IMO the chin strap adjustment should not change between wearings. You should only need to adjust it once and it should stay adjusted. It certainly does on my Giro helmets, also owned by Bell.
If the adjustment is changing then adjust the strap length correctly then sew the straps together so they cannot change adjustment.
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Gear Hubs Owned: Rohloff disc brake, SRAM iM9 disc brake, SRAM P5 freewheel, Sachs Torpedo 3 speed freewheel, NuVinci CVT, Shimano Alfine SG S-501, Sturmey Archer S5-2 Alloy. Other: 83 Colnago Super Record, Univega Via De Oro
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