Run Flat Technology - in the Rim as Well as the Tire?
 

Could use some education... looking to put 6-series style 121 wheels on my '05 E53. However I want run-flat tires, and don't know if I should look for rims manufactured after '07? Does that matter, or is the run-flat technology ONLY in the tire, and not in the rim at all? Any advice appreciated! Thanks!

run flat is tire technology.. not rim dependent..

Not exactly. What is different on rims designed for run flats then others is that the inner lip has a nice ring the tire's inner bead snaps over just like the outer bead to keep the inner bead from rolling off the rim lip in no pressure situations. So there is a difference in the rim to keep the bead from rolling/unseating in no pressure driving. But if I remember right, all 6 series came with run flats from the lack of a spare, so all style 121's should be set up for them.

that doesn't make sense.. you can swap every single oem tire from every make from their oem run flats to regular tires and add run flats to any wheel... any tire shop does that daily...

i've swapped all of my run flats for regular tires with no issues...

When it comes to tire shops that simply may not know, or care, of the difference, you can't go off of just that.

This is what is taught in one of the training classes from BMW. And here's a scanned page from a training manual to help with illustrations.

http://i140.photobucket.com/albums/r.../rftrim017.jpg

looks like the inner hump is meant to retain the bead and sidewall against the outer lip hump. makes sense as the side walls are stiffer and put more force on the bead connection.

hmmm... goodyear rep told me otherwise when they rolled out their rft system.

Behold the power of proper information! :D Keep in mind the goodyear rep likely just didn't know better as he is a sales rep... not technition or properly trained on all aspects of the subject. Just what he knows for sales purposes.

well.. he's the race tire specialist.. not a sales rep nor a street tire expert...

:dunno:

It isn't a problem at all going from a RFT to a non-RFT on a RFT rim. It may be a problem going the other way.

There are various run flat bead designs out there, and not all the tire manufacturers use the same. They don't even all call them runflats (my Dunlops are DSST, not RFT, but Dunlop offers two designs as I recall).

I remember reading about the BMW rim design when they came out, and BMW was promoting that it was safer not using standard rims for RFTs.

Edit: I looked up the Goodyear design (used on the Corvette) and it used standard rims. Goodyear is now moving to the PAX system with Michelin, which uses a ring inside the rim to support the tire, instead of a stiff sidewall. It uses a special rim.