RB5 (SP2) has a 270mm wheelbase, RB6 has 285mm wheelbase, the RT5 has a 286mm wheelbase.
If you consider the swept angle of the driveshaft and suspension arm (due to toe-in angle), a longer arm reduces the wheelbase relative to a shorter arm... This angle of driveshaft and suspension arm seems the same on the RB5 and RT5, so if only the tub changes the wheelbase on the RT5, then you could expect a +14mm-ish wheelbase I guess?
