This thread was from when Silent runner wheels first came out and we were all trying to fix them together and working out the joining strip. I actually contacted the manufacturers who confirmed the 9" and 12" have different lengths of joining strip. The 9" is about a centimetre shorter. So it can't be I have the wrong joining strip or there'd be a bigger gap, but it may be a faulty joining strip.
New Silent Runner wheel in Uk
Cloudy - yes I can imagine those Tic Tac wheels would be sturdier on the stand and it also maybe depends on how strong your cage bars are for cage mounting. Looks like it will last forever!