Last post on Sep 18, 2013 at 7:28 AM
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BMW Z4, Coupe, Convertible
#60 of 86 Twitchy, Jumpy Steering--'07 Z4 Roadster
Feb 13, 2010 (6:58 pm)
I bought a new '07 Z4 from a Denver dealer in July 2007. At about 3,000 miles, the dealer aligned the front-end. After that, the steering was sensitive to every bump, bulge or break in the road. Smooth roads at highway speeds were fine. But when driving in town between 25 and 50 mph the car was hard to handle.
On a crowned road, the steering pulls "downhill". If I hit a bump or pothole, the steering abruptly pulls to one side then the other. If there is a seam that runs parallel to the direction of travel, the wheels grab onto the seam. The steering feels jittery, twitchy and unpredictable. It's impossible to drive in town without worrying that the car may lurch into a curb or a hit parked car. So I drive with a "death grip" on the wheel.
I took the Z4 back to the dealer 4 times in 18 months, each time expecting the problem to be fixed. First the alignment was re-adjusted (apparently it was incorrectly aligned to M-model specs). On later service appointments, the alignment was checked again. Tire pressures checked. Nothing helped.
Frustrated, I took my car to an independent BMW garage. After a test drive, the shop owner confirmed the problem. He asked if the run-flat performance-rated tires (Bridgestone RFT (225/45 R17 front, 245/40 R17 rear) had ever been evaluated as a possible cause. To my knowledge, "no".
So I took the car to a second Denver BMW dealer. After hearing my concerns, the service manager said he thought the tires were causing the problem. So he swapped tires with another Z4 on the lot. After the swap, my car drove normally once again. Oh, happy day!!! But he had to swap them back. So I drove home with a jumpy car.
Now I'm headed back to the original dealer to see if I can get them to replace the tires. I think I'm entitled to new ones. The original set was covered for defects by a $750 tire policy I bought when I took delivery. The dealer may try to weasel out of that. Plus I don't know what to do about Run-Flat Tires. Does anyone have enough experience with this issue to know that RFT's are (or are not) part of the problem. Or is it the "performance" design of the tire? Or is it because they are Bridgestone tires? Or is it just a bad set of tires?
I would appreciate any advice, especially on how to get the dealer to "man-up" and take responsibility for replacing all four tires. I want to feel safe on the road and with spring just around the corner (maybe) I want to enjoy the ride again!
#61 of 86 Re: Twitchy, Jumpy Steering--'07 Z4 Roadster [steveclemens]
Feb 15, 2010 (11:23 am)
Twitchiness of the Z4 is built into the design. It is an unfortunate con to the tilt of the front wheels when you turn. The pro is that you can take tight corners at higher speeds. The con is that the car quickly pulls left or right when you get close to ridges or ruts. Once used to it, it's no big deal.
I think the issue is made worse with the run flats. Run flats let you feel the road surface more, every bump, every pull and ridge. Its all trade offs. I have 50,000 miles now on my Yokohama's AVID 4 all season radials. They grip better than ever on clean dry roads, there's still an 1/4 inch tread left - but I can't take the car out if its snowing - I mean at all. It was fine up until about 40,000 miles, but no snow/ice handling at all now. I'm trying to get them to stretch to May. I hate getting tires more often than once every 2 years - but then at $500 for a set of 4 mounted and balanced - I have no complaints.
I've got 80,000 miles on my 04 Z4 and have yet to need an alignment. I've hit some pretty bad pot holes and a curb once - but this car rides true and straight without pull or side wall wear. I think the car is a marvel of engineering perfection. Only the ridge affect is all I've noticed and it is minor since I dropped the run flats.
#62 of 86 Re: Twitchy, Jumpy Steering--'07 Z4 Roadster [markwell]
Feb 15, 2010 (11:57 am)
Thanks for sharing your views about my steering problem. In almost every other respect, I love my Z4. However I've had more than my share of problems. I'm on my third manual transmission--the first two frequently got so stuck in 6th gear I had to pull over, stop and use both hands to get the transmission into neutral! I'm also on my second radio--the first one would light up but no sound would come forth.
