[Wills2]

First thing you should do in weather conditions like that is take full control of the car and reduce speed and increase the distance to the car in front, I'm actually quite shocked someone would just continue on cruise control regardless.

[Sportstick]

Originally Posted by GRB60

Not trying to escalate this, but you attached a lot of information, none of which seemed to support your assertion.
Keeping in mind that most car owners don't spend great amounts of time reading government sites (or even their owner's manual), it seems much more likely that they'd put the RECOMMENDED cold pressures on the door, where it's easily referred to.

I don't own a BMW (yet) but the manual on my 2020 RAM 1500 says:
"The proper cold tire pressure is listed on the driver's side B-pillar or rear edge of the driver's side door."

It is not that much. It is one rule and it is directly on point. If you read it, you will find the context about maximum cold pressures unless the GVWR rating is lower. The label pressures are not OEM recommended pressures, although, as noted, they may coincide with those in the manual. They are certification values for those maximums for vehicles at 10,000lbs GVWR or less.

Consider why the label even exists (referred to as a "placard" in the rule). The label adds cost and complexity to every vehicle and assembly plant. It's another step for the operator on the line. An OEM would be delighted not to have to have this additional part number, especially as recommended tire pressures are addressed in owner manuals. If a wrong label was applied from the different ones with different air pressures, it would create a non-compliance leading to a recall. I know this as I was part of the industry response to the advent of the air bag labels on visors way back when. The label only exists because the FMVSS reg requires it. As such, the content of the label is that which NHTSA requires the OEM to post for certification for safety in a maximum load condition, not some set of numbers the OEM thinks performs best.

[iulianm]

I also found that my 330i xDrive with 19" all-seasons tires is dealing worse on standing water during heavier rain (I live in Seattle) than my other car with 18" all-seasons; I got scared once when it started to move under me as I was driving together with traffic under the speed limit (same as I was used with my other car) and the car in front of me didn't seem to experience anything.
Maybe the RF tires that my car came are not good on wet; they however have a tread-wear pretty high which means they would last more and I'll have to deal with them for longer (or spend $$$ and replace ).

My 330i xDrive came with: 225/40/R19 Bridgestone Turanza LS100A A/S with "Treadwear 560, Traction A and Temperature A".
The other car (also AWD) has: 215/45/R18 with Toyo Proxes A/S with "Treadwear 300, Traction B and Temperature A".


I use 35PSI/42PSI on my 330i xDrive as per recommended on sticker and 36PSI/36PSI on my Mazda3 AWD as per sticker.

[Sportstick]

Originally Posted by iulianm

I also found that my 330i xDrive with 19" all-seasons tires is dealing worse on standing water during heavier rain (I live in Seattle) than my other car with 18" all-seasons; I got scared once when it started to move under me as I was driving together with traffic under the speed limit (same as I was used with my other car) and the car in front of me didn't seem to experience anything.
Maybe the RF tires that my car came are not good on wet; they however have a tread-wear pretty high which means I will keep them for longer.

My 330i xDrive came with: 225/40/R19 Bridgestone Turanza A/S with "Treadwear 560, Traction A and Temperature A".
The other car (also AWD) has: 215/45/R18 with Toyo Proxes A/S with "Treadwear 300, Traction B and Temperature A".


I use 35PSI/42PSI on my 330i xDrive as per recommended on sticker and 36PSI/36PSI on my Mazda3 AWD as per sticker.

There may be differences simply in the tread efficiency to channel water from the Toyos versus the Bridgestones. But, it's not the run flat and not so much the 18" vs 19" as the 225 vs 215 width increase. You are familiar with how snowshoes distribute your weight so you don't sink into snow but walk on top? Wider tires do the same on snow or water. When buying snow tires, the advice is as narrow as possible to fit. You can't change tires every time it rains, but be aware that wider creates more likelihood of riding over the water, so slower speeds are prudent.

[PrinceM340]

I have hydroplaned with brand new (under 500 miles) Michelin Sport A/S 3 tires

I don't think it's a G20 issue. I think speed + huge puddle is the issue lol

[TiMSport]

Yes, let's be clear here. There are no tires completely immune to hydroplaning when the conditions are severe. The only thing you can do is slow down.

[HighlandPete]

Originally Posted by TiMSport

Yes, let's be clear here. There are no tires completely immune to hydroplaning when the conditions are severe. The only thing you can do is slow down.

