A handling question…

Y

Yorkshire_lad

Member
Afternoon folks.

My 2015 Z4 (35is) really doesn’t like oddly cambered or lumpy/undulating road surfaces (I don’t mean “broken” and/or potholed surfaces). The handling seems to get very flustered on anything but nice smooth road surfaces, which are getting rarer and rarer in the UK! It’s led to a few “white knuckle” moments when I really didn’t feel like I was pushing hard at all.

I’ve had my local BMW garage check the suspension geometry and they say everything is as it should be so I don’t think there’s anything obviously wrong.

Assuming the suspension is basically correct I’m now thinking about tyres, shock absorbers and springs. They’re all standard (I think) and it’s just been serviced and MOT’d so I believe they’re all generally working as they should be. Tyres are Bridgestone Turanza T005 225/40R18 on the front and Bridgestone Potenza RE050A 255/35 R18 on the back, all run flats. It was previously on Potenzas all round and still had the same handling characteristics.

I’m wondering whether replacing the tyres with non-run flat might be one option, but it’s a fairly expensive option to do with no real idea of whether it will help 🤷🏼‍♂️. My other thought was to find a really good independent BMW garage with experience in setting up suspension and se what they say.

Has anyone had similar experiences or have any wisdom to share?
 
Your Z4 35is's skittish behavior on undulating surfaces is actually a well-documented characteristic of the E89 chassis, particularly with the sport suspension fitted to the 35is model. The issue stems from the combination of run-flat tires, relatively stiff suspension tuning, and the short wheelbase—when the car encounters mid-corner surface changes or camber transitions, the run-flats' stiff sidewalls prevent the contact patch from conforming quickly enough to the surface, causing momentary traction loss that feels unsettling. The 35is's more aggressive damper and spring rates amplify this because they're optimized for smooth track surfaces rather than typical UK B-roads with their crowns, dips, and patchy repairs.Switching to non-run-flat tires is genuinely transformative for this issue and is the single most effective modification E89 owners report. The more compliant sidewalls allow the tire to maintain better contact through surface irregularities, dramatically improving confidence on imperfect roads. You'll want quality tires like Michelin Pilot Sport 4S or Continental SportContact 7 in the proper staggered sizes. The trade-off is carrying a mobility kit or space-saver spare, but most owners find the handling improvement absolutely worth it—it essentially gives you a different car on real-world roads while maintaining the performance on smooth surfaces.Before spending on tires, do verify your current shock absorbers aren't tired (the 35is's adaptive dampers can degrade subtly) and check that tire pressures are set correctly for mixed driving rather than just track pressures. A specialist independent familiar with E89s could assess damper performance and potentially adjust your setup, but honestly, the run-flat switch is where you'll see the biggest return. Many owners wish they'd done it sooner rather than persevering with run-flats that make an otherwise capable chassis feel nervous.
For the most detailed answer on this and 200+ E89 topics — including full diagnostic sequences, repair procedures, and extracts from the book — join the Atacama Yellow BMW Z4 Facebook group.
Source: The Definitive BMW Z4 E89 Book — P. Bondar, 2026
 
Common BMW Z4 E89 Chassis IssuesThe E89 Z4's chassis can develop several characteristic problems, primarily related to its suspension bushings and components. **Control arm bushings** (particularly the front lower control arms) are prone to premature wear, causing clunking noises over bumps, imprecise steering, and uneven tire wear. The **subframe bushings** can also deteriorate, leading to similar symptoms plus potential vibration through the chassis. These rubber components degrade from age, exposure to road chemicals, and the dynamic forces of spirited driving.**Suspension component failures** are another concern. The front **thrust arm bushings** and **tension strut bushings** commonly wear out, creating wandering steering feel and poor stability. The **shock absorbers and springs** can also deteriorate, reducing ride quality and handling precision. On higher-mileage examples, **wheel bearings** may develop play or noise, particularly if the car has seen track use or aggressive cornering.**Corrective action** involves systematic inspection during regular service intervals—checking for torn bushings, play in suspension joints, and leaking dampers. Most bushing issues require complete arm replacement since BMW typically doesn't offer separate bushings. Address worn components promptly, as delayed repairs accelerate tire wear and can compromise other suspension parts. A proper four-wheel alignment after any suspension work is essential to restore handling characteristics and prevent premature tire degradation.
For the most detailed answer on this and 200+ E89 topics — including full diagnostic sequences, repair procedures, and extracts from the book — join the Atacama Yellow BMW Z4 Facebook group.
Source: The Definitive BMW Z4 E89 Book — P. Bondar, 2026
 
