Last post on Sep 18, 2013 at 7:28 AM
You are in the BMW Z4
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BMW Z4, Coupe, Convertible
#69 of 86 Re: RunFlat Tire Info [claires]
May 26, 2010 (5:46 pm)
Here's the article I found on the web that finally enabled me to convince my BMW dealer that newer runflat tires might help eliminate the tramlining problem I was having. It helped so much that between BMW and the dealer they picked up 2/3 of the cost of four new Bridgestone RunFlats for my car.
Bridgestone 3G RFT Tires take the shock out of run-flats
by Michael Harley on Jul 6th 2009
Compared to a conventional tire, the construction of a self-supporting run-flat requires additional material thickness in the sidewalls to prevent the tire's collapse once it has lost pressure. It is this additional reinforcement that adds weight, reduces ride comfort, and increases rolling resistance (these characteristics are the kiss-of-death to performance).
Consumers embraced the additional mobility and safety benefits of the 2G RFT, but they never warmed to the handling compromises as a result of the additional unsprung weight, the harsh ride (the sidewalls are a noticeable 15 percent harder than a conventional tire, says Bridgestone), or the expensive replacement cost (up to 30 percent higher, in some cases). Frustrated, many vehicle owners exchanged their run-flat tires with conventional tires even before it was time for their replacement.
Bridgestone research and prowess resulted in three new cutting-edge technologies:
Unique ply construction: The reinforcing layers of a tire are called the "ply." Bridgestone developed a tire ply that uses the heat generated by a deflated tire to contract and curb deformation. In simple terms, the material in the new sidewalls automatically shrinks to abate damage from abrasion and heat. When the tire cools, the ply automatically returns to its original state.
New rubber compounds: Laboratory-engineered rubber compounds, Bridgestone calls them "NanoPro-Tech," are also used in the sidewalls to limit heat. Conventional tire compounds warm through friction between the carbon and polymers (two common tire ingredients). By optimally distributing the polymers, friction and heat are minimized.
Innovative heat control: Bridgestone developed so-called "cooling fin" technology for the new tire. Molded into the sidewall are small protrusions (think of them as miniature spoilers). While this seems rather rudimentary, they effectively disrupt the airflow at the surface to help radiate heat and cool the tire.
Bridgestone encouraged us to try its new third-generation run-flat (3G RFT) from behind the wheel. Strapped in near identical late-model BMW 5 Series vehicles, Bridgestone offered us the opportunity to drive three variants of its high-performance RE050A tire: Conventional, 2G RFT, and 3G RFT.
We drove the conventional RE050A first. A high-performance tire fitted to such cars as the Nissan 370Z and Lexus IS-F, the standard rubber was comfortable on the smooth sections. The course/rough pavements didn't provide much of a challenge either as the compliant sidewalls absorbed the abuse without drama.
Next, we tried a set of RE050A "2G" run-flats. While they were comfortable on the smooth sections, the compromises of the 2G run-flats were immediately evident when we entered the first sections of rough pavement. What had been damped by shock-absorbing sidewalls on the standard tires was now transferred into the cabin in the form of sharp, and rather uncomfortable, impacts. This test reinforced what many owners have expressed and what we have personally experienced.
The final run through the test course was done with the all-new RE050A "3G" run-flats. Eureka! Surprising even the skeptics among us, the third-generation tires were nearly imperceptible in ride quality from the standard tires (non run-flat) we had driven on merely minutes earlier. The ride was very comfortable. According to Bridgestone, test instruments reveal that the slight difference in ride quality was a near-imperceptible 5 percent change in harshness.
Another fleet of late-model BMW 5 Series vehicles were fitted with 2G RFT and 3G RFT tires for back-to-back comparisons. The roads were in fairly lousy condition, but they again demonstrated the newfound compliance one can expect with the third-generation run-flat.
The track sessions and test drives made it clear that Bridgestone has eliminated the biggest objection to run-flat tires – abusive ride quality. We never had an opportunity to push the performance envelope of the tire, but Bridgestone says the tread compound of the RE050A 3G RFT is identical to that on the conventional tire, so the grip levels should be very high.
But wait, there's more to the story:
There are two "However's" and one "Therefore" to add to my post. However #1: The dealer could not get their hands on 3G RunFlats, even though the factory is currently delivering 2010 Z4's with them installed. So they installed 2G's all around on my Z4. However #2: The 2G's did not make a noticeable improvement in handling.
Therefore #1: After driving on the 2G's for a month and finding the Z4 still incredibly difficult to handle, I traded it in and bought a new Lexus IS 250C. After three very frustrating years of coping with "superior German engineering" that never translated into an enjoyable driving experience, I'm now a very happy man. Plus I now have two more seats, a slick convertible hardtop and a ton of goodies that actually make driving fun--for the about the same $$.
I hope others have better success . . .
#70 of 86 Snow tires plus Wheels
Jul 31, 2010 (9:39 am)
Please give me advice about snow tires and wheels for a Z4. Just thinking of buying the snow tires and not the wheels.What do you think?
Looking to buy '08. Plan to buy the Blizzak tires. I am on a budget
#71 of 86 Z4 tire wear
Jan 12, 2011 (10:02 am)
I have a 2007 BMW Z4. I wanted a six-speed so I got a 3.0i with the sports package. Probably should have done my homework a bit better. I bought the vehicle used (after having driven and loved my BMW Z3 for ten years and 130,000 miles). I was not aware that the car has different size tires on the front and the rear so they can't be rotated. I don't know what genius of German engineering decided this was a good idea. (Yea, I know it is about performance and handling, but practicality should enter into the equation somewhere.) Between the fact that the tires can't be rotated and the negative camber, the rear tires wear out in 10,000 miles, with more wear on the inside than the outside. It is my understanding that the inability to rotate them and the uneven wear voids any mileage warranties that come with the tires. I have received a suggestion to use Michelin Pilot Sport A4 Plus tires on it. However, if all of the tires are going to wear out in the same amount of time (and the warranty will not be valid) I would rather go with something cheaper. Any experiences or advice you can share?
#72 of 86 Re: Z4 tire wear [z4lady]
Jan 13, 2011 (8:47 am)
I believe all factory Z4's have the same size front and rear wheels.
The 2007 Z4 came with 17 x 8.0 in. wheels with 225/45R W tires.
If you you have different sizes, they are courtesy of the person you bought your car from.
#73 of 86 Re: Z4 tire wear [markwell]
Jan 13, 2011 (7:03 pm)
Sorry, but all Z4's with the sport pakage came if staggered tires (different tire sizes front to rear) and the rim widths are different front to rear as well.
#74 of 86 Re: Z4 tire wear [markwell]
Jan 21, 2011 (11:59 am)
My 07 Z4 Coupe (completely optioned out) has different sized tires between the front and back. It came from the factory that way, and I purchased it new.
#75 of 86 Re: Z4 tire wear [capriracer]
Jan 21, 2011 (3:09 pm)
I live and learn. Thanks for the info. I previously thought only high end $65K plus exotic cars came stock different tire sizes. Surprised BMW does that for the Z.
The plus side is larger rear tires with smaller tires in the front looks cool as ever - almost dragster like.
The down side is you can't rotate the tires (ugh). At the end of the day, I think I'll stick with my size 17s front and rear.
#76 of 86 Re: Z4 tire wear [markwell]
Jan 24, 2011 (6:27 pm)
Toyota MR 2 spyder came with different size tires on the front and rear axles. I believe it sold for 25k when new.
#77 of 86 Re: Z4 tire wear [snowallergy]
Jan 25, 2011 (4:26 am)
Thanks for sharing the tire size delta on MR2's.
As said before, while some sports cars and novelty cars were made with off size tires, it still doesn't dissuade me from my original premise, it is uncommon for standard production cars to be made with different sized front and rear tires.
Why? It costs more, it generally doesn't improve handling and it limits ones ability to "rotate" tires extending tread wear life. Does this stop car makers from doing it. No. Why? Because they think it may increase the look and appeal; hence, sales for certain sports-oriented car designs.
Speaking of the MR2, back in the mid-80's, the MR2 was one of the finest handling fun sports car gems available at a reasonable price. A friend of mine had a red one with black rag top. Riding in it was so much fun I took a dealership test ride. Both were white-knuckled experiences that took hours to wipe the smile off my face. The combination of top of the line handling performance, Toyota reliability and top down fun for thousands of dollars less than its competition made it second to none in my book. Unfortunately, I was starting a family at the time and it wasn't practical.
This is why the market for pure 2 seaters is very limited - practicality. If you enjoy driving the twisties without slowing down, get yourself an old MR2 with a new set of rubber - you won't be disappointed.
Then again, older now, I'm not planning to let go of my BMW Z4 anytime soon. Weeeeeeeeeeeeeeeeeeee!!!
Aug 10, 2011 (2:17 pm)
A reporter is interested in talking with roadster fans who would like or dislike the idea of a smaller engine in the new BMW Z4. If you care to share your comments, please send an email, including your daytime contact info, to predmunds.com no later than 5:00pm Pacific on Friday, August 12, 2011.