This paper presents the $N$-dependent analysis of the 
$(1,\lambda)$-evolution strategy (ES) with isotropic mutations for the ridge 
functions including the special cases of sharp and parabolic ridges. The new 
approach presented allows for the prediction of the dynamics in ridge 
direction as well as in radial direction. The central quantities are the 
corresponding  progress rates which are determined in terms of analytical 
expressions. Its predictive quality is evaluated by ES simulations and the 
steady-state behavior is discussed in detail.