I have both the Spit and the Corsair and yes, the supplied wheels are too small. On the Spit I have taken the vac-formed wheel wells out and opened them up to 4" dia using 3.5" wheels with 7/16" oleos. Much better for grass.

I'm using Robart 609HD mechanical retracts and have had no problems with them in 9 months flying.

Still not sure what retracts to put in the Corsair as I haven't started it yet.

Pete