When to Engage AWD

[marlinleg]

Hello to one and all, and thank you . Engaging AWD I am asking before I need to ,can AWD be engaged while driving , or do I need to stop then engage AWD . Just saying  I am driving along snow free road then turn into my estate with snow on all the roads and it's up hill to my home 

[philip42h]

You can't engage AWD; you can't prevent AWD engaging. The car knows exactly what to do - you just drive it ... gently ... 😉

 

[marlinleg]

Thank you  phillip42h 👏👏👏 I saw the trail switch and overthought it 🥴 . Thank you again 

[philip42h]

1 hour ago, marlinleg said:

Thank you  phillip42h 👏👏👏 I saw the trail switch and overthought it 🥴 . Thank you again 

I'm not entirely sure that I can see the need for Trail mode ... supposedly it tells the car to allow the wheels to spin a little more than it otherwise would. Useful if you've got a slew of stones and gravel over an otherwise firm surface so that the spinning wheels can shift them out of the way in order to find better grip lower down. I'll try it the very next time I'm on such a gravel trail - or not, as the case may be.

Earlier RAVs like my 4.3 and 4.4 came equipped with a 'Diff Lock' button to make the car behave a little more like a permanent four wheel drive - I never found a use for that either! 🙂

[chris ha]

I do think Trail mode has its uses in snow,

[marlinleg]

1 hour ago, chris ha said:

I do think Trail mode has its uses in snow,

for the last 10 years I have run on winter tyres . As you may know they have a different rubber compound that's shorter stopping distance in cold weather . They as have a secondary advantage of being good in the snow. I have linked a YouTube video from auto express a to wheel drive car on winter tyres out performing a 4 wd car on summer tyres at a snow slope 

 

 

 

[philip42h]

2 hours ago, philip42h said:

I'm not entirely sure that I can see the need for Trail mode ... supposedly it tells the car to allow the wheels to spin a little more than it otherwise would. Useful if you've got a slew of stones and gravel over an otherwise firm surface so that the spinning wheels can shift them out of the way in order to find better grip lower down. I'll try it the very next time I'm on such a gravel trail - or not, as the case may be.

Earlier RAVs like my 4.3 and 4.4 came equipped with a 'Diff Lock' button to make the car behave a little more like a permanent four wheel drive - I never found a use for that either! 🙂

 

2 hours ago, chris ha said:

I do think Trail mode has its uses in snow,

I suspect that you may well be correct Chris - and what I wrote previously was mostly wrong ... I was basing my expectations on experience of a diesel powered 4.3 and 4.4 ...

The AWDi / E-Four automatically applies power to the rear axle when conditions require. So there is nothing that the driver needs to do the engage AWD mode. But this really means having two driven axles - and therefore four driven wheels. And that's all that most of us will need 99% of the time.

But, in a 4.4 hybrid when one wheel looses traction on a very slippery surface or by being lifted into the air all the 'power' goes to the spinning wheel and the wheel on the opposite end on the axle looses drive. Trail mode was introduced in the 4.5 to apply braking force to the spinning wheel to create the effect of a limited slip differential. So, exactly as Chris says, Trail mode will have its uses on snow and ice ...

(... which is what the earlier ICE powered RAV4s did automatically)

I'll still have to find the right conditions to try it out ... 😉 

[IanML]

9 hours ago, philip42h said:

Earlier RAVs like my 4.3 and 4.4 came equipped with a 'Diff Lock' button to make the car behave a little more like a permanent four wheel drive - I never found a use for that either! 🙂

I think that would be the center differential lock.  Its purpose is to prevent one or two wheels on one axle spinning away at high speed if they drop into a mud bath or some such, and robbing the other axle of torque.  With the diff locked, the axle which has lost traction will not turn faster than the one which has not.

[philip42h]

10 hours ago, IanML said:

I think that would be the center differential lock.  Its purpose is to prevent one or two wheels on one axle spinning away at high speed if they drop into a mud bath or some such, and robbing the other axle of torque.  With the diff locked, the axle which has lost traction will not turn faster than the one which has not.

Exactly so, and which is the case at low speeds anyway - its not a physical diff lock as such but an electronic preference setting. But my point was / is that I never found a situation in which I needed to press the button - the system worked amazingly well in 'normal' mode anyway - and I did try!

[IanML]

Fair enough, but I hit a sloping (uphill) icy drive.  My Suzuki Grand Vitara could not get grip to climb up in 2WD.  I shifted to 4WD (no center diff, so equivalent to a locked center diff), and up she went with no problem.  I debate whether an unlocked center diff, assisted by clever brakes applied to the rear, would have coped.  Maybe.