Damaged tyre in AWD

[The Thong]

Greetings,

I have a V60 AWD Cross Country. My NS front tyre has tyre wall damage so it needs changing preferably. Do I need to change both front tyres? I replaced both tyres October last year and the motor has done circa 5k since. Can I get away with changing one tyre? Or I have I gotta change both?

TT

[b1mcp]

I would say you can replace just the damaged tyre.

Don't know what you have, but if say you have 18" wheels, that's a rough radius of 220mm. If you had say 235/60 tyres that would give an extra radius of 141 mm so 361mm total radius.

Nominally, that gives a rolling circumference of 2269mm.

If that radius is reduced by wear then

1mm wear (radius 360) gives circumference of 2262mm (0.3% less)
2mm wear (radius 359) gives circumference of 2255mm (0.6% less)

So, intuitively I can't believe the inbuilt systems in the car cannot handle a variation across tyres of that small amount.


Any issues with the calculations above should be directed to Mr Latham, my GCSE maths teacher.

[The Thong]

Originally Posted by b1mcp

I would say you can replace just the damaged tyre.

Don't know what you have, but if say you have 18" wheels, that's a rough radius of 220mm. If you had say 235/60 tyres that would give an extra radius of 141 mm so 361mm total radius.

Nominally, that gives a rolling circumference of 2269mm.

If that radius is reduced by wear then

1mm wear (radius 360) gives circumference of 2262mm (0.3% less)
2mm wear (radius 359) gives circumference of 2255mm (0.6% less)

So, intuitively I can't believe the inbuilt systems in the car cannot handle a variation across tyres of that small amount.


Any issues with the calculations above should be directed to Mr Latham, my GCSE maths teacher.

Cheers, I thought as much. Luckily they’re budgets so if I’ve gotta replace both it won’t be a big slap of the face

[Tannaton]

Yes you can replace just the one tyre. There is no risk whatsoever to the AWD drivetrain - even if you had four different brands of tyres with different tread depths, the system can cope, just as it does with space saving spare wheels.

[The Thong]

Excellent news mate, thanks

TT

[Easington]

Originally Posted by Tannaton

Yes you can replace just the one tyre. There is no risk whatsoever to the AWD drivetrain - even if you had four different brands of tyres with different tread depths, the system can cope, just as it does with space saving spare wheels.

Pity other manufacturers cannot get a system to work like this (xDrive)

[The Thong]

Originally Posted by Easington

Pity other manufacturers cannot get a system to work like this (xDrive)

I’m assuming on X Drive, you change one then you have to change them all? I remember Vauxhall had this issue too.

TT

[Tannaton]

Originally Posted by The Thong

I’m assuming on X Drive, you change one then you have to change them all? I remember Vauxhall had this issue too.

TT

The Vauxhall Cavalier/Calibre and Land Rover Freelander 1 AWD systems used the thermoviscous coupling rather than a centre diff or haldex. The principle is that any slip (i.e. difference between the front and rear axle speeds) causes the fluid in the coupling to heat up and become more viscous and the coupling "locks up".

Problem was having unmatched tyres could cause this to happen at motorway speeds and this then exerted considerable stress on the drive train that would eventually damage the transfer box or rear diff.

On those cars you need to rotate tyres regularly and change them all at once with matching sets. You still see a lot of FL1's for sale with the prop removed to mask a knackered/missing transfer box.

FYI AWD Volvo's up to the early 2000's had a similar system but for whatever reason we don't seem to hear of problems.

[The Thong]

Originally Posted by Tannaton

The Vauxhall Cavalier/Calibre and Land Rover Freelander 1 AWD systems used the thermoviscous coupling rather than a centre diff or haldex. The principle is that any slip (i.e. difference between the front and rear axle speeds) causes the fluid in the coupling to heat up and become more viscous and the coupling "locks up".

Problem was having unmatched tyres could cause this to happen at motorway speeds and this then exerted considerable stress on the drive train that would eventually damage the transfer box or rear diff.

On those cars you need to rotate tyres regularly and change them all at once with matching sets. You still see a lot of FL1's for sale with the prop removed to mask a knackered/missing transfer box.

FYI AWD Volvo's up to the early 2000's had a similar system but for whatever reason we don't seem to hear of problems.

I had a Freelander Mk1 with a canned coupling, cost me an IRD. One of the many issues it suffered from. Very practical car built badly which was a shame, it wasn’t a bad drive.

TT

[Tannaton]

Originally Posted by The Thong

I had a Freelander Mk1 with a canned coupling, cost me an IRD. One of the many issues it suffered from. Very practical car built badly which was a shame, it wasn’t a bad drive.

TT

I’ve had two... nice and comfy and very capable. For me it was confirmed ruined when they shoehorned the BMW 2 litre (td4) engine in. There’s always problems fitting an engine into a car which was never designed for it. Having THREE Fuel pumps was just ridiculous and a reliability issue waiting to happen.

You still see a lot on the roads though....