Strictly speaking they all vary slightly one way or the other from 'true' 60D. 60D is an all-encompassing generic Tamiya term, no more than that.

And pretty much all the Tamiya Mini tyres (except for the ones on the XB kits) are this size.

I dont double stuff - it's just another thing that distracts you from getting out and actually running, which is WAY more important than any amount of messing around with inserts.

Keep it Simple...