TD5 Disco tyre size query

[Juz]

hi there,
i am about to swap my standard tyres for an all-terrain (either BFG or Cooper).
I am also contemplating upping the size from 70 series to 75 series but am concerned about registration legalities etc.
I am based in NSW.
Anybody have any answers re how tall is still legal for rego?
I realize it should only be a minimal jump between the two, but have been told that anything more than 12mm higher is not legal in NSW.
cheers,
Juz

[Slunnie]

In NSW, and I think most states you do need to keep the tyre dia with 12 or 15mm of the original dia. How you do this when even the manufacturers at times cant, I'm not sure. The equivilennt tyre in a 75 profile is the 225/75, but at the end of the day you still have the same wall height, just a narrower tyre.

Here is the most accurate and complete tyre guide for the D2 that I have seen
http://www.disco2.com/howto/offroader/tyresizes.phtml

[101RRS]

The legal max is 15mm increase in diameter over the largest listing on the tyre placard.

While different tyres from different manufacturers vary ,the increase is measured on from the size listed on the placard.

eg 245/70 X 16 means the theoretical diameter is 16"+(70% of 245mm)+(70% of 245mm) = about 749mm - so you could increase this to 764mm

In a 75 series tyre this equates to a width of 238mm so in metric terms a 235mm tyre - about 10mm higher tahn what you would start off with.

You can do similar calcs using imperial widths etc.

[Juz]

thanks, guys.
much appreciated!
juz

[LandyAndy]

Hi Juz
I have just fitted 255/70X16 CooperS/T to my Disco2.They fit no probs,didnt rub on the offroad day I went on recently.
One thing they have done is raise the gearing,its a bit slower off the mark,hill starts are a tad tougher,but once up and going all is OK.Speedo error at 100 ks is +3.6kmh according to a tyre convertor programme.
The tyres are slightly more noisy on smooth bitumen,but un-noticable on coarse bitumin.
Goodluck
Andrew