 'feels' the same weight and resistance from both axles but also the TPMS which works from the ABS sensors isn't fooled either by the increase in rotating mass or the difference in rolling radius.


April 17, 2018, 08:25:46 AM
Reply #47

Spandex

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Re: A star tyres , myth or fact
« Reply #47 on: April 17, 2018, 08:25:46 AM »
For example:

A response from Dunlop on another forum gavce the info that the star marked tyres are made to a specific rolling weight AND radius (which works out the same no matter what size is on the sidewall) so not only the transfer box 'feels' the same weight and resistance from both axles but also the TPMS which works from the ABS sensors isn't fooled either by the increase in rotating mass or the difference in rolling radius.
I read that thread before. That quote is a bit ambiguous, because clearly a 275 and a 315 tyre of the same design, radius and sidewall height are not going to be the same weight. Which makes me believe they are actually referring to quality control for an individual tyre size - i.e all of the 315/35/20 tyres of a particular design will be rigorously checked to ensure they’re the same size and weight. Basically, it makes me think either the spokesperson from Dunlop misunderstood the question, or the response has been taken to mean something that wasn’t intended.

If you look on page 3 there is a post from someone who claims to work for a tyre manufacturer that kind of backs up that theory. They say that the star rating is a quality control stamp only, and there is no reason why you shouldn’t fit non-star marked tyres, as long as you ensure they meet the tolerances for your vehicle.

<edit>Just to add to the top paragraph, obviously 10J and 12J wheels will also be different weights, so there is no point whatsoever trying to get the tyres the same weight, only to stick them on different weight wheels. Something about that Dunlop response doesn't add up.

April 17, 2018, 10:28:34 AM
Reply #48

asoni

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Re: A star tyres , myth or fact
« Reply #48 on: April 17, 2018, 10:28:34 AM »
I read it as Dunlop saying they check each tyre in every batch meticulously so basically every 315 tyre made will be exactly the sameness correct  spec and so on. I don’t think he means all tyres will be the same regardless of size as that wouldn’t make any sense.

The main point however is that it gives a bit more background on what the * system is and how it works. From reading that, I’ve concluded that if I buy approved tyres they will 100% be the correct spec. If I buy non approved, I might get one where the rolling radius or weight is not quite to spec. On 99% of cars this wouldn’t cause an issue but on certain cars especially x5 it might.

April 17, 2018, 10:51:22 AM
Reply #49

Spandex

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Re: A star tyres , myth or fact
« Reply #49 on: April 17, 2018, 10:51:22 AM »
Ahh, ok. I still think the person who posted that in the PH thread thought it means the size/weight would be the same for different sized tyres in a staggered set up.

I think your last paragraph is broadly correct, in that star marked will be guaranteed to start off within tolerance, whereas non-star marked means there is a risk. I'd just love to find out how big that risk really is, because sticking to star marked tyres seriously limits your choice, and as others have noted recently, prevents you from moving to non-runflats (with all the benefits that brings).

April 17, 2018, 02:46:05 PM
Reply #50

asoni

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Re: A star tyres , myth or fact
« Reply #50 on: April 17, 2018, 02:46:05 PM »
Yes I’d love to as well, as I really want to try a set of non run flats. Are there really no approved ones that are non run flat?

Another post from that link showed how someone took off a brand new premium tyre to swap for a approved one, as he was getting the usual issues. He noticed when side by side the star marked tyre was quite different even though stamped size was the same!

April 17, 2018, 07:43:35 PM
Reply #51

X5Sport

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Re: A star tyres , myth or fact
« Reply #51 on: April 17, 2018, 07:43:35 PM »
All wheels are driven to some extent all of the time.  I think kkx5 has previously said that it never falls below 10% but I may be recalling that incorrectly.  It shifts to predominantly RWD though.

I believe the Haldex system on my VAG Škoda cuts the rear wheel drive above a certain speed unless the traction system needs it back on.  Clutch controlled.
:type:

April 17, 2018, 08:30:10 PM
Reply #52

kkx5

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Re: A star tyres , myth or fact
« Reply #52 on: April 17, 2018, 08:30:10 PM »
Yes I’d love to as well, as I really want to try a set of non run flats. Are there really no approved ones that are non run flat?