We also need to note that the speeds often mentioned for typical hydroplaning, refer to new tires with full tread.

Tires only have two ways to prevent hydroplaning, storing the water in the tread/grooves and water dispersal. The shape of the footprint can make a little difference. Michelin indicate the rounded footprint is more efficient in water dispersal. Higher pressures can assist by helping with the wave front.

I know from experience, that when we are in the mid range of tread wear, I find my winter tires are more efficient in coping with standing water than the summer set. Primarily due to the ability to store and disperse more water.

[TristarL10]

When I'm driving in "heavy rain", mine automatically turns itself off and warns me to take over manually.

Once the roadway is obscured by heavy rain, the radar and camera sensors recognize this issue.

When the anti skid senses "wheel slip" it also has input into the issue.

[alpinewhite3]

Originally Posted by -EndOfAnEra-

Hello everyone,

It's been a great year with my car even if its been horrid everywhere else! So it was bound to not last forever. I have a problem that's totally shot my confidence in my car and I'm not sure if its me, the car, or just the freak weather.

The last three days in Cleveland we've seen some REALLY heavy rain. The kind that makes it almost impossible to see on the highway. I discovered on my morning commute two days ago that adaptive cruise would make my car hydroplane, lightly and then more severely. I noted an immediate improvement when I turned it off and reasoned that its attempt to constantly hit a specific speed (usually about 65 to 69 MPH) was overwhelming traction with so much water. Turning it off and relying on engine braking by letting the foot off the accelerator improved and I figured that was that.

Then today, same kind of very heavy rain on my commute home. I quickly turned off adaptive and had less problems, but the car still wanted to hydroplane at much lower speeds than I expected.

I checked my tire tread depth and it seems fine:

Left Front = 4.44 mm (between 5/32 and 6/32 of an inch)
Right Front = 4.41 mm
Left Rear = 5.4 mm (between 6/32 and 7/32 of an inch)
Right Rear = 5.08 mm

These are the tires I've had with the car when I picked it up in April 2020. I didn't drive the car much during the pandemic and swapped to winters in October of 2020 until April of 2021. My rule of thumb has always been to seek replacements for my summers when they hit 3 mm on an axle, or 4/32 of an inch. I'm closer than I'd expect but quite surprised at the life I've gotten from them.

Pressures are 42 PSI front, 44 PSI rear. Mind you, I had a devil of a time finding the "real" pressures for an American RWD M340i on staggered 792Ms so anyone has input please speak up.

My previous car, a RWD E90 335i 6MT never had any issues with hydroplaning, even on the same Michelin PS4S tires with less tread depth (less than 3/32" - never going that low again ). I'm hoping to debunk the variables here and get to the bottom of this issue. Anyone skilled in the science behind hydroplaning, please let me know your thoughts.

1. New car is heavier than the old, any factor?

2. New car tire specs are front 225/40/R19, rear 255/35/R19, old car's were front 225/40/R18 and 255/35/R18, so nearly identical but with a slightly taller sidewall from the diameter change, any factor?

3. New car is 8AT, old car is 6MT. Generally I would cruise the old car in 6th but in inclement weather might downshift to 4th for better engine braking. In the M340i, I tend to run in manual 8th on clean highway and use sports auto S6 when I feel I may need more engine braking or better reactivity.

Appreciate any and all thoughts for me!

Your tire pressures are wayyyy too high. At those speeds the tires will be very slick as the contact patch is minimal at best. If youre running RWD, 35-36 front 37-38 have worked well for me in for best grip & sharp turn in. i bet you can get the tires to squeal pretty easily at those pressures.

[alpinewhite3]

Originally Posted by hockeymen14

Interesting. I did not know that was for full capacity rating. Makes sense though. I just got these tires a month or so ago and thought the pressure was a little low but what you're saying makes me think this is what the dealership intended. They were at 35psi. I like the feel better and performance at 38psi but maybe I am accelerating tread wear. How are we actually supposed to know what ideal tire pressure is? I knew enough from the OPs 44psi that it was too high but low 30s seem too low.

Input or sources from others?

Check how your tires are wearing. I was running 40 psi in the rear and realized it was over inflated by the constant squealing and confirmed via wear pattern.

[-EndOfAnEra-]

Thanks everyone, appointment is set for Monday for an alignment check.

For those thinking of me as a devil-may-care madman, I assure you my wife would have a good laugh at that!

