GrumpyGregry
Here for rides.
Spot of thinking out loud...
Singlespeed/fixed road bike 42t x 16t = 70" or so. fine and dandy. On my commute we have one or two 17% - 20% climbs which I can only just manage. I want to buy a Sturmey S2C to use for club runs of a weekend (much longer than my commute) and set it up as 2nd = top + 1st as a hill climbing gea,r rather than direct drive 1st and overdrive 2nd, as we regularly tackle these hills on the back of the club run when I'm knackered.
Can't get my head round the basically simple maths! on this hub 2nd is 138% of 1st. If I want a 70" ish top and 100 is 72% of 138 then I need ratios that give me 72% of 70 inches right? Which works out at 50"ish yes?
So if I keep my 42t chainring and put a 22t sprocket on the S2C then in top I'll have what I want more or less yes?
Ok now during the week I'll want to run her fixed using the stock wheel 16t and weekends 2 speed using a wheel with the sturmey in. 16t to 22t difference is 6t. With a normal chain pitch and using the same chain my next question is how much further back in the frame will the 16t wheel sit vs the 22t wheel? I think I read somewhere 4mm is 1t so 6 x 4mm = 24mm or nearly an inch. Does that sound right? Best I measure my track ends.
20t sprocket would give me 56" inches in direct drive and thus about 77" in top right? But would cut the shift in the drop outs to 4 x 4mm = 16mm which sounds more realistic to me. A slightly higher top for club runs is no bad thing if I've got a bail out gear for the steep bits right? So maybe 19t is also an option?
Singlespeed/fixed road bike 42t x 16t = 70" or so. fine and dandy. On my commute we have one or two 17% - 20% climbs which I can only just manage. I want to buy a Sturmey S2C to use for club runs of a weekend (much longer than my commute) and set it up as 2nd = top + 1st as a hill climbing gea,r rather than direct drive 1st and overdrive 2nd, as we regularly tackle these hills on the back of the club run when I'm knackered.
Can't get my head round the basically simple maths! on this hub 2nd is 138% of 1st. If I want a 70" ish top and 100 is 72% of 138 then I need ratios that give me 72% of 70 inches right? Which works out at 50"ish yes?
So if I keep my 42t chainring and put a 22t sprocket on the S2C then in top I'll have what I want more or less yes?
Ok now during the week I'll want to run her fixed using the stock wheel 16t and weekends 2 speed using a wheel with the sturmey in. 16t to 22t difference is 6t. With a normal chain pitch and using the same chain my next question is how much further back in the frame will the 16t wheel sit vs the 22t wheel? I think I read somewhere 4mm is 1t so 6 x 4mm = 24mm or nearly an inch. Does that sound right? Best I measure my track ends.
20t sprocket would give me 56" inches in direct drive and thus about 77" in top right? But would cut the shift in the drop outs to 4 x 4mm = 16mm which sounds more realistic to me. A slightly higher top for club runs is no bad thing if I've got a bail out gear for the steep bits right? So maybe 19t is also an option?
