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VTD vs MPT

BeeJ

Forum Member
Joined
Nov 12, 2012
Messages
106
Location
Perth Western Australia
Found this video on foz.org and thought it was worth sharing:

[ame="https://www.youtube.com/watch?v=2uu_mN062M8"]Subaru Forester with VTD ag. Forester 2.0 - YouTube[/ame]

Shows the difference between the auto with VTD, auto with MPT and dual range manual.
 
Except the first foz was an na 2.0L driven reasonably conservatively and the second was a 2.5 turbo and they gave it some beans too.

VTD isnt bad but I don't think the difference would have been that profound in a equal test on that sort of surface.
 
Gidday BJ & David

I have to agree with you, David.

1) The vehicles were driven in a manner that deliberately accentuated the differences - i.e. not driven in anything like the same manner.

2) The tests were specifically designed to show the differences - i.e. the ramps set up at exactly the Forester's wheel base apart; and the drivers specifically stopped at the worst possible point (in a couple of cases reversing back to that point ... ), rather than maintaining some momentum that would have carried the vehicle over with ease.

3) If they were trying to demonstrate the benefits to a completely incompetent driver driving in conditions that they should have avoided like the plague to begin with, perhaps they have a point.
However, one simply doesn't rev the rings off the car in those situations the way they obviously did ...
If one gets a bit stuck, allow the car to roll backwards a little bit and regain grip, then gently power on allowing the momentum to carry one over the 'hump'.
If you power on when you have lost momentum and grip, you will spin the wheels like crazy, while travelling backwards (as they did), you are almost guaranteed to lose traction (as they did ... ).

I am sure that there are positives to all this, but if there are (specially in the ramp test), why does Subaru recommend turning the VDC OFF when off road?

Personally, I find that my SG with 5MT/DR without VDC is more stable than SWMBO's SH 4EAT with VDC, in all the conditions I have been in, specially on road where I have driven the SH more miles. I have never driven the SH on anything approximating a dirt road. One must also bear in mind that the SH is higher, longer, wider and heavier than the SG II.

IMO, the SH is a far better family type car than my SG; but I far prefer the SG for my driving, precisely because it is lower, shorter, narrower and (slightly) lighter than the SH. I also far prefer the MT to the AT, regardless that the 4EAT with SportShift is better than any other auto box I've driven.
 
yeah not a very fair test but VDC does seem pretty good!

I liked the manual on the ramps, just shows how limited open diffs are! :(
 
Gidday NL

Only the front diff is open on the MY06/07 SG. Centre is vLSD and so is the rear.

Really shows what a "stunt driver" can make a car do, more than anything else, IMNSHO.

Any experiment without controls on the non-random variables isn't worth a bumper statistically, or otherwise ... :lol: :rotfl:.

I have got myself into that kind of position. The solution was to roll back to where I could get good grip, and use a different line with a bit more power while I had grip so that the momentum took me over the hump, back off the power as I hit the loose stuff just before the hump, then power on again when the front wheels had something to grip on. Venom pointed me to a better line. It worked.
 
It's important to distinguish between the two systems -

VTD: a centre differential with an electronically controlled lockup feature which is used on some higher-end automatic models in place of the simpler MPT system used on cheaper models

VDC: a stability and traction control system that can cut engine power and apply the brakes to the individual wheels in cases of oversteer, understeer or wheelspin

Why does Subaru recommend turning the VDC OFF when off road?

Turning it 'off' (with the button on the dashboard) only disables the ability of the VDC to cut engine power - it still leaves active the facility whereby individual wheels are automatically braked in the case of wheelspin. This is handy for offroading as you still have full engine power (and at low offroad speeds, this represents less of a safety risk) but still have enabled the brake traction control that curtails cross-axle wheelspin.
 
Thanks for the detailed explanation, Simon.

What I was rather perplexed by is that only VDC was available on the models being "tested", AFAIK. Just checked in the OM for our MY06. Mine does not have VDC. It states "If Equipped", so was an option somewhere in the world ... .

If one stripped out all the items marked "If Equipped" out of my car, I am not sure how much would be left! :poke: :lol:. The OM would be about half the thickness it is :iconwink:.
 
seriously RB
VTD isnt VDC
why are you talking about SH foresters? The test was SG foresters.

1) This doesnt make the results less true, and I disagree
2) whats your point? Its a test, arent you supposed to create a scenario to highlight the differences
3) Thats your opinion but I dont think the test pits in competent drivers against each other, think its a great illustration of diagonal situation and the centre manual diff, vs auto MPT vs VTD

vLSD is sh!thouse! almost everyone agrees its almost a poop as a open diff!

