Atk Chain Tensioner

ATK Chain Tensioner

EVALUATION

Besides transmitting power from the transmission to the rear wheel, the chain drive on a motorcycle affects the rear suspension and vice versa. And as rear suspensions gain in travel the effects of the chain on the suspension and the suspension on the chain have been amplified.

The problem is that the swing arm doesn’t generally pivot at the center of the countershaft sprocket, so that as the rear wheel goes up and down the chain tension changes. Also, because of the differing angles between the swing arm pivot and rear sprocket-chain tangent and the countershaft to rear sprocket tangents, the pull of the chain during acceleration tends to extend the rear suspension.

Street bikes have generally survived these problems because of limited suspension travel, while off-road machines have used a variety of chain tensioners. Horst Leitner wasn’t content with that approach. What bothered Leitner most was the effects of chain tension on suspension loading. His solution is a bolt-on chain tensioner that mounts on the swing arm pivot and spreads the chain into a parallelogram shape from the swing arm pivot to the rear sprocket.

Mechanically, the ATK is a straightforward bit of hardware. There are two rollers to spread the chain, one a rubbercovered non-toothed roller and the other a metal toothed roller. Both spin on roller bearings. The rollers are held in nicely formed aluminum housings that clamp around the swing arm pivot with a pair of long bolts.

With the ATK installed on a motorcycle, all the various sections of drive chain remain a constant length whether the rear suspension is bottomed or fully extended or anywhere in the middle. And what is most important to Leitner is that the chain runs parallel to the swing arm from swing arm to rear sprocket, without pulling the rear wheel up or down during acceleration or braking.

Leitner has pages of figures showing that the normal chain tension can have up to 500 lb. of downward force on the rear wheel, extending the shocks, raising the chassis and reducing suspension effectiveness. After looking at all those figures, we wouldn’t want to argue that with him.

There are other factors at work here, though. During acceleration there is substantial weight transfer to the rear wheel, loading the rear suspension as the force on the chain seeks to stretch the rear suspension. Ánd Leitner will admit that his ATK would not be an advantage to a drag racer because of that. Where the ATK benefits a motorcycle, he says, is on a road racing course. It’s especially important for exiting bumpy corners when application of throttle will tend to force the rear wheel down and out, reducing traction, he says.

To prove his point he invited members of the motorcycle press to Riverside Raceway to ride around on a fleet of Kawasaki KZ550s, some with the ATK and some without.

The editor who raced a KZ550 in box stock rode his 550 to the track and rode around on the bikes (from the California Superbike School) with and without ATK. His conclusion was that he noticed more difference between stock bikes and other stock bikes than between the stock and ATK equipped bikes. He reported no noticeable improvement, overall.

Next, Leitner volunteered to install an ATK on a test bike. The Suzuki GS1100 was volunteered. Installation took a couple of hours for the designer of the ATK. When he was done the apparatus wasn’t immediately noticeable on the Suzuki. On the first ride after installation two things became immediately obvious. The rear wheel was misaligned and the chain hit the chain guard.

Re-adjusting the rear wheel so that it was aligned properly brought the handling of the motorcycle back to original condition. The noise persisted. During sudden deceleration the chain would slap at the chain guard, making a banging noise. Even during steady cruise the large 630 chain would make a loud howling noise with the ATK. No one noticed any improvement in handling or ride on the already plush riding and generally good handling big Suzuki.

The ATK remained on the Suzuki for about 2000 mi. until after a trip up the coast. Half way through the trip the chain began producing a much louder grinding noise and the rider assumed the bearings had gone out. He limped home without serious problem, the chain producing threatening noises all the way back.

Back at the Cycle World garage the ATK was removed. One of the two bolts holding the ATK to the swing arm had broken, enabling the device to rotate on the swing arm and causing more interference with the chain.

Leitner’s claims for the ATK are for improved roadholding, increased comfort and reduced tire wear because wheelspin is eliminated. Our experience does not support these claims.

The ATK system is available for a wide variety of modern motorcycles from the Leitner Corp., 5132 Skinner St., Irvine, Calif. 92714. List price is $98.