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Sedans BMW 3-Series BMW 3-Series Run Flat Tires
2421 messages, Last post on Dec 02, 2009 at 1:06 PM
You are in the BMW 3-Series Forum. Your Hosts are pat & karens
There's been quite a lot written here about the heavier weight of runflats and the affect of that additional weight on handling. To put that in context, the weight difference between the runflat and GFT RE050A is 28 v 25 lbs front and 30 v 27 lbs rear (per Tirerack stats). Add the weight of the rims, and three pounds per corner is more weight, but not much more. Perhaps the references to additional weight pertain more to the Michelin PAXs on the Honda minivan that use special wheel technology (with an inner raised band to support the collapsed tire) rather than the Bridgestones on the BMW. Also, note that 12 lbs total increase in weight is considerably less than the weight of a full spare and supporting hardware.
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Replying to: nkeen (Jul 22, 2007 2:07 pm) But that's unsprung weight. In addition to inconsistent damping and stiffness from the tires it counts for something. How much I don't know but considerable efforts go into reducing unsprung weight in performance circles and manufacturing... lightweight wheels, tires, brakes and suspension components. |
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nkeen and designman, you are both correct. The Honda PAX system carries a HUGE weight penalty (something like 25 pounds per tire over the same tires mounted on other Odysseys) as they weigh in at about 75 pounds per tire and wheel assembly! While the weight difference between the wheel and tire assemblies on a 335i non-SP and what it would be if the car came shod with GFTs is truly only about 12 pounds, those 12 pounds are outside of the sprung body of the car and as such greatly exaggerate the seemingly insignificant 3 pounds per wheel. FWIW, on the 335i SP, the Bridgestone GFT rear tires actually weigh one pound more than the RFTs. Odd. That said, the GFTs from other manufacturers in the proper size weigh between two and four pounds less than either version of the Bridgestones. What also is missing in this discussion is the fact that the 335i has rather low profile tires and as such, the differences between GFTs and RFTs will be minimized (maybe why many folks consider the 335i SP to suffer less from the adoption of RFTs than its non-SP sibilings). Consider the 328i non-SP instead, it has 205/55 R16 tires which in RFT form weight 27 pounds per tire when shod with ContiProContact all-seasons, and 28 pounds per tire when shod with poorly received Bridgestone EL42s. The same Continental tire in GFT form weights only 20 pounds (Bridgestone doesn't make a GFT EL42 in that size). IIRC, the wheels on a 328i weigh around 23 pounds, meaning that the entire RFT wheel and tire assembly weighs around 50 pounds (still waaaaay less than the PAX assembly), however, the GFT version would weigh 43 pounds, meaning that the RFT setup weighs fully 14% more than the GFT setup. Not an insignificant difference. Best Regards, Shipo |
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Replying to: shipo (Jul 22, 2007 5:37 pm) |
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Replying to: ptruitt (Jul 23, 2007 5:52 am) |
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Replying to: nkeen (Jul 23, 2007 2:38 pm)
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Replying to: ptruitt (Jul 23, 2007 5:52 am) I talked to BMW and they told me the whole industry was going to be following with excluding spare tires. I don't believe that except for maybe small sports cars, but certainly not luxury sedans. I've since talked to audi, thinking of the upcoming new A5 instead of the new convertible 335 (since it doesn't have a spare) and they confirmed with me that other than their small TT, all their cars will continue to have spares. GO AUDI!! Even the tiny little VW EOS has a full size spare in the trunk!
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Replying to: adethier (Jul 24, 2007 1:13 am)  I was trying to offer an admittedly poor solution to what was phrased as an immediate problem.
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Replying to: adethier (Jul 24, 2007 1:16 am) Regards, OW |
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With all the talk about saving weight by excluding the spare tire and BMW much lauded 50/50 weight distribution. Can someone explain to me how the fact that the 335 engine is 40 lbs heavier than 328, gets corrected/balanced. I looked for maybe a 40 lbs dumbell in the back ...or wait how about a SPARE WHEEL !!!
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