4.1 will give your more lowend power
4.1 is the amout if times the tailshaft turns to 1 rotation of the axles compared to 3.9 so higher the number the lower the gearing
dude shits goin crazy in doncaster at the moment guys getting stabbed all over the place, i advise people to stear clear for a while
me mate got bashed and stabbed at school for f@$k sake