[ArcticFormula]

So with my new car had an opportunity to test the X-Drive in the rain. It was good and fine, but like any car not immune to hydroplane. So as any driver, one needs to be cognizant of the hydroplane. End of day, was quite pleased on how the summer tires which came with car did in the rain. Cranked it safely to 95mph at times generally cruise at 80 and car was very stable I'd say 110+ x-drive rain or maybe 120+rain with no pooling water would be just fine for this car. Not advocating same, just an observation.

[overcoil]

Read and heard a few times that at high speed on the lambo Miura the front got so light you could turn the front wheels left to right and the car would track straight.
If you search YouTube you should be able to find videos of hydroplaning testing where the car track straight but you can turn the wheel left and right.

This video is close but not the crazy amount of lift I’ve seen in some test

[dradernh]

Originally Posted by ScottSinger

This video...

...was shot at Palmer Motorsports Park, a track which, unlike tracks with wider pavement and plenty of runoff room with no fixed objects in sight, is no place to practice car control - wet or dry.

I doubt he was hydroplaning. My experience is that playing with the steering wheel while hydroplaning has no effect upon the direction the car is going (i.e., that's the definition of hydroplaning). Nevertheless, the driver did well to keep the car on the track.

[CP911]

AWD is good for accelerating quickly in slick conditions. Nothing more. Adds weight, complication, and cost. Does not turn or stop any better than RWD. Some claim AWD will "pull you out of a corner" better, but that's only after you enter the turn slower or to make up for plowing understeer from the additional weight towards the front of the car. Unless one is a rally driver or after stop light victories in the rain, I'm not sure I understand the obsession with AWD cars. I had a '16 WRX for a year and a half. Do not miss the poor handling and inability to rotate the car with throttle input.

[Sportstick]

Originally Posted by CP911

AWD is good for accelerating quickly in slick conditions. Nothing more. Adds weight, complication, and cost. Does not turn or stop any better than RWD. Some claim AWD will "pull you out of a corner" better, but that's only after you enter the turn slower or to make up for plowing understeer from the additional weight towards the front of the car. Unless one is a rally driver or after stop light victories in the rain, I'm not sure I understand the obsession with AWD cars. I had a '16 WRX for a year and a half. Do not miss the poor handling and inability to rotate the car with throttle input.

I agree with this assessment. Also, the conventional approximation formula for determining the top end of pooling water speed before hydroplaining is the square root of the tire pressure x 10, e.g., square root of 40 psi is about 6.3 x 10 = roughly 63mph. This is measure of downward force to counteract the tendency to ride up on top of the water film surface. It is a "rule of thumb" and doesn't account for variations in road surface (grooving) nor individual tire capability differences.

I don't see how on a truly water covered surface one can drive safely any tire without hydroplaning at 100mph unless tires are at unreasonably high tire pressures. (Notwithstanding the issue of driving 100mph on any public road, even in the best conditions.)

[BenDiem]

In its simplist form: Tires, tires, tires. This is the main key!

A good set of specific tires (bearing in mind the weather & road conditions) will suffice in most cases...

Due to the fact I live in the Midwest, with varying temp changes & inclement weather, I would always choose AWD & a good set of A/S tires, all day long, but that's just me...

If I lived where the temps barely drop below 40 degrees Fahrenheit, I'd never consider AWD, but again, that's just my opinion.

If I only owned one car, and lived in the Midwest, I'd pick a vehicle w/AWD, due to reasons outlined, supra...

Cheers/B

[DaleHeinz]

Originally Posted by ArcticFormula

So with my new car had an opportunity to test the X-Drive in the rain. It was good and fine, but like any car not immune to hydroplane. So as any driver, one needs to be cognizant of the hydroplane. End of day, was quite pleased on how the summer tires which came with car did in the rain. Cranked it safely to 95mph at times generally cruise at 80 and car was very stable I'd say 110+ x-drive rain or maybe 120+rain with no pooling water would be just fine for this car. Not advocating same, just an observation.

Just like others have said. Tires is where it's at. 2 or AWD makes no difference at cruising speeds, only acceleration in slick conditions.

The run-flats that came on my M240Xi were shit in the rain at higher speeds. When I switched to Pilot Sport A/S 3+, the car grew some balls in slick conditions. Even with the tires at half life, their still much better than the crap OEM run-flats in the rain. Snow and dry are no comparison as well.