Comprehensive Technical Analysis: Z4 E89 35is Handling on Undulating SurfacesYour experience is actually quite common with the E89 Z4, particularly the 35is model, and there are several interconnected technical factors at play. Let me provide a thorough analysis.## Understanding the Core IssueWhat you're describing—loss of composure on cambered, undulating surfaces rather than simply rough roads—points to **suspension compliance and damping characteristics** rather than basic wear or geometry problems. The Z4 E89, especially the 35is with its M Sport suspension, was designed primarily for smooth tarmac performance, and this design philosophy creates specific challenges on typical UK B-roads.## The Run-Flat Tire Factor (Primary Contributor)### Technical Impact of Run-Flat TiresYour Bridgestone run-flats are almost certainly a **major contributing factor**. Here's the technical explanation:**Sidewall Construction:**- Run-flat tires (RFT) use heavily reinforced sidewalls (typically 50-100% stiffer than conventional tires)- This reinforcement is necessary to support vehicle weight with zero air pressure- The trade-off is dramatically reduced sidewall flex and compliance**Impact on Suspension Dynamics:**1. **Reduced contact patch variation**: On undulating surfaces, normal tires flex to maintain contact patch; RFTs transmit surface irregularities directly to the suspension2. **Higher unsprung mass**: RFTs are typically 1-2 kg heavier per tire, increasing unsprung weight and reducing suspension responsiveness3. **Compromised damping**: Your shock absorbers must work harder to control the tire/wheel assembly, and on rapid surface changes (undulations), they can become overwhelmed4. **Reduced tactile feedback precision**: The stiff sidewalls transmit harshness but actually reduce the quality of road surface information to the driver**Specific to Your Tire Mix:**- Turanza T005 (front): These are grand touring RFTs—comfortable for run-flats but still very stiff compared to conventional tires- Potenza RE050A (rear): These are performance summer RFTs—even stiffer, designed for the original Z4 specification- This **mixed tire setup** (touring front, performance rear) creates inconsistent compliance characteristics between axles, which can contribute to unpredictable handling transitions### The Run-Flat Recommendation**Switching to non-run-flat tires would likely provide significant improvement**, with typical owners reporting:- 30-40% improvement in ride quality- Noticeably better handling composure on uneven surfaces- Improved steering feedback and predictability- Better overall tire life**Recommended Non-RFT Options for 35is:****Front (225/40R18):**- Michelin Pilot Sport 4S (excellent all-around performance, good wet grip for UK)- Continental SportContact 6 (sharper handling, slightly firmer)- Goodyear Eagle F1 Asymmetric 5 (good balance, strong wet performance)**Rear (255/35R18):**- Match the front tire brand/model for consistent behavior- Critical for predictable handling characteristics**Important Considerations:**- **No spare tire**: E89 Z4 has no spare wheel well; you'll need a tire mobility kit (tire sealant + compressor)- BMW part number for mobility kit: **71 10 2 333 674** (approximately £60-80)- Many Z4 owners consider this an acceptable trade-off- Consider joining a roadside assistance program with tire coverage**Cost Analysis:**- Premium non-RFT set: £600-900- RFT replacement set: £800-1,200- **Net additional cost of trying non-RFTs: £0-200** compared to staying with RFTs- This makes it a relatively cost-effective diagnostic step## Suspension Components AnalysisEven though your BMW dealer confirmed geometry is correct, there are several wear-related and design factors specific to the E89 35is:### 1. Electronic Damping Control (EDC) - If EquippedThe 35is typically came with **adaptive M Sport suspension** with EDC. Check if your vehicle has this:**Identification:**- EDC button on center console (suspension firmness settings)- Different
Source: The Definitive BMW Z4 E89 Book — P. Bondar, 2026
 
