[markouk]

Is it necessary to replace all 4 tyres on an xdrive if you have only 1 or 2 worn?

I'm sure I read a post on here to that effect.

[Hprice1099]

Originally Posted by markouk

Is it necessary to replace all 4 tyres on an xdrive if you have only 1 or 2 worn?

I'm sure I read a post on here to that effect.

Depends how worn, what is the mm on the 4?

[teaston]

No of course not, it's not a Calibra 4x4!

[markouk]

Originally Posted by teaston

No of course not, it's not a Calibra 4x4!

Well that was my thought as it isn't a true 4 wheel drive.

On the Calibra...I had a 4x4 turbo when I was about 23. It had a switch which toggled something that made it 2wd (so the garage told me). It was wild and I owned it for 3 weeks and nearly crashed twice in it...very scary.

It went into the same garage that sold it to me to fix the speedo cable. Garage went on fire over the weekend. Car had been due back to me on the Monday but they called me to say it was a charred shell. Think that was an omen

[teaston]

Originally Posted by markouk

Well that was my thought as it isn't a true 4 wheel drive.

On the Calibra...I had a 4x4 turbo when I was about 23. It had a switch which toggled something that made it 2wd (so the garage told me). It was wild and I owned it for 3 weeks and nearly crashed twice in it...very scary.

It went into the same garage that sold it to me to fix the speedo cable. Garage went on fire over the weekend. Car had been due back to me on the Monday but they called me to say it was a charred shell. Think that was an omen

Which isn't a true 4 wheel drive?

I would just change them in pairs on same axle, as you would on any car.

[markouk]

Originally Posted by teaston

Which isn't a true 4 wheel drive?

I would just change them in pairs on same axle, as you would on any car.

I meant the xdrive isn't 4 wheel drive.

[teaston]

Originally Posted by markouk

I meant the xdrive isn't 4 wheel drive.

It definitely is 4 wheel drive! One of the most advanced 4 wheel drive systems on the market! Obviously it's not an off roader with locking diffs or a low ratio box though.

[russtic]

Originally Posted by teaston

No of course not, it's not a Calibra 4x4!

The worst 4x4 ever? Even under inflating a tyre could kill it..

[Rukka]

When I was getting px values for my 435d one of the things that the dealer was interested in was tread depths. Apparently, tyres have to be within 2mm of each other otherwise they would need to change all 4 before they could sell it as an AUC.

I took it with a pinch of salt until the second dealer said the same :

[teaston]

Originally Posted by Rukka

When I was getting px values for my 435d one of the things that the dealer was interested in was tread depths. Apparently, tyres have to be within 2mm of each other otherwise they would need to change all 4 before they could sell it as an AUC.

I took it with a pinch of salt until the second dealer said the same :

Maybe they were both Vauxhall salesmen in the 90's!?

[Rukka]

Originally Posted by teaston

Maybe they were both Vauxhall salesmen in the 90's!?

More like a ruse to knock another £1k off to he trade value

[JNW1]

Originally Posted by Rukka

When I was getting px values for my 435d one of the things that the dealer was interested in was tread depths. Apparently, tyres have to be within 2mm of each other otherwise they would need to change all 4 before they could sell it as an AUC.

I took it with a pinch of salt until the second dealer said the same :

Interesting, not heard that one before! I did replace all four on mine but only because I didn't want to mix run-flats on the rear with conventional tyres on the front. However, given the X-Drives are meant to retain a RWD bias, I was actually quite surprised to find that the front tyres wore more quickly than the rears...

[rich100]

Originally Posted by teaston

No of course not, it's not a Calibra 4x4!

Always wanted a calibra in the 90s but never actually drive one in the end.

Was the turbo version just badly set up or was it a combination of things that made it bad?

[rich100]

Originally Posted by JNW1

Interesting, not heard that one before! I did replace all four on mine but only because I didn't want to mix run-flats on the rear with conventional tyres on the front. However, given the X-Drives are meant to retain a RWD bias, I was actually quite surprised to find that the front tyres wore more quickly than the rears...

I found this, rears seem fine with plenty of tread but I've had to replace the fronts.

I can only think because the fronts do the steering they probably get more wear but I'm no expert.

[teaston]

Originally Posted by rich100

Always wanted a calibra in the 90s but never actually drive one in the end.

Was the turbo version just badly set up or was it a combination of things that made it bad?

The 4x4 transfer box was just crap, if any of the tyres had different treads depths or pressures then the transfer box would fail and need replacing at about £2k for a new one!! It really was a joke, especially as it was around in the same era as the Escort Cosworth & Impreza which had brilliant 4WD systems!

[Alscoob]

On some 4x4 systems you have a tolerance in tread depths front to rear, if this is too great the rotation of the smaller diameter is greater and as a result will 'windup' the centre diff causing problems. If you have a clever system where you can change the bias front to rear then I believe it doesn't matter.

[RobUK]

Originally Posted by Rukka

I took it with a pinch of salt until the second dealer said the same :

That just means they're both crooks

[NISFAN]

There is a wet clutch in the transfer case. If both front and rear axles are turning the same speed, there is no slip on the clutch.
If there are different axle speeds the clutch is continuously slipping which will wear it out over time. The bigger the difference the more wear takes place.
So it is advisable to have similar rolling radius front and rear, but as BMW have chosen to fit staggered tyre sizes that aren't equal in the first place, they are obviously not that concerned.

[Rich9600]

Originally Posted by teaston

It definitely is 4 wheel drive! One of the most advanced 4 wheel drive systems on the market! Obviously it's not an off roader with locking diffs or a low ratio box though.

Don't you mean AWD?...

I thought 4WD systems had to be fixed or mechanically variable and possibly even have locking diff's.

AWD systems are the electronically variable ones... Clutches vs diff's.

Just being pedantic. (And, hopefully correct)

[rich100]

Originally Posted by teaston

The 4x4 transfer box was just crap, if any of the tyres had different treads depths or pressures then the transfer box would fail and need replacing at about £2k for a new one!! It really was a joke, especially as it was around in the same era as the Escort Cosworth & Impreza which had brilliant 4WD systems!

2k?? Glad I never got one..... I do recall at the time the motoring press didn't seem that impressed.

Do still see them very occasionally but almost unrecognisable due to the industrial strength chav makeover they appear to have gone through.

[markouk]

Originally Posted by Rich9600

Don't you mean AWD?...

I thought 4WD systems had to be fixed or mechanically variable and possibly even have locking diff's.

AWD systems are the electronically variable ones... Clutches vs diff's.

Just being pedantic. (And, hopefully correct)

That was what I was getting at but without the technical rationale.

Is the power distributed evenly to each wheel on a conventional 4 wheel drive? On the xdrive is it biased to the rear or actually always fluctuating so never locked at equal portion to the corners?

[teaston]

Originally Posted by Rich9600

Don't you mean AWD?...

I thought 4WD systems had to be fixed or mechanically variable and possibly even have locking diff's.

AWD systems are the electronically variable ones... Clutches vs diff's.

Just being pedantic. (And, hopefully correct)

AWD & 4WD are the same thing! (On a vehicle with 4 wheels):

"Four-wheel drive, 4×4 ("four by four"), 4WD, and AWD is a form of drivetrain capable of providing power to all wheel ends of a two-axled vehicle simultaneously. It may be full-time, or on-demand, and may be linked via a transfer case to provide multiple gear ranges."

And xdrive is the full time full time type, unlike my sister's Rav4 which is two wheel drive unless their is wheel slip or at under 20mph you press the 4WD button.