who has more down-force - LMP1 or F1?

[silente]

as far as i know, current (both 2013 and 2014) LMP cars have less downforce than F1 cars, but are far more efficient.

Difficult to have reliable number about big teams like toyota and Audi, but there is something available about some other LMP1 and LMP2 cars, and you can easily see that the downforce they have is far below the one you could expect from an F1.

On the other hand, a good LMP car has much much less drag, so at the end the efficiency should be much higher (i guess it is possible to find LMP cars with an L/D around 5).

As somebody said, Combustion Engine power is much lower than F1, but still in 2011 (so before the hybrids came in, but the rest was regulation wise pretty similar to what they look like in 2013) Le Mans top speeds were around 331 km/h.

LMP downforce is also pretty front biased but this is also a consequence of weight distribution and the possibility to use traction control. Oversteer and understeer are not the only metrics i would consider when judging how such a car is handling.

[Juzh]

As somebody said, Combustion Engine power is much lower than F1, but still in 2011 (so before the hybrids came in, but the rest was regulation wise pretty similar to what they look like in 2013) Le Mans top speeds were around 331 km/h.

Just for comparison: Sergio Perez reached 349.2 kmh in 2011 during quali. Pole sitter and race winner Vettel only managed 327, but that was gear ratios limitation, not drag. All out acceleration and screw top speed approach.

[silente]

What i meant was that, unless they have less power, they still reach high top speeds.

That should just confirm LMP low drag compared to F1.

[Andres125sx]

Marc Gene once talked to spanish tv about differences between LMP1 and F1 cars. He didn´t talk about downforce, but said drag can´t be compared. The covered wheels and cockpit make a huge difference he said

[wesley123]

https://twitter.com/alex_wurz/status/381849296855126016 Toyota driver Alexander Wurz says that LMP's run more downforce, which does not seem so surprising to me. There is much more area to create downforce on, there is a much larger front section to create downforce and the rear wing has about as much area as an F1 wing, yet there is bodywork around it to create downforce on.

So an LMP generates more downforce, but has higher weight and less power to fight against the drag.

[Blanchimont]

From some onboard videos ( WEC 2012 Race and F1 Q 2013 ), i stopped the time through Maggots, Becketts and Chapel. The f1 car did the lap in 1:29,607 and the lap of the LMP1 Audi was 1:44,655, the Audi was 16,8% slower over the whole lap.

The timed section through Maggots to Chapel was 8,66s for the F1 vs. 10,13s for the LMP1 car, a difference of 17,0%.
But we have to consider the weight of the cars, which would be ~650kg for the F1 car in qualifying and ~925kg for the LMP car at the start. Not bad!

Another number from the telemetry in the videos, let's assume the telemetry speed is close to the real speed:

Apex Speed Copse:
F1 269km/h
LMP 230km/h

Minimum Speed through Maggots to Chapel:
F1 191km/h
LMP 162km/h

To take a certain corner, the tyres need to produce a total lateral force of:
m*v^2/r = ( downforce [kg]+ weight [kg] ) * 9,81 * friction_coefficient

F1 Copse: 650 * (269/3,6)^2 / r = ( downforce_F1 + 650 ) * 9,81 * friction_coefficient_F1
LMP Copse: 925 * (230/3,6)^2 / r = ( downforce_LMP + 925 ) * 9,81 * friction_coefficient_LMP

If i assume that the friction_coefficient is 1,3 for the F1 tyre and maybe 1,25 for the LMP car, and r_copse is about 130m, the downforce numbers are:
F1: 1539kg @ 269km/h ( 1125kg @ 230km/h )
LMP: 1443kg @ 230km/h ( 1974kg @ 269km/h )

What do you think, is this estimation realistic?

[Lycoming]

First, I don't know if those tire friction coefficients are a good estimate. I wouldn't really pick different numbers based on what I know, I'm just not sure if they're good numbers to use.

Second, they're running at different speeds through the corner, so it would be preferable to nondimensionalize downforce for a more direct comparison.

Finally, it would be better if possible to compare against an lmp1 qualifying lap. Their pace doesn't vary nearly as much between qualifying and race as in F1 these days, but apples to apples, right?

[Juzh]

Vettel took copse flat at the rev limiter @ 300 km/h in 2010. Apex speed probably something like 290-295.

[youtube]http://www.youtube.com/watch?v=pBkpgQ19uZc[/youtube]

[Blanchimont]

In 2010, the weight limit was still 620kg while now it is set to 642kg. That, and the different tyres and maybe track conditions, could explain the difference.

With 628kg the calculation results in a downforce of: 2002kg @ 300km/h ( 1610kg @ 269km/h, 1177kg @ 230 km/h ).


@ Lycoming:
The assumed friction coefficient for F1 is just a guess, but is based on some calculations i did from older onboard qualifying videos. For the WEC friction i simply assumed a value a little decreased, alhough i don't have done any calculations.

The reason for calculating the total amount of downforce in kg is the thread title which for me asks for total downforce, not cl. If you're interested in cl, just solve: downforce[kg]*9,81[N/kg] = air_density/2 [kg/m^3] * cl * cross_section [m^2] * speed^2 [m/s].

And as you said, WEC runs almost the same speed in qualifying and race, so the video of the race start was a good base to do the estimations. The fastest lap in 2012 was a 1:43,628 from free practise, not that far away from the 1:44,655.



Now let's do it the other way around. What if the LMP Audi would only weigh 650kg, how high would the speed be for Copse?

650 * (v)^2 / 130 = ( 1443*(v/230/3,6)^2 + 650 ) * 9,81 * 1,25

650/130* v^2 = 1443*9,81*1,25/(230/3,6)^2 * v^2 + 650*9,81*1,25

5* v^2 = 4,3351 v^2 + 7970,625

v = 109,5 m/s = 394km/h -> could be easily taken flat out (or my calculations are wrong )

[Lycoming]

Ok, I see your point. What I really meant to say was, would they make the same amount of downforce if they were going at the same speed?

[Blanchimont]

Well, my first post has an answer to this question as i scaled the calculated downforce numbers to 230 and 269km/h. It would look a bit different if both cars would use 1,3-friction coefficient tyres, but the LMP still would have more downforce.

F1: 1539kg @ 269km/h ( 1125kg @ 230km/h )
LMP: 1443kg @ 230km/h ( 1974kg @ 269km/h )

[Lycoming]

My apologies, I missed that.

[Juzh]

That, and the different tyres and maybe track conditions, could explain the difference.

Yes, tires were much harder than 2013 which is a disadvantage. Track was more or less the same. Turn 9 at barcelona was also flat in RB6 that year. The only car to ever do so.
I still simply can't wrap my head around lmp having more DF than f1.

[Lycoming]

What's so hard to get? They have a much wider (and more efficient) rear wing and a much, much larger floor. Additionally, they don't have open wheels, which generate huge amounts of lift and drag and decrease the efficiency of aerodynamics downstream of the wheel. If it's the lack of a front wing that bothers you, bear in mind that they do have a front diffuser as well as a rear one. And it looks something like this:

[wesley123]

Or if you want a front wing;


Audi R15