updated AI Bot..better formatting now

Full detail — Atacama Yellow BMW Z4 group
Copy for forum
Good afternoon and welcome to the forum. Your experience with the Z4 E89 35is on undulating UK B-roads is actually quite a common complaint, and you're right to be thinking about the interaction between run-flat tyres and the suspension setup. Let me break down what's likely happening and what your options are.

The fundamental issue here is that the E89 Z4, particularly the 35is with the M Sport suspension, has a very firm setup that was optimized for smooth surfaces. When you combine this with run-flat tyres, which have substantially stiffer sidewalls than conventional tyres, you create a suspension system that simply cannot react quickly enough to rapid surface changes. The run-flat sidewalls prevent the tyre from absorbing small to medium imperfections, which means every irregularity goes straight through to the suspension. On cambered or undulating surfaces, this creates a situation where the tyres are constantly fighting to maintain proper contact with the road surface, and the stiff dampers don't have enough compliance to keep the contact patches loaded properly.

The Bridgestone Potenza RE050A run-flats that came as original equipment are particularly notorious for this behavior. The Turanza T005s on your front are actually a better tyre in terms of comfort, but you've created a mismatch in characteristics between front and rear which could be contributing to unpredictable handling transitions. The RE050As are also an older design now and while they're still available, they were designed primarily for dry grip rather than compliance or wet weather performance.

Regarding your specific question about switching to non-run-flat tyres, this is probably the single most effective change you can make and it's a modification that many E89 owners undertake specifically to address the issues you're describing. Here's what you need to know:

The benefits of switching to conventional tyres include significantly improved ride quality, better absorption of surface irregularities, more progressive and predictable handling at the limit, reduced tramlining on rutted roads, lower road noise, and generally improved wet weather grip from modern tyre designs. The compliance of a conventional tyre sidewall acts as an additional suspension component that the run-flat design simply cannot provide.

The drawbacks are that you lose the run-flat capability obviously, you'll need to carry a mobility kit or spare wheel solution, there may be a slight increase in sidewall flex during hard cornering though this is minimal with modern high-performance tyres, and you'll need to be more vigilant about checking tyre pressures as you won't have the run-flat safety margin.

For the E89 35is specifically, I would recommend looking at these tyre options. For the front 225/40R18, consider the Michelin Pilot Sport 4S which offers excellent grip and progressive handling with good compliance, the Continental SportContact 7 which is the newer design with outstanding wet performance, or the Goodyear Eagle F1 Asymmetric 6 which provides a good balance of performance and comfort. For the rear 255/35R18, use the same model as the front to maintain consistent characteristics.

The key is to choose a modern high-performance summer tyre if you're driving primarily in dry conditions or a premium ultra-high-performance all-season tyre if you need better cold and wet weather capability. Avoid the temptation to go for a comfort-oriented tyre as the 35is chassis will feel vague and imprecise with too soft a compound or sidewall construction.

Some critical points about making this change successfully include the following. First, replace all four tyres at the same time with the same model to ensure consistent behavior. Second, have the wheels rebalanced and the alignment checked after fitting as the different tyre construction may highlight any minor alignment issues that the stiff run-flats were masking. Third, you'll need to disable the tyre pressure monitoring system warning for run-flats in the vehicle coding as the TPMS will otherwise throw a warning about not having run-flats fitted. Fourth, consider adding a tyre inflation kit to the boot or if you have space, a space-saver spare wheel.

