mismatched Tires on AWD ZB's... thoughts and opinions?

[me_like_fuelBurners]

I have driven Falcons and Commodores all my life, I replaced all 4 tyres at the same time. How hard are you driving to flog them out 3x the rate of front? Rather I found on family member's FWD shitboxes, the fronts needed replacing twice as often as rears.

Yeah true, I was having a cheeky stab at those of us that, in our younger days, took every & any opportunity to create large, noxious plumes of smoke from those back tires... hence the accelerated wear

 

[vc commodore]

I have driven Falcons and Commodores all my life, I replaced all 4 tyres at the same time. How hard are you driving to flog them out 3x the rate of front? Rather I found on family member's FWD shitboxes, the fronts needed replacing twice as often as rears.

Fronts on a FWD car need replacing more often, because they do all the work...The rears basically hold the rear off the road....Not much else...Don't rotate a FWD cars tyres reguarly and they start scalloping, making noises like wheel bearings are foobarred....

Driving style can determine wear....Rotation regularity, even alignments effect wear rates....

 

[hademall]

I am currently running Michelin PS4S on the rear and PSSS on the front and I don't have any problems. My car had it's diff issues when it had PSSS on all 4 corners so it cannot be tyre related.

My Michelin PS4s wore down on the rears twice as quick as the fronts, on my 2017 Wagon.

 

[Skylarking]

Differentials are a mechanical device that by design allow for rotational wheel speed differences between the axles so the vehicle can cope with turning. Without a differential, the vehicle’s wheels would bind up and skip across the road which is unsafe and why we have differentials.

How much of a wheel speed difference can be accommodated by a differential is anyone’s guess but over the 100 years of their use I’m sure they’ve coped with millions of abusive owners. Owners who over that time have installed hugely wrong size tyres (left to right), haven‘t maintain correct tyre pressures (one side over inflated, the other side very under inflated), haven‘t ever replaced diff oils, love to do burnouts, etc, etc… Yet these diffs for the most part have just lived on and on…

Interestingly a 4 wheel drive doesn’t change the fundamentals of needing to cater to different wheel speeds when the vehicle is turning. As such older 4x4’s and AWD’s can have a mechanical front, centre and rear differentials to cope with different drive shaft speeds. Often these differentials are simple open diffs but can also use mechanical diff locks, be Torsten limited slip differentials or some another form of clutch pack limited slip differential.

All these 4x4/AWD mechanical solutions have been around for a long time and use the same differential action to cater for axle speed difference so I just don’t see minor tyre size, tyre wear or tyre pressure differences as being a huge cause of concern. But it’s always best to stick with manufacturer recommendations and check tyre pressures often, for safety sake more than mechanical sympath…

The interesting bit is how some newer AWD drive mechanicals work when differentials aren’t being used where computer processing, electronics and multi plate set clutches are instead called upon to do the differential duties.

The VW Golf R is an example of a modern AWD that uses a conventional front drive layout with an open(?) front diff and cleaver Haldex multi plate clutch pack(s) to apportion the amount of drive at the rear. Aspects of it are similar to Holdens Twinster rear diff…

As I see it, the problem with multi plate clutch pack type systems that are under computer control and they operate by slipping the plates. Such slip must generate heat that in theory the oil carries away (do any have oil coolers?). How that heat is handled and whether that heat is effectively dissipated into the air stream via a cooler or whether software logic is used to avoid overheating the fluid is anyone’s guess. But I’d expect slipping plates will always need maintenance.

It would be interesting to hear how the Nissan GTR crowd cope with maintenance of the wet plate clutch packs within these vehicles

Whether Holdens ZB diff issues are because of poor software control or poor manufacture is anyone’s guess but I really doubt the problem is caused by tyre wear or tyre pressure issues..

Below is what Holden’s Twinster rear diff assembly looks like

 

[me_like_fuelBurners]

Differentials are a mechanical device that by design allow for rotational wheel speed differences between the axles so the vehicle can cope with turning. Without a differential, the vehicle’s wheels would bind up and skip across the road which is unsafe and why we have differentials.

How much of a wheel speed difference can be accommodated by a differential is anyone’s guess but over the 100 years of their use I’m sure they’ve coped with millions of abusive owners. Owners who over that time have installed hugely wrong size tyres (left to right), haven‘t maintain correct tyre pressures (one side over inflated, the other side very under inflated), haven‘t ever replaced diff oils, love to do burnouts, etc, etc… Yet these diffs for the most part have just lived on and on…

Interestingly a 4 wheel drive doesn’t change the fundamentals of needing to cater to different wheel speeds when the vehicle is turning. As such older 4x4’s and AWD’s can have a mechanical front, centre and rear differentials to cope with different drive shaft speeds. Often these differentials are simple open diffs but can also use mechanical diff locks, be Torsten limited slip differentials or some another form of clutch pack limited slip differential.

All these 4x4/AWD mechanical solutions have been around for a long time and use the same differential action to cater for axle speed difference so I just don’t see minor tyre size, tyre wear or tyre pressure differences as being a huge cause of concern. But it’s always best to stick with manufacturer recommendations and check tyre pressures often, for safety sake more than mechanical sympath…

The interesting bit is how some newer AWD drive mechanicals work when differentials aren’t being used where computer processing, electronics and multi plate set clutches are instead called upon to do the differential duties.

The VW Golf R is an example of a modern AWD that uses a conventional front drive layout with an open(?) front diff and cleaver Haldex multi plate clutch pack(s) to apportion the amount of drive at the rear. Aspects of it are similar to Holdens Twinster rear diff…

As I see it, the problem with multi plate clutch pack type systems that are under computer control and they operate by slipping the plates. Such slip must generate heat that in theory the oil carries away (do any have oil coolers?). How that heat is handled and whether that heat is effectively dissipated into the air stream via a cooler or whether software logic is used to avoid overheating the fluid is anyone’s guess. But I’d expect slipping plates will always need maintenance.

It would be interesting to hear how the Nissan GTR crowd cope with maintenance of the wet plate clutch packs within these vehicles

Whether Holdens ZB diff issues are because of poor software control or poor manufacture is anyone’s guess but I really doubt the problem is caused by tyre wear or tyre pressure issues..

Below is what Holden’s Twinster rear diff assembly looks like

@Skylarking awesome post mate. This is the sort of response I was hoping for... informative and respectful - champion effort, thanks for taking the time.
I'm definitely starting to think the tires make about 1% of **** all difference to the problems we are seeing in the ZB diff's, but me being the engineer that I am, enjoy throwing ideas out there as you never know where they might lead