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Messages - Spandex

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How would you design a sharp, responsive 4x4 system which can compensate 4 different rolling radius????? ???
That’s what differentials do all day long (unless you somehow only ever drive on arrow-straight roads). So the issue isn’t 4 different wheel speeds, it’s the degree of difference and amount of time that difference is present - I.e. it’s down to the heat generated.

Dealing with this isn’t impossible, it’s just an unnecessary additional cost for car manufacturers. The additional cost of warranty repairs is probably significantly less than the cost of over-engineering the drivetrain.

General X5 Forum (E70) / Re: Cic IDrive
« on: May 03, 2018, 01:04:57 PM »
I think they changed over in Q4 2009 in the factory, although you have to bear in mind the registration date will always trail the build date. I don't think I've seen CIC on anything with a 59 plate.

If you're just looking at photos, the best way to identify CIC is the shortcut buttons surrounding the iDrive knob. The user interface itself is very different, but obviously you'd have to be sitting in the car (or there be photos of it switched on) to see that.

General X6 Discussion / Re: Huge sat nav screen.
« on: May 02, 2018, 09:40:29 PM »
Normally I don’t like aftermarket head units in a car, but that wouldn’t put me off buying an e70 one bit. In fact, it would be a selling point. They do look nice, and you still have full access to the idrive when you want.

General X6 Discussion / Re: Huge sat nav screen.
« on: May 02, 2018, 03:53:57 PM »

General X5 Forum (E70) / Re: A star tyres , myth or fact
« on: April 28, 2018, 11:18:27 PM »
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.

General X5 Forum (E70) / Re: A star tyres , myth or fact
« on: April 27, 2018, 10:53:55 AM »
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!"

General X5 Forum (E70) / Re: 4.8 V8 economy
« on: April 22, 2018, 09:51:28 AM »
You’ll get more than 17. I get 18mpg as a long term average and that is almost entirely my rush-hour commute of about 15 miles with a mixture of flowing 70mph dual carriageways and stop-start traffic. For a mostly motorway run (with a bit of normal roads either end) I’d expect low 20’s.

General X5 Forum (E70) / Re: A star tyres , myth or fact
« on: April 21, 2018, 05:12:08 PM »
If you can get a photo of the fronts next to the rears on a flat surface for comparison, that might help others considering them too.

General X5 Forum (E70) / Re: A star tyres , myth or fact
« on: April 18, 2018, 11:53:04 PM »
There are numerous threads across various forums where people discuss uneven wear front to back on these cars. It’s not uncommon.

Regardless, it’s a hypothetical question. How the treads end up different isn’t really relevant. Do you know the answer?

General X5 Forum (E70) / Re: A star tyres , myth or fact
« on: April 18, 2018, 11:05:00 PM »
I’m not talking about wearing unevenly across the tread of a single tyre. I’m talking about the fact that the front pair will wear at a different rate to the rear pair. Nothing to do with alignment.

General X5 Forum (E70) / Re: Tow weight chassis plate
« on: April 18, 2018, 08:15:07 AM »
Isn’t your max towing weight a legal definition, rather than a technical one? What I mean is, if the registration documentation says you can only tow 2500kgs, then that’s all you’re allowed to tow legally, and what’s written in a manual, or chassis plate, or what you’re technically capable of towing, is completely irrelevant.

General X5 Forum (E70) / Re: A star tyres , myth or fact
« 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.

General X5 Forum (E70) / Re: A star tyres , myth or fact
« on: April 17, 2018, 11:19:50 PM »
Err... what are?

General X5 Forum (E70) / Re: A star tyres , myth or fact
« 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.

General X5 Forum (E70) / Re: A star tyres , myth or fact
« 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).

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