Thruxton Wheels On Speed Twin 1200 (2021 Model)

The Thruxton "R" and Speed Twin wheels are completely interchangeable, I fitted ST wheels to my Thruxton R and sold my Thruxton wheels to a Speed Twin owner. As far as I know the RS is no different to the R, so it should be OK. Is it the front wheel or the rear you are having problems with?
When you say "mounting rod" is that the rod that goes through the forks and the middle of the wheel hub? That is called the "spindle".
I will have a look at the compatibility of the RS.
****UPDATE*** After looking at the Speed Twin specs, I've found the 2021 (and later) bikes have different and larger (Marzocchi) forks. The Thruxton RS has the same Showa forks that the Thruxton R had. All of which means the Thruxton wheels are only interchangeable with 2019/20 Speed Twins.

 

I think I have found your problem. The forks on your 2021 Speed Twin are different to the 2018-2020 Speed Twins..The old model had 41mm forks - (I can't find out what make, but they might be Showa), the 2021 ST uses 43mm Marzocchi's. The Thruxton RS still uses the same Showa forks as the older Thruxton R. You might be able to sell the wheels to a Thruxton R owner as they're black.