car ramp width

basic question folks.

i am looking at getting some basic car ramps to enable me to get underneath my 110 more easily.

all the ones i've seen at places like halfords and on-line seem similar and not really wide enough.

the halfords ones clearly state 15 x 185 max tyre size. i have general grabber 16 x 235 and may soon be getting bfg 265's.

am i being overly cautious? will standard ramps work fine or can anyone recommend wider/higher/better more suited to a defender?

thanks in advance

mike