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The first and most obvious difference is the elimination of the tire to roller interface on a conventional roller dyno.
The Dynapack™ eliminates this variable by using a hub adapter that provides a direct coupling to our Power Absorption Units. There can be no tire slip, no rolling resistance, and no chance of the vehicle coming off of the dyno at high speeds. Notice that we call this a variable. Sometimes it may be a problem area, other times it may not. Tire temperature, pressure, traction, etc, are all variables that can change – not only from run to run, but during the run as well.
Throw an unknown variable like this into the equation and your data has now become subject to a potentially high margin of error. It is obviously better if these variables could be eliminated – which is exactly what we have done. There are other associated problems with the roller method as well. Take tie-down straps for example, most roller dyno’s use ratcheting tie-down straps to attempt to hold the vehicle in position while being tested. If the straps are cinched down tightly, the tire has become loaded even further, in an unpredictable manner.
While this may be good for enhancing traction, it changes the rolling resistance of the tire – skewing the data further. Since these tie-down straps aren’t perfect, the vehicle squirms around on the rollers – dramatically changing the tire drag during the run. If the vehicle is tested in two different sessions, the straps can’t be set exactly the same way twice in a row. Again, the data will be inconsistent.
We have heard of cases where the ratcheting tie-down straps were loosened by two clicks and the measured power increased by ten horsepower. What if the straps stretch – either from run to run, or during the run itself? Wouldn’t it be great if all of these problems could disappear? With a Dynapack™, they were never there in the first place.