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Avr overl~~cng rotor was experimentally tested i n two sets of five shoe tilling pail 6enrings. The preload factors of the two sets were 0.1 rriid 0.5, respectively. The rotor had critical speeds at 3 0 0 0 nni16800 I p~n When mounted on the Jirst set of bearings, the rotor re~tu~ineil .stnOleJi)r speeds over I 1 000 rpm. However, when mounted i n the second set i f be(~ring~s the system went unstable due to whip irt 1 0 4 0 0 rpm. A ttieoretical ana1y.si.s was performed on the stability rf the mtor system to determine f the bearings were the cause of ttic wl~ip. Tire nnnlysis indicc~tes thal the system is margznally stable, the bearing design. T h e load carrying capacity is also affected by the design parameters.A typical five shoe tilting pad bearing is shown in Fig. 1. Each pad has a radius of curvature Rp, which is not necessarily equal to the nominal bearing radius Rb. If Rp is larger than Rb, which is usually the case, the bearing is said to be positively preloaded since each pad when centered forms a converging-diverging wedge which generates a hydrodynamic load. T h e preload factor m is defined as: n,id thnt SIIL(LII cro.s.s couplings generuled by the disk-shaft mountings m = 1 -cbl(Ry -R ) rlestnbilized tlie system. Also, pad inertia has little affect on the [I1 stn0ility cf this pnrticular rotor. The system was predicted to be the Another important parameter is the offset factor a which most stable when ~r~ounted on the bearings with a preload of 0.1, is defined as: so tlrc~t the j)redicted trends with varying preload were correct. The prc!dictiol~s c~lso indicnte that subsynchronozlsly reduced bearing a = PIX 121 coiflicicnts ( a s opposed to syncttronously reduced coefficients) sliould be ii.sail i n .stobilily nnelyses.