AWD question

[Dr_Watson]

Plenty proof of it not working too!

https://www.youtube.com/watch?v=iSj9UEVYI8o

I'm on the edge with this system, had plenty chances to use it, sometimes is quite obvious it is engaged, other times not. Sometime I will get my camera out on the tripod and see how it looks from outside, would ask the wife, be she would just hold her head in shame

 

[xtrailman]

The wheel spin I had towing off a wet grass field could have been due to the tyres, I hadn't thought of that.?

Summer Toyo tyres on the CX-5, with new tyres, all season Dunlop SP20 on the xtrail.

 

[xtrailman]

Plenty proof of it not working too!

https://www.youtube.com/watch?v=iSj9UEVYI8o

I'm on the edge with this system, had plenty chances to use it, sometimes is quite obvious it is engaged, other times not. Sometime I will get my camera out on the tripod and see how it looks from outside, would ask the wife, be she would just hold her head in shame

That's exactly what I was getting on the wet grass, fronts spinning. But why don't the rears cut in?

 

[Chris_Top_Her]

Lol im saving this for future use

 

[vroom]

The wheel spin I had towing off a wet grass field could have been due to the tyres, I hadn't thought of that.?

Summer Toyo tyres on the CX-5, with new tyres, all season Dunlop SP20 on the xtrail.

Possibly. All seasons usually have a more agressive tread. That would probably help get some grip on wet grass...

 

[Beefy]

That's exactly what I was getting on the wet grass, fronts spinning. But why don't the rears cut in?

They do cut in, but the applied torque still needs to be sufficient to get the car moving against the slope/inertia. In ALL of the 'AWD fail' videos from all manufacturers they do this to some degree (in the video Mike posted, the Rav4 has front wheels stopped while rear wheels spin; same thing different geometry). At the absolute worst, you could say that the CX-5 is more conservative in applying torque to the rear; this is only an issue against a very heavy load, and is not evidence of delays for the AWD kicking in under normal driving conditions.

The so-called time delay is non-existent.

 

[xtrailman]

Absolutely! I've run into a lot of red neck types around here that think the old school 4x4's are better than the modern AWD systems but they have no experience with modern AWD systems. I've driven all kinds of 4x4's over the last 35 years including Jeeps, Toyotas, Nissans, Fords and Chevrolets as well as AWD systems from Subaru, Volvo and Mazda. As an avid snow skier and off-road driver in the very slippery, rocky and muddy PNW since I was 17 or 18 years old, I've been in plenty of positions, winter and summer, where I could no longer make forward progress up a hill so I know how these systems behave when you need them.

Most off-road newbies are shocked to learn how easily they can get stuck, regardless of their 4 wheel drive (which is not really 4 wheel drive except on the most purpose built rock-crawler with full locking differentials front and rear) which is impractical for normal transportation. Then there is the AWD systems that use a viscous coupling in the transfer case.

I actually prefer Mazda's computer controlled implementation of AWD using wet clutch packs over ANY 4WD or AWD with a standard viscous coupling I've driven because it can be left engaged and cuts in as needed. Any delay is measured in milliseconds. The primary limitation of the CX-5 AWD system is that it will transfer a maximum of 50% of the torque to the rear wheels. Normally, one would never notice this but one situation where it may be noticeable is if a trailer with a high tongue weight is transferring weight from the front to the rear wheels or you are on a steep slope and front traction is very limited. I will point out that AWD's with viscous couplings between front and rear have this same limitation, only worse. That's because the transfer case acts like an open differential (except between the front/rear). This means torque gets transferred away from the end that has traction and towards the wheels that are already spinning, exactly the opposite of what you want.

The computer controlled AWD works opposite of this, the torque is transferred to the wheels that need it the most (but only up to 50% rear). Any time delay is inconsequential. If front wheel slippage is obvious it is because the AWD clutches have already transferred the maximum torque to the rear wheels but the hill is steep or the load is high and the power was applied too suddenly. The secret is a little driver skill, apply power gently and let the 50% torque to the rear wheels work it's magic, applying additional power will simply cause the front to spin faster and add extra wear to the clutch packs. This type of system is very capable but is not designed for pedal to the metal, ham fisted driving. It does work well in conjunction with the traction control system because it will detect excessive wheel spin and reduce power automatically. Don't think you should turn traction control off!



