Here are some of my thoughts. I don't have any math or data to back
anything up, only my first hand experience. Which may not be worth a whole
lot. So keep in mind this is only guess work.
When I started racing my /CC was about 3" off the ground in the front
and 6" in the rear. Over the years we have lowered it gradually and as we
have the speeds have gone up and the handling has gotten better. We are now
down to 1 to 2" front and 2 to 3" rear. This car has a full belly pan,
always has. Now keep in mind that some of this extra speed could be due to
other changes we made as well. I can tell you I wouldn't raise it back up
again.
As for Quick Changes being less efficient. Well they do have an extra
set of spur gears and two extra bearings as well. However the larger ring
gear is a better lever. So maybe its a wash. Practically, when I changed
from a 9" Ford to a Winters QC my car went faster. Maybe in part because I
could now pick the exact final drive ratio necessary for my engines RPM
band. A loss in one efficiency area may be a gain in another?
As for other drive train losses, and I know this as fact. The NASCAR
boys put an engine on the Dyno and measure flywheel HP. They then put the
engine in the car and on a Chassis Dyno and measure rear wheel HP. They
expect to see only a 15% loss. Some of the stuff we (LSR racers) run could
be as high as 25%, but probably not lower than 15%.
As for differences in the surfaces we run on, well its all driver feel
to me. I'm sure rolling resistance is a factor of some sort, but how big?
Having driven on concrete and salt I don't think its much, especially with
70 to 90 PSI in the tires. I can't speak about dirt yet as Muroc 2000 will
be my first attempt on that surface. Concrete has traction you can feel, and
there is a positive difference in handling too. Salt is slippery, sometimes
very slippery, with some negative aspects to the handling as well. Tire
slippage is a real big factor, and a negative factor for speed, on the salt
and I guess dirt too.
Hey last year running over the bumps on the salt at 200 MPH my data
recorder was showing 700 to 800 RPM jumps...the jumps didn't look that big
on the tach... That's a lot of slippage, just wondering if that gets
misinterpreted as rolling resistance in the final count?
Just my thoughts
John "no data" Beckett, ECTA/BNI #79
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