Sure, the AWD will launch much better in the rain, snow, ice, and even the dry, but what it won't do is turn, slow, cruise, or stop better. That's all tires.

[morphomeman]

What does CA man consider to be rain?
My experience is that a shower in SoCa gets the reaction that a hurricane gets on the east coast. I can't imagine driving at those speeds in serious rain in any vehicle. The lack of visibility compounded with the likelihood of hydroplaning strike me as a sure death sentence.
Also, DO NOT EVERY USE CRUISE CONTROL IN THE RAIN!

[swunder]

Automakers need to make it clear to people that AWD doesn't have anything to do with what the OP is talking about. I have a feeling a ton of people think this way...

Don't go 95 in the rain because you have AWD.

[XutvJet]

Originally Posted by CP911

AWD is good for accelerating quickly in slick conditions. Nothing more. Adds weight, complication, and cost. Does not turn or stop any better than RWD. Some claim AWD will "pull you out of a corner" better, but that's only after you enter the turn slower or to make up for plowing understeer from the additional weight towards the front of the car. Unless one is a rally driver or after stop light victories in the rain, I'm not sure I understand the obsession with AWD cars. I had a '16 WRX for a year and a half. Do not miss the poor handling and inability to rotate the car with throttle input.

Amen to all of that. With a stellar suspension, tire, and alignment setup, my 2012 WRX would still plow like a FWD when pushed 80%+. It did make up for driving skill in slow, tight turns though. The thought of an x-drive M235/240 for rally racing sounds awesome though!

Lastly, why in the world would someone want to go so fast in the rain on a public road or non-professional sanctioned race event If there is any standing water, one should dial back speed. There are enough obstacles to contend with on the street in the dry. Why push your luck in the wet?

[TajoMan]

Originally Posted by CP911

AWD is good for accelerating quickly in slick conditions. Nothing more. Adds weight, complication, and cost. Does not turn or stop any better than RWD. Some claim AWD will "pull you out of a corner" better, but that's only after you enter the turn slower or to make up for plowing understeer from the additional weight towards the front of the car. Unless one is a rally driver or after stop light victories in the rain, I'm not sure I understand the obsession with AWD cars. I had a '16 WRX for a year and a half. Do not miss the poor handling and inability to rotate the car with throttle input.

To be honest, M240 xdrive is not as bad as WRX in terms of understeer.
It actually drives fairly close to RWD.
(Randy Pobst understeer/oversteer scale from -10 to 10, it may be 1 to 1.5 vs -0.5 for M235 RWD he drove in Motor Trend review )

Also, one of the instructor from a BMW driving event mentioned that Xdrive car will be faster than RWD by about half second around the AutoX course they used. (Although it was 540)

xdrive does have it's advantage for quick acceleration. (start line, out of the corner...etc)

However, everything else will be on tire, not the drive train.
(especially like hydroplaning, pretty much 100% on tire)
I don't even understand why OP even mentioned hydroplaning and xdrive together.

[XutvJet]

BMW's xdrive system is one of the least "performance" focused AWD systems out there. The AWD systems used in the higher end Audi, Nissan, and Subaru win that game. Xdrive is one size fits all in BMW cars. Compared to those systems, it's pretty slow to react plus no limited slips diffs on the xdrive either.

[P2]

Originally Posted by Sportstick

I agree with this assessment. Also, the conventional approximation formula for determining the top end of pooling water speed before hydroplaining is the square root of the tire pressure x 10, e.g., square root of 40 psi is about 6.3 x 10 = roughly 63mph. This is measure of downward force to counteract the tendency to ride up on top of the water film surface. It is a "rule of thumb" and doesn't account for variations in road surface (grooving) nor individual tire capability differences.

I don't see how on a truly water covered surface one can drive safely any tire without hydroplaning at 100mph unless tires are at unreasonably high tire pressures. (Notwithstanding the issue of driving 100mph on any public road, even in the best conditions.)

I know you said "rule of thumb". But I'm not so sure 9x √tire pressure is really applicable to auto tires with modern tread that's engineered evacuate water. That formula assumes 1/10 inch of water and aircraft tires that at most, have some longitudinal groves. Even then, that is the speed when dynamic hydroplaning may begin. If it were a hard limit, thousands of jets would have departed the paved surface today alone 😳. Your point is well taken however, that the faster you go over water, the more likely one is to hydroplane. I think that was your point. 😀.