My experience exactly! Especially on particularly slippery ice the CX-5 will accelerate harder and maintain more composure than either 4WD or most AWD's with a viscous coupling. There are more sophisticated and more expensive AWD systems using a viscous coupling and computer controlled torque transfer that can out perform the CX-5 in pure acceleration or steep climbing but these systems cost more, weigh more, take up more room, are not as efficient and are more expensive to work on. But in typical icy conditions where an experienced driver will drive smoothly and judiciously, the CX-5 is very capable and maintains skid-free control right up there with the best of them. And you would have to do something pretty stupid to actually get stuck.




I've never driven an xtrail but I thought it was marketed more as a light off-road vehicle. I doubt it would maintain control as well on very slippery icy roads. The CX-5's AWD system has excellent sensitivity and lightning fast reaction which translates to effortless driving. In most cases you will not even feel the AWD working except that you will maintain traction in situations where a 2WD vehicle (and many 4WD and other AWD systems) would break into a slide.

I think AWD in general is over-rated. I'll take winter tires and driver skill over AWD every time. AWD is just one tool of many in your toolbox.

Like you say you have never driven an Xtrail. I have never driven an old school 4x4 so can't comment.

So what's happening to cause the wheel spin on the front wheels clearly shown in Docs video?

 

[MikeM.]

Plenty proof of it not working too!

https://www.youtube.com/watch?v=iSj9UEVYI8o

Actually, that's more photographic proof the back tires kick in with no perceptible delay as soon as the front tires break traction. Unlike the video I posted, the tires on the other side of the car are not visible but you can still see the visible back tire start spinning simultaneously with the front. In the one clip where the back tires do not spin at all, that is not because the AWD didn't kick in immediately, it's because the transfer case is only capable of transferring 50% of the torque. So the back wheels were being driven but not hard enough to spin them (weight transfers to the back wheels on steep inclines).

People don't buy AWD cars to climb super steep, soft and muddy grass hills, they buy them for snow and ice. And at this the Mazda system excels. I know, I'm in my third winter of driving the CX-5 to one of the snowiest ski areas on the globe. This is something I've done countless times in the previous 35 years in various vehicles including Subaru's. The road is considered very steep and treacherous but of course it's not as steep as the silly grass embankment in your video.

 

[MikeM.]

Like you say you have never driven an Xtrail. I have never driven an old school 4x4 so can't comment.

So what's happening to cause the wheel spin on the front wheels clearly shown in Docs video?

See above (it's the 50% torque transfer limitation).

 

[xtrailman]

Pulling a caravan is an extreme edge case. If the front wheels have close to zero grip at a standing start, then anything less than the absolute maximum amount of torque sent to the back wheels isn't going to be able to overcome the inertia of the extra weight. If the Xtrail comes on to maximum torque sent to the back quickly/aggressively, that is great for that particular use case, but does not represent real-world on-road usage or responsiveness of the AWD system.

If you want to appreciate how quickly the AWD kicks in for the Mazda, you could recreate the drive home from work I had yesterday...... a few centimetres of semi-wet snow sitting on top of ice. Too much throttle through a corner and the back end instantly slips out just a touch as the rear wheels kick in. Absolutely no understeer as the front wheels spin alone, no imaginary two second delay, little-to-no TCS light - just instant application of power to the back wheels.

I never had any wheel spin with the xtrail, in fact it was very impressive in that respect. But my Mazda does have 420nm of torque. More than enough to pull a caravan on virtually a wet grass field, even on two back wheels on reduced power.

Its rated in the UK to start off on a 12% gradient towing 2000kg, my caravan weighs 1565kg.

