track chain length

i have a brand new chain and need to size it correctly

i have a 46, 50 and 51 chainrings and 14/15/16 cogs (does anyone have a 49t in 151 bcd?)

so...

the largest length of gear i have will be a 51/16, the smallest is a 46/14

to get the most out of this chain, which gear should i use to get the most useful length?

I use 48 links which lets me fit 47-51T on the front with 13-15T on the back.

It also depends on the length of your rear dropouts

[Gemm]

I think you need to think of which is the largest gear by chain length you are ever going to use (if that is a 98.4" 51/14 then so be it), fit wheel into dropouts almost to the limit forwards, fit chain. If it is too long for your other common applications, take a link or two out.

But Luke is correct the overall dropout length is the determining factor, old frames like yours have shorter dropouts when compared to something like a BT! So you almost certainly need two chains (or an extra link setup) to run all your possible combinations. An extra link (or two pairs of links) are handy to have anyway, just get some 'fish' type old-school connectors and whatever is left over from your new chain to make them.

And remember, the fish always swim forwards, kids!

ok well i guess ill just go to my most used gear (90) and give it a bit of room to move both ways

was not sure if there was a more scientific way than that!

[DanielS]

Good timing with this thread.... I'm going to install a new, longer track chain this evening so that I can run a 50 up front. I think I just need a link or 2 more than whats in my current chain...

[Gemm]

ok well i guess ill just go to my most used gear (90) and give it a bit of room to move both ways

was not sure if there was a more scientific way than that!

Well it's pretty basic science, the distance between each pair of chain pins is 1", so ignoring the chain angle coming off the rear sprocket, removing or adding one set of links will move the rear axle in the dropouts half that distance (slightly less in real life). So adding or removing one chain link = 1/2" of rear axle movement.

And you can again work from that in adding a tooth to the front chainring or to the sprocket is therefore a 1/4" movement at the axle forwards. Or removing a tooth, same thing backwards....

Is that enough science for you Stab?

that is pretty much the ideal answer, thanks