This isnt a thread about how you think your DR manual 5 speed with vLSD is completely adequate and no one should modify or challenge standard subaru, I see a comment like this on almost any thread that someone talks about modding a foz, inadequate diffs, inadequate LR

Thanks for adding a VDC discussion
Thanks for adding a discussion for the millionth time on auto vs manual
Thanks for adding sportshift vs standard auto

It was supposed to be a thread to show a centre VTD vs a MPT

/rant
 
Just checked in the OM for our MY06. Mine does not have VDC. It states "If Equipped", so was an option somewhere in the world ... .

Don't quote me but no SG Foresters (in Australia anyway) have VDC apart from I think in the SG2 era when there were some XTs available with a special option pack that included VDC and a navigation unit that replaced the lift-up compartment on the dashboard. Might have only been available in auto too but my memory is hazy on the whole thing and I suspect they are quite rare. "If equipped" indeed!
 
Well, 2015- US OBs will have neither VTD, nor MT so....

(it seems that VTD will be replaced by another, simpler yet faster system; I do not know how well it will work off-road).
 
a great illustration of diagonal situation and the centre manual diff, vs auto MPT vs VTD

VTD in itself is of no help in a 'diagonal spin' situation as it only controls the front-rear disribution. It is the VDC that overcomes cross-axle wheelspin and helps with 'diagonal spin' by braking the spinning wheels.

vLSD is sh!thouse! almost everyone agrees its almost a poop as a open diff!
Certainly my rear VLSD may as well be open. It provides no resistance to cross-axle wheelspin at all. The centre one is a bit better however.
 
No, it was discussed briefly over at subaruoutback.org. The VTD is a feature of 5 EAT Subarus. The last of those are going off the lots now....:(

I guess we will know more in April. But initial reactions have ranged from "yes, what we will have is even better" to "no, it is just cheaper to make, not as good."
 
No, it was discussed briefly over at subaruoutback.org. The VTD is a feature of 5 EAT Subarus. The last of those are going off the lots now....:(

I guess we will know more in April. But initial reactions have ranged from "yes, what we will have is even better" to "no, it is just cheaper to make, not as good."

We do not really know, but the Legacy press release says nothing exciting.
 
VTD in itself is of no help in a 'diagonal spin' situation as it only controls the front-rear disribution. It is the VDC that overcomes cross-axle wheelspin and helps with 'diagonal spin' by braking the spinning wheels.

Spot on.

Certainly my rear VLSD may as well be open. It provides no resistance to cross-axle wheelspin at all. The centre one is a bit better however.

I drove a modified 4.44 VTD auto with an early VLSD rear offroad for about 7 years. I don't necessarily agree here. A VLSD works by getting hot. If you keep the boot into it you will feel the rear lock up and propel you forward. obviously not something you want to do all the time but it got me out of trouble plenty of times.
 
by the way VTD has been around since the early 90's. its not a new thing

I have 2 VTD rear ends I need to get rid of if anyone wants to modify their auto...
 
Don't quote me but no SG Foresters (in Australia anyway) have VDC apart from I think in the SG2 era when there were some XTs available with a special option pack that included VDC and a navigation unit that replaced the lift-up compartment on the dashboard. Might have only been available in auto too but my memory is hazy on the whole thing and I suspect they are quite rare. "If equipped" indeed!

Hi simxs,

Yes, you are correct! The only XTs that had VDC available as an option were the top of the range XT Luxury with the 4EAT transmission. Still, it was only fitted as a package with the OEM navigation unit. The VDC is an add-on feature of the VTD centre differential.

My car is a 2007 SG2 XT Auto (4EAT) with the OEM navigation. But mine's not a LUXURY, so I don't get the VDC, only the VTD centre diff as opposed to the MPT standard on other 4EATs. This was the case with all 2007 XT autos.

From the video on the first post, what really makes the difference is the VDC, in other words, the traction control monitoring of wheel-spin and individual brake application where required.

You can see on the first ice section how much the vehicle looses control when VDC is off. Straight after, with VDC turned on, it goes through in total control.

Now, my personal experience with VTD alone is also quite positive when compared to other 4EAT autos I've driven with the standard MPT, so I tend to agree with the results shown on the video:

1) VTD + VDC - best control
2) VTD only - good control
3) Auto MPT - ok control

I haven't spent enough time behind a Subaru manual to comment.

BeeJ, I thought your video find was a very nice one and certainly aligns with my view/experience.

Pedro.
 
Out of interest, I will quote my sources:

The MY07 brochure and specifications can be found here.

And the explanation of the MPT vs VTD centre differentials, as well as VDC is here.

Both documents are interesting reads on a range of topics. They are not my finds, I collected them from other posts on the forum.

Pedro.
 
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