Morning all

Sometime back I recall reading that permanent AWD vehicles like a Subaru, require all tyres to be changed at the same time.

Does the same logic apply for 4 motion?

No it doesn't.

I see a lot, as in A LOT of mixed emotions on this topic. Read up on VWVORTEX aswell. Everyone has their own opinion. I just replaced all4 on mine to be safe, rather safe than sorry

Deranged_9n3 wrote: ↑Fri Jun 14, 2019 12:55 pm I see a lot, as in A LOT of mixed emotions on this topic. Read up on VWVORTEX aswell. Everyone has their own opinion. I just replaced all4 on mine to be safe, rather safe than sorry

My wifey is currently driving a Tiguan 4 motion and they also need to replace all 4 tyres at the same time.
Its been in the family since 2008.

Deranged_9n3 wrote: ↑Fri Jun 14, 2019 12:55 pm I just replaced all4 on mine to be safe, rather safe than sorry

What reasons can there possibly be that one must replace all 4 to rather be safe than sorry? Physics stay physics.

Getting worried here. What is the difference of replacing say 2 fronts with the exact same brand/size etc as the back?

Superslik wrote: ↑Fri Jun 14, 2019 1:27 pm Getting worried here. What is the difference of replacing say 2 fronts with the exact same brand/size etc as the back?

From what I have seen, they wear all 4 quicker than on a 2WD car.

I can't see a problem with you just changing the fronts or just the rear to a different brand. According to me, the fronts should use more tyre life than the rears.

The issue (or non-issue, depending how you look at it) is the difference in rolling circumference between the worn and the new tyre. (Which is about 2% if you do the sums.) This would cause the centre diff to compensate the 2% difference between the slower and the faster axle.

Personally, I don't see this as a problem, but internet wars have been waged on the topic...

VAG Fan wrote: ↑Fri Jun 14, 2019 1:46 pm The issue (or non-issue, depending how you look at it) is the difference in rolling circumference between the worn and the new tyre. (Which is about 2% if you do the sums.) This would cause the centre diff to compensate the 2% difference between the slower and the faster axle.

Personally, I don't see this as a problem, but internet wars have been waged on the topic...

And that is exactly why it has a centre differential. Anyone that has driven a 4 x 4 with a locked centre diff on tar will tell you things don't sound so good! Even if everything is 100% in sync, as soon as you turn there is a difference front to back and voila centre diff

And, are these 4motion Tigs not Haldex based? so FWD most of the time?

VGTI wrote: ↑Fri Jun 14, 2019 2:58 pm

And, are these 4motion Tigs not Haldex based? so FWD most of the time?

Exactly, the only time the tyres will be equal is when they are brand new. The Haldex allows 5% power to the rear all the time, the rest is on the front anyways so there goes the internet theories

I am about to replace the tires on the A8, the front ones are the only ones that are a bit worn, rears are literally still new. But then I am worried that if I only change the fronts, will end up damaging the drivetrain which im sure will cost more than the 12k i am trying to save by changing fronts only....

Titleists wrote:

Deranged_9n3 wrote: ↑Fri Jun 14, 2019 12:55 pm I just replaced all4 on mine to be safe, rather safe than sorry

What reasons can there possibly be that one must replace all 4 to rather be safe than sorry? Physics stay physics.

The speed difference in tyres with more wear will activate the haldex Moe often , think it's 2% speed difference allowed. Used to kill the units in the LR Freelanders

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I sat down one day and did a massive calc. with a 2% difference in wear front to back if you drive in an absolutely straight line there will be a 3 rpm rotation difference front prop shaft to rear propshaft over 1 km. I would not even spend 1 sleepless second over that.

mueneni12 wrote:I am about to replace the tires on the A8, the front ones are the only ones that are a bit worn, rears are literally still new. But then I am worried that if I only change the fronts, will end up damaging the drivetrain which im sure will cost more than the 12k i am trying to save by changing fronts only....

Impossible as Panic said

Anyway the A8 is Torsen not Haldex, it’s not affected by rotational differences


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So, I can actually change the front set alone

Mmm, some differing views.

I'm going to wing it and when the time comes, will change the fronts only - as I don't anticipate chucking it into bends to activate the haldex so the fronts will wear out first.

panic-mechanic wrote: ↑Fri Jun 14, 2019 7:18 pm I sat down one day and did a massive calc. with a 2% difference in wear front to back if you drive in an absolutely straight line there will be a 3 rpm rotation difference front prop shaft to rear propshaft over 1 km. I would not even spend 1 sleepless second over that.

Would this be an issue on our V10 Touaregs?

4 new tyres or can you fit only 2 new ones?

On jeep grand cherokees, 2011 till now, it is essentail to replace the tyres with the exact same brand and size as the rolling circumference cannot be more than 8mm. It causes the transfercase to compensate too much and causes wear on the clutches inside the t.case. We have replaced numerous t.cases because the clients fail to understand the concept.

You can replace 2 tyres on their own but it has the be the same brand and size. Different brands have different rolling circumferences for the exact same tyre size and that is something that clients fail to understand.

I am not clued up with vw and how the system works. Just thought I would give my 2c

Puni wrote: ↑Tue Dec 03, 2019 7:10 pm

panic-mechanic wrote: ↑Fri Jun 14, 2019 7:18 pm I sat down one day and did a massive calc. with a 2% difference in wear front to back if you drive in an absolutely straight line there will be a 3 rpm rotation difference front prop shaft to rear propshaft over 1 km. I would not even spend 1 sleepless second over that.

Would this be an issue on our V10 Touaregs?

4 new tyres or can you fit only 2 new ones?

The Touareg uses Torsen based 4wd and as @PoLonY has mentioned is not affected by rotational size differences. The smaller Audi's and VW's use Haldex which is continuously variable using an electronically variable coupling between front and rear axle's and are affected by rotational size differences.