“Power on demand”
There are many reasons why people dyno their bikes. For some, it’s simply to find out and talk about how much power they have. For others, it’s a way to evaluate modifications and performance. But what do those numbers mean? how accurate they are? and do they really matter anyway? Here is all you need to know about dyno
The payoff for allowing your bike to be violated is that little sheet of paper with some wriggly lines, which allows you to say, “My bike makes X horsepower” or simply to know if your performance upgrades are actually doing their job as it is claimed by the manufacturer.
How is a “Dyno Run” done?
These days, when we talk about dynos, we’re talking about chassis dynos (also called inertia dynos), but some engine dynos are still popular with manufacturers and some tuning shops. There are several different makes of dyno machines but, at the most basic level, they all work in a similar way. A bike is attached to dyno in such a way that it can’t move, while driving wheel act on a heavy, metal roller. The dyno operator puts the bike in gear and rides just as he would on the road. The difference is, rather than pushing the bike forwards, the real wheel spins the metal roller and this is how power and torque figures are calculated.
There are different types of test, with varying names, like “Roll on”, “All gears”, “Cruise”, “Fast acceleration”, “ Negative horsepower”, step and load testing as well as breaking-in a new motorcycle on dyno machine. The easiest and most repeatable of these is the roll-on test, which is the one printed in magazines and nearly always done first. To do this the bike is generally put in fourth gear although the actual gear doesn’t matter but if the gear is too short (lower gears) there will be a lots of wheel spin and it will appear that power has been lost, equally, if the gear is too tall (higher gears) the engine will take a long time to spin the roller, getting hot in the process and in extreme cases won’t rev out completely. Ones in gear, the rpm’s are allowed to drop, before the operator quickly but smoothly opens the throttle to the stop. At the same time the operator activates the sampling button and computer start recording the run, when the engine hits the rev limiter, the operator shuts the throttle and stops sampling. The dyno now has a record of the engine revs and the rate at which the roller was accelerated. The process will be repeated several times until power output reaches consistent level.
Different results? If you look at the dyno results for the very same bike from two different dyno shop you may see different numbers. There are two different ways to interpret results. At the ignorant end of the spectrum, you can say there was a fair bit of difference between highest and the lowest figures recorded sometimes 4,5,6,7,8, hp . In fact , in internet bikers forums, this disparity is more than enough to inspire ill-informed geeks to get condemnation – happy about certain dyno shops or brands. But if you apply a little bit of thought , you will see things in a different light. It is very simple….
Dynos are tools that provide reference points, you can compare any results produced by the same dyno, but comparing sets of data from different dynos carries risks – especially if the dynos are different makes or models. Take your bike back to same dyno all the time , if you can especially if you want to make meaningful comparisons. If you are thinking about getting some tuning work done, your claims about performance gains will only be valid if you used the same dyno. So as long as you see the hoped for before-and-after figures (and feel the difference when riding) . Don’t worry if your bike records a lower result on a different dyno.
I will be adding more info here, please stay tuned.
Y.T.