22 replies to this topic

[slipstream]

How much Downforce does a Current F1 Car produce ? I was reading that the Lola used in Cart has 5,000 lbs of Downforce at 200 MPH with a Drag penalty of 1330 lbs. I would think that a F1 car would produce more Downforce than a Champcar, all drivers who have driven both types have said the the F1 cars are much quicker in the faster corners, but I never seen any Downforce numbers for a current F1 car.

[wegmann]

That's not exactly the same question I asked a while back, but I think you'll find the answer in this thread:

how much drag?

[slipstream]

Wegmann Thanks for the link. I have another question, How much does the total Downforce effect a Cars corner speed ? The Toyota Eagle GTP was said to produce over 7,000 lbs of Downforce at 180 MPH, So would it be quicker through the corners than a Current F1 Car ?

[Greg Locock]

Crudely

The centripetal force on the car is m*v^2/r

The downward force on the car is (m*g+1/2*rho*Cl*A*v^2), ie weight plus downforce - note that rho*Cl*A always stay together so you can back calculate them without worrying what they are individually.

For a given 'vehicle coefficient of friction' (a very bad approximation) mu then at steady state cornering the car will be on the limit when

m*v^2/r=(m*g+1/2*rho*Cl*A*v^2)*mu

so for a given corner etc the max cornering speed is sqrt((m*g*mu*r)/(m-r*mu*.5*rho*A*Cl)) if I haven't made a mistake

which answers your question, sort of. grin

[Yelnats]

Originally posted by slipstream
How much Downforce does a Current F1 Car produce ? I was reading that the Lola used in Cart has 5,000 lbs of Downforce at 200 MPH with a Drag penalty of 1330 lbs. I would think that a F1 car would produce more Downforce than a Champcar, all drivers who have driven both types have said the the F1 cars are much quicker in the faster corners, but I never seen any Downforce numbers for a current F1 car.

I doubt if an F1 car produces significantly more downforce than a CART car because it doesn't need as much due to it's 30% lower mass which would generate 30% less centrifugal force at a given speed. This is complicated by the difference in the tires used in the series but due to the lack of competition between tire brands in CART, I doubt if this the true slicks used in CART have a great traction advantage over the grooved tires used in F1.

[gbaker]

Originally posted by Greg Locock
Crudely

The centripetal force on the car is m*v^2/r

The downward force on the car is (m*g+1/2*rho*Cl*A*v^2), ie weight plus downforce - note that rho*Cl*A always stay together so you can back calculate them without worrying what they are individually.

For a given 'vehicle coefficient of friction' (a very bad approximation) mu then at steady state cornering the car will be on the limit when

m*v^2/r=(m*g+1/2*rho*Cl*A*v^2)*mu

so for a given corner etc the max cornering speed is sqrt((m*g*mu*r)/(m-r*mu*.5*rho*A*Cl)) if I haven't made a mistake

which answers your question, sort of. grin

Now that's what I call an answer.

[Paolo]

The problem is that the friction coefficient is not fixed. It can easily show a 50% variation depending on load condition (weight , downforce) and the centripetal force itself (because of lateral weight transfer).
Also, much of the theorethical adherence available on the rear wheels is used to fight drag.
Actual calculations are not really easy.

[Greg Locock]

Well, I did say that the concept of a vehicle coefficient of friction was dodgy - but not useless, after all that is what a g-g plot gives you in effect.

The sensitivity of mu to vertical load isn't quite as bad as you make out, I suggest. I guess the quickest way to examine that would be to examine the Avon F3000 tyre data

Here's the results at 7 degrees of slip for the rear tyre, first chart in the 6/8/1 tests

FZ(kgf) FY(kN)
150 2.5
250 3.7
350 4.8

so the coefficient of friction falls from 1.7 to 1.4 for a 130% increase in load. Hmm, you are right, that'd be around a 50% reduction for a car with 3g of aero. It would be interesting to work through the shape of the friction 'circle' for a vehicle using these tyres at various speeds, I haven't got the energy today!

I agree about the reduced lateral capacity of the rear tyres, but had to start somewhere. One interesting factor then is that a low drag setup makes you faster through corners... obvious in retrospect.

[Yelnats]

Originally posted by Greg Locock
Well, I did say that the concept of a vehicle coefficient of friction was dodgy - but not useless, after all that is what a g-g plot gives you in effect.

The sensitivity of mu to vertical load isn't quite as bad as you make out, I suggest. I guess the quickest way to examine that would be to examine the Avon F3000 tyre data

Here's the results at 7 degrees of slip for the rear tyre, first chart in the 6/8/1 tests

FZ(kgf) FY(kN)
150 2.5
250 3.7
350 4.8

so the coefficient of friction falls from 1.7 to 1.4 for a 130% increase in load. Hmm, you are right, that'd be around a 50% reduction for a car with 3g of aero. It would be interesting to work through the shape of the friction 'circle' for a vehicle using these tyres at various speeds, I haven't got the energy today!

