Despite attempts to keep their older ICBMs in working order, Russia has apparently realized that this effort would be a great waste of money. So they have decided to scrap their Cold War era (Russian designation in parentheses) SS-18 (RS-20) and SS-19 (RS-18) ICBMs, along with the mobile (on railroad cars) SS-24 (RS-22). The remaining missiles will be the more modern SS-25 (RS-12M or Topol) and SS-27 (RS-12M2 or Topol-M). 

As the designations indicate, the SS-27 is an upgraded SS-25. Both are comparable to the American Minuteman III, and both carry only one warhead, although they could carry as many as six warheads per missile. The 45 ton SS-25 entered service in 1985, and was so successful (meaning reliable), that work began on an upgrade. This became the 52 ton SS-27. All other Russian ICBMs suffered reliability problems and were expensive to maintain. Many Russian generals, and some politicians, argued for keeping many of the older missiles, and their many warheads in service. But the current force of 400 SS-25s and SS-27s are more than adequate for destroying any potential foe. And you can rely on those two models to work when you push the button. Tests of the older missiles too often resulted in a launch failure, or something breaking down even after a successful launch. In addition, some SS-27s are going to be mounted in railroad cars, like the older (and heavier, at 94 tons) SS-24. 

Junking older weapons is a break with Russian tradition, where quantity tended to outrank quality. But with a market economy, the Russians are learning that efficiency has an edge over quantity. Moreover, a shortage of money has prevented mass production of the SS-27. Not having to spend billions a year to keep the older missiles going will provide the cash needed to build the more efficient SS-27s.