Setup question: ride height

[Giovaneveterano]

Hi folks. I'm a bit confused regarding the correct way to set up the ride height of an aero-type car (GT, open wheels, Proto...)

The lower the better?
I generally keep the same space from the tarmac as I change suspensions stiffness to get the same camber/aero balance.
Some tips?

 

[PhilS13]

You won't like that but like many setup questions the answer is : it depends.

Some cars the lower the better yes. The lower limit will be when the body scraping the ground becomes a nuisance.

Most cars there is a lower aero limit than once you go beyond you lose a lot of downforce way before the body scrapes. For those cars you will want to keep the heights high enough not to lose performance in high speed corners or big braking zones. Most GT3 cars are like that so you don't want to run them too low.

Doing it by feel is basically lowering them little by little until something feels very wrong in the fastest corner of the track. Both front splitter and rear diffuser can lose downforce, it's important to test both.

If you need data the wings app tells you at which height you lose downforce, you just need to know where to look.

 

[Giovaneveterano]

If you need data the wings app tells you at which height you lose downforce, you just need to know where to look.

Thanks for the answer.
I thought about weight transfer, so a car that's pretty heavy on the front car gain some grip on the rear by lowering it. Or vice versa with a Porsche 911.

In the wing app I basically watch the diffuser value I suppose.

 

[PhilS13]

On the mechanical side of things yes the lower the better most of the time because less weight transfer. There are cases where too low makes the suspension geometry go out of useful range and it brings issues but it's rare on the race cars.

On GT, open wheel, proto cars the ride height is really aero driven and not mechanical so that's why I talked about aero only.

In the wings app GH is ground height, CL is lift coefficient. You want to watch CL closely and notice when it starts going crazy (if you test on a perfectly flat surface instead of going crazy it will simply drop). That's the zone you don't really want to go into while on track. For GT cars you need to check both splitter and diffuser.

 

[Glaurung]

In tracks like Spa with strong compressions you may accept a compromise where the car touches the asphalt but runs lower in other more flat sections. This is particularly important with cars without very stiff wheelrates and not very aero depending, like for example the Moby Dick, where a ride height dictated only by the wing app check results in a too high front.

 

[Neilski]

Most cars there is a lower aero limit than once you go beyond you lose a lot of downforce way before the body scrapes.

Whoa, really? Have you seen that in the telemetry?
My assumption was always that lower = more downforce, for any car, ever. But that was just an assumption and observations always trump assumptions

 

[garyjpaterson]

Whoa, really? Have you seen that in the telemetry?
My assumption was always that lower = more downforce, for any car, ever. But that was just an assumption and observations always trump assumptions

You can see it in the Wings App - just look at the front splitter/diffuser, if its too low (in height or springs too soft) then you will see the downforce values drop significantly.

Takes a bit of experimentation to determine at what height this starts happening, but well worth it if your using the car seriously.

 

[Neilski]

You can see it in the Wings App - just look at the front splitter/diffuser, if its too low (in height or springs too soft) then you will see the downforce values drop significantly.

Takes a bit of experimentation to determine at what height this starts happening, but well worth it if your using the car seriously.

Will have a go, ta.
Is that physically realistic though? My (admittedly weak) understanding of car aerodynamics led me to believe that lowering a car (keeping rake the same) would always reduce the air pressure under it and therefore increase downforce.

 

[mclarenf1papa]

Will have a go, ta.
Is that physically realistic though? My (admittedly weak) understanding of car aerodynamics led me to believe that lowering a car (keeping rake the same) would always reduce the air pressure under it and therefore increase downforce.

It's realistic to an extent (in that it does happen IRL), but it's exaggerated in AC.

 

[Neilski]

Thanks guys.
I'd be grateful for any links which help me understand the physical processes that reduce the downforce IRL - after some creative googling I'm no wiser. (The only "almost" hit I got was on an iRacing page! LOL)

 

[mclarenf1papa]

Thanks guys.
I'd be grateful for any links which help me understand the physical processes that reduce the downforce IRL - after some creative googling I'm no wiser. (The only "almost" hit I got was on an iRacing page! LOL)

Cars with underbody aero produce downforce by speeding up the air underneath the car; if there's not enough air, they can stall (and there goes your downforce).

