Particle motion in storage rings is confined by various aperture 
 limits, the size of which restricts the performance of the ring in 
 terms of injection efficiency, lifetime, etc. Intra-beam scattering 
 makes particles sweep a large portion of the phase space where their 
 motion may eventually be resonantly or chaotically excited to large 
 amplitudes leading to collision with the vacuum chamber. We report 
 here the studies performed at the Advanced Light Source (ALS) on the 
 on- and off-momentum particle motion that provides a good 
 understanding of these limitations. Using off-momentum simulations and 
 experiments together with Frequency Map Analysis, we could precisely 
 correlate the beam loss areas with the resonance locations. The very 
 good agreement between simulations and experiments allowed  us to 
 provide guidance for avoiding these dangerous areas. This analysis 
 results in  predictive improvements of the momentum aperture which 
 actually led to a lifetime increase of 25% at the ALS for very high 
 bunch charge.