[Land-speed] Chassis Dyno Operations

[drmayf]

Well, this wasn't an exercise to try and find out why a dyno I have 
didn't work (I don't have one).  I was asking why we do testing the way 
it is done. What is the rationale for doing it that way?  You see, one 
of the things I don't understand is that there are a zillion rear end 
ratis and yet we always use high gear in the gear box. The dyno doesn't 
have a clue as to what is riding on it.  So why does it matter what gear 
is used. It is simply an inertial mass that is accelerated by the 
applied torque at the tire / roller interface.   So the questions were 
geared to educating me as to why things are done the way they are.  Why 
technical reasons are there for doing a high gear pull when the final 
drive  for all the cars that go on a chassis dyno are different.  I 
guess, it is simply..Because that's the way we've always done it.    

mayf
Kirkwood wrote:

>So many questions before you had your coffee! LOL
>
>Many years ago, on an early Go Power dyno, it would not hold the load due to
>torque multiplication at lower RPM and would cavitate. We had to use direct
>drive just to apply load. Don't know the nature of your dyno but could the
>braking mechanism efficiency be the reason?
>
>If high gear is more efficient because it is DIRECT drive (i.e., torque is
>not transferred through a cluster shaft) then overdrive would be less
>efficient for the same reason.
>From: drmayf drmayf at mayfco.com
>More fun dumb questions from me.  Why do we use high gear during a chassis
>dyno pull?  The dyno does not know what gear the car is in, does it?  Is
>there
>a general limit on the acceleration rate of the rollers?  If high gear (1:1
>in
>the gear box) is better than a lower gear, then would overdrive be better
>that
>the 1:1 gear?  Is there some final drive ratio that is best?
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