Chain Slack Calculation?

[cb23]

Hi guys -

I run a 2-stroke race car (which is why I hang out HERE). the final drive is a 2 inch wide belt. For various reasons (dramatic weight savings (major power train mods), 2 less bearings + 1 less CV joint + 1 less U-joint, and less rolling resistance), I am considering going to chain drive.

My concern is that as envisioned, the chain will go from tight to very loose, very quickly, based on what the rear axle is doing.

Center-to-center will be roughly 18 inches. Max axle movement is probably 2 inches up or down. Detailed drawings indicate that the chain will get about 1/2 inch longer or shorter during this movement. Taking a length of string this long and moving it in 1/2". . . Seems to create almost TWO INCHES of slack, measured with rulers.

So, first question: Anyone know the equation to calculate the slack created from changing center-to-center distances? Google searches fail me.

Second, are chain rollers/guides/slides up to such a task without robbing all the horsepower I hope to gain (83 hp now at crank)

 

[Jaybird]

The calculation can varry some depending on the application.
For our (and your) purposes, you should have ~2-3% of the total shaft distances in chain free play. (this is total up and down play)
This should be checked when the suspension is in it's tightest possible condition.
I recommend going with the larger percentage on shorter shaft distances. In other words, with such a short distance between your shafts, I would keep the chain at the 3% number.

http://www.best-motorcycle-chain-lube.com/chain_maintenance.htm#intitial-chain-adjustment