I agree about the reduced lateral capacity of the rear tyres, but had to start somewhere. One interesting factor then is that a low drag setup makes you faster through corners... obvious in retrospect.

Obvious??? Please explain the last sentence.

[Greg Locock]

For a given amount of downforce a low drag setup allows you to 'spend' more of the rear tyre's friction circle on latacc and less on traction. I probably confused you by not explicitly stating "for a given downforce". I'm an engineer, I only change one thing at once, given the choice!

[Yelnats]

Your point is well taken as lower drag for a given downforce it has been the Holy Grail of F1 aerodynamics for decades. For a given car design optimally setup, a lower drag setting reduces downforce so one would have to change cars designs (or install narrower tires which leads to other problems) to achieve lower drag without reducing downforce. Your proposition seemed to imply that were dealing with a single car design but of course your statement is perfectly accurate in the broader context.

[kenjafield]

Originally posted by Yelnats
Your point is well taken as lower drag for a given downforce it has been the Holy Grail of F1 aerodynamics for decades. For a given car design optimally setup, a lower drag setting reduces downforce so one would have to change cars designs (or install narrower tires which leads to other problems) to achieve lower drag without reducing downforce. Your proposition seemed to imply that were dealing with a single car design but of course your statement is perfectly accurate in the broader context.

They found the holy grail: the Brabham fan car. So they banned it and told the designers to keep trying

[MclarenF1]

Originally posted by Greg Locock

It would be interesting to work through the shape of the friction 'circle' for a vehicle using these tyres at various speeds, I haven't got the energy today!

There are some very interesting g-g-v diagrams in Peter Wrights book, compaining different early and late model F1 cars. Interesting to see the early cars g-g-v diagram look like a column and the current ones are a cone.

I had never thought about an "optimum" level of downforce for a given corner before. i.e. as low downforce as possible to get you through the corner produces the highes CoF....Seem obvious, now if we could just get the FIA to allow movable aero devices

[panzani]

According to an article at formula1.com F1 cars can produce 3.5g of downforce, that is, near 2,100Kg.

[golfball]

Originally posted by slipstream
Wegmann Thanks for the link. I have another question, How much does the total Downforce effect a Cars corner speed ? The Toyota Eagle GTP was said to produce over 7,000 lbs of Downforce at 180 MPH, So would it be quicker through the corners than a Current F1 Car ?

Current F1 cars generate approx 4000lbs of downforce at 180mph in a corner (if such a corner exists!!).

I'd therefore be VERY suprised if that 7000lbs for the GTP was correct. I can't imagine anyone makes racing tyres that can handle that.

[Wuzak]

Originally posted by golfball


Current F1 cars generate approx 4000lbs of downforce at 180mph in a corner (if such a corner exists!!).

Blanchimont??

[DOHC]

Originally posted by MclarenF1
There are some very interesting g-g-v diagrams in Peter Wrights book, compaining different early and late model F1 cars. Interesting to see the early cars g-g-v diagram look like a column and the current ones are a cone.

They're not cones but close to paraboloids, because both drag and lift are proportional to v^2.

For old cars with wings, this was not the case. For example, if you look at the Lotus 72, you have much more of a cylinder-like g-g-v diagram. That's because the downforce was in part generated by the wedge-shaped body, the front wings which did run in clean air were vefy small, and in early versions of the car the rear wing, which was large, did not run in clean air because oil coolers were placed right under the wing. There was also interference from the engine. It wasn't until 1973 that the rear wing had reasonably clean air under it, when the supporting center pylon neatly integrated the oil radiators.

In modern cars the aero is much more pushed to its limit, and the aero devices are closer to producing the theoretical v^2 proportional downforce. There are no nearby oil radiators, there's a clean airbox and engine cowling, and supporting pylons are aerodynamcially shaped (if they at all exist, as the rear wing's endplates now do the job there). So the wings are less affected by turbulence, and there are few if any devices or parts of the body work that block the free flow to the wings.

On top of that, wing profiles are far more sophisticated today.

[MattPete]

Originally posted by golfball


Current F1 cars generate approx 4000lbs of downforce at 180mph in a corner (if such a corner exists!!).

I'd therefore be VERY suprised if that 7000lbs for the GTP was correct. I can't imagine anyone makes racing tyres that can handle that.

I can believe it. Those GTP/Group C cars were monsters. Massive ground effects with an enclosed body. Check out the discussion of the Toyota Mk3 GTP's rear wing:

http://prototyp.org/...eators_002.html

[dosco]

Originally posted by golfball


Current F1 cars generate approx 4000lbs of downforce at 180mph in a corner (if such a corner exists!!).

I'd therefore be VERY suprised if that 7000lbs for the GTP was correct. I can't imagine anyone makes racing tyres that can handle that.

Why do you doubt it? How much downforce did the Williams FW12, 13, and 14 generate?