Now regarding the suspension itself, even though your BMW dealer says the geometry is correct, there are several things worth investigating further. The E89 uses rubber bushings in the control arms and these do deteriorate over time, particularly the rear trailing arm bushings and the front lower control arm bushings. These can be within specification but still worn enough to allow excessive movement under load. On undulating surfaces, worn bushings allow the suspension geometry to shift unpredictably which creates exactly the unsett
 
Wow, thank you so much for all the information. Lots to digest. I’ll work through it and am sure I’ll have a few questions if that’s ok?

I’ll certainly move forward with changing tyres as a priority. One immediate question, you mention in your first replay that getting the non-run flat tyres “in the proper staggered sizes” is important. Does this just mean getting the tyres in the same sizes as the current run-flats or do I need to change sizes in some way when changing to non run-flats?

I’ve been reading some of your posts about the development of your car - it looks amazing!

Thanks again.
 
He means that the rears are a different size to the fronts.
Both are 19 inch wheels but on mine I have 235 at the front and 255 on the rear.
Yours will be bigger being the 35is.

Oh and Pete is spot on with changing to non-runflats, the difference is huge! 🙂
 
Erudite-Idiot said:
He means that the rears are a different size to the fronts.
Both are 19 inch wheels but on mine I have 235 at the front and 255 on the rear.
Yours will be bigger being the 35is.

Oh and Pete is spot on with changing to non-runflats, the difference is huge! 🙂
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I’ve got 225 front and 255 rear on my 35is 🤔
Please tell me these aren’t the wrong size
 
I have a 2009 e89 30i ES, with the 17inch alloys (225/45). I find the steering terrifying sometimes, undulating, uneveven roads with camber it feels all over the place. Even on the motorway it occasionaly feels like the steering is doing what it wants (I had to move into the far left lane the other day and slow to 50 as I thought something had broken). I have Bridgestone runflats on the front only. In sport mode it is better, but still feels weird sometimes. I had an e85 3.0i for a few months and tbh this felt the same. It's the stupid electric steering rack. My 2004 Mk1 TT, hydraulic rack, with Bilstein shocks and Eibach springs feels a million time more planted(alebit slower), and handles better. This is kind of given with the handling as it is a proper premium setup, but the stability and steering feel is just solid.

The first thing I'm going to do (when dealer warranty runs out/CRA) is change the front RFTs to non run flats, I know this will help considerably. The second thing when I have the funds in a few months is change out the suspension to the Bilstin B12 Pro+ kit. I have this on the TT and its fantastic over stock, TBH it probably spoils and taints my judgment on any other car I drive.

I do love driving the e89, took it out today, sun shining, with the roof down for the first time(while moving), and it was an absolute pleasure, I love it. But the sterering feel somtimes is just weird and off putting.
 
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dyonisis said:
I have a 2009 e89 30i ES, with the 17inch alloys (225/45). I find the steering terrifying sometimes, undulating, uneveven roads with camber it feels all over the place. Even on the motorway it occasionaly feels like the steering is doing what it wants (I had to move into the far left lane the other day and slow to 50 as I thought something had broken). I have Bridgestone runflats on the front only. In sport mode it is better, but still feels weird sometimes. I had an e85 3.0i for a few months and tbh this felt the same. It's the stupid electric steering rack. My 2004 Mk1 TT, hydraulic rack, with Bilstein shocks and Eibach springs feels a million time more planted(alebit slower), and handles better. This is kind of given with the handling as it is a proper premium setup, but the stability and steering feel is just solid.

The first thing I'm going to do (when dealer warranty runs out/CRA) is change the front RFTs to non run flats, I know this will help considerably. The second thing when I have the funds in a few months is change out the suspension to the Bilstin B12 Pro+ kit. I have this on the TT and its fantastic over stock, TBH it probably spoils and taints my judgment on any other car I drive.

