Generally, the speed of the bike determines the ideal front/rear braking-force ratio. At slower speeds, say, between a parking-lot pace and a typical surface-street speed of 35 mph, the breakdown is more evenly split; a 50/50 front/rear mix will likely work well here. But as speeds increase the braking emphasis needs to move forward. At 45 mph, for instance, you'll want to back off the rear brake somewhat, maybe go with a 60/40 front/rear ratio. At 60 mph, the split needs to move forward yet again; a 70/30 or even 80/20 ratio will be better. The higher the speed, the more important practiced and proficient use of the front brake becomes.