diff --git a/cadnano_segments.py b/cadnano_segments.py
index e2619209f0e7d41a3cc78ae8758081cf3ebe4c8a..585b3681a04191024dd7f666027e67dbb9bfdfae 100644
--- a/cadnano_segments.py
+++ b/cadnano_segments.py
@@ -625,7 +625,7 @@ def run_simulation_protocol( output_name, job_id, json_data,
         simargs['timestep'] = 50e-6
         model._update_segment_positions(coordinates)
         model._clear_beads()
-        model._generate_bead_model( 1, 1, local_twist=True, escapable_twist=True )
+        model._generate_bead_model( 1.03, 1.03, local_twist=True, escapable_twist=True )
         model.simulate( outputPrefix = output_prefix, numSteps=fine_steps, **simargs )
         coordinates = readAvgArbdCoords('%s.psf' % output_prefix,'%s.pdb' % output_prefix, '%s.0.dcd' % full_output_prefix, rmsdThreshold=1)