4wd warning light on

[miner-matt]

Hi all, after a bit of advice from those who know more than me... Yesterday on our trip to the beach hut I put the nav into 4H as I usually do before the climb up the dirt track over the hill and noticed for the first time ever the 4WD light slowly flashing at me. The 4wd indicator(wheels/diff diagram lcd indicator)was saying it was in but the top light was slowly flashing. So I erred on the side of caution to take the beach track as I was towing my boat and took the back track in case the 4wd wasn't working. After reading the owners manual this can come on when there is a large difference between the circumference of the front and rear wheels. And there is, not what I would call large though. I had a front set of BFG AT 265/70/17 put on yesterday, the back set(same BFG's) I figured I would get at least another 10k from. Sooo after all that should it be ok to run like this? Or should I bite the bullet and get the rear set ASAP?? I don't wont to do any damage to the driveline as the manual suggests but I wouldn't have thought the difference would be so great to cause grief?? Thoughts ??

Cheers
Matt

 

[Old.Tony]

The problem with any size differential is that it eventually catches up with you.

On standard tyres (2398.29mm circumference) if you wear just 2mm off one tyre, the circumference becomes 2392.00mm - a difference of just over 6mm. Doesn't sound like much, eh?

To travel just ONE kilometre, the new standard tyre has to do 1000/2.39829 = 416.96 revolutions. The worn tyre has to do 418.06 revolutions - almost two full revolutions more. In just ONE kilometre.

Your car is doing you a favour by protecting itself. Those new tyres should be on the agenda before the next "4WD Time" - you'll save money in the long run.

This is also a good - nay, a brilliant - reason to rotate your tyres.

 

[teamkiwi]

My god Tony. Is there anything you dont know haha. Or should we call you Yoda lol

 

[miner-matt]

The problem with any size differential is that it eventually catches up with you.

On standard tyres (2398.29mm circumference) if you wear just 2mm off one tyre, the circumference becomes 2392.00mm - a difference of just over 6mm. Doesn't sound like much, eh?

To travel just ONE kilometre, the new standard tyre has to do 1000/2.39829 = 416.96 revolutions. The worn tyre has to do 418.06 revolutions - almost two full revolutions more. In just ONE kilometre.

Your car is doing you a favour by protecting itself. Those new tyres should be on the agenda before the next "4WD Time" - you'll save money in the long run.

This is also a good - nay, a brilliant - reason to rotate your tyres.

Thanks for that tony, I won't be putting it in 4wd till I get the new back ones on. So there shouldn't be an issue in 2wd then? Just got another trip out to work 700ks return before I can get back to town..

 

[Old.Tony]

In 2wd your front and rear drive isn't linked so there's no problem (or possibility of one).

Really, it was just a math problem and I had written a formula for tyre sizes in an Excel spreadsheet - it was really just a case of punching in the numbers and representing the result in a different way (the formula I'd written takes tyre size into consideration to account for odometer error in fuel usage calculations).

It's as easy as this:

(rim size * 25.4 + width * 2 * profile / 100) * 3.1415926536 = circumference in mm

 

[kevinm1962]

tony ah i dont no what to write, same thing happened to me when i first bought the car it had different tyres front and back changed them after a read problem solved.

 

[Old.Tony]

I suppose that brings another point to light as well.

Don't mismatch tyres left-to-right. The D22 might get away with one of its front tyres mismatched as long as the hubs stay in the unlocked position, but the diffs would suffer from prolonged travel with a large difference in tyre sizes on each side too.