diff --git a/nhf/parts/joints.py b/nhf/parts/joints.py
index 2f5b62b..bb1c449 100644
--- a/nhf/parts/joints.py
+++ b/nhf/parts/joints.py
@@ -271,6 +271,8 @@ class TorsionJoint:
 
     groove_radius_outer: float = 35
     groove_radius_inner: float = 20
+    # Gap on inner groove to ease movement
+    groove_inner_gap: float = 0.2
     groove_depth: float = 5
     rider_gap: float = 1
     rider_n_slots: float = 4
@@ -285,7 +287,7 @@ class TorsionJoint:
     def __post_init__(self):
         assert self.radius_track > self.groove_radius_outer
         assert self.radius_rider > self.groove_radius_outer
-        assert self.groove_radius_outer > self.groove_radius_inner
+        assert self.groove_radius_outer > self.groove_radius_inner + self.groove_inner_gap
         assert self.groove_radius_inner > self.radius_spring
         assert self.spring_height > self.groove_depth, "Groove is too deep"
         assert self.radius_spring > self.radius_axle
@@ -415,7 +417,7 @@ class TorsionJoint:
         contact_profile = (
             Cq.Sketch()
             .circle(self.groove_radius_outer, mode='a')
-            .circle(self.groove_radius_inner, mode='s')
+            .circle(self.groove_radius_inner + self.groove_inner_gap, mode='s')
         )
         if not self.spring_hole_cover_rider:
             contact_profile = (