SALEEN S7R- lateral load 2,6 G

[lemanfan]

Originally Posted by MulsanneMike

I must say I'm a bit skeptical of the downforce figures quoted above. That would be 2750 lbs. @ 161 mph which extrapoltes out to better than 4200 lbs. at the theorectical 200 mph. That is potentially more downforce or equal to many of the top LMPs. Based on the lap times between the two car types and noting their performance difference for reasonably known factors (weight, power, brakes, tires), I still have my doubts. Consider the Saleen's conservative aero architecture with its single element rear wing in close proximity to the production side profiled cockpit, the small rear diffiuser, and the lack of any kind of agressive front underbody solution and the additional lack of significant air management of that area (as it is limited by the car's production origins) leads me to further doubt the figures. GT type cars must maintain the production silhoutte from the wheel centerline upwards. So there are significant limitations to their ability to produce large amounts of downforce.

Mike,

can you imagine other way to pull 2.6 G of lateral load than to produce huge downforce? My calculations are verry simple:

M x A = Fv x n

M= total weight of the car , let say 1250 kg
A= lateral acceleration , this is 2,6G
Fv= vertical load /weight+downforce/
n= friction coefficient of the tyres, let say n=1,4

than Fv=(MxA)/n=(1250x2,6)/1,4
Fv=2321 kg

so the downforce= 2321-1250=1071 kg
so we need to generate ower 1000 kg of downforce to produce so much lateral load and sticky tyres. I know that is very simple model but in general it should be OK.
If I make a mistake or I´m wrong please let me know!

[Goran Malmberg]

Lemanfan,
Looks ok as a brief calculation. However, n is not a constant and get less by raising load. It may fall off by 5% from weight transfer allready at 1g of corninring, depending on CGH. When it comes to these numbers of downforce Iwould imagine n to become 15% less. So we need even more downforce for the stipulated 2,6g.
If no downforce is used we will rely on rubber quality and size, track surface and eaven loading of the total rubber area in contact with the road.

Less weight per area of footprint will raise n, and the cornering force gets greater. Therfore wide tires, wide track width, low CGH is the only key appart from rubber quality and pavement. We are pretty much limited to say 1,5g then.
Goran Malmberg

[lemanfan]

Originally Posted by Goran Malmberg

Lemanfan,
Looks ok as a brief calculation. However, n is not a constant and get less by raising load. It may fall off by 5% from weight transfer allready at 1g of corninring, depending on CGH. When it comes to these numbers of downforce Iwould imagine n to become 15% less. So we need even more downforce for the stipulated 2,6g.
If no downforce is used we will rely on rubber quality and size, track surface and eaven loading of the total rubber area in contact with the road.

Less weight per area of footprint will raise n, and the cornering force gets greater. Therfore wide tires, wide track width, low CGH is the only key appart from rubber quality and pavement. We are pretty much limited to say 1,5g then.
Goran Malmberg

Goran,

You right I just made a very simple calculation to find out the downforce levels
It is not so simple there is a lot of other factors just like you said. This calculation does not include weight transfer.
We need even more downforce to pull 2,6 of lateral G. I just want to say
that car which can corner at 2,6 g must produce much more downforce than
we expect from such a car.
I agree with Mike about the downforce levels of Saleen "but 2,6G seems to don´t agree whith it".

[Goran Malmberg]

Originally Posted by lemanfan

Goran,

You right I just made a very simple calculation to find out the downforce levels
It is not so simple there is a lot of other factors just like you said. This calculation does not include weight transfer.
We need even more downforce to pull 2,6 of lateral G. I just want to say
that car which can corner at 2,6 g must produce much more downforce than
we expect from such a car.
I agree with Mike about the downforce levels of Saleen "but 2,6G seems to don´t agree whith it".

Just a note, even if you allready had it clear, my theory was....
Load transfer raise the load on the outside tires, therby reducing N. But even the aero-downforce raises the load on ALL 4 tires. This means that if we at 1250kg static weight load got n=1,4, we may at 2,6g and 2321 kg load have only n= 1,2 as the load has icreased on all tires. This was beside of load transfer, then even load transfer comes in to picture.
But I agree whith you, a lot thingas allways come in to the picture. I just wanted to point out that if we should susspect the car to corner 2,6g on a continious basis, we need A LOT downforce.
Kind regards
Goran Malmberg

[marcush.]

Hm .the saleen runs quite a bit lower than 3 inches at the front ,i suppose...and has quite a bit of frontoverhang.
But in the end I believe the figures result of the car being compressed into the dip andrunning very close to the ground when changing direction and so the big number apears in the data log ..it is not really representing the cars capability it shows the stress going into the car in that dip.

[lemanfan]

Originally Posted by Goran Malmberg

Just a note, even if you allready had it clear, my theory was....
Load transfer raise the load on the outside tires, therby reducing N. But even the aero-downforce raises the load on ALL 4 tires. This means that if we at 1250kg static weight load got n=1,4, we may at 2,6g and 2321 kg load have only n= 1,2 as the load has icreased on all tires. This was beside of load transfer, then even load transfer comes in to picture.
But I agree whith you, a lot thingas allways come in to the picture. I just wanted to point out that if we should susspect the car to corner 2,6g on a continious basis, we need A LOT downforce.
Kind regards
Goran Malmberg

I calculated tyre friction coefficient n= 1,4 assuming rising vertical load.
I was taking the tyre with friction coef. of 1,8 at zero vertical load which will drop by 0,065 on every 100kg of vertical load. After adding weight and downforce we will get around n=1,4.