Simple question

..... or at least i thought so before i asked a few places.....

i have a standard off the peg 2007 defender.
i've finally had enough of the General Grabber TR's that came attached to it.
i also feel like replacing the standard Boost alloys for some black alloys (or possibly steel)

The question:
what is the range of tyre sizes that i can get WITHOUT modifying the vehicle?

i was told the mods i would need to fit bigger tyres too, but i forget them- was it 3 things?

if it helps, i would like some BFG's A/Ts. though i do like M/Ts but cant hereally justify the potential increase in fuel consumption.
Also thinking about Cooper STs.

all help greatly appreciated
i apologise for my 'greeness'

cheers

I have 235/85X16 Insa Turbo A/T's on Modulars on mine without modification. I think it looks over tyred and I will go for 237/75's next time