Steve - Close, mine is actually this one > Mulsanne's Corner Race Car Aerodynamics Database: 1992 Nissan NPT-91 GTP
so at 150mph your 9xxkg car generates 2,360kg’s of downforce and at 200mph its 4,196kg!!!
OK so that’s just out of the Exige league
I also assume that it means items on the vehicle must be rated to that as a notional kerb weight?
Steve - Close, mine is actually this one > Mulsanne's Corner Race Car Aerodynamics Database: 1992 Nissan NPT-91 GTP
so at 150mph your 9xxkg car generates 2,360kg’s of downforce and at 200mph its 4,196kg!!!
OK so that’s just out of the Exige league
I also assume that it means items on the vehicle must be rated to that as a notional kerb weight?
Thats right, everything has to be pretty sturdy. For example we run 7000lb spring on the front, in period they used anything up to 9000lb. Had an enlightening chat to the Nisan Aero guy who let me know that the early Goodyear tyres had a habit of letting go with all that downforce and the resulting explosion would take out the rear wing. The car went up and over twice, almost killing Geoff Brabham .
I take it by “lift” they mean good lift - as in the wing is upside down and actually provides 7% more downforce?
I’m confused by the website now - in the relevant sections it states:
"A note about terminology
Typically the term ‘lift’ is used when talking about any kind of aerodynamically induced force acting on a surface. This is then given an indicator, either ‘+’ or ‘-’ as to its direction. In racing the term ‘lift’ is generally avoided as its meaning is almost always implied as positive, i.e., lifting the car off the track. With in this database, when ever the term ‘lift’ is used its meaning should be implied as positive force. The term ‘downforce’, therefore, should always be implied as negative force, i.e., pushing the car to the road."
but the section on the endplates states:
“Wing endplates act as span increase aerodynamically. That is, in general terms, a wing with an endplate is equal to a wider wing with out one”
but
“With endplates attached to the wing, the lift increased by 7%”
I think they have it slightly wrong…but we know what they mean, ie, endplates are good
Had an enlightening chat to the Nisan Aero guy who let me know that the early Goodyear tyres had a habit of letting go with all that downforce and the resulting explosion would take out the rear wing.
Do you run wheels with beadlocks?
Randy, why do you doubt the Exige has been in a wind tunnel? I’m just curious because we all know that various other Elises have been properly tested. I’m quite sure they didn’t spend much time honing the aerodynamics because they just designed the car to look cool, but I would have thought they probably tested the car to get the rear wing at at optimal angle for decent balance.
I appeciate the fact that the Exige’s downforce is miniscule compared to a proper racer like your Datsun (thoses figures posted earlier (although perhaps not your car) suggested something like 7.4 * the effect!
However, I do believe the quoted figures would make a noticable difference. 80 kilos @ 100mph for a car weighing less than 800 kilos would mean around 10% more grip at that speed. It’s certainly going to add a few more mph peak cornering speed surely?
Not much by your standards, but a nice little difference for us mere mortals.
On wing you have one surface with high pressure and the other with low pressure. On the outside edges of the wing (where end plates would be bolted) The high pressure air spills over and reduces the lift (be it +ve or -ve depending on the orientation). All end plates do is physically stop the air spillage so the wing runs more efficiently.
According to someone who used to run the MIRA wind tunnel there was “minor” work done on the Exige.
HTH the discussion … carry on
Andy
S1 or S2?
Randy, why do you doubt the Exige has been in a wind tunnel? I’m just curious because we all know that various other Elises have been properly tested. I’m quite sure they didn’t spend much time honing the aerodynamics because they just designed the car to look cool, but I would have thought they probably tested the car to get the rear wing at at optimal angle for decent balance.
I appeciate the fact that the Exige’s downforce is miniscule compared to a proper racer like your Datsun (thoses figures posted earlier (although perhaps not your car) suggested something like 7.4 * the effect!
However, I do believe the quoted figures would make a noticable difference. 80 kilos @ 100mph for a car weighing less than 800 kilos would mean around 10% more grip at that speed. It’s certainly going to add a few more mph peak cornering speed surely?
Not much by your standards, but a nice little difference for us mere mortals.
I know various Elises have been tested. Apparently a standard Elise has circa 50kg -ve at the front and 10kg +ve at the rear so maybe an Exige does have 80kg total. Maybe an Exige has been in the tunnel but I doubt any changes were made. If Lotus had even the slightest worry about aerodynamic performance they wouldn’t have made the rear clam with those silly overlapping bits.
80kgs of downforce is really very little and no way would it account for even nearly 10% more grip. To be honest with these small numbers the balance will be much more important than the outright downforce and this is one area where the Exige is a bit better than an Elise. We pay for it down the straights though.
