Aerodynamic Drag / Speed Test (2.08)

[shirakawaa]

I think you should add the X2010/2011, which I believe has the highest downforce values possible in GT5.

 

[bigbear]

Agreed. The RBX-10 and/or RBX-11 are on the list for testing. I just have to find time to run them.

 

[eran0004]

For best and more reliable results, you should change the top gear in each test so that top speed is reached at peak power rpm.

You mean have one gearing for max downforce and another for min downforce? And then change as well when the new patch hits and changes the drag? I say no, the gearing should be the same. This study is about aerodynamic drag, not top speed. Top speed is only used here as a tool to measure the impact on drag from downforce. If the tuning stays the same with the only exception of the downforce, then we know that the differences is because of downforce only, because we haven't touched anything else. If we start messing around with gearing then we no longer know what is causing the different result, or how big the difference is. When we know how big the impact on drag from downforce is, then we can start optimizing gears and measure top speed, but that's another study.

On another note, I think it would be interesting to also measure the difference in front downforce vs rear downforce. Test a racecar (or two) with max front - min rear, min front - max rear, max front and rear, min front and rear.

 

[Exorcet]

We don't need to change gearing for the test. We can actually back out drag numbers if we have the max speed, RPM at that speed, and power vs RPM. Using that we can get the drag force in pounds for each car, the only real source of inaccuracy would be not knowing how much transmission losses are modeled in GT5.

I suggest adding 1/4 mile and 1 mile (or equivalent) acceleration times to the test if possible.

Most importantly though, if downforce changes speed significantly, we need laptimes on road courses. The whole point of this update, I think, is to make it such that throwing max downforce on a car is no longer the fastest way around a track. Max downforce cars should be slow around Sarthe, Monza, and possibly other tracks.



==EDIT==

Here are the mph formulas for calculation drag:

Drag = power/velocity [SI units]

Drag (lbf) = 333.35711820612086153405992114236 * HP / mph

To correct for powertrain losses, we could assume a number, like 10%. So:

Drag (lbf) = 333.35711820612086153405992114236 * HP * .9 / mph

=

Drag (lbf) = 300.02140638550877538065392902813 * HP / mph

Round Drag to 300*HP/mph

So for example, the F10, assuming it reached 700 hp in min drag config and 690 in max drag config:

Max drag = 983.44 lbs
Min drag = 939.24 lbs

This automatically corrects for gearing.

You could set it up in a spreadsheet, perhaps in Google Docs, for all to see

 

[mistersafeway]

What's the point of measuring front versus rear downforce? Front downforce increases drag properly, just like real life, albeit possibly in incorrect amounts. Rear downforce reduces drag currently, causing a higher top speed and also this update. I see no reason to bother with that, unless someone can think of one.

 

[joetruckv8]

I was working on something just like this, great job!

 

[Exorcet]

What's the point of measuring front versus rear downforce? Front downforce increases drag properly, just like real life, albeit possibly in incorrect amounts. Rear downforce reduces drag currently, causing a higher top speed and also this update. I see no reason to bother with that, unless someone can think of one.

Front downforce, depending on the method, usually is not very hurtful in terms of drag. This should be reflected in GT5.

 

[Furinkazen]

Rear downforce does not increase top speed.

 

[Niop]

Rear downforce does not increase top speed.

In some situations it actually does.

 

[CJSpencer77]

I think we would all be surprised if SimonK didn't have anything negative to say really. The guy spreads doom & gloom in virtually every thread he goes into.

Seriously, I reckon the guy would goto a funeral dressed as the Grim Reaper as he would think things are not depressing enough

Lmao, so its not just me who noticed, lol every time i see that walk animation i already know what to expect !

To Op, dont let the nay sayers put you off, for one ill definatly be back after the update to look over your findings.

The fact that 99% of the time its better to run full aero doesnt make any sense so maybe the patch will
make this more life like.

