A second way to reduce the encounter velocity is reduce the total mass of the galaxy pair. Simply scaling down the mass of each galaxy in lockstep will not help; the circular velocities of the disks will then also be reduced, leaving the ratio of orbital to rotational angular velocity unchanged. Instead, we change the mass ratio of the pair, slowing down the encounter while keeping fixed the circular velocity of one of the galaxies (hereafter referred to as the ``primary"). However, while the slower encounter may help tail-making, the tidal field from the low mass companion is weaker than in an equal mass merger, and may completely offset the gain from the reduced encounter velocity.
To see which of these two effects dominates, we performed two calculations
involving mergers of unequal mass galaxies, using 2:1 and 3:1 mass ratios.
In each case, the low mass companion is constructed using galaxy Model D,
scaled down in mass, and with a scale length derived from a 
relationship expected if the galaxies follow the 
scaling
implied by the Tully-Fisher relation. The primary galaxy is each merger
is an unaltered Model D galaxy. The galaxies are then placed on a parabolic,
prograde orbit with impact parameter 
and an initial separation of
. The resulting perigalactic separation is 
for each case.
Figure 10 shows the evolution of these two unequal mass mergers. The evolution proceeds in much the same way as the equal mass case, short spiral arms are thrown off each galaxy and wrap up before the second encounter. The second encounter is nearly head-on and hot tails and shells are thrown off instead of thin tails.
Figure 10: Mergers of unequal mass Model D galaxies.
Several factors conspire to limit the tails produced in these unequal
mass encounters. First, the reduced mass of the
companion galaxy results in much weaker tidal forces acting on the primary
in comparison to the equal mass mergers shown in . Second, although the
encounter velocity is slowed somewhat in these encounters, it is not
a great effect: 
and 3.4, respectively, for the 2:1 and
3:1 mergers, compared to 
for the comparable 1:1 merger.
As the mass of the companion is reduced, the parabolic encounter speed
simply drops asymptotically towards the escape velocity for the primary
galaxy, 
at the given perigalactic distance,
and not much time is gained for the encounter to
strongly perturb the disks.