Active cruise control will shut itself off if the rain is too heavy, it didn't do so those times. It did surprise me because I thought any traction loss would deactivate it!

Taking a role as a scientist, after the first time when I recognized the active CC was contributing to the issue, I stopped using it until the next time it rained.
I only turned it on again to test my hypothesis. I turned it off quickly.

I've not had crazy rain since those times but due to this experience I've begun using more downshifting and engine braking with just enough brakes to slow/stop in the hopes of improving brake and tire wear on my fronts. Eagerly looking forward to BMW giving me a yay or nay on any issues!

Thanks again!

One interesting wrinkle which I will get a pic of later. iDrive itself is telling me that my PSI should be in the 40s which is why I set it there. I also thought that sounded high as my old car was around 34 PSI front, 36 PSI rear but figured BMW knew something I didn't.

[HighlandPete]

Originally Posted by -EndOfAnEra-

One interesting wrinkle which I will get a pic of later. iDrive itself is telling me that my PSI should be in the 40s which is why I set it there. I also thought that sounded high as my old car was around 34 PSI front, 36 PSI rear but figured BMW knew something I didn't.

The cold setting pressures which are being debated and the warm working pressure the iDrive will be recommending, are two different things.

Many who argue the case for something like a 35psi cold setting pressure, will be running near to 40psi once warm and driving distance.

40+psi "working" pressure on a RWD BMW, is not at all uncommon on the rear axle.

[alpinewhite3]

Originally Posted by HighlandPete

The cold setting pressures which are being debated and the warm working pressure the iDrive will be recommending, are two different things.

Many who argue the case for something like a 35psi cold setting pressure, will be running near to 40psi once warm and driving distance.

40+psi "working" pressure on a RWD BMW, is not at all uncommon on the rear axle.

Sorry i should have clarified - my recommended pressures were hot running pressures-cold would be 33F35R.

The rear axle will increase more than the front when running hot. So i usually en up at 34-38 /35-38.


I never let it go over 40 now after seeing how my rear tires wore out down the middle after 10k mile.

And then dont forget - every season you have to adjust b/c of temperatures changes. 10 degree mean 1 psi change.

[HighlandPete]

Originally Posted by alpinewhite3

I never let it go over 40 now after seeing how my rear tires wore out down the middle after 10k mile.

Also remember middle wear is not always due to over inflation.

From Continental:

[Davg31]

If you take the time to read the instructions it is not recommended to use it in heavy rain, here in Europe on some roads it is even forbidden with loss of insurance in case of accident

[galaxiez2020]

Idk how you drove around with 44psi in the first place... That's just outrageously...dumb (to put it nicely). Thankfully you caught this before it became a bigger problem.

[rostrata]

Never never ever ever drive using CC in the rain. Ever. It does not know how to modulate and predict standing water and the direction that water may be traveling (or not) at a given moment.

Second... cars hydroplane. If it happens, drive slower until it stops.

[Wills2]

Originally Posted by rostrata

Never never ever ever drive using CC in the rain. Ever. It does not know how to modulate and predict standing water and the direction that water may be traveling (or not) at a given moment.

Second... cars hydroplane. If it happens, drive slower until it stops.

Agreed, those that allow the systems to continue to be engaged thinking that will be able to handle a given situation or hand over control in a timely manner to the driver are playing fast and loose with their safety and those of others, the ACC cannot "see" the road or the conditions and cannot anticipate what is about to happen.

Given that BMW still haven't managed to get rain sensing wipers to work properly yet, I'd rather back myself.

[Andy234]

Had a similar problem in X3, I've crashed it few months ago on highway due to ACC and hydroplaning. Had 225/60 R18 both in front and rear. Once you get the tire tread under half of so its starts to get pretty bad same aplies for tire width, thinner is better. But BMW cruise control really sucks in this case whether on snow or wet, way worse than on cars i had before....

[G30M]

the problem is the rear tires are too wide too low profile and that's the cause of the hydroplane

i have the same car and it hydroplanes at anything over 50mph

[Montaver]

I have driven my m340i in biblical rain to the point you can barely see the car infront of you, on 225 square run flats which are the worst tires you can get. At 55mph the car does not hydroplane and feels completely stable. Always drive to the conditions.

[HighlandPete]

Originally Posted by Montaver

Always drive to the conditions.

And to the condition of the tires.