 

[Cyber_stig_77]

Um, maybe start the thread once you've actually got the update and done the test.

um, how would you get the pre-update results if you waited until the update was out ???

@ OP, great idea setting this up in advance so people can get as many cars tested as possible before the update arrives.

 

[Exorcet]

In some situations it actually does.

That's a glitch though, I believe. If you're not trying to wheelie, rear downforce will slow you down (barely).

On my suggestion for collecting drag force data, we'll also need to make the data comparable. The easiest way is by generating a V coefficient by dividing the drag by mph^2. This number is proportional to the drag coefficient, but easier to computer.

Another way that might be more intuitive to use is to convert the drag forces to what they would be at a standard speed. For example, make 150 mph the standard speed. To get the standard drag, just multiply every absolute drag number by (22500/max speed^2).

For the F10, the 150 mph standard drags are:
Max - 499 lbf
Min - 423 lbf

The V coefficients are
Max - .022194
Min - .018786

 

[Niop]

That's a glitch though, I believe. If you're not trying to wheelie, rear downforce will slow you down (barely).

I don't think it's really a glitch, just more so how the physics work in the game. But I hope they fix it with the new patch.

 

[HoneyBadger]

Thanks bigbear. Looking forward to the 2.08 update.

 

[KinLM]

What I'm wondering is if this update will mean that cars with less downforce will go even faster than before, if anybody understands what I mean. I know that it's increasing the drag for high downforce cars. But I hope that PD doesn't do something stupid and end up decreasing drag on low downforce cars..

 

[Denilson]

bigbear: Great idea! 👍
How about throwing in say the Ferrari 458 as "stock", then with a GT-Auto wing @ minimum, default and max aero settings?
Would love to see the results on a road going car as an alternative to the race cars.

Exorcet: I wonder if we should assume 10% loss thru the drivetrain across all cars. I'm not saying that it's wrong, but if PD do simulate loss of power thru the drivetrain (which imo is quite possible when comparing RR cars with FR cars - The RR cars are faster @ identical p/w ratios), my guess is that they do have different % depending on the drivetrain configuration.
How about:
FR: 12,5%
MR: 10%
RR: 7,5%
4WD: 10%
?

 

[Ealirendur]

Excellent idea. Perhaps also test at least one example of extreme Ride Height changes? Say, a car with no adjustable DF, with min front, max rear, then level, then max front/min rear? I'd be happy to do it - any particular car suggestions? Low inherent DF may be a good idea - Veyron/SLS et al with active spoilers probably bad for this particular purpose.

 

[GODfreyGT5]

Edit

I derped.

 

[shirakawaa]

Excellent idea. Perhaps also test at least one example of extreme Ride Height changes? Say, a car with no adjustable DF, with min front, max rear, then level, then max front/min rear? I'd be happy to do it - any particular car suggestions? Low inherent DF may be a good idea - Veyron/SLS et al with active spoilers probably bad for this particular purpose.

In theory a fully lowered car should have better aerodynamics than one that hasn't been (due to decreased frontal area). Currently this doesn't appear to be factored in GT5.

 

[Grandi]

Excellent thread. As a suggestion, would it be sensible to measure this with a car limited to a constant power for a range of RPM (easy with e.g. Peugeot 908).

Regarding drivetrain/auxiliary losses, I would think the values actually used within the GT5 code vary significantly... however, a single-valued assumption (proposed by Exorcet) would be a good start imo.

BTW - does anyone actually have an idea what the downforce number in GT5 represents? Directly negative lift, or some wing setting which is a variable in the function of lift? I guess one way to find out would be to compute drag / downforce setting and see changes in the indicated lift/drag values, assuming the former...

 

[Ealirendur]

In theory a fully lowered car should have better aerodynamics than one that hasn't been (due to decreased frontal area). Currently this doesn't appear to be factored in GT5.