80kgs of downforce is really very little and no way would it account for even nearly 10% more grip. To be honest with these small numbers the balance will be much more important than the outright downforce and this is one area where the Exige is a bit better than an Elise. We pay for it down the straights though.
My understanding is that tyres produce grip roughly in proportion to the weight on them. Hence 1G cornering is more or less standard for road cars because there’s 1G of force downwards due to gravity (at least on my planet )
Now 80 kilos is over 10% of the weight of the car, so the downwards force on the tyres is 10% more than it would be without the downforce. Therefore I would expect roughly 10% more grip. This is all a bit approximate, but I’m sure in principle this is correct
No scientific basis mearly anecdotal, but I’ll throw my 2p in anyway.
My old S2 felt very light and wafty at the front end at speed (100+). The S1 Exige feels much more planted. Now not having driven a proper race car with serious downforce I can still appreciate the difference between +ve lift and the little -ve lift produced by the Exige.
Perhaps if I got to drive a racecar with high -ve lift (hint) then I may be able to appreciate real downforce.
This thread has really disappeared up it’s own arse in more ways than one.
My car has more downforce than a standard Exige.
I was able to feel noticable downforce at Donington on Saturday under the Dunlop Bridge.
Whether a Nissan racecar generates twelvty gajillion kg of negative lift at a snails pace is a complete non-sequitur.
This thread has really disappeared up it’s own arse in more ways than one.
I quite agree…but just to prove that there is more to having a big wing than just high downforce:
[image]http://fishki.net/podborka2/88/picccszn_12.jpg[/image]
Brendan � You are sort of on the right track but things are no way that simple. A tyres coefficient of friction increases with vertical load, different tyres will respond in different ways but the increase in CofF will be nowhere like 1:1. Theoretically this means that a heavier car has more �grip� but in practice the laws of physics dictate that the extra weight will cause the heavier car to turn slower. Downforce is great because it increases the vertical load on the tyre without increasing its weight, perfick. As I said before, almost all road cars have a sizable amount of +ve lift and less drag than an Exige which has zero or maybe very slight �ve lift but shed loads of drag which is predominantly why the car feel stable at speed.
To say that an average car can corner at 1g because of the force of gravity is very wide of the mark. A car�s ability to corner is predominately effected by (in no particular order): Weight, Tyres, CofG, Aerodynamics and suspension geometry/kinematics.
So to add to your list Mr Admin�
We all love our Exiges but lets not believe Lotus�s marketing gabble .
Oh and Steve - nice bit of Barbecued pork
Donington responds to quite a �loose� car.
I wouldn’t know what anything other than a loose car feels like
Randy
next thing you be telling us is that this doesn’t generate downforce either
[image]http://fishki.net/podborka2/77/picccszc04.jpg[/image]
Donington responds to quite a �loose� car.
I wouldn’t know what anything other than a loose car feels like
I prefer loose women!!
Brendan � You are sort of on the right track but things are no way that simple. A tyres coefficient of friction increases with vertical load, different tyres will respond in different ways but the increase in CofF will be nowhere like 1:1. Theoretically this means that a heavier car has more �grip� but in practice the laws of physics dictate that the extra weight will cause the heavier car to turn slower. Downforce is great because it increases the vertical load on the tyre without increasing its weight, perfick. As I said before, almost all road cars have a sizable amount of +ve lift and less drag than an Exige which has zero or maybe very slight �ve lift but shed loads of drag which is predominantly why the car feel stable at speed.
To say that an average car can corner at 1g because of the force of gravity is very wide of the mark. A car�s ability to corner is predominately effected by (in no particular order): Weight, Tyres, CofG, Aerodynamics and suspension geometry/kinematics.
Randy, thanks for the patronising response I do have a reasonable understanding of the physics here.
Basic physics tells us that the sideways force a tyre can produce is directly proportional to the downwards force applied to it. That basic physics fails to take into account all kinds of complex aspects of tyre behaviour, but it’s a pretty reasonable approximation.
Obviously if we were talking about multiplying the forces greatly, the slightly non-linear relationship would make it impossible to guess the effects, but we’re talking about a small change of 10%. If you apply 10% more force on the tyre you absolutely WILL get approximately 10% more grip. Your assertion that the coefficient of friction will not increase by this amount is correct. The CoF stays roughly the same, only the forces vary.
Are you saying that my understand of physics is wrong?
On what basis do you suggest that the Exige doesn’t make this amount of downforce? I’m not saying it definately does, but I’d like to know why you don’t believe it. It’s not as if it’s a huge amount that’s being claimed, is it?
My responce was not intended to be patronising FYI…
10% is a HUGE difference and you won’t see this sort of difference by adding only 80kg of downforce. Agreed on the CofF thing but it’s terminology that people understand.
But 80 kilos is about 10% of the weight of the car, so it does mean 10% more force on the tyres. I can’t understand where our difference of opinion lies
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