disco transfer box ratio change,How?

i want to fit some tyres which are 32.8" diameter to my 300tdi disco Auto,
these are a lot larger than standard so id like to lower the ratios to compensate, and not over stress the gearbox motor ECT.
do i use a defender transfer box, change the diffs for drfender ones, im not sure, may be ashcroft do a conversion? any ratios reccomended, i tow occasionally- never go over 75 mph do a few motorway miles and green lane most weekends any help much appreciated

You could fit a defender transfer box easy and cheap. Try it first though you'll be surprised how well your tdi will pull taller gearing. No point changing diffs they're all the same ratio in discos, defenders and rangies. Ashcrofts will probably be able to part you with a large wad of money but will in fact just convert your tranny box to defender spec.

IT will pull the tyres ok anything over 34 or 35 inch then would say change it, money would be better spent getting the engine some more grunt best of both worlds then Jai

I have 31" tyres on my Disco, stock is about 29" ... the only difference was a reluctance to pull the caravan on long hills. Best part though is that the speedo now reads bang on between 30 and 70 mph ... the 7% gearing change exactly matched the speedo 7% lower reading! (All checked before and after tyre changes using GPS.

However, the reluctance to pull on long hills is easily overcome by de-catting the front pipe, removing the egr valve and gubbins and improving the strength and bore (slightly) of the turbo intercooler hoses and cleaning out the intercooler, plenum etc etc which gives further benefits all round.

As Jai says a gearing change probably isn't needed until you get to 35" tyres. Then the cheapest/easiest way to change the gearing might be to change diff crown wheels, and/or pinion gears, if you can get them!

many thanks for the advice, its much appreciated,
i will give it a go and see how we get on, i had heard a decat pipe makes a fair bit of differance to the grunt of the engine, (another thing on the wish list then) !