I don't think posters should be attacking my driving ability either, that hints at desperation to me. Driving 44 years towing for 30 years has given me enough practise to tow off from a stand still.

Don't forget the diesel delivers max torque at only 2000rpm, I tow at 1500 rpm, so no high revs are needed to set off even with a caravan in tow.

 

[xtrailman]

I cant read this do you have a link, or am I missing a joke here?

 

[xtrailman]

See above (it's the 50% torque transfer limitation).

The 50% I believe is the same with the Xtrail, 50/50. Never had that wheel spin only on the fronts with the Xtrail, and that only had 266 pound feet of torque.

Ifs that's what's happening it appears the Mazda system is worst than I first thought, the latest CRV has been heavily criticised for doing this Honda say its to protect the 4wd system by limiting the torque to the rear.

https://www.youtube.com/watch?v=jkiv-bWbLIo

 

[Kedis82ZE8]

I am curious what videos would look like if they had offroad traction tires on there and also tried it with TCS turned off. I have had to turn the TCS off on my G35x starting out in deeper snow. Once moving I would turn back on.

Page 4-84 in owners manual.

"When TCS is on and you attempt to free the vehicle when it is stuck, or drive it out of freshly fallen snow, the TCS will activate. Depressing the accelerator will not increase engine power and freeing the vehicle may be difficult. When this happens, turn off the TCS."

 

[xtrailman]

Yes I've read the same.

 

[Dr_Watson]

Actually, that's more photographic proof the back tires kick in with no perceptible delay as soon as the front tires break traction. Unlike the video I posted, the tires on the other side of the car are not visible but you can still see the visible back tire start spinning simultaneously with the front. In the one clip where the back tires do not spin at all, that is not because the AWD didn't kick in immediately, it's because the transfer case is only capable of transferring 50% of the torque. So the back wheels were being driven but not hard enough to spin them (weight transfers to the back wheels on steep inclines).

People don't buy AWD cars to climb super steep, soft and muddy grass hills, they buy them for snow and ice. And at this the Mazda system excels. I know, I'm in my third winter of driving the CX-5 to one of the snowiest ski areas on the globe. This is something I've done countless times in the previous 35 years in various vehicles including Subaru's. The road is considered very steep and treacherous but of course it's not as steep as the silly grass embankment in your video.

First time I have heard it explained clearly. So the 50% torque limit is a limiting factor in some situations. Vast majority will never experience this I guess, and for those that do, they should buy a Scooby.

 

[MikeM.]

But my Mazda does have 420nm of torque. More than enough to pull a caravan on virtually a wet grass field, even on two back wheels on reduced power.

You are completely misunderstanding the physics at play here.

The torque limitation of the AWD system has nothing to do with rated engine torque, it has to do with torque applied to the front vs. rear wheels. Maybe I can use an extreme example so you understand. Let's say your tongue weight was so high the front wheels were not touching the ground. In this case they would have zero traction and no torque could be applied to the front drive line except the amount it took to spin the components up to speed. Once they reached a steady state speed (spinning) the only torque being applied would be that necessary to overcome friction of the turning components. Therefore, the AWD system could only apply an equal amount of torque to the rear wheels and you would not move. The 50% limitation is torque DISTRIBUTION between the front and rear.

The Mazda AWD system is particularly good on very slippery surfaces to avoid breaking into a slide because the back wheels are driven at the same speed as the front wheels. On a two wheel drive the driven wheels must obtain enough traction to PULL the back wheels along and this extra work can be enough to break traction and initiate a slide in a very slippery corner (or simply due to the slope of the crown on the road).

Its rated in the UK to start off on a 12% gradient towing 2000kg, my caravan weighs 1565kg.

I know you guys across the pond get higher tow ratings but that doesn't mean it will tow any better at your longitude than in North America. It's just rated differently. Regardless, the tow rating assumes a reasonable traction surface. On a soft surface the tires sink in and the grade effectively steepens because the wheels are constantly climbing "up" out of the hole they have created. And as tongue weight is added, this increases the effect.

What is the max rated tongue weight on a CX-5 over there and what is the measured tongue weight of your tow setup?

