>>1204812>>1204717I'm getting 45mph/70kph with the cadence maxed out at 120rpms since he said he was spinning out.
That's about the fastest I ever clocked myself. I was spinning out, too, but it was on a moderate downhill and I have no idea what the gearing was. But it was a "corncob" cassette so my uncle probably had it set up to a similar max. It was also in traffic so it was hard to maintain a straight shot.
It's good if you can hit that on a flat, and more impressive if you can sustain it for any meaningful distance. But I don't think it's terribly unusual, I mean I was in shape to hit that but I didn't train at all. I was riding 5 days a week then but usually only 20-40 mile days.
Anyway, the answer to your original question is to put a 52 tooth or higher ring on, which is easy and cheap, although fancy rings get pricey. the ring has to match the BCD measurement of your crankarm spider. grease and tighten the bolts well to prevent creaks. There are a few 9 and 10t cog cassettes out there but probably expensive. Not esp hard to swap out but you do need a cassette cracker tool. Rings just need a standard allen wrench (hex key).
You can play around with this:
http://www.ritzelrechner.de/?GR=DERS&KB=34,50&RZ=11,13,15,17,19,21,23,25,27,30,34&UF=2150&TF=120&SL=2.3&UN=KMH&DV=teeth 