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The Tire Rack's Tire & Wheel Forum
Use this forum to discuss anything in relation to wheels to tires to offsets.
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Old 12-04-2012, 09:56 PM   #21
cityjohn
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God please send us the Tweel. We have waited so long....
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Old 12-04-2012, 10:35 PM   #22
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Most of the car tests I read indicate that the professionals are not liking RF's.
BMW can design around them, but not eradicate the effect of lousy riding and handling tires.
I'll do my best to avoid them.
Yeah they still have their issues, but Bridgestone is putting lots of research into making them as smooth as normal tires. They're certainly rougher due to the stiffer sidewalls and handling suffers as well for some reason or another that I've yet to understand.

The safety aspect of them is nice in the fact that they'll never blow out, but you gotta pay for that safety - A new tire every nail. Youch.
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Old 12-04-2012, 11:18 PM   #23
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My engineering mind is alway open to new technology, so when the RF's get as good and cheap as regular tires I'll embrace them. But in decade of driving I've very rarely had a problem with tires and changing one is really very simple.
As long as my Pilot Super Sports are as amazing as they are, wake me when the RF's can come close to competing!
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Old 12-04-2012, 11:19 PM   #24
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The day that they make repairable runflats, I'll buy them. That's the #1 issue for me. They're more expensive, and you can't repair them.
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Old 12-05-2012, 10:35 AM   #25
WDE46
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Most of the car tests I read indicate that the professionals are not liking RF's.
BMW can design around them, but not eradicate the effect of lousy riding and handling tires.
I'll do my best to avoid them.
Tire sidewalls are a very functional part of the suspension. Your springs and dampers will help to suppress road disturbances at around 10 Hz. Tires help filter out disturbances of higher frequency (100 Hz). You can't really design a suspension that can filter out both low frequency and high frequency road disturbances. That's why we have to have pneumatic tires.



Here you can see how you can create a pretty basic suspension model using mass, springs, and dampers. K2 is the tire stiffness and b2 is tire damping. It's actually a pretty accurate model for frequency response analysis (+/- 10%). A RFT will have a very high stiffness (K2) and a lower damping (b2).

Last edited by WDE46; 12-05-2012 at 10:36 AM.
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Old 03-19-2013, 02:22 PM   #26
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How much stiffer are RFTs, really?

I have an '02 330Ci, sport package with no aftermarket suspension mods, optional style 72s with 225/40R18 and 255/35R18. I'm looking for good all-seasons and considering Michelin Primacy MXM4s, but the front size is only available in run-flat. I'm looking at this tire specifically because it IS a non-Z-rated, softer-riding tire which is a priority.

I hear concerns about not being able to tell if an RFT loses pressure. My car doesn't have TPMS or whatever other monitoring system is out there.

Is it unsafe/unwise to mount RFT on the fronts only? Rear size is available in non-RFT.

If not unsafe/unwise, how much harder is the RFT going to ride than the non-RFT on the rear?

Alternatively, 235/40R18 will fit on the front but will introduce a 1.5% variance in wheel speed between front and rear, which I'm hearing may cause all kinds of problems with DSC. 225/40 is 25.1" diameter, 235/40 is 25.4", but the 255/35 on the rear is only 25.0". Anybody ever run slightly different-diameter fronts vs rears and lived to tell about it? How crazy did your DSC go?
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Old 03-19-2013, 02:50 PM   #27
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If you've got to ask such a series of convoluted and complicated questions, my usual considered and experiential answer is: KISS!

I wouldn't touch this experiment with a ten foot pole.
Surely there are simpler solutions.
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