touring/gearing question

[agentpineapple]

dam that gearing commander website confuses me.
so atm i'm running lower gearing and a 520 pitch chain, i'm 15/42.
it's great fun when going for a blast, I really like it, but dam the fuel economy suffers, as you become more addicted to the throttle
on a recent 700+ mile ride to Madrid and Valencia my fuel economy was poor, ok i'm built like a brick shite house, so it's always going to be worse than an average sized person.
but I was riding with a friend, and he's a self confessed plodder, and after a while I began to see the appeal of slower riding, hey we were touring after all.
so i'm looking into lengthening my gearing for when I go touring.
i'm trying to work out the chain length if I was say either 17/40 or 17/41 maybe even 16/40
has anyone an easy way to figure out what chain length I would need, I have a spare std length 520 chain, iirc it's 102 links, so maybe I can work it so my gearing is higher than std and I can keep the std chain length.
any ideas ladies and gents?

[Cadbury64]

My dumb approach would be that with gearing changes, the chain runs between the sprockets stays the same, so the added length is just down to the additional runs around the sprockets. And then assume that you only go around half of each sprocket. If you currently have 15/42 then the chain is running around half of 57 teeth (28.5). If you change to 16/40 then the chain is now running around half of 56 teeth (28). In that example, no need to change the number of links in the chain, you will just end up with the rear axle slightly further back in the adjuster to take up that additional 1/2 tooth length.

[tony.mon]

Just order a longer chain than is needed and cut off links that you don't need.
The cost is the same.

[popkat]

Fit your standard chain and standard size sprockets, bike is quick like that anyway, with the 520 you could be releasing up to 2 hp with less friction loses. std gearing works well, top gear is a bit of an overdrive but it'll cruise nice at 80-85 in top without revving too high.



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