Just a quick question.

Since they measure WHP and since more weight on the drivetrain will increase the loses between the crank and the wheel. Then it would seem that the wheel weight would have a large effect on you chassis dyno.

Now could this explain why some people can run on a dyno with say the JCW kit against someone with just a intake and 15% pulley and the JCW showing very poorly. If the 15% car had wheels/rims of ~30 pounds while the JCW had say stock s-lites of ~48 pounds.

Or am I completely of the mark. (This is in regards to several threads where people have complained about thier hp based on thier mods, but few if any list what wheels they are running)

 

https://www.northamericanmotoring.co...ad.php?t=24843

 

I haven't had the patience to read all of these posts, but the conclusion should be that:

-an inertia dyno will show different results for different weight (mass) wheels; and
-a load dyno, at a steady state measuring power at a given RPM, would not.

Regards,

Jeff




andy@ross-tech.com


Yup

Andy,

Still not quite sure about the outcome here. I understand that the two types of dynos measure different forces - one accelerating (curved) and one constant.

By example, and as a way for me to understand the relationships, I race bicycles. Much of my training occurs indoors this time of year on a fixed trainer - no aero forces. I have a computer and heart rate monitor hooked up to me while training. I occasionally use different wheels in my training - a short but boring story. Assuming my results are repeated accurately - and I try very hard to repeat speed and cadence accurately - the heavier wheel takes more energy to maintain at a constant speed. My PF as it's called - Percieved Effort, and HR - heart rate, show this clearly. And the efforts increase with increased, but constant speed. I'm compelled to write that a heavier wheel is in fact harder to maintain at a constant speed. ???

 

if so, you have violated the sacred laws of Newton. In reality, it is extra friction or some other parasitic load (maybe due to the extra weight) that makes the heavier wheel harder to keep at a constant velocity.

 

Okay so when people post dyno's (chassis ones) for comparison then they should include thier wheel weight since it does appear that it will have an effect.

 

This test shows not too much difference between very heavy wheels, and very light wheels (14 lb difference per wheel alone!):

http://www.nissanperformancemag.com/may01/dyno.shtml

 

Andy, thanks.

jlm "maybe due to the extra weight" That's the question. I've only read Netwton's Optiks, not much else - by Netwon!

Never mind, got it; more weight=more friction. So just how much more psi does it take to overcome friction generated by additional weight? Might be an interesting, albeit, academic experiment. Tires are maxed at 140 psi.

You guys Attorneys? You sure do quote a lot of laws.

 

How about this one:

Do your brakes have zero drag?

 

Are you trying to hurt my brain Cheese? They do to a certain degree, correct? If so, brakes affect dyno results too.

 

Are your rotors perfectly straight or do they brush the pads for 20 degrees of rotation?

--
Cheese

 

Okay, I'll bite. But, not quite sure what question to ask here. I know some rotor designs are design to push pads away from the rotor - can't remember how, I'm old. But assuming rotors are not absolutel square or plumb to the pads I would say that there is contact.

 

I was speaking more about possible larger frictional losses related to the heavier wheel being heavier. as far as a rotating mass, angular velocity is independent of mass, but angular acceleration depends on mass and its geometric location to the rotation axis (moment of inertia; remember why flyweels have heavy rims?)

 

yes my brakes have -0- drag because the warp in my rotors & clearence in my wheel bearings pushed the pads with their little clips & sensors out o da whey/curds. The reason Dynos don't see wheel changes is the same reason they cant give the same results twice if nothing is different. Next question. Is it because they are that sensitive, or ,that insensitive? Tag your it.