Triathlon on single-speed

^that's a BMX freewheel - it won't fit on your hub, so you'll have to go 48t anyway.

Larger cogs/chainrings roll better - that's the theory anyway. You don't need to replace the crankset, just the chainring. Just let BC fit it if you're unsure of wrenching protocol.

fair-e-muff, think that's what the chaps at Brixton said. ta.
http://cgi.ebay.co.uk/Vintage-Dural-Force-48-Tooth-Chainring-130mm-BCD_W0QQitemZ110274272953QQcmdZViewItemQQptZUK_sportsleisure_cycling_bikeparts_SR?hash=item110274272953&_trksid=p3286.c0.m14&_trkparms=72%3A1683%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A0%7C293%3A1%7C294%3A50