[JustChris]

....

[Alice Coupe]

Originally Posted by TouringPleb

I'm confused..

If you think of the contact surface of sDrive and xDrive cars with the road, they are the same. If the tyres are the same they have the same grip to hold the car in place - consider them parked on a hill for example. But apply power to the wheels, only the xDrive can apply traction to all 4 wheels.

[HighlandPete]

Originally Posted by Tengocity

If it was my car I'd have replaced the tyres 10k miles ago, but as it's leased the lease company won't do it till it's below 2mm!

Lease companies can be a pain to deal with over tyres and safety. Should work with BMW's recommendation for changing tyres with less than 3mm tread.

I've the habit of looking at tyres when crossing car parks, so many cars (and that includes high performance cars) have such poor tread, often with the shoulders knocked off as well. I suspect quite a few are below the legal limit. I don't understand why folks allow their tyres to get like that. Often this is in winter, talk about increasing your risk of losing it in ordinary driving, let alone in adverse conditions.

[Wills2]

Originally Posted by TouringPleb

Aren't grip and traction the same thing?

No, as an example a 335d xdrive has more traction out of corner or if you like can apply more tractive force to the road due to all 4 wheels been driven, however a RWD car like an M4 will be able to corner with more G force due to it's superior mechanical grip, the xdrive's front end will have started to wash out well before the rear end of the m4 starts to go.

In the same way an awd drive car can use its traction to get going in low grip situations (snow as an example) but doesn't have anymore grip on the road when it comes to braking than a RWD car.

If we had a drag race from zero on a wet road 0-60-0 m3 vs 335 xdrive I guarantee you'd win in the xdrive but you wouldn't stop any quicker, you be able to gain more traction through the AWD system in the first phase, but you'd have no more grip under braking.

[teaston]

Of course Xdrive would make a difference in these conditions, the driver probably floored it and lost traction which would be far less likely to happen with 4WD!

[HighlandPete]

Interesting description from Michelin.

If there were no such thing as grip, cars just would not be able to move at all. The wheels would spin and the driver would not be able to budge the vehicle. Even on a straight road and at steady speed, there is no alternative to grip. This is because a moving vehicle has to deal with natural forces, such as the banking, the slope or the unevenness of the road, or rolling resistance, which are constantly trying to slow the vehicle down or push it off its path. However it is only during cornering or braking that a driver or passenger is really aware of grip, because the vehicle has to be steered or speed has to be reduced without skidding, even on a wet road. In all circumstances, grip and safety go together. As the only contact point between the vehicle and the road, the tyre ensures two fundamental functions. It gives the vehicle its directional stability, which the driver needs to steer it. The tyre acts as a transmission component for brake and drive torque.

The conclusion, as there is no braking without grip, there is no traction without grip. Traction (drive torque) is a 'product' available due to grip.

Grip is also shared.... again from Michelin.

However, grip is involved mainly in two types of situation: when we alter the vehicle’s speed (deceleration - acceleration) and when we modify its direction (cornering). These two situations involve the two components of grip: longitudinal grip and transversal grip.

Conclusion: xDrive has no more grip than sDrive, either can only use what grip is available. We can't have the best of both worlds, it is shared between longitudinal and transversal grip, which are often in competition.

[HighlandPete]

Originally Posted by teaston

Of course Xdrive would make a difference in these conditions, the driver probably floored it and lost traction which would be far less likely to happen with 4WD!

Yes, the difference is how the grip is shared between the tyres. RWD can overwhelm the grip available from the rear tyres. Not enough grip to cope with high longitudinal forces, nothing left for lateral/transversal grip.

[Soul_Glo]

In the snow yes it helps. Anyhow, driver error.. misjudgment of speed and braking... driving like it is dry weather.. tyres.. you name it. Looks like he was just being a bampot.

[admg]

Tbh I'm not convinced xDrive would help there and I have a 320i xdrive. I've went round a roundabouts at not overwhelming speed before and skidded. From what I understand tho, thats because I have the dodgy se suspension and need to get the acs springs

A lot of the time I wish I'd skipped xdrive, saved up another grand or so and got a 330i sdrive instead.

[Tengocity]

Having now seen the video I'd point out that the accident happens right at where the traffic from the left joins on, which causes the traffic to slow down there, so most likely scenario is that a momentary loss of concentration whilst going a little too fast meant a loss of control under hard braking. Nothing to do with xdrive would have helped there.

