Unequal tread depths

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NightPHEVer

Well-known member
Joined
Aug 15, 2016
Messages
303
Location
Forres, Scotland, UK. 2014 GX4h with clear rear li
I'm sure this subject has come up before in regard to the Outlander PHEV and indeed all other 4X4s. I can confirm it becomes more interesting when you find yourself in the unfortunate position of having to come to terms with the potential cost, when it happens to you. I've just been to Scotland and back with my PHEV and a half tonne trailer, I decided to take a spare wheel with part worn R37 "just in case - well, you never know do you". On a blustery snow covered Northumberland hill I came to know as I had an almighty puncture that flattened a rear tyre in around 20 seconds. The TPMS definitely works anyway. I have no idea what caused it - didn't see anything or hear anything. If I'd tried the goopy gloop and the electric pump that would have been a waste of time as it was a 3inch 'slash' on the inner wall of the tyre. Jacked it up, changed the wheel. Apart from some very stupid irate driver's passing too fast and too close to my disabled vehicle (including lorries! - Did they think I was stopped by the road in the snow changing a wheel for fun) no problem really.

Well actually there was a problem shortly after I'd changed the wheel as in my haste I left the power button in the first blue light position, with the hazards, lights and heater on and after 10 minutes succeeded in flattening the auxiliary battery. Fortunately very helpful Mitusubishi rescue man Adam sped from Newcastle to 'jump' start me again. That auxiliary battery is a bit of a weak point in the system though, If I'd left the 'charge' button running - or in fact just left the hazards on and nothing else I guess all would have been ok. My fault. God help anyone who gets really stuck in a snowdrift or something and doesn't know how fast that battery goes flat. Make sure you always have a torch that has its own batteries with you (I did- had it for years and never used it before!). I'm going to buy one of those little li-lion starter pack things in case it happens again.

Anyway, as my 'spare' tyre was a slightly worn £50 S/H item that's been in my loft for a year it just happens to have 7mm of tread on it - which is the same as the other three. So that's ok, but my now new 'spare' R37 has 8mm of tread on it, because it's new (perhaps I should have waited and got another part-worn with 6-7mm of tread left on it?). So due to the difference in the tread size at what point is my 8mm going to be too large in diameter compared to the other four on the car at 7mm, or is it already. The HiQ fitter in Montrose did point out that Toyo and Mitsubishi state clearly that all four tyres have to have the same tread depth.

I wonder how many 4X4 owner's are aware of this potentially costly requirement and as a result what relevance does an un-used spare wheel/tyre (most Land Rover 4X4s I think still have a spare wheel/tyre supplied) actually have? Are you supposed to fit the spare on your £100,000 Range Rover and hope for the best in regard of any resulting transmission or diff damage? Or perhaps the breakdown man (assuming you haven't been killed by a lorry while you're waiting for him to turn-up) will have four new tyres of your choice with him and a fitting/balancing machine (no, he won't).
 
Having had the problem of replacing one tyre myself, I looked into this on-line. It seems the only requirement is that tyres on the same "axle" should be the same - no need for 4 the same.

So keep the "new" tyre until you need to put in on the car. At this point irrespective of actual wear you will need another "new" tyre anyway. So having bought it, you put it on the other end of the "axle" and keep the good worn one as your spare. hopefully, you only have a mismatch for a few days.

The only caveat is that the newer tyres should be on the rear.
 
My rear tires are brand new. My front tires are due for replacement (<< 3 mm). No issues. And why would there be any? There is not even a center diff in the car ...

Indeed, left vs right is more of a topic. But 1 mm diff? Can you even measure that? ;)
 
And as it's not a limit slip differential ( :cry: ) I don't think there is an issue in operation.
Only if there is a significant wear difference, I can see there might be a performance issue.
 
I am really surprised you didn't get "bonged" to death. This car bongs and buzzes for the slightest misdemeanour..! How annoying that a car with enough electric power to potential run a house can't have enough power on board to fire the engine up!
 
Mine came from the dealer with worn Toyos on the back and new Hankooks on the front, and I've not yet had an issue (fingers crossed). But people have reported issues with new tyres. The S-AWC system measures the rotation of each wheel, and detects slippage across an axle or between the two. I've seen someone mention a 2.4% difference triggering a warning, but I've no idea where that figure came from...
 
I've had no problems when fitting new pairs on one axle and worn on the other. BTW it is normally recommended to have the new ones on the back instead of the front with 4WD cars.
 
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