Another tyre thread!

[Surfer]

On the 2018 Jeep Grand Cherokee CRD Overland we have 4 x Continental Cross contract UHP tyres.  The rear tyres have a date stamp 2416 (week 24 in 2016) so they nearly 2 years old when fitted onto the Jeep.  They still have approximately 2.7mm tread however as they are on the rear this seems to indicate that the tyres have never been rotated despite it being recommended on the service manual.

The front tyres have a manufacture date of 4121 or week 41 in 2021.  However they seem to be down to about 5mm.  Obviously all legal and will get through a MOT however I always change tyres when they reach about 3mm. 

The concern here is that difference in tyre tread may affect the transfer case which could turn out to be an expensive repair.  This mentioned or discussed on other US Jeep forums and also on a Your tube video.  I am angling at changing all 4 tyres at the same time despite the front tyres having ample depth.  What are your thoughts?

See

 

[frosty]

i would definitely change all 4, then rotate regularly, i know it is a bit of a waste of rubber, but still cheaper than changing your transfer box, and some peace of mind. 

[digger]

Does anyone know from what year onward is this a possible problem please?

[jerryg]

Is it an issue for any vehicle that is in permanent 4 wheel drive? Just a thought.

 

[Surfer]

11 minutes ago, digger said:

Does anyone know from what year onward is this a possible problem please?

Apparently from 2011 onwards, but not sure if the issue was resolved with later models after 2014?

[V]

10 minutes ago, jerryg said:

Is it an issue for any vehicle that is in permanent 4 wheel drive? Just a thought.

 

Those with viscous couplings in the centre differential appear to be affected worse than those with a normally open differential. On NP242 transfer cases it can affect the ability to shift selections in the transfer case, often making it harder to shift between 2wd and 4wd.

[V]

16 minutes ago, Surfer said:

Apparently from 2011 onwards, but not sure if the issue was resolved with later models after 2014?

I believe it goes back earlier than that to 1999/2000 with the NP247/NP249 transfer cases in the WJ/WG Grand Cherokee.

[digger]

I've had the problem of difficulty shifting between H and L.  The first time I tried it a couple of months after buying mine ,it was very difficult. the net said it was caused by lack of use and as a result the solenoids became gummed up. I eventually got it to start working by changing whilst rolling backwards. Since then I change once a month on the drive as a minimum (ie when i think about it!) Over the last 5 years there have been no more issues.

Surely if it affects all those years, we would have heard about it before!

[V]

57 minutes ago, digger said:

Surely if it affects all those years, we would have heard about it before!

Yes, I was wrong. The NP249 problem goes back to 1993 in the ZJ Grand Cherokee. The NV247 was an improvement over the NP249 but it is still sensitive to mismatched rolling radius between axles.

 

There is a tweak that can be done to the NV247 that makes it bleed down quicker and creates more of a rear wheel drive bias. I don't think I would do this on an off road WJ even with a new gerotor pump.

[Surfer]

As a follow up I ordered at gauge to read tyre depth and these are the results.

 

Checked my tyres for wear.  Checked outside groove and then inner groove and results as follows;

 

Offside front outer 7mm   Inner 6mm

Nearside front outer 9mm   Inner 9mm

Offside rear Outer 5mm   Inner 4mm

Nearside rear outer 4mm    Inner 3mm

 

I understand that it is time to change the rear tyres as they are the original tyres and have seen in excess of 36,000 miles.  The rear are dated week 24 2016.   Front nearside week 41 2021 and other front offside week 16 2019.  However possible both front tyres were fitted at the same time?  The nearside front seems almost new and would have been fitted last year.  If both fitted at the same time then substantial wear on front offside?

 

Would you change all four tyres or just the three?  Concern is the transfer box.

[Stew the Jeep]

If the difference in tread depth could cause transfer case issues change all 4 tyres

[V]

I would replace all four and keep the 9mm and 7mm as unfitted emergency spares in case of future tyre damage requiring a replacement tyre. Depending on your annual mileage, the unfitted spares can be scrapped next tyre change or the one after.

 

The older NP249 transfer case was sensitive to 1/4"+ difference in tyre diameter, which is about 3mm of total tread depth variation between all of the tyres fitted. I have no idea how sensitive modern Jeeps are.

 

Your lowest tread depth is 3mm, highest is 9mm. This gives a total variation of 6mm between front and rear axles.

[V]

I have just read a reference to the NP249 variation being 1/4" on circumference not diameter. I have just done the calculation and for a 30" diameter tyre the sensitivity variation is still 3mm using either circumference or diameter.

 

If you can find a published reaction time between switching from rear wheel drive to all wheel drive for a given tyre size we can work out the sensitivity variation.

[frosty]

i would just shop around for a set of 4 new tires, there are good deals to be had. 

[Surfer]

Went through Blackcircles although Kwikfit and Halfords were cheaper.

[Raakhee]

9 hours ago, Surfer said:

Went through Blackcircles although Kwikfit and Halfords were cheaper.

If you are using Google to search, use Incognito mode as I found tracking cookies push the pricing up