[creepy coupe]

I don't think 4wd is a must have . But it does put two more driven wheels on the road.

Example would be in slippery conditions you avoid excessive braking pressure and would change down a gear to help the car slow. With 4WD you have four wheels taking the transmitted resistance through the drive train. This will bring you to a stop more quickly and with less brake pressure.

The opposite of this would be to knock the car into neutral and then try and stop. You would be completely reliant on the brakes.

[r1cey]

Originally Posted by KCH1984

+1

As I drive that motorway regularly myself I would say 100% that in those conditions my 330d xDrive felt far more secure than my M135i ever did.

I get the point about lateral grip but take 2 330d's for example, in the RWD car all the power and torque is going through the back axle whereas in the AWD car it is being spread across 4 driven wheels. Therefore, surely the chances of overwhelming the available grip from the tyres (as less torque is going through any one wheel) is less overall? It would seem to me the type of accident mentioned is a result of the rear tyres being overwhelmed in poor conditions resulting in a loss of control, much in the same way as the dramatised top gear vid with Clarkson in the M135i.

EDIT: I'm looking at this from a preventative angle as I appreciate that once the accident has begun, the xDrive isn't a magical get out of jail free card.

The M135/140 has MPSS as standard, with 225/40 R18’s on the front and 245/35 R18’s on the back, BUT the tyre design is significantly different between both, with the grooves on the rear much narrower, and therefore higher risk of aquaplaning....

Refer to the pics in this thread from babybmw...

https://www.babybmw.net/viewtopic.ph...aning#p1392332

As others have said, drive to the conditions!!

The tyre treads on the MPSS are another reason why winter tyres are a must on the M135/140, but there are still lots of those driving gods out there that claim they are not needed!!

[HighlandPete]

Originally Posted by creepy coupe

I don't think 4wd is a must have . But it does put two more driven wheels on the road.

Example would be in slippery conditions you avoid excessive braking pressure and would change down a gear to help the car slow. With 4WD you have four wheels taking the transmitted resistance through the drive train. This will bring you to a stop more quickly and with less brake pressure.

The opposite of this would be to knock the car into neutral and then try and stop. You would be completely reliant on the brakes.

Engine barking vs. applying the brakes, you still only have the same grip, nothing more available due to xDrive. Hopefully braking and ABS function is the better master for fast deceleration.

Grip is grip, overwhelm it due to whatever manoeuvre/conditions and we are out of control. Overcoming lack of grip is the biggest challenge, particularly in an emergency, once we lose grip. If DSC cant catch us, not much hope for most situations.

[creepy coupe]

Originally Posted by HighlandPete

Engine barking vs. applying the brakes, you still only have the same grip, nothing more available due to xDrive. Hopefully braking and ABS function is the better master for fast deceleration.

Grip is grip, overwhelm it due to whatever manoeuvre/conditions and we are out of control. Overcoming lack of grip is the biggest challenge, particularly in an emergency, once we lose grip. If DSC cant catch us, not much hope for most situations.

Well the off road courses I've been on all say the same for downhill slippery decent. " low gear, foot off the brake" As it minimises the chance of a wheel lock up

[HighlandPete]

Originally Posted by creepy coupe

Well the off road courses I've been on all say the same for downhill slippery decent. " low gear, foot off the brake" As it minimises the chance of a wheel lock up

Different conditions... I'll come back to this as I'm just going out.

[Ajs_435d]

Xdrive is completely useless don't know why anyone would want it /why more manufacturers are moving to it. Of course there is a difference between 4wd and all wheel drive.

I suppose if I didn't have I'd try and justify to myself why it's not useful and why rwd and good tyres is all I need mainly not including driving pleasure.

[Wills2]

Over the years I've had quite a few phone calls from friends with 4wd cars after they've called me to say they nearly crashed in the snow stating it's so bad out there! I set off OK but then couldn't stop or steer?! WTF, I thought 4WD would sort all that out? I bet your M3 won't move in this. No it's fine because my winter tyres have grip. Often they reply with how does that work?

Of course anyone that wants to maintain the efficacy of their awd drive system would also put winters on and drive to the conditions.

