Q&A Forum
Hi, I have just done a retrofit on my bike dyno, Inertia type. I am familiar with Your dyno ( I have braked chassis and engine dynos using Your dyno). My result input data seems good RPM gear ratio etc. The run seems to match the bike rpm and mph but I am getting High HP readings (factory bike is 29 HP (engine)) and I get around 42 HP, too much of a difference. I have NO compensations on for losses so it should be just raw calculations and a small weather correction. What have I over looked? I built the roller, three different moi calculators give me the same result and I did weigh it when I made it and the total weight matches the Moi calculator weights so it must be close (11.57Kg/m²). I only want power at the rollers. Any suggestions would be appreciated.Cheers
Hi,
For an inertia dyno there are only two possibilities:
1) The number of pulses per revolution in the RPM setup0 is wrong. This would also give wrong speed if the diameter is right. The Engine RPM will be right since you set the gear ratio
2) Wrong MOI
Thanks for the reply. roller rpm is around 800, I have a 40 tooth wheel which i think is ok. The roller rpm data is stable. I have used Dtec, performance trends and sport devices roller inertia calculators and they all give the same result. I'm quite sure I have overlooked something. I shall revisit the issue with a fresh mind tomorrow.
So, with the Moi re visited, my old notes checked I am locking in my inertia value as correct. Which only leaves RPM setup. The now removed Performance trends setup used one magnet on the roller, I had a disk rotor on the shaft so i used a hall effect directly pointed at the cooling fins for the Your dyno conversion. So today I machined the rotor outer diameter and the fins deep enough to produce a sharp square edge on each fin instead of the cast surface. Problem solved, I have gone from 42hp to 10hp. This is more like it. Tomorrow I can do a coast down test and add back the dyno losses. I think the problem is solved. I don't understand how the data like rpm,mph didn't show any erratic readings and the graphs were quite smooth but im sure there is a perfectly good explanation. I'm only Guessing but a bike with advertised 29Hp should show around 20Hp at the wheel. Cheers