What your saying is that a precision engineered device, designed specifically for the purpose of measuring rwhp,rwkw isnt accurate because of factors that you think they forgot about. I can assure you they havent. Properly calibrated and with the correct software they give correct readings. In fact hub dynos are known to be more reproduceable than roller dynos. Im sure if you emailed dynapack they would be able to supply you with volumes of testing data to show they are accurate. Common misconceptions on car forums doesnt always make for good facts. No they give you a value in rwhp, as Ive said for the third time now, the difference is corrected for so they are universally compareable. It would provide dynapack and other hub dyno manufactureres no benefit to be producing numbers different to other dynos. Again, your missing the point. Because the hub dyno is so high it is likely to not be accurate. What Im telling you is because one hub dyno isnt accurate, its not a reflection on all hub dynos. As I said, in perth I can get 80rwhp difference on roller dynos on the same day. It isnt the dyno machine that it depends on but rather its calibration and software. Roller dyno quotes are what appear in my sig. In fact I only ever use a roller dyno when I test my mods because I know the one I use is accurate. The hub dyno I have used was within 5-10rwhp at all times.
Hehe, now this debate is quite interesting ... just hope it doesn't degenerate like so many before...
but nathan we not after perfect exact results. if we wanted that then the dyno would be in a climate controlled room at a certain dew point.I know where youre heading and you getting off the topic. If you can get hold of the data from dyno pac and if we could find out about the parameters programed with a: unsprung wheel weight: b : tyre noise and viabration; c: tyre profileing.. Then we can make ashuptions about the final output. As it is the the dyno list used by most of the member use a rolling road dyno {iso spec} . to add shifters dyno chart to it most of the members would want a correction to it. A 5 percent correction would not be a hard ask and most of the members would agree thats a fair correction to it. so at 286 KW at the rear wheel would be fair and the correction can be used further down the track. I know what you are getting at, but you got to realise that the equipment is only as good as the operater and most ofthe hub dynos either have no correction for different wheels or weight of the wheels themselves. lets face it you can lose 3 hps in a 30 gram out of balance wheel. shifter can tell us if his wheels where weighed at all??? shadow
Firstly Dont Quoute ME on that first one. That was a general feeling from forums across the world I haven't made any statement like that yet Can you perhaps tell me how it factors in the wheel and tyres into the calculations then? You said the weight of the wheel and tyres makes NO difference from the hub to the rollers (or road) I just figured as a man with a 'science degree' you can appreciate the concept of physics. Spinning a wheel requires energy. I didn't think they were after the same dyno numbers as roller dynos. Just ones that dont suffer drivetrain loss through the wheel because the that is a CONSTANT variable because of teh changine tyre temps, etc. (also the fact that its portable, quieter, doesn't take much space etc, could be why they are popular) Forget about my graph for a sec and ask if these dynos (dynopacks) results is what you put on the road out there My hub dyno looks high, but 40Kw too high? I'm guessing its meant to read higher than that of a roller.
lol your still missing the point There is no correction factor required to compare between a roller dyno and a hub dyno. The end measurement of rwhp or rwkw is the same. Yes there can be minor variations due to wheel differences, most of which is taken into account, but then the same can be said for roller dynos. The dyno shifter has used simply sounds inaccurate. To say that he should make a 5% correction, for no reason other than you obvioulsy think the dynpack engineers didnt know what they were doing is both pointless and unfounded in anything factual. What he needs to do is use a dyno that he knows to be correct, which he has. If shifter goes to another roller dyno which gives an extra 60rwhp should we also start correcting it down so it matches a hub dyno?
Dont know if the wheels were weighed On Monday, i'll check with them and see if they were weighed and their opinion if it does give a higher reading then roller dynos.
If you want to know their precise calculations then I suggest you email dynapack and ask them. It will essentially be based on an average wheel diameter and weight and Im guessing also a place in the software for you to enter it exactly if you have the details. Of course they are. They are quoting your graph in rwkw or rwhp hence that is what they are telling you they measured. To answer your last question with a question, forget about dynapacks for an instant and explain to me your argument for when you put your car on a roller dyno and it reads high. Fact is many are known to read much higher than they should. So how do you explain this away, is the roller dyno suddenly not reading rear wheel horsepower, has your car miraculously gained this hp during the drive between dynos or is it simply that the dyno is reading incorrectly? Your trying to make huge assumptions on hub dynos from a single innacurate one. If I took a single innacurate roller dyno then I could do the same thing.
Ive just dropped them an email They should have figures and documentation on exactly how accurate they are on quoting rwkw and rwhp figures when properly calibrated. Will let you know when I hear back from them.
Hmm There is no quote on my graph that says anything to do with rear wheels. My dyno sheet simply says 'Kw SAE' nothing about it being at the wheels or anything. And everywhere I see dynapak mentioned, it talks about being conncted to the hubs. I'm not just using my own dynapack graph here to base its 'high readings' on. Many people who have used different ones (if you read other forums across the world about it) all believe they give higher readings.
lol I know what you are saying for the newbies the problem is all dyno measure the force at the rear axles not the tyre. when you see a dyno chart for rwhp it corrected for the drive shaft reading not what is happening at the contact patch for the tyre. The problem is all dyno's do this correction automaticly. However hub dynos no not need that much of a correction because its measureing at the hub. hence hub dyno's tend to be more precise. The problem is most shops dont have acess to hub dyno's. so what this thread started out as ,was shifter noted the reading seemed high compared to rolling road dyno's and offered a correction of 10 percent. { 270 hps} I think thats a bit high and the correction should be 5 percent. the problem is nathan most people really want to now what the car puts out at the tyre contact patch and not at the axle. We got to have a level playing feild as well and a simple correction should be easierly entered. No one is saying that your wrong in the fact the hub dyno is more precise . It would be nice if they where in climate controlled room as well. however te problem is with the rolling road thats standard and the calibration that allowed from the ISO standard. { JP might be able to go through his manual and tell us what it is?????} it like the old beta vs VHS we all new beta was better but we all brought VHS due to it was cheeper and marketed better. that close enought Nathan? shadow
yeah I agree personally I prefer to know whats happening at the hub though. On the road I run 225s which are fine but dont grip very well on a roller dyno. However on the drag strip I run MT ET streets which grip a lot differently. I want to know what power Im putting out under maximum traction and what is "available" to the car. I think this is where the comment that hub dynos are generally a bit higher comes from. They never suffer traction loss so the reading is more accurate and hence slightly higher. As for the rest of it, personally I'l just be interested to hear back from the company and see what they have to say.
Reply from EVO re: hub dynos So I guess, taking your car to a hub dyno you can expect higher results then going to a roller kind. Didn't answer if the wheels were weighed but I guess they aren't. As all that would do is add another variable to the result and it would simply be 'best guess'. (hub dyno advertisments brag about taking away lots of the variables). But we'll wait see what the company says. IMO Roller dynos are good to see what power you put on the the actual road out there, where hub dyno results are great to see what power your engine puts to the w heel and comparing before/after modifications. I wouldn't use the results of a hub dyno to be my rear wheel kW thats all, its just a little miselading as people may think I was on a roller dyno then (as one meausres at the hubs and the other at the wheels) Fleet, as much as I love 2nd place only to Johns slot car, Chewy is more deserving of it, and my other dyno of 277kW result I once got is probably more realistic
Easiest way to settle this - Dyno Dynamics in Shootout Mode. If accredited... you should be able to go to any of their dynos in Australia and read within 1%.