Yes, and that might also be worth re-checking, but just to make sure we're clear, I'm referring to checking drag (or indeed lift side-effect?) differences with extreme front and rear ride height splits, as opposed to simply raised or lowered.

Happy to pitch in and do some spade-work myself, but I'm looking for car suggestions. Ones that happen to have well known real-life figures might be good (if for no other reason than correlation), but I don't know those.

 

[Exorcet]

BTW - does anyone actually have an idea what the downforce number in GT5 represents? Directly negative lift, or some wing setting which is a variable in the function of lift? I guess one way to find out would be to compute drag / downforce setting and see changes in the indicated lift/drag values, assuming the former...

I think they're just made up numbers created by PD. The closest I came to figuring out what they mean was estimating total downforce produced by the 908

Peugeot 908

DF max
226 mph
DF min
235 mph (I really hit 233, but I think the power started falling off)

I decided to do some further testing on the 908

2.0 g lift = -1064 lb, .1064 coeff (max DF at GVS tunnel)
1.8 g lift = -701 lb, .086 coeff (min DF at GVS tunnel)

https://www.gtplanet.net/forum/showthread.php?p=6148921#post6148921

So the difference in lift for the 908 at 100 mph, between min and max downforce is about 360 lbs. Or max downforce is 24% more effective at generating downforce.

Drag only differed by 12%.

 

[bigbear]

Added three more cars to the list:

Honda INTEGRA TYPE R (DC5) RM '04
Gran Turismo Red Bull X2011 Prototype
Ferrari 458 Italia '09 (w/ GT Auto Aero Kit)

Lots of good ideas and discussion from everyone. It's almost hard to keep up with it all.

I've tested some different Front/Rear downforce settings and found spotty, inconclusive results. The F10, Jag, and IMPALA were all fastest with a low/high downforce setup. Other cars however were fastest with low downforce all 'round. It will be interesting to see if this changes at all with the update.

Example: Jaguar XJR-9
high/low.... 60 front, 50 rear, 110 total, speed: 236.1
high/high... 60 front, 85 rear, 145 total, speed: 237.9
low/low....... 30 front, 50 rear, 80 total, speed: 241.7
low/high.... 30 front, 80 rear, 110 total, speed: 243.6

Top speed tuning has been thoroughly covered in other threads so I don't plan on going too in-depth with different settings. My guess is that the effect of things like front/rear downforce ratio, and ride height settings won't be changed directly. We'll find out soon.

 

[Exorcet]

It might be too late, I wonder if a test of the ACR is possible. Right now, it's as if the wings aren't even there (downforce wise and drag wise). I can't test anything since I don't have PS3 at the moment, but I know the ACR can go well over 200 mph. It should be limited to about 180. Hopefully this update gives it downforce and drag.

 

[bigbear]

I tested the ACR and will post the data sometime after the update. 2.08 should be available soon.

 

[MOTORTRENDmitch]

I tested the ACR and will post the data sometime after the update. 2.08 should be available soon.

It's up. Let's see some Data

 

[Windfire1010]

I decided to lend my hand to this cause with the Audi A4 Touring Car.
Pre 2.08 the car was able to do 189.0 with max downforce, and 193.4 with min downforce. After the update 184.7 with max downforce, and 196.6 with max downforce.
The differece between min and max downforce went from 4.4 mph to 11.9 mph.
I am going to post the other cars I did when I get to it.

 

[diegorborges]

Just tested a slightly tuned Maserati Granturismo... 15 degrees of rear aero give me 313.0kmh, 5 degrees give me 317.8...

Just wanted to share. I didn't had the data before 2.08... Sorry.

 

[Slirb]

X2010 S. Vettel.

2.07
Max DF - 250.5 MPH
Min DF - 297.0 MPH
Difference - 46.5 MPH

2.08
Max DF - 234.8 MPH
Min DF - 307.1 MPH
Difference - 72.3 MPH

 

[bigbear]

First