Tach Truths

TACH TRUTHS

Tall tales of the tachometer

Sportbike enthusiasts the world over got revved up when Yamaha unveiled its new YZF-R6 last fall, a bike featuring a tachometer scaled to 20,000 rpm with a whopping 17,500rpm indicated redline. No streetbike had come this close to producing Formula One engine revs, something Yamaha ballyhooed loudly in the YZF’s ad campaign. The industry was abuzz.

Independent dyno tests following the bike’s release, though, revealed that the R6’s rev-limiter actually cut in around 16,000 rpm. Oops! News of this quickly spread, and Yamaha found itself under fire from consumers who believed they had been misled. To Yamaha’s credit, it has admitted the screwup and offered full refunds to R6 owners dissatisfied with the bike’s true rev limit, even covering finance costs for those who took out loans to get their bikes.

The simple truth is that optimistic tachometers are quite common on today’s bikes. To illustrate this fact we checked the tach accuracy on each of these middleweights, comparing indicated rpm with readings acquired on CW's Dynojet Model 150 rear-wheel dynamometer. Of the five bikes, only Honda’s tachometer provided dead-nuts accuracy all the way to redline. Of the offenders, the Yamaha was found guilty on not one, but two counts.

While the Kawasaki, Suzuki and Triumph all display a certain error (about 8 percent) that remains largely consistent throughout the rev range, the Yamaha’s tachometer error increases in magnitude as revs rise. The error is 2 percent at 5000 rpm, increasing quickly to 5 percent at 10,000 rpm and nearly 12 percent at redline. This, along with the flat nature of the R6’s power delivery below 10,000 rpm, produces an effect that makes it appear as though the engine accelerates more quickly than it really does in the upper rev range. Mistake, marketing ploy or outright deception?

Before we take tachometers totally to task, consider the fact that speedos have been chronic liars for years. Goes to show, there really is something in the company one keeps.

Don Canet