Gentlemen
V1 is a take off decision speed. It is based on runway length and conditions that affect your "point of no return" ability to lose an engine or other no go decision, and stop on the available runway. Tailwind, wet runway, snow or ice would all have the affect of lowering this take off decision point.
VR is based on weight and power setting. It is the speed at which you may safely defy the laws of gravity and get the beast over the tree at the end of the runway with out scaring the birds nesting in there too badly.