Rad Mini ST Shuddering in 7th Gear

[TNOutback]

I just bought a Rad Mini 4 and a Step Thru 2.  The ST, while in 7th year (and 6th to a lesser degree) shudders and vibrates severely.  The derailleur and the High/Low stops are correctly adjusted, and I get good shifts up and down in all gears. However, when the bike is in 7th gear, the chain vibrates severely and you can feel shuddering in the cranks and the bike.  You can sense it a little in 6th gear, but mostly in 7th gear.  The remaining gears are smooth.

Any ideas?  This does not occur in my Mini 4.

[Altema]

Perhaps a defect or mismatch in the freewheel cog. I'd take to to a bicycle shop and have it checked by a mechanic. If they determine what the problem is, you can contact Rad and they can send you the replacement part.

[TNOutback]

Upon closer inspection, the chainring is bent!  Turning the cranks you can see that it is warped.  Rad will replace under warranty, but they have none in stock and no idea when they will get them again.  Supply chain woes!