Like many age-old arguments, the bitter battle over chain tension has been discussed for decades. Although chains have their downfalls like high maintenance and more friction compared to a belt-drive, a chain strikes the best balance of strength, efficiency and cost.
But unlike belt-drives that have self-tensioners and driveshafts that are equally unadjustable, chain-drive systems have an element of user involvement. Along with having to keep the chain/sprockets clean and greased, the chain tension must also be properly set. And therein lies the gray area that’s prompted the controversy. Some have said that a tight chain is the best way to accurately transfer power to the ground, following the belief that the tighter it is the better it performs. On the other end, some feel that a tight chain can cost upwards of 10 HP at the wheel due to the increased friction.These folks stick to the factory specs when it comes to chain tension.
If the chain's too tight it...
If the chain's too tight it ain't right, and will steal power throughout the entire rev range.
Since measuring actual chain tension would be difficult, we took the unscientific route of tightening the chain to oblivion. It was tightened so much that there wasn’t a hint of chain movement and the adjustment nuts were so tight it was difficult to turn them with a wrench. For the baseline, we adjusted the chain to the standard measurement of approximately one-inch of slack at midpoint between the countershaft and the rear sprocket without a rider sitting on the bike.
Like always, the dyno runs were conducted on the same day, within five minutes of each other with water temps at the same points and without altering variables like tie-down tension, etc. in order to keep it as scientific as possible. ssb
With the 2009 Kawasaki ZX-6R test bike up to normal operating temperature we hit the dyno with a baseline of 109 HP and 42.7 LB-FT. After cranking the chain tight enough that it scared us, we again spun the drum, but this time to the tune of 106.8 HP and 41.8 LB-FT. for losses of 2.2 HP and just under 1 LB-FT.
Unlike our 520 conversion last month, that cut friction (and weight) by way of a smaller chain and sprockets, the increased friction of the severe chain tension killed over 2 HP at the wheel. This was a double bust, because a tight chain robs power, but it certainly doesn’t rob over 10 HP at the tire.
Instead of the extremes, keep your chain adjusted to the factory recommendations and remember that tight isn’t right since it’ll cost you power, puts premature wear on the chain/sprockets and loads the countershaft to the point of potentially ruining the bearing.
2.2
Horsepower lost at the wheel with overly-tight chain
Special thanks to Gene Thomason Racing