It's pure physics. Rotating inertia affects angular acceleration, hence at
constant engine speed (and therefore wheel speed) the torque output at the
wheels is independent of wheel weight (which is a major factor in rotating
inertia). I have no idea how horsepower is measured, so I don't really know
if wheel weight will affect that or not. HOWEVER: you WILL notice a
difference in acceleration on the street with heavier wheels. That's
because the torque exerted by the engine through the drivetrain not only has
to work through the wheels to exert force on the pavement, but it also has
to work ON the wheels to spin them up. Basically, the lower the rotating
inertia, the more of the engine's torque can be used to accelerate the car.
You never get to 100% though because the engine also has to accelerate the
crankshaft, the camshaft, the flywheel, the transmission, the alternator,...
you get the picture. Remember those lightweight flywheels? You can blip
the engine up to redline a LOT quicker with those...but not with the clutch
out. Saying wheel weight should affect dyno torque is the same as saying
flywheel weight will affect dyno torque. The answer is, it shouldn't. If
it does, there's something seriously wrong with the dyno. Hope this clears
things up.
Dave
-----Original Message-----
From: Young, Michael W.: [mailto:[EMAIL PROTECTED]]
Sent: Sunday, May 06, 2001 10:04 AM
To: Sentra Mailing List
Subject: RE: SML-NON-P: May SOLM
[EMAIL PROTECTED] wrote:
>Hmmm...I don't get how wheel weight would affect torque. Torque is torque,
>you could attack a 100 lb. wheel to the car and the amount of torque would
>have to (neglecting the extra tire friction from the extra 70 lbs. at the
>wheel) be the same.Dunno about horsepower, but it's possible (although
>unlikely)
Are you saying torque and horsepower output should not be affected by 100
pound wheels?
I'd like to see a dyno chart for that...!!...or slap some 19" 100lb wheels
on your car and we can 1/4 mile for pinks.....haha
Seriously though, If you take a look at the Excel worksheet or charts it's
obvious the torque and horsepower are both diminished slightly with the
heavier larger wheels especially during the acceleration phase of the
powerband. As stated they do catch up and even surpass the lighter wheels
higher on the curve, only to be beaten out again at peak.... Although the
over all differences are very minimal, they do still exist...
I'm not a Physics Professor, but I can read the charts and that's what they
indicate.
Michael Young
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