[pmgreenwood]

There is another issue in car design caused by the effects of climate change on our weather, and that is wading depth. For example, I was In Suffolk last week using rural roads with poor drainage during two days of heavy downpours. the F30 series of cars have a very low air intake and hence low wading depth irrespective of whether Xdrive or RWD. the minor and B roads were regularly under 8 or 9 inch of water for short distances last week. Fortunately, the friend I was traveling with had a Skoda Yeti which was able to cope. we decided to use his car again next day in similar conditions rather than risk my F31 which would have been very marginal. Unless the G20 improves on wading depth, my looking for something like a Macan next time. Although F30 the manual says 250mm is wading depth, the safe figure apparently is about 150 mm

see this past forum threads:-
https://f30.bimmerpost.com/forums/sh...1209976&page=3

https://f30.bimmerpost.com/forums/sh....php?t=1212135

[lethbridge]

I agree with most, can't see xDrive would help there (no more grip) - it could help if your car is stuck in gravel/grass after the accident (more traction)! Seems most likely the driver wasn't paying attention and didn't spot slowing/stationary traffic ahead, slammed on the anchors & swerved onto the gravel to miss the car in front where it all got a bit messy - so ABS/DSC ensured he had control while he was on the tarmac and didn't hit a car but after that he was on gravel and on his own... In fact the extra weight of xDrive could have cost the extra foot needed to swerve around the car in front - all academic I know as we don't know what did happen.

Blowout seems an unlikely cause unless he'd ditched his runflats + looks like tyres were pretty low profile so wouldn't have a massive impact... Useful thread though - doesn't matter what tricks your car can pull there are basic laws of physics that ultimately can't be defeated - so stay attentive & drive to conditions - easy to criticise others but I expect we've all had many times when we haven't paid enough attention but they didn't happen to coincide with the split second when something unexpected was playing out in front of us...

My ownership of an xDrive 335d for 3 years told me:

1) it was really good at getting me out of mud/snow when I would not have had winters on (a) because mud was in middle of summer, and b) regardless I don't bother with winters as I live in the SW and I just need the AWD to get out of my road - if the main roads are bad I wouldn't go out)
2) I enjoyed flooring it out of junctions/traffic lights - there's not much on the road to compete with it - ultimately is that a necessary feature - no, was it fun, yes (and made up for the less than perfect handling/steering feel)...
3) it has no positive affect whatsoever on your ability to stop or your cornering speed in the real world on public roads (though obviously you are less likely to unsettle the car by using the accelerator when you really shouldn't - but you really should be nowhere near those limits on a public road) although engine braking on all 4 wheels rather than just the rears can also make the car slightly more stable on a bend in the wet although I think DSC would take care of this anyway

[KCH1984]

Originally Posted by Wills2

Over the years I've had quite a few phone calls from friends with 4wd cars after they've called me to say they nearly crashed in the snow stating it's so bad out there! I set off OK but then couldn't stop or steer?! WTF, I thought 4WD would sort all that out? I bet your M3 won't move in this. No it's fine because my winter tyres have grip. Often they reply with how does that work?

Of course anyone that wants to maintain the efficacy of their awd drive system would also put winters on and drive to the conditions.

Originally Posted by r1cey

The M135/140 has MPSS as standard, with 225/40 R18's on the front and 245/35 R18's on the back, BUT the tyre design is significantly different between both, with the grooves on the rear much narrower, and therefore higher risk of aquaplaning....

Refer to the pics in this thread from babybmw...

https://www.babybmw.net/viewtopic.ph...aning#p1392332

As others have said, drive to the conditions!!

The tyre treads on the MPSS are another reason why winter tyres are a must on the M135/140, but there are still lots of those driving gods out there that claim they are not needed!!

Yip - a good solution is to have winter tyres on, a better solution is winter tyres on xDrive

[RobUK]

I know a good many people who have bought 4WD/AWD cars in the belief that it makes them immune to slippery conditions. Said people have usually never heard of winter tyres or think it's some marketing gimmick by tyre companies

[r1cey]

Originally Posted by RobUK

I know a good many people who have bought 4WD/AWD cars in the belief that it makes them immune to slippery conditions. Said people have usually never heard of winter tyres or think it's some marketing gimmick by tyre companies

To be fair, I was educated on this forum with respect to X-Drive / winter tyres.



I had an X3 prior to my last 3 series x-drive, but as the X3 was on all seasons, as opposed to summers on the 3 (and 19” as well), I learnt that tyres were the most important factor, so invested in winter wheels for the 3, and it made a massive difference.
To be fair, the all season pirelli scorpions on the X3 handled great, and were unflappable even in the deep snow we had in 2010 for many weeks.

As I said in an earlier post, wouldn’t dream of 340 horses, RWD and summers on the M140 in winter!!