Trikester, I think between your new tires and the chain conversion, your speedo is a little further off than originally from the factory.
The chain conversion may have made the error larger, I don't know what the ratio difference is from the stock belt drive.
The larger tire diameter would bring the difference down since the bike's readings are high. On my '12 DS I increased the rear wheel diameter a lot because I increased the rim diameter
and put on a larger tire, it brought the error down to almost nothing since that bike was also reading high before the change. An increase in wheel diameter brings down the bike's speedo / Odo readings since they come from the motor. I was lucky that on the '12 it just about cancelled the bike's error in readings.
Harlan, do you know the chain ratio and the belt ratio for my FX?
Trikester