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@853Superfly Thanks so much for your help. After all this great advice I've decided I'm going to ditch the Mango and try and build my own for the same budget. Hopefully it'll be a lot better! I'll probably make a thread in the projects section and see what people recommend for individual parts...
CJWilliams
@853Superfly
No worries we were all learners once :)
the larger numbers mostly 42/46/48 etc etc refer to the front chainring size.
the smaller numbers are rear sprocket/freewheel sizes 14/15/16/17/18
Track bikes and fixed wheel bikes tend to go on GearInch ratios, this also applies to Single speeds, it's the langauge used for bragging rights or working out how hard your gear is going to be to spin up.
http://www.bikecalc.com is fun, feed it your details, tyre size (as this affects gear inch) and ring sizes and it will work out how fast you go at certain RPM of your legs.
I put in the Mangos 46x16x25mm tyre to work out it's GI of 76.2 when you look at a broad chart of many ring sizes you see overlap in gear ratios.
So Dancingjames 48x19 = 15mph with legs spinning at 75rpm and 66.9GI
My lower 42x18 = 15mph with legs spinning at 82rpm and 61.6GI
The Mangos 46x16 = 15mph with legs spinning at 66rpm and 76.2GI
That dosen't look much of a RPM difference, but on fixed your legs always spin no coasting, so while i might be quicker off the mark than James he can catch up and match my speed with less effort in cruising speed, James can drop the hammer wind his RPM up and i might spin my feet off the pedals trying to keep up, going down a hill on a spinny gear is not fun either.
So the lower the gear inch number the more spinny but easier to push it will be.
So the fairly high Mango rating of 76.2 tells us that a newbie may struggle to pull away from lights and junctions and you might experince knee pain and be a bit wobbly as you try to ride off. Sticking another freewheel on is cheap and going to 18t brings you down to 67.7GI so still a good cruising speed but easier to spin up, going to a 20t freewheel will drop it again to 60.9 so it will be super easy to start on, but high speed cruising will be spinny.
I did run a 22t for offroading, that was rideable on the road but slow cruising speed, 42x22 = 50.5GI and at 15mph a spinny 100RPM.
It's about tailoring how fast you want to cruise in comfort, how far you want to ride and how demanding is your ride, and how fit you are. There is no right ratio to reccomend, the right one is whatever your happy with and SS and Fixed are cheap to play around with to find the magic one for you.