[OXO cube]

hi guys 

does anyone have any experience with:-
 'Slot.it S1 Silicon Slick F1 Tyres 20.4x12.4 Dwg 1068 ' ?

i need silicon tyres for a proxy , which is using silicone rears in the rule set
   
this is the tyre before truing 
   
this the tyre after the 1st rough grind
   
after a fine grind with wet&dry 


these tyres are supposed to be silicone , but do not feel very soft , and grind very similar to stock Scalextric tyres ?

this is my 1st time using silicon tyres , is this normal ? or are these tyres not the correct type ?
if they are wrong , does anyone know a UK supplier for similar ( does not need to be exact same ) size proper silicon tyres ? 

thankyou in advance 
Kev