 

[Glaurung]

Thanks guys.
I'd be grateful for any links which help me understand the physical processes that reduce the downforce IRL - after some creative googling I'm no wiser. (The only "almost" hit I got was on an iRacing page! LOL)

The air flow that goes under the splitter is faster than the upper one, generating a lower pressure and then a global downward force.
As the splitter closes the gap to groud the underflow gain speed creating more downforce. This happens until the gap is too little breaking the laminarity of the underflow loosing efficiency, i.e. less downforce.
http://www.formula1-dictionary.net/splitter.html

 

[PhilS13]

http://www.racetechmag.com/2017/08/willem-toet-explains-motorsport-diffusers/

AC is not exaggerating. It is if you consider a front splitter to be the dumb type you find in Nascar but a modern race car is pretty much having front diffusers instead of "splitters". For those, the heights at which they stop working in AC are fine.

 

[Giovaneveterano]

Thanks @PhilS13 for the interesting article
"A high angle diffuser will have peak (downforce generating) performance at higher ride heights while a lower angle diffuser will perform best at lower ride heights. For any given set of engineering and atmospheric conditions there will be a range of diffuser angles which all achieve virtually identical peak performance (each at a different height) – as far as downforce is concerned."

 

[bigbawmcgraw]

Thanks guys.
I'd be grateful for any links which help me understand the physical processes that reduce the downforce IRL - after some creative googling I'm no wiser. (The only "almost" hit I got was on an iRacing page! LOL)

If the gap underneath the car is too small, no air gets to the diffuser (stall).

 

[dud]

As low as possible is what you want, the question is how low can you get away with? Without bouncing off the ground/the bump stops every now and then. Wait, is it really that terminally bad to hit the ground? Maybe it is a tradeoff. What do you care if you also hit the suspension limit in a lap that is already ruined, if a lower car improves your non-ruined laps.

Generally, a person like me who likes his cars floppy will have to give the now softer suspension (with relaxed anti-roll bars) more room to play with. For the same risk of hitting bottom. Once you have decided on your acceptable risk of hitting a hard bottom you will then put the car higher for software suspension and you can go lower with a stiffer suspension.

Except of course there is more than just springs. A soft spring still down not allow the car's floor to hit an individual bump when the dampers are set to low change rates for bump. That setup would and problems with larger obstacles, though.

Then you have the actual bump stop, which is a bit like a fallthrough suspension, a very very stiff one. For me, I want a floppy car in normal operations, but hitting the bump stop more often when I screw up is acceptable to me. I want a clearly defined zone where the car behaves "optimal", which for me is softer, and I'm willing to pay a higher price when I push it out of that zone.

 

[Neilski]

Nice one guys - thanks very much!

 

[mclarenf1papa]

http://www.racetechmag.com/2017/08/willem-toet-explains-motorsport-diffusers/

AC is not exaggerating. It is if you consider a front splitter to be the dumb type you find in Nascar but a modern race car is pretty much having front diffusers instead of "splitters". For those, the heights at which they stop working in AC are fine.

They're a bit high on most cars (the front ends of GT cars are still pretty far removed from a full diffuser - they won't stall at the same height) and in any case lose 100% of their downforce, which is not fine.

 

[dud]

The downforce from the underside of the car is making all this much more complex than it was.

Regardless of whether there can be too little airflow, the rear diffuser creates downforce by dragging a bubble of severe underpressure behind the lower rear of the car.

If your car lifts off the ground (you hit a curb or whatever), then that bubble gets flooded with fresh air. Downforce drops to zero in an instant. The same does not happen to wings. A wing loses effectiveness when the car lifts off the ground unevenly (nose up), but the diffuser turns into useless goo even on level flight.

This issue is, BTW, one of my major concerns about recent high-power road cars. Going on the Autobahn in a car 300 km/h car that generates much of the downforce from a diffuser is very dangerous when the car hits a bump. Let me see whether I can dig up that Youtube video of the Lamborghini that had that happen to it a couple years back.

This also makes me want to scream at Porsche for their decision to offer the manual transmission 991.2 GT3 only without a wing (or the 991R for that matter). It's still the same power car. Except with less drag now. This is unsafe nonsense. It's fine to offer it without wing because who knows it might only see 55 mph America. But now they force people who want to go fast on the Autobahn to do that without aero that is resistant to car lifts.

 

[BhZ]

Whoa, really? Have you seen that in the telemetry?
My assumption was always that lower = more downforce, for any car, ever. But that was just an assumption and observations always trump assumptions

@RasmusP I think Neil doesn't read the messages on telegram...