LMP performance

[silente]

Hi all!

today i had some time and watched some on board laps from AUDI's WEC Races.

A very nice features of these videos was the presence of a sort of accelerometer showing values of longitudinal and lateral accelerations in different parts of the circuit.

Since these videos cover normally race situations, it is probably quite difficult to really extract from them very useful/reliable info about real car limits, but still they could tell something about these cars performances.

Looking to Silverstone race, for example, i have seen that maximum lateral accelerations values for one of the AUDIs were around 3.8g in fast corners, around 1.8g in slow ones, while maximum longitudinal accelerations were around 2.5g.

So here comes my firs question: why such a big difference between the two? normally when you start braking you still have a very huge downforce and i would expect to see here higher decelerations (at least in strong breaking points, at least).

My other (more general) question is: does anybody knows which level of accelerations these cars can reach in different Aero configurations (In Le Mans they have for sure less downforce than in Silverstone or in Interlagos, so i would expect a higher "gs" potential in these tracks than in France)?

Thanks!

[Ogami musashi]

Even if 3,8g is quite big for an lmp car they still have much less downforce/weight than F1 cars. In addition they have lower drag which means they less benefit from that on braking (it used to be around 1g worth in F1 so that's quite significant).

As for accelerations rate is don't know but all i know is that the Toyota TS030 is worth 820 bhp for 900kg which is quite a good power/weight ratio.

[Tommy Cookers]

@silente
the 3.8g is not the true centripetal acceleration
it is the vector sum of the readings from all the accelerometers
often there is eg high centripetal combined with substantial tangential acceleration
the true values will be obtained by later processing

this is what I have been told when asking the same sort of question, and I believe it
Silverstone has (into 1?) corner gradient changes ('compressions') that give momentarily very high contact force/vector sum g
other corners will suggest that the car's max centripetal g would be less than 3

[silente]

Tommy Cookers,

thanks very much for your answer.

I am pretty sure the value i have read was shown as pure centripetal. There was another one for the pure longitudinal. Unfortunately (but not unsurprisingly) no one for the vertical to account for banking. But i don´t know how they calculate/measure these values (maybe GPS), how fast they log them (they seemd to have a huge daly comparing to the video images) and if they "trick" them somehow.

I will try to post the link of the youtube video.

It was a surprising value for me as well, but i remember also Wurz talking about something like 4g in some corners. This seems to me far too much, but since i have no real data about these cars, i was wondering if that would be possible. The 3.8 g in that video seemed (surprisingly) to answer that 4 g are not too far in fast corners...

What your source said instead? no more than 3.2g even in fast corners?

[Tommy Cookers]

I'm sure this has been covered in other threads, it's worth a search

modern Silverstone has a downhill entry into a very fast level corner so the car has (briefly) extra adhesion
which means they have very high cornering force simultaneous with high braking
that's where the big numbers come from, and everyone likes that

[silente]

So in others track with similar downforce levels the real potential is 3.2 g according to your info?

What about braking?

[Tommy Cookers]

AFAIK the true figure for F1cornering is 'only' about 3.4g
I suspect that the display you have is from GPS based data processing, not from real accelerometers
GPS is more believable for braking than for centripetal, surely
(recently a kart person was claiming over 3g, but this was shown to be false)

if I can find any thread(s)I will post

[Ogami musashi]

I too discussed with a michelin engineer that worked in F1 during the high times (the tire war) and he told me that indeed 3,5G was really the real sustained max value for F1. And being a kartman i also know very well the problem of telemetry that shows too high values of cornering (with indeed some peak above 3g's).

However we would need much deeper analysis of the this topic and for the sake of comparison between lmp and F1 is not really a problem to take the initial 3,8G figure since the F1 telemetry is also a bit exagerated.

[silente]

any idea also about the difference between braking and cornering? Is it connected only to GPS (or anyway video data mistakes) or to a real difference in car performance?

Could it be somehow related to durability? We are always talking about endurance racing after all.

Too bad there are no qualifying laps around. Only race videos.