Downforce - how much?

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Joined: 17 Nov 2010, 05:23

Re: Downforce - how much?

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How much does a modern stock car weigh, and how much DF do they create?

Or... what would the bigger challenge be: dealing with huge lateral loads during cornering (group c/gtp) or radial loads of a heavy car at top speed (NASCAR; banked turns help out, surely). (I don't know much about tires, pardon the guess at nomenclature)

A little non-technical insight on an IMSA GTP entrant pushing the limits of tire & suspension:

http://bluntobject.wordpress.com/2009/1 ... epid-rm-1/
Many of the day’s GTP cars were designed to run at fast European tracks like Le Mans (for obvious reasons), or inspired by cars that were. This was before Le Mans introduced two chicanes onto the Mulsanne Straight, and before Ayrton Senna’s fatal crash in 1994 prompted track owners to add chicanes damn near everywhere to slow the cars down — top-end speed was critical to winning in Europe. Riley noted that most of the tracks on the IMSA tour were short, bumpy circuits where downforce was more important than sheer velocity, and designed a light GTP car with maximum aero grip in mind. The Intrepid’s steep nose and three-section wing generated a lot of drag but a phenomenal amount of downforce — so much so that the car subjected its Goodyear GTP tires to more load than they were designed to carry.

Image

Unfortunately, the Intrepid also created more downforce than its rear suspension uprights could handle. At Watkins Glen in 1991, after qualifying half a second off the pole, Tommy Kendall’s #65 Intrepid lost its left rear wheel as the track’s high speed banked corners created more vertical load than the car’s components were ever expected to see. Kendall broke both legs but survived the crash thanks to the carbon-fibre monocoque, and sat out the rest of the season but would race for Jim Miller again in 1992.

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Joined: 17 Nov 2010, 05:23

Re: Downforce - how much?

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Jersey Tom wrote: Certainly a unique challenge though, designing around the RANGE of load, from peanuts to tons.
I imagine one has to end up compromising low speed, low aero load performance in the interest making sure the tire can survive operating under x,000lbs of downforce and high-g cornering. Is that a basic compromise dealt with in tire design? Makes me wonder if a variable tire pressure system (similar to a HUMVEE) could be developed for this purpose...

DaveW
DaveW
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Joined: 14 Apr 2009, 12:27

Re: Downforce - how much?

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Ogami musashi wrote:... the actual figures are far lower and in many case, again as stated by the owner of MC, the 200 mph are purely speculative since the drag is far greater than power available.
I don't want to make too much of the comparison between LMP & F1, but in Le Mans trim the lead LMP vehicles were, I believe, achieving >335 kph along the Mulsanne this year.

I don't know L/D numbers for LMP vehicles, but much evidence exists for the downforce potential of the vehicles. For example, control of porpoising was a major set-up consideration until the splitter regulations were amended to reduce the likelihood of stall. Also, despite the weight of the vehicles, solo flights are still too commonplace when all goes wrong, despite several regulations introduced specifically to make the aero more benign.

Ogami musashi
Ogami musashi
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Joined: 13 Jun 2007, 22:57

Re: Downforce - how much?

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The 200mph figures in MC are mainly about former GTP/F3.5 cars that ran in high downforce trims;


in 2008 the L/D ratio for LMP were around 4,5 (in high downforce tims, low downforce trim bring lower L/D ratios, same for F1).

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Artur Craft
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Joined: 05 Feb 2010, 15:50

Re: Downforce - how much?

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shelly wrote:agree with ogami
efficency around 4, front wing Scz 1.2 to 1.5, front wing load 500 to 700 kg @300kph
I once saw in a Williams documentary that their 2008 front wing generated around 800kg at 300kmh

Some IMSA and Group C cars, such as the Toyota Eagle MKIII, could generate more downforce than a F1 because of bigger area of bodywork, bigger rear wing and more freedom to use underbody, HOWEVER, F1 cars weighted 595kg and 605kg with driver included in 90s and 00s.

IMSA and Group C cars always weighted much more like 850kg, 900kg or the lightest in 92 750kg but without driver.

2006-2008 F1 cars could generate like 3200kg of downforce at 300/320 kmh which is more than 5 times it's weight!!! No other car, be it Indy, Group C, IMSA or whatever, have ever come close to that and this is the reason why F1 cars have always been the fastest ones in corners.