BMW 3 Series Runflat Tyres

Honest John Back Room » Technical matters
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Sat 20 May 2006 21:40
BMW 3 Series Runflat Tyres - J.B.
The new 3 series has no provision for even a spacesaver spare wheel whereas the 5 series does. It would be really handy to have one in the boot for long journeys. Does a spacesaver's diameter always have to be exactly the same as the original tyres. I think I've seen ones that are slightly smaller as well as thinner. The real question I would like answered is would the 5 series spare fit a 3 series both technically and legally? Any thoughts?
On a slightly different tack (no pun intended); can tyre sealant such as porsche supply in their cars be used in a punctured runflat to extend the 50 mile range after a puncture?
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Sat 20 May 2006 23:19
BMW 3 Series Runflat Tyres - George Porge
I'd say that the ABS would have a fit if the tyre diameter were different
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Sun 21 May 2006 00:20
BMW 3 Series Runflat Tyres - David Horn
Don't think the ABS would care, after all wheels turn at different speeds every time you go around a corner.
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Sun 21 May 2006 00:52
BMW 3 Series Runflat Tyres - Dynamic Dave
Don't think the ABS would care, after all wheels turn at
different speeds every time you go around a corner.


Yes, but it's when they're turning at different speeds all the time the ABS system gets upset.
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Wed 7 Jun 2006 14:56
BMW 3 Series Runflat Tyres - IanJohnson
ABS (and similar systems) work by measuring the difference in rotational speeds between wheels and if it is greater than a figure carved in its memory it operates. SWMBO's A2 has an expanding space saver with the same rolling radius as the full size wheels meaning that ASP/ESP and all the other systems with TLAs still operate when the spare is fitted.

Different sized wheel is OK if you can turn the systems off, a problem if you cannot for example turn of the traction control and then cannot get drive because it keeps cutting in because the wheels are different sizes.

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