List;
At lunch today I had an opportunity to ask John Horsman about the GT-40's
aerodynamics and he was quite helpful. He had photographs of some of the
Ford GT-40s and their later variants such as their Gulf Mirage. In a photo
taken in April 1964 at the trials (practice) at Le Mans, John pointed out
that the original GT-40 design had a rather high "pointy" nose and a tail
with no spoiler. It was so unstable that those two cars went off into the
weeds on the fast 3.5 mile long Mulsanne Straight (sounds like Maxton).
A spoiler was added and it helped but another photo taken of that car at
high speed showed the nose lifted by what looked like about 4 to 5 inches! A
new nose was designed and it helped, but the early GT-40s suffered from the
FIA regulation that required a full- width windshield and that could have
made the lift problem even worse (my opinion).
I found some data that may illustrate the point:
1967 Ford GT40 MkIV Lift:
213 lbs. @ 180 mph, with 554 lbs. of drag
263 lbs. @ 200 mph, with 648 lbs. of drag
318 lbs. @ 220 mph, with 828 lbs. of drag
1966 Ford GT40 MkII Lift:
144 lbs. @ 180 mph, with 756 lbs. of drag
177 lbs. @ 200 mph, with 933 lbs. of drag
Compare this with a modern street- driven sports car:
2000 Porsche 911 Lift:
600 lbs. @ 150 mph
Aero. Balance @ 150 mph:
F: 228 lbs.
R: 372 lbs.
These all generate LIFT-- not a good thing! Compare those with a much later
race car:
2001 Bentley EXP Speed 8 LMGTP
High downforce configuration: Downforce:
3094 lbs. @ 150 mph
5500 lbs. @ 200 mph
Low downforce configuration: Downforce:
2200 lbs. @ 150 mph, with 600 lbs. of drag
3911 lbs. @ 200 mph, with 1066 lbs. of drag
Lift-to-drag ratio: 3.7:1
Most modern competition cars have more BHP than they can deliver to the road
so they trade off loss of horsepower (drag) for the ability to put the power
onto the road (downforce).
I realize that GT cars don't run under the same rules as SCTA but I wanted
to pass this info along for what it's worth. I'll save the wide tire /
narrow tire controversy for another time.
Regards, Neil Tucson, AZ -- boring everyone to tears by now......
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