Another post from that link showed how someone took off a brand new premium tyre to swap for a approved one, as he was getting the usual issues. He noticed when side by side the star marked tyre was quite different even though stamped size was the same!
Thats what my pictures shows. Same size approved vs non.

April 17, 2018, 08:38:07 PM
Reply #53

kkx5

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Re: A star tyres , myth or fact
« Reply #53 on: April 17, 2018, 08:38:07 PM »
All wheels are driven to some extent all of the time.  I think kkx5 has previously said that it never falls below 10% but I may be recalling that incorrectly.  It shifts to predominantly RWD though.

I believe the Haldex system on my VAG Škoda cuts the rear wheel drive above a certain speed unless the traction system needs it back on.  Clutch controlled.
All xdrive bmw's. Initial: front:rear, 50:50 then, from 30mph 38:62, above 100mph 0:100. System can switch to 50:50 at any time. If the rears are not running the fronts will never move, quite opposite to haldex.

April 17, 2018, 08:39:14 PM
Reply #54

X5Sport

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Re: A star tyres , myth or fact
« Reply #54 on: April 17, 2018, 08:39:14 PM »
Thanks for the confirmation, and I knew the Haldex was very different in operation and split  :)
:type:

April 17, 2018, 08:49:57 PM
Reply #55

Spandex

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Re: A star tyres , myth or fact
« Reply #55 on: April 17, 2018, 08:49:57 PM »
Thats what my pictures shows. Same size approved vs non.
But it doesn’t matter if the non approved tyres are a different size to the approved ones. What matters is if a non approved staggered set of identical make/model are different in size. It would also be interesting to see a side by side staggered set of star marked tyres too, to see if they really are identical.

In theory, if BMW really are specifying rolling radius as part of the star mark program, then approved tyres from different manufacturers should be identical sizes too.

April 17, 2018, 09:08:28 PM
Reply #56

kkx5

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Re: A star tyres , myth or fact
« Reply #56 on: April 17, 2018, 09:08:28 PM »
...and they are.

April 17, 2018, 11:19:50 PM
Reply #57

Spandex

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Re: A star tyres , myth or fact
« Reply #57 on: April 17, 2018, 11:19:50 PM »
Err... what are?

April 17, 2018, 11:44:58 PM
Reply #58

ommis

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Re: A star tyres , myth or fact
« Reply #58 on: April 17, 2018, 11:44:58 PM »
So I can put non rft on a staggered set up as long as the tyres meet the right specifications
We’re would one find this info
Will it be in the tray marked
Hens teeth and unicorn horns
I phoned a tyre shop today and enquired about four new boots
The guy said I needs *run flats because there what Bmw specify
I asked about non run flats
And was told they mash up the transfer box so I shouldn’t have them
No more info was given when I asked why
Special tyres for a special car
A little knowledge is good for his business though
Was quoted £1500
I need the tyres and there sizes non run flats
Please ,

April 18, 2018, 08:03:14 AM
Reply #59

Spandex

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Re: A star tyres , myth or fact
« Reply #59 on: April 18, 2018, 08:03:14 AM »
I think it’s generally agreed, even amongst those who only fit star rated tyres, that if you fit 4 tyres that are the same tread pattern and the same rolling radius (actual, not calculated from the sidewall size stamp) then you’ll be fine.

The debate here is more about how far you can move from “exactly the same size” without causing damage. Clearly there is some tolerance because even star rated tyres won’t stay the same size throughout their life and these cars don’t wear tyres evenly front to back.

Kkx5, you clearly have a fair bit of info on this, so maybe you can help out - if I have a complete set of star rated tyres fitted new and over the miles the fronts wear differently to the rears, at what point would I have to bin them and buy a new set? What tread depth difference is dangerous, assuming the tyres started off the same depth and same overall radius.