I generally agree that if you can do RSR, you should be okay doing the TT speed portion. The speed portions feel different to me, so it really depends on what things your Mom does or does not like. If it's pure speed, then TT goes faster (the peak speed is 65 mph for TT and under 40 mph for RSR). I personally think you can feel the speed difference between the two, but it is similar to riding in a convertible or any open top vehicle. In terms of turns and drops, TT's speed portion has no drops and only wide, sweeping curves. RSR has many more hills/valleys and much sharper turns.