[Sportstick]

Originally Posted by P2

I know you said "rule of thumb". But I'm not so sure 9x √tire pressure is really applicable to auto tires with modern tread that's engineered evacuate water. That formula assumes 1/10 inch of water and aircraft tires that at most, have some longitudinal groves. Even then, that is the speed when dynamic hydroplaning may begin. If it were a hard limit, thousands of jets would have departed the paved surface today alone 😳. Your point is well taken however, that the faster you go over water, the more likely one is to hydroplane. I think that was your point. 😀.

Well, it was 10x, not 9...but seriously, you may be right about current state of the art tires doing better. I learned this from a chassis engineer at the car company where I used to work, and that was in the 90s. Given that the formula is a rough measure of downforce, based on the psi pushing down against the ground, the mass of an aircraft would seem to raise the threshhold dramatically versus an automobile in any event. I believe most agree about hydroplaning and speed, and that approaching triple digits in the rain is inviting disaster.

[TajoMan]

Originally Posted by XutvJet

BMW's xdrive system is one of the least "performance" focused AWD systems out there. The AWD systems used in the higher end Audi, Nissan, and Subaru win that game. Xdrive is one size fits all in BMW cars. Compared to those systems, it's pretty slow to react plus no limited slips diffs on the xdrive either.

It's slow to engage and that's why it's very much like rwd.

I do wish that I have LSD though. That will be a killer.

[ArcticFormula]

I appreciate everyone's thoughts, and I came here to learn about the car as well. So all input is appreciated. As someone who has been on various car message boards for over 20 years nothing shocking with what I consider some of the admonishment type posts. Point taken. I've owned powerful RWD cars in the past, and currently have a 2011 vette with 4S tires. End of day, everyone has opinions and such, some are purists, and like the option of widowmaker oversteer on tap and that, and it's all good. Realistically, to chastise 95 mph straightline motoring in a heavy rain seems a bit of a disservice to the capabilities of the car (my opinion, and I never said it was a public road, but that is neither here nor there). Again, everyone has thoughts, and I respect that. Equally interesting is how some folks are quick to throw the BMW AWD technology under the bus. Alas, I don't know yet. Had a 2010 Audi S5 which I put about 60K on and sold for $ for this car, which is not even out of break in, but seems to possess similar properties and capability. So what do some folks say, Cheers .

[CP911]

Originally Posted by ArcticFormula

I appreciate everyone's thoughts, and I came here to learn about the car as well. So all input is appreciated. As someone who has been on various car message boards for over 20 years nothing shocking with what I consider some of the admonishment type posts. Point taken. I've owned powerful RWD cars in the past, and currently have a 2011 vette with 4S tires. End of day, everyone has opinions and such, some are purists, and like the option of widowmaker oversteer on tap and that, and it's all good. Realistically, to chastise 95 mph straightline motoring in a heavy rain seems a bit of a disservice to the capabilities of the car (my opinion, and I never said it was a public road, but that is neither here nor there). Again, everyone has thoughts, and I respect that. Equally interesting is how some folks are quick to throw the BMW AWD technology under the bus. Alas, I don't know yet. Had a 2010 Audi S5 which I put about 60K on and sold for $ for this car, which is not even out of break in, but seems to possess similar properties and capability. So what do some folks say, Cheers .

I wouldn't sweat the comments too much. Sounds like you are open-minded enough, so gotta just take everything with a grain of salt. xDrive may not be as RWD-biased as some of the highest performance AWD models from the other brands, but I do believe it is a better AWD system. I am too lazy to dig it up, but I've posted some YouTube videos elsewhere that explain the differences between xDrive and Quattro. Turns out Audi's famed Quattro AWD is nothing more than a marketing term at this point. They are now using electronically-controlled clutches to move torque to different wheels, just like BMW has been doing from the start.

I probably should have clarified, but my comments above were in regards to how AWD affects overall handling capabilities and characteristics of a traditional sports car or sports coupe, which is the type of car that one usually buys for thrills and smiles. This does not mean AWD doesn't have a place in motoring. The reality is that someone who commutes daily in year-round or long-season wet or winter conditions would be foolish to not choose an AWD system. No one should be taking hard corners or enjoying the benefits of RWD balance in those conditions... AWD also makes sense in super high HP cars where there simply isn't enough rear wheel grip to make use of all the power even in dry conditions. Think F90 M5, Porsche 911 Turbo, etc.

