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"Fast Bikes", May 1, 2013


Most would like to know exactly how much power their bike makes. But how, why and what is a dyno?

Have you had your bike on a dyno yet?

Frank Wrathall Snr. has been running Dynojet UK, the official importers of Dynojet kits, Dynos and Power Commanders, for nearly ten years. In that time Frank has completed between 50 and 60,000 dyno runs and owns two fixed dynos and one mobile one. He knows a thing or two about machines that tell you your bike’s power...

“There are two types of dynos, or dynamometer to give them their correct name. The Dynojet models we import are a rolling road dyno, however there are also engine dynos. An engine dyno doesn’t involve anything other than the engine. Engine dynos come in either static or dynamic form. The static one just measures the engine’s output while a dynamic one can alter the resistance and effectively simulate being on a specific track. F1 teams use dynamic dynos to set up and test their cars’ motors for each race using this technique.

“Most bike riders are likely to encounter a rolling road dyno, which tests the horsepower produced by a complete motorcycle, rather than just an engine on its own. A dyno consists of a metal structure that supports the motorcycle in place and beneath that is a very accurately machined drum that sits below the rear wheel. This has a knurled surface and is the ‘rolling road.’ The drum itself is hollow, weighs around 200kg and is 18-inches in diameter, so it’s no small item!

“When the bike is run the rear wheel turns the drum and the dyno starts working. There are two ways of measuring the bike’s horsepower. If the dyno is fitted with load control then the horsepower can be measured dynamically, or statically by putting some resistance against the drum. However, the more commonly used technique is to measure the tractive force. We know the inertia of the dyno’s drum and also the resistance of the bearings, etc, within the dyno and by using these figures the computer can work out the tractive force, which is the force the bike exerts to turn the drum during an acceleration sweep. From this figure a computer program calculates horsepower and torque.

“The computer then displays to the operator a result chart with power and torque on it. These charts have correction factors – SAE, DIN, EEC, JIS – which are various country’s recognised correction factors. Basically, they are used to standardise dyno results as they take into account temperature, air pressure and humidity in the various regions around the world and alter the results to bring them all into line.

“Finally, when your bike gets dynoed you will notice that the operator inserts a sensor into your bike’s exhaust pipe. This is a lambda sensor and is used to sample the air/fuel ratio in the exhaust gases. For optimum performance you want an air/fuel ratio of between 12.8 to 13.2 parts air to one part fuel, which has been calculated as the best ratio for a good burn. Emissions laws, however, prefer the bike to run closer 14.7 to 1 to pass tests.

“So, what’s the point in a dyno? Simple, a dyno can not only measure your bike’s power, it can also ensure the bike is fuelling correctly and also help with engine, airbox and exhaust development without harming the engine. A skilled operator puts no more strain on a bike’s motor than a bike being used on the road.”

Fancy owning your own dyno, Frank will happily sell you one for £16,000. Failing that you can always pop down to your local Dynojet centre. See www.dynojet.co.uk for a list of dealers and tuning centres to take your bike to today!

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