Z4 handling on wet roads

bchmiel

New member
Quick summary:
In the rain, it feels like I'm loosing traction on all four wheels at speeds above 75 km/hr (45 mph). It only happens on uneven paved surfaces that have a slippery finish however I am surprised that it's happening at all. My tires are slightly worn but I think it might be something else about the Z4 that causes this. Has any one else experienced it? What are the causes?

The long version:
I bought a 2011 Z4 30i 2 months ago. Yesterday, I was driving on the highway at about 80 km/hr (50 mph) and the front wheels hydroplaned for a brief moment. It was quick enough that the car self corrected and there was no loss of control. The pavement was flat and there was a moderate amount of water building up on the road but nothing exceptional.

A few kilometers later at about 70 km/hr, it felt like all four wheels were hydroplaning for brief moments as I drove down the road. The movement was subtle but it was definitely the beginning of a situation where you might lose control. I slowed down to 60 km/hr and just took it easy the rest of the way home.

Today, it was raining again so I drove around trying to get the car to repeat what happened yesterday. The car felt solid on any of the wet surfaces I tried.

I did however drive on an uneven two lane road with pavement that looked slippery. Driving straight at 75 km/hr, I can feel the entire car start to come loose. All four wheels seem to lose grip and it's like the entire car starts floating a bit. I was in disbelief because I was going so slow. I drove this road up and down several times trying to understand what was happening and it was the same behavior every time. At any speed lower than 60 km/hr, the car is fine. Anything above that and it's like you're on ice.

It's not the dynamic stability control (DSC) because the car did the exact same thing when I shut it off (push and hold the traction control button for about 5 seconds and you'll see DSC off on the display), although the car seemed to do it less when it was off.

The tires are the original and the tread is low especially in the back but not bad enough that I would have predicted that I would lose grip in the rain at these speeds. I'll attach photos.

I should mention that the temperature is a little low, around 10 degrees C or 50 F. I checked the pressure in my tires two weeks ago and added air to the recommended pressure (38/44 PSI or something high).

Has anyone ever experienced this? Is this normal and what is the reason for it (tight suspension, wide tires)?
 
I don't know how to post a photo so I'm posting a link to my drop box folder:
https://www.dropbox.com/sh/q1mqw16h5smf2vk/AAAgVTzOljifH-0-INcStkoEa?dl=0
 
When I changed my tires on my previous Z4 the car was completely different in wet. Although the tires I changed from were not worn to the last check mark they were getting close. I changed all 4 since I had a puncture in one and decided that I might as well change all four in one go. No pulling on the steering when driving through puddles and felt much more secure. Having a look at your tires looks much like mine just before changing. I kept the tires type the same btw. In my case the factory fitted Bridgestone 050 RFT.
 
Maniac said:
10C, summer tyres? Low tread? I think you're on your way to an answer.

What Maniac said. RWD cars can be pretty sensitive to tyre pressures and tread levels. Even though the 3mm markers are the bare minimum, you should really change out before you get to this point. If they're the original tyres, they'll probably be quite hard now too (rubber looses it's grippyness as it gets older).

Does the Z4 have adjustable geometry? If so, it might be worth getting it checked - my old S2000 was super sensitive to geo changes.
 
Maniac said:
10C, summer tyres? Low tread? I think you're on your way to an answer.

This. As your tread depth decreases, your stopping distance and loss of traction in wet weather will increase.

How much tread do your tyres have left at their most worn points?

At 4mm tyres begin to lose their effectiveness in terms of wet braking/traction - this would be even more pronounced on smooth concrete/asphalt in wet weather.

Judging by the photos, your'e very close to the 1.6mm tread marker - it's probably time to change those tyres :D
 
The more I think about it and look at the photos of my tires, the more I realize they really are worn out. They are about 0.75 mm from the markers at the worst spot. Conclusion: I'm getting new tires. I'm still surprised I'd start hydroplaning at 75 km/hr but any way...now I know!

I do know that as tires wear and the tread depth decreases, so does their grip. After a drive, I can tell that the rubber just doesn't seem to have the stickiness they have when they're new.

I haven't checked to see what geometry is adjustable on the Z4. My car tends to go slightly to the right (on a very flat road). But it is very, very minor. When I get new tires, I will get the wheels aligned.

Thanks for the replies! I appreciate it.
 
Back
Top Bottom