Changed Free Boss type sprocket

I used Shimano 7s MF-TZ21 ( 14-16-18-20-22-24-28T ) for rear free boss type sproket.
For front chain wheel, I use no maker logo 42-52T, But Front derailleur can't attached, because the BB's shaft is too longer. it is for belt drive.

My top speed is 32 km/h with front 42T x rear 14T. Now I can ride more stably.
So I want to try riding more speedy.

Then, I bought New Boss free sprocket made by DnP in Taiwan.
LY-1107HFN ( 11-13-15-18-21-24-32T ).

I rode with this sprocket in this early morning. I can get the speed 35.5 km/h with front 42T x rear 11T.
Off course, Safety driving is the first one.
Fine.