When Is Awd Not Awd?

[MarsKy]

I always wondered how different 4WD, AWD, 4x4 systems compared, but could never find a test which compared them.

But there's a video on-line: Automatic v Real AWD

Incidentally, I always suspected the T180 had torque steer. Anyone expereinced that too?

My driveway is easily twice as steep as the test platform in the video, and on thin snow and ice, the T180 would lunge side-to-side and fail to climb. Even with winter tyres.

[CharlieFarlie]

But surely that's why We have the diff lock button ? I believe that if that button is pressed then the diffs are locked and ensure power is spread to all four wheels and all wheels will turn at the same time ???

This is cancelled out when the car reaches something like 28MPH and returns to the auto or electric set up shown in the video ??

Wee Charlie.

[MarsKy]

You would hope so :D

It just demonstrates that you don't really know what you're getting with 4WD/ AWD/ 4x4 unless someone has done some testing and cares to share the results.

[CharlieFarlie]

From memory when looking at both Ravs and Honda CRVs the Honda doesn't have a Diff lock button ? If this is correct then what's the point of it having 4WD at all ?? Without a diff lock these vehicles would be no more use in bad conditions than say a normal estate car ??

Wee Charlie.

[MarsKy]

It's an extreme (but not unrealistic) test simulating 2 and 4 wheels starting off uphill on ice.

For other winter driving, you would have momentum to get you over the slippery bit, and otherwise the system would kick-in on the Honda and help it regain grip.

Of course, you will also get a better grip with your new winter tyres (when your alloys arrive - FYI: it took 2 weeks to ship my Catanias over from Italy).

[CharlieFarlie]

It's an extreme (but not unrealistic) test simulating 2 and 4 wheels starting off uphill on ice.

For other winter driving, you would have momentum to get you over the slippery bit, and otherwise the system would kick-in on the Honda and help it regain grip.

Of course, you will also get a better grip with your new winter tyres (when your alloys arrive - FYI: it took 2 weeks to ship my Catanias over from Italy).

The wheels have landed They are at the company who are supplying the whole lot as a package.. 2 of the tyres landed with them today and I hope the other two will land on Monday so the whole lot can be sent up to Me... Im not impressed with the company one bit !! Essentially They sold Me and took My money for something They did not have !! Failed delivery and not getting phone calls returned is in today's marketplace simply not on !! I wouldn't mind if they were courteous enough to ring Me and explain instead of burying Their heads in the sand..................................

Wee Charlie

[anchorman]

The lock button doesn't lock up any diff's. It only locks the front and rear axles together. It is quite feasible to lock it up and have one front and one rear wheel spinning and in this case the vehicle would be well and truly stuck.

Cross axle diff locks are the domain of military vehicles and could soon wreck a transmission if not treated very carefully. We have to accept that RAV is not a true off roader although it is a very capable compromise.

[CharlieFarlie]

Does locking the front and rear axels together not mean that all 4 wheels are then driven ???

Wee Charlie.

[anchorman]

Fraid not Charlie. I cant think of any modern 4WD that does so.

You do have traction control that will attempt to stabilise any wheelspin but that can also leave you stuck and only the later post 2009 models allow you to turn it off.

[CharlieFarlie]

Fraid not Charlie. I cant think of any modern 4WD that does so.

You do have traction control that will attempt to stabilise any wheelspin but that can also leave you stuck and only the later post 2009 models allow you to turn it off.

Err So what's the point of that button then ??

Wee Confused (Again) Charlie.

[anchorman]

OK = when you move away from rest, your vehicle is in 4WD. On the front of the rear axle there is a multi-plate clutch that is capable a variably and steplessly backing off the drive until it is a pure front wheel drive. This saves a lot of fuel. However, if you punch the accelerator it will bring in the rear axle but as the speed increases and the torque decreases there will be less and less drive to the rear.

If you get stuck in the snow or mud, the electronics that sense what is happening can get confused and interfere with progress so you can press that button and it takes away the auto function up to 25mph. The max distribution is 55/45% front to rear which is usually enough to get out of trouble but as stated there is nothing locked side to side, you rely entirely on torque control engaging and apply the brake on the spinning wheel.

[CharlieFarlie]

CCOOOORRRRR Thats clever !! Didn't understand a word but very good Mate .. Days like this I wish I had listened at School ...

Wee Thick Charlie.

[anchorman]

I suppose you could sum up by saying it is 4WD as required but for the most part it backs off to FWD. The clever part is when it starts to integrate with the vehicle stability control but it is grumpy old mans night round the corner with my very old very grumpy mate so that little story will have to wait!!!

You would be stunned at the computer controlled electronics that are lying in wait to dig you out when you do something silly.

2 tins of beer and a noggin of whiskey are calling

[CharlieFarlie]

Tidy !! Have a good un Mate !!................................. :thumbsup:

Wee 4WD or not ?????? Charlie.

[MarsKy]

Read some of the articles on that website's left-hand-side menu. They'll help you understand how an AWD does its thinking and how it can get confused.

[webleymk3]

Fraid not Charlie. I cant think of any modern 4WD that does so.

You do have traction control that will attempt to stabilise any wheelspin but that can also leave you stuck and only the later post 2009 models allow you to turn it off.

Anchs. My old man's pathfinder has cross axle lock I'm sure. Does the Landcruiser not have it?

[anchorman]

Is it morning?

Yes - sorry, I was meaning in the sub £30k sector in similar vehicles to ours. You can get a psuedo lock up on a Land Cruiser and a full lock up on the £60k Amazon.

[bitman]

wondering what my kia sorento does in this situation.

from factory it has rear wheel drive with a TOD (Torque On Demand) transfer box what sense the speed difference between the rear and the front drives... when the rear spins faster then the front it will start locking up the transfer box and sending 50% to the front wheels.

but i modified this TOD system so i can put it on rear wheel drive (green led), auto 4 wheel drive (TOD) or 4 wheel drive lock (red led + 4x4 led on dash)

thanks for this video

btw, who has a ramp like this?

[webleymk3]

That's one heck of a mod.. Messing with the 4wd system. Your a brave man!

[MarsKy]

thanks for this video

It's good but it ends up being a Subaru advert.

What you don't see is off camera there are 4 burly men pushing the Subaru up the ramp :-)

[bitman]

if i jack up one wheel on our rav 4 i can spin it around by hand

[webleymk3]

Sure. Is that not because it's either in neutral or the engine is off.

I cannot think of a way you can make the system work like that.

In winter I was amazed at the car. Going round a bend on ice too fast and the car woul tweak the breaks to make sure the right wheels had the power. It was astounding how effective it was.

[anchorman]

If you jack up a front wheel on a FWD you can turn it.

Its just the diff working backwards and why one wheel will spin on ice.

[bitman]

If you jack up a front wheel on a FWD you can turn it.

Its just the diff working backwards and why one wheel will spin on ice.

i think it's more the central diff as the 2003 rav 4 is permanent 4 wheel drive. but it also means that if one wheel loses grip the whole vehicle stops?

[anchorman]

I did a full explanation once on all this if somebody can find it.

BT - there is no centre diff on yours. If you look underneath there is a simple transfer box but it works by picking up on the front diff.

If you jack up both front wheels or both rear wheels and turn one side clockwise you will find the other side goes anti-clockwise. Another strange but normal feature of any diff!