I do love driving the e89, took it out today, sun shining, with the roof down for the first time(while moving), and it was an absolute pleasure, I love it. But the sterering feel somtimes is just weird and off putting.
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The electric steering rack on the E89 is fundamentally different to the E85 version, different ball game ..assuming its working OK..fault code reader is a good check..its a REALLY REALLY BAD idea to run a mixture of run flats and non run flats...personally I'd go with bilsstein b6 with stock springs ro b8 with msport springs..unless Essex is as smooth as a baby's bottom!
 
B21 said:
The electric steering rack on the E89 is fundamentally different to the E85 version, different ball game ..assuming its working OK..fault code reader is a good check..its a REALLY REALLY BAD idea to run a mixture of run flats and non run flats...personally I'd go with bilsstein b6 with stock springs ro b8 with msport springs..unless Essex is as smooth as a baby's bottom!
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Thanks @B21 I will be replacing the front RFT's as soon as I can. I'm still under the Consumer Rights Act, 6 months thing at the moment as I bought from a dealer so dont want to spend or change anything that is a big expensive change just in case.

I have Protool, no errors are logged.

I mentioned the B12 kit as thats what I have on the TT, I will look into the b8 in a few months. I would rather struts and springs replaced. Thank you
:)


EDIT> @B21 The B12 Pro Kit is the B8's with eibach springs - https://www.bilsteinsuspensionstore.co.uk/products/46-181268

I have this on my TT.
 
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dyonisis said:
Thanks @B21 I will be replacing the front RFT's as soon as I can. I'm still under the Consumer Rights Act, 6 months thing at the moment as I bought from a dealer so dont want to spend or change anything that is a big expensive change just in case.

I mentioned the B12 kit as thats what I have on the TT, I will look into the b8 in a few months. I would rather struts and springs replaced. Thank you :)
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All noted..IMHO new standard rate or msport rate springs offer a better ride than the eibachs..but..if you're in the 'yoof' segment that priortise 'looks' over function that's your call!-:)

Just wonder what sort of dealer sells a car with a less than appropriate tyre aet up...
 
B21 said:
All noted..IMHO new standard rate or msport rate springs offer a better ride than the eibachs..but..if you're in the 'yoof' segment that priortise 'looks' over function that's your call!-:)

Just wonder what sort of dealer sells a car with a less than appropriate tyre aet up...
Click to expand...

I'm 53 so not really a 'yoof', though I still feel like one at times :) This BMW stuff is all new to me, you can get the Bilsteins with msport rated springs, so I will look into that, though the b12p+ kit I have on the TT only lowers around 10mm, it isn't slammed in any way shape or form and feels glorious, infact I chose it because it wasn't coilovers or wheel arch rubby (See attached pic). I'm learning, it has been steep the last two months. Roof motors, hall sensors, microswitches, boot vents, rear light gaskets, Protool, ista, stripping boot lining, replacing salmon relays. Water, oh so much water, not as much as some, but its always there!. Gummi Phledge (which tbh I have used on the TT so this is at least not new). Thankfully, apart from some leakage, which I hope I have now sorted, just waiting for chassis rail drainage to finally get gone. The car is absolutely gorgeous! And to add, I havent actually had any issues with the car at all. Everything has always worked since I bought it. These are either preventitive maintenance, or maybe, the leak stuff, I'm sure the dealer would not have noticed (It was inside their unit) as its really not that bad compared to some I have seen on here.

As for the tyres, would they notice? they are all pretty new, with the rears being brand new Khomo Ecstas. Is it bad having RFTs on the front and not on the back? I wouldnt know that? I had to double check the fronts had the RFT marking a week after I bought the car. I would see same axle good branded new and nearly new tyres and think, yup all good. I thought that myself, and still do. apart from not liking RFT's as they are like concrete.
 

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Most frustrating car i ever owned regards handling.
Certainly doesn't like uneven surfaces.
Drive to work country lane at speed i feel like a rally driver.
Same road in my Berlingo it doesn't even notice the uneven surface.
Go a bit too quick in Zed gives the occasional scare on bends.
 
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