Tongue weight is a double whammy because not only does it cause the rear tires to sink deeper but it removes weight (and therefore traction and useable torque) from the front wheels.

Don't forget the diesel delivers max torque at only 2000rpm, I tow at 1500 rpm, so no high revs are needed to set off even with a caravan in tow.

Again, engine torque is not the issue if you are traction limited.

 

[MikeM.]

First time I have heard it explained clearly. So the 50% torque limit is a limiting factor in some situations. Vast majority will never experience this I guess, and for those that do, they should buy a Scooby.

Yes, but some Subaru's have the same limitation. If this is a concern for a particular usage, make sure you get the one with the more expensive, bigger, heavier AWD and expect to get worse MPG. And don't cry when it needs to be worked on.

 

[xtrailman]

You are completely misunderstanding the physics at play here.

The torque limitation of the AWD system has nothing to do with rated engine torque, it has to do with torque applied to the front vs. rear wheels. Maybe I can use an extreme example so you understand. Let's say your tongue weight was so high the front wheels were not touching the ground. In this case they would have zero traction and no torque could be applied to the front drive line except the amount it took to spin the components up to speed. Once they reached a steady state speed (spinning) the only torque being applied would be that necessary to overcome friction of the turning components. Therefore, the AWD system could only apply an equal amount of torque to the rear wheels and you would not move. The 50% limitation is torque DISTRIBUTION between the front and rear.

The Mazda AWD system is particularly good on very slippery surfaces to avoid breaking into a slide because the back wheels are driven at the same speed as the front wheels. On a two wheel drive the driven wheels must obtain enough traction to PULL the back wheels along and this extra work can be enough to break traction and initiate a slide in a very slippery corner (or simply due to the slope of the crown on the road).



I know you guys across the pond get higher tow ratings but that doesn't mean it will tow any better at your longitude than in North America. It's just rated differently. Regardless, the tow rating assumes a reasonable traction surface. On a soft surface the tires sink in and the grade effectively steepens because the wheels are constantly climbing "up" out of the hole they have created. And as tongue weight is added, this increases the effect.

What is the max rated tongue weight on a CX-5 over there and what is the measured tongue weight of your tow setup?

Tongue weight is a double whammy because not only does it cause the rear tires to sink deeper but it removes weight (and therefore traction and useable torque) from the front wheels.



Again, engine torque is not the issue if you are traction limited.

The Nose weight limit as we call it is 88kg, I usually set it up for 80-88kg, it drops very little at the back with that.

 

[xtrailman]

Actually, that's more photographic proof the back tires kick in with no perceptible delay as soon as the front tires break traction. Unlike the video I posted, the tires on the other side of the car are not visible but you can still see the visible back tire start spinning simultaneously with the front. In the one clip where the back tires do not spin at all, that is not because the AWD didn't kick in immediately, it's because the transfer case is only capable of transferring 50% of the torque. So the back wheels were being driven but not hard enough to spin them (weight transfers to the back wheels on steep inclines).

People don't buy AWD cars to climb super steep, soft and muddy grass hills, they buy them for snow and ice. And at this the Mazda system excels. I know, I'm in my third winter of driving the CX-5 to one of the snowiest ski areas on the globe. This is something I've done countless times in the previous 35 years in various vehicles including Subaru's. The road is considered very steep and treacherous but of course it's not as steep as the silly grass embankment in your video.

In the UK we caravanners buy AWD cars to tow of wet fields, not for driving through snow.

We have only had one fall of snow last year on boxing day, yet it rains all year.
Myself I like the extra traction in the wet all year both solo and towing, which is why I was disappointed with the wheel spin towing off a wet field.
Site owners are not happy when the grass pitches are chewed up, and often only allow 4x4 on to wet pitches.

 

[xtrailman]

Perhaps I should buy a Hummer?
This link is worth a read, its on the last page, but its all worth reading as it has easy to understand animations.

http://auto.howstuffworks.com/four-wheel-drive4.htm