4Motion with different tyre wear front/rear

[stew]

Hi,

Due to a nail in a front tyre which couldn't be repaired, I've replaced both fronts with new Sport 01s. The rear has the original Sport 01s with about 4.5mm left on them, so time to replace soon, but not necessary right now.

Since I had the new tyres on, I've noticed a distinct but subtle 'throbbing' noise when the drivetrain is under load, especially around 30-50mph.

I'm wondering if it's something to do with the 4Motion differential acting strangely because of the new/old tyres. I checked the manual and there is no recommendation to switch all 4 tyres at once, it only says that tyres on the same axle should replaced as a pair and that all 4 should be the same size/width/type/tread pattern etc.

I was thinking that as the old, rear tyres have a smaller diameter than the fronts, they will rotate faster and perhaps the diff is trying to push power to them as it thinks they are 'spinning', hence a noise I haven't noticed before and perhaps more wear on the diff?

Does anyone know what the explanation could be?

Thanks,
Stu

 

[briwy]

I'm not sure about the Cali as it has a different four wheel drive system but our old 4wd Mazda Bongo was very sensitive about tyre size/wear.
Recently when I had new tyres on the front of the Cali the tyre man said that ideally all four should be replaced at the same time and then rotated to ensure even wear.
I'm pretty sure I have read somewhere in the Cali/Transporter bumph that that is what should be done on the 4 Motion.

 

[stew]

I'm not sure about the Cali as it has a different four wheel drive system but our old 4wd Mazda Bongo was very sensitive about tyre size/wear.
Recently when I had new tyres on the front of the Cali the tyre man said that ideally all four should be replaced at the same time and then rotated to ensure even wear.
I'm pretty sure I have read somewhere in the Cali/Transporter bumph that that is what should be done on the 4 Motion.

Thanks, I did some more research but never found an 'offical' answer, just recommendations (http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=18) and talk about tolerances varying between 2/32-4/32 inches (1.5 to 3mm) between tyres depending on the system being used.

I just called VW UK, they need to ask their technical team and they are calling me back tomorrow with an answer, so I'll post it.

 

[KernowLad]

We recently had our 4Motion front tyres replaced - very uneven tyre wear and it looks like the tracking was way out from new. This was at 14k miles.

The rears have got stacks of life left in them.

The 4Motion system varies the amount of power to the fronts (AFAIK it can be 100% FWD) and rears depending on conditions - not sure exactly how the system is set up for the California (we had a Golf R32 with 4Motion that was definitely set up very differently) but it does seem to eat front tyres quicker than rears maybe more due to weight distribution than anything else.

Match tyres left and right but really don't worry about front and rear.

 

[bjt4]

My 4motion is running on 18in sportlines with nexen tyres.It has done 11000 miles, the rears are
due replacing, the fronts look like they have got another 5000 miles left.all tyres wearing
Normally.no issues 4 motion noise! Or problems with 4motion kicking in.

 

[JockMacMad]

24,500 miles and about to change all 4. Totally even wear front to back with no rotation.

 

[Andy]

24,500 miles and about to change all 4. Totally even wear front to back with no rotation.

That is good mileage for tyres, but I guess you do a lot motorway work on your commute.

 

[bvddobb]

I was thinking that as the old, rear tyres have a smaller diameter than the fronts, they will rotate faster and perhaps the diff is trying to push power to them as it thinks they are 'spinning'

I have no idea where your sound might come from. But the 4Motion system does not push power to spinning wheels, quite the contrary! When it detects a wheel spinning, it will distribute more power to the other axle.
In normal driving conditions, 90% of power is delivered to the front axle, 10% to the rear. Effectively, in normal conditions, you have thus a sort of front drive. Intuition tells me therefore to expect more wear on the front, also because of steering friction. So, rotating tyres to stimulate even wear and eventually changing all tyres together at once seems like a sound idea.

 

[gatvol]

Don't want to sound reactionary, but .....

I heard a story a while back where an aftermarket warranty provider declined to pay out (on a differential related failure) on a car as the tyres had different tread depths. This was in relation to a mk 3 range rover and I was stunned by this.

Certainly when I had my audi s5 which was 4wd all the advice I got on tyres was to keep similar tread wear on your front pair and rear pair respectively. I did this as it was putting down 340bhp.

I only have a 2wd Cali. But if I had a 4motion, I would personally ask the question of vw to be safe from a warranty perspective. If there are three certainties in life they are death, taxes and that modern vw cars will go wrong more often than we would like