In GTP/enduro cars, enclosed bodywork allows for a front and rear diffuser, across the entire bottom of the vehicle (GTP undertrays have more surface area than F1 cars). Add in the biplane rear wings, with double slotted flaps, that were as wide as the car.....according to an interview with Hiro Fujimori in "Mulsanne Mike's" website (www.mulsannescorner.com), the Toyota Eagle Mk III was generating over 9,000 lbs of downforce with the biplane rear wing.

With some of the older F1 cars generating perhaps 4,000 to 5,000 lbs of downforce (check out Mulsanne Mike's aero database - Lotus T79 rated at over 4,400 lbs of downforce at 200 mph) over 20 years ago, it's easy to think that F1 cars of the mid 80s were producing over 5,000 lbs of downforce.

So why is it so hard to believe the figures of a Le Mans-style prototype racer or GTP car?

FWIW, I really miss the GTP cars.........then again, I don't miss the ever-changing rules and "equivalency" formulas......but the cars were really cool. Aaaahhhhh..........

[DOHC]

Originally posted by dosco
Why do you doubt it? How much downforce did the Williams FW12, 13, and 14 generate?

- - -

Lotus T79 rated at over 4,400 lbs of downforce at 200 mph) over 20 years ago, it's easy to think that F1 cars of the mid 80s were producing over 5,000 lbs of downforce.

Wright mentions lower figures in his book. There's a diagram on p 24, plotting downforce history over the years, for a given speed of 150 mph.

The peak downforce @150 mph when skirts and venturis were banned is quoted to be 3,000 lbs, with a figure of about 2,000 lbs in 1978, the heydays of the T79.

For flat bottom cars, FW14-15 in 1993, a peak of 3,500 lbs @150 mph is reached. And for the year 2000, Wright mentions 2,500 lbs @150 mph.

If downforce really increases proportionally to v^2, the @200 mph figures would be about twice the figures mentioned by Wright. But flow past the aero devices is not entirely laminar, so downforce might not grow that fast with increasing speed.

Because there are 150 mph bends, Wright's figures for 2000 would indicate a vertical load on the tires corresponding to 3g (where 1g comes from car weight, and 2g from downforce). With a friction coefficient of 1.7 (also mentioned by Wright for contemporary tires) one has a theoretical lateral acceleration of 5.1g. But according to Wright p. 9, peak lateral accelerations are around 4g. This indicates that it is unlikely that today's F1 cars generate much more than 2,500 lbs downforce in any cornering situation.

Of course, one must factor in that 150 mph corners are very fast, probably on a fast track where the cars would run a low downforce setup.

Also, the downforce figures @200 mph are a bit less interesting, as one wouldn't corner at such speeds (except at Indy's banked turns, perhaps). In particular, wheras it might be possible to generate such high downforces @200 mph, setups for such high speeds would most likely favor less downforce, as downforce is always bought at the price of increased drag.

[Greg Locock]

Because there are 150 mph bends, Wright's figures for 2000 would indicate a vertical load on the tires corresponding to 3g (where 1g comes from car weight, and 2g from downforce). With a friction coefficient of 1.7 (also mentioned by Wright for contemporary tires) one has a theoretical lateral acceleration of 5.1g. But according to Wright p. 9, peak lateral accelerations are around 4g. This indicates that it is unlikely that today's F1 cars generate much more than 2,500 lbs downforce in any cornering situation.

Nice argument, but you are ignoring the effect of vertical load on the tyre's capabilites.

Avon F3000 tyre data

Here's the results at 7 degrees of slip for the rear tyre, first chart in the 6/8/1 tests

FZ(kgf) FY(kN)
150 2.5
250 3.7
350 4.8

This gives a grip coefficient of 1.7, 1.5 and 1.3 respectively. Now, the 1.7 figure is a coincidence, does Peter specify at what condition that is measured? If it as 1g vertical then I'm happy to use these numbers.

So I'd /guess/ for this tyre at 3 g (starting from 150kgf=1g, unlikely) a grip coefficient of 1.1, indicating a max latacc of 3.3g...!

Plus some of the friction circle is used up by the traction force, and as your downforce increases that value increases. In other words, that 4g vs 5.1 g looks pretty easy to explain.

Cheers

Greg

[Yelnats]

Quote "Plus some of the friction circle is used up by the traction force, and as your downforce increases that value increases. In other words, that 4g vs 5.1 g looks pretty easy to explain.

Cheers

Greg"

Very illuminating stuff. I presume that what is reffered to by the "traction force" is the reduction of cornering force due to the engine/braking traction forces passing through the tire. This does not apply during maximum G force phase which is experienced during the portion of the turn done while semi-coasting, i.e. decelerating on minimal throttle (no engine drag) and no braking. It's a well know phenomemom that backing off the trottle during the maximal cornering forces phase (usually near the apex) or applying more, will cause a snap spin for exactly the reason you described.

[CONOSUR]

Originally posted by Wuzak

Originally posted by golfball


Current F1 cars generate approx 4000lbs of downforce at 180mph in a corner (if such a corner exists!!).

Blanchimont??

Exactly! As I recall, during the '02 race, Schumacher's Ferrari was said to be taking Blanchimont at over 190mph.