[aerobod]

The Quattro system on the transverse engined Audis in the A3, S3, RS3 and TTRS use a Haldex centre clutch system that can only send a maximum of 50% of power to the rear wheels, one of the reasons it is optional to have wider front tyres than rear tyres on the RS3 to quell understeer. The BMW system is a lot more flexible in power distribution than the Audi Haldex system.

[XutvJet]

There are different types of Audi AWD systems as there are Subaru and some a better than others. BMW's Xdrive system isn't has good as the best systems from Audi and Subaru. If BMW incorporated at least a rear LSD with the Xdrive M235/240 and forced even more RWD bias through better management, it could be a pretty good performance AWD system on a 2 series.

The current gen M5's "M"-xdrive is pretty clever. Though I still think the car should be RWD only, I can see why BMW did it as most drivers aren't good and would have trouble keeping such power on the road only driving two wheels. The M x-drive system uses the trick eLSD and has a ton of RWD bias. Better yet, it can be shut off and be full on RWD.

With that said, an RWD M235/240 is entirely fine in the wet and snow with the proper tires. I've been doing it for 3 years in the Midwest winters on performance winter tires and even those are overkill. I'm going back to Conti DWS06s.

[msej449]

It's often forgotten, in the discussions over winter tyres for snow, that they are as much engineered to reduce aquaplaning as they are for running in cold conditions. In a typically wet British winter, the wet-weather handling on my M235i is noticeably improved when I switch to my winters (Pirelli Winter Sottozero S3). And there have been occasions in midsummer thunderstorms when I'd much rather be on my winters. As you can see, the winters simply have much more water-carrying and dispersion capacity, and note how the tread pattern allows drainage to occur both sides of the contact patch on the winters (right):

[TajoMan]

Originally Posted by XutvJet

There are different types of Audi AWD systems as there are Subaru and some a better than others.

I am not sure what Audi or Subaru system you are referring, but they are just as good/bad as the BMW's.

Subaru still uses Viscous coupling center differential and open front and rear differential for WRX.

Only WRX sti has LSD in front and rear as well as the adjustable center diff.

Audi's quattro recently added torque vectoring rear diff for their S and RS models as an option.

Their regular AWD is not any better than BMW's.

One of the most advanced AWD is from Acura. SH-awd was the first torque vectoring diff. Then Evo copied it and called 'active yaw control'. lol

[omera60]

Originally Posted by P2

I know you said "rule of thumb". But I'm not so sure 9x √tire pressure is really applicable to auto tires with modern tread that's engineered evacuate water. That formula assumes 1/10 inch of water and aircraft tires that at most, have some longitudinal groves. Even then, that is the speed when dynamic hydroplaning may begin. If it were a hard limit, thousands of jets would have departed the paved surface today alone 😳. Your point is well taken however, that the faster you go over water, the more likely one is to hydroplane. I think that was your point. 😀.

That’s why when landing on contaminated runways PIC will intentionally slam the aircraft to disperse any standing water thus making perfect contact between the tire and runway surface. Safety first comfort later. There are even limits on how much of standing water you can land on as it can effect the performance of the engine parallel to the water it ingests and brakes efficiency (AvGeek here)

Originally Posted by CP911

I wouldn't sweat the comments too much. Sounds like you are open-minded enough, so gotta just take everything with a grain of salt. xDrive may not be as RWD-biased as some of the highest performance AWD models from the other brands, but I do believe it is a better AWD system. I am too lazy to dig it up, but I've posted some YouTube videos elsewhere that explain the differences between xDrive and Quattro. Turns out Audi's famed Quattro AWD is nothing more than a marketing term at this point. They are now using electronically-controlled clutches to move torque to different wheels, just like BMW has been doing from the start.

I probably should have clarified, but my comments above were in regards to how AWD affects overall handling capabilities and characteristics of a traditional sports car or sports coupe, which is the type of car that one usually buys for thrills and smiles. This does not mean AWD doesn't have a place in motoring. The reality is that someone who commutes daily in year-round or long-season wet or winter conditions would be foolish to not choose an AWD system. No one should be taking hard corners or enjoying the benefits of RWD balance in those conditions... AWD also makes sense in super high HP cars where there simply isn't enough rear wheel grip to make use of all the power even in dry conditions. Think F90 M5, Porsche 911 Turbo, etc.

You mean this one;