I wish I could agree with you about the steering. But I'd rather have predictable steering than a car that tramlines with every defect in the road. As far as I'm concerned, this is a serious safety issue. If I can't get it resolved fairly soon with new tires, this baby is going bye-bye! Why would I want to take tight corners at high speed if I end up hitting the curb or another car!
#63 of 86 A Smoother Ride?
May 12, 2010 (2:44 pm)
I just joined this forum on the advice of a friend who owns an import repair shop. I purchased a 2005 Z-4 (probably the last "boy toy" my wife will let me have) and I just love it!!! It has every option available for this year to include the premium sport package. It rides firmer than I am accustomed-not like say; a TR-6 I had some time ago. Yes, I am a senior citizen (South of 64 yrs.) so, the question becomes what can I replace the original RFT's with to increase ride comfort to the maximum? My Z-4 has about 40k + miles and the only thing my guy tells me after he went through it before I bought it is: oil change, possibly some brake work, rotate/balance tires. All of this: "sometime this year." The tires look very good but I am told after a certain amount of time, one should consider replacement. What is available, run flat or other wise, that I should consider to get the smoothest ride?
#64 of 86 Re: A Smoother Ride? [cliff23]
May 12, 2010 (3:35 pm)
I asked a lot of questions and did a bunch of reading over a 6-month period because I could not get answers from BMW. I finally replaced the OEM tires with the same brand/model but in a newer design about a month ago. My Z4 runs a little smoother but it still does not handle the gaps and seams in the road as easily as I would like. OEM tires were Bridgestone Potenza 225/45 R17. The new tires are exactly the same except they're Generation II. BMW is putting Gen III tires on the new Z4's but said they were unable to get those shipped to the dealership yet as replacements. That may change by summer.
In the meantime, you may want to consider a non-runflat tire option. One tire dealer recommended that route if I wanted a really smooth ride. The downside is that you need to carry a can of tire inflator plus some sealant or "slime" to enable you to get to a repair shop in the event of a flat.
If you'd like, I'd be happy to share the full text of an article by an auto writer about testing runflat tires on BMW's. It's pretty interesting background and provides a glimpse of the future of runflat tires.
Let me know if I can be of more help!
#65 of 86 Re: A Smoother Ride? [steveclemens]
May 13, 2010 (5:09 pm)
Thanks Steve. I appreciate your prompt response. Of course I would be interested in you forwarding any info you have: (cliftonburrisatt.net). After your comments, I checked my tires and they are; Bridgestone Pontenza 225/40 R18, 88W. It seems from your comments I also conclude that the "seams and gaps" are less than to be desired. I also attribute this to a minor difference between hydraualic as opposed to electric operated steering. Suffice to say, I am a person who loves to drive this car when it can be done safely--not at my expense or others. These times are rare in my area.
May 14, 2010 (7:38 am)
I assume from your note that you have hydraulic steering on your '06 Z4, is that correct? The electronic steering on my '07 Z4 may be a contributing factor to the tramlining I experience. BMW seems to be going electronic on many components to provide more feedback to the driver and more precise control. But as a real amateur about these things, that may also mean more feedback than I really want.
In response to my handling concerns, the dealer performed several alignment checks & adjustments. They also re-calibrated something called the steering angle sensor. Apparently this is another electronic device that constantly monitors the direction in which the front wheels are pointing. Again more feedback to the steering wheel.
I will send you a copy of the 3G runflat article directly to your email address along with a couple of additional comments so we can avoid doing all this sign-in stuff.
Have fun with your new toy, especially now that spring is here--at least it's supposed to be. We had a good shot of snow here in Denver two days ago but it may finally warm up enough this weekend to get our tomato plants in the ground!
#67 of 86 Re: RunFlat Tire Info [steveclemens]
May 26, 2010 (1:39 pm)
If you don't mind, I'd very much appreciate getting a copy of that article as well. Please send it to curethebluesaol.com. Thanks!
#68 of 86 Re: RunFlat Tire Info [steveclemens]
by Claire@Edmunds HOST
May 26, 2010 (3:39 pm)
It would be great if you could share the info right here in the forums too -- I'm guessing a lot of people would be interested.
Automotive News & Views | Coupes & Convertibles
#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 . . .