Chain length?

[FNG]

I'm putting 15/51 tooth sprockets on my '98 steelie and wondering what link length chain I need to get. Anybody know??
I don't have an old one lying around to compare it with...

[lewisclan]

get a 120 then you can break it where you need to

[sabreguy]

get a 120 then you can break it where you need to

Yup

[AlisoBob]

I'm putting 15/51 tooth sprockets on my '98 steelie

15 on the countershaft = Go fast

52 on the rear = Go slow

Your confusing your bike.....

[Roostius_Maximus]

go smaller gears that are similar ratio and sling less inertia

[AlisoBob]

go smaller gears that are similar ratio and sling less inertia

Yuppers......

http://www.dropbears.com/u/utilities/sprocket.htm

13x45 is 3.46:1

15x51 is 3.40:1

[bearorso]

He may be thinking of chain and sprocket life. Bigger sprockets last a Lot longer, and the chain lasts longer as well.

I use 14/51 and 15/51 for those reasons - the 14 gives me the lower gearing for my normal tight stuff, the 15 brings it back to just a tad higher than the 14/49 my bike came with as std.

The swing arm chain slider wears much better, plus I prefer the way the rear suspension works with bigger sprockets.

[seanmx57]

The bigger rear gives it a mechanical advantage if you are comparing identical ratios. Pro bikes are set up like that to.

Cut the 120 for sure.

[AlisoBob]

The bigger rear gives it a mechanical advantage if you are comparing identical ratios.

How you figure?

[seanmx57]

The bigger rear gives it a mechanical advantage if you are comparing identical ratios.

How you figure?

I'm prolly wrong, I've read well over a dozen times in MX mags how they run bigger sprockets for more mechanical advantage. Maybe it has more to do with spilling a tooth ratio wise. IE going from a 14 to a 15 yields 3.5 on the rear. most likely they are not identical gearing.

[MojoScojo]

Gonna talk out of my ass because I really don't have a clue here...

My thoughts:

Larger sprockets = more mass.
Larger sprockets = longer chain = still more mass.

It seems going that route means more flying mass and a greater flywheel effect. Might be good, might be bad depending on what you're after.

As for mechanical advantage. I'm not seeing that. I understand how larger rotors on brakes = better brake performance, but that has more to do with controllable friction over a larger surface area. Entirely non applicable on propulsion.

BMX'ers are currently going the small sprocket route for weight savings. After having just bought one for my kid, it's clearly effective and it seems to be at least as effective as large sprockets. I would think a mechanical advantage of that nature would show itself quite clearly in that arena. It's pretty impressive what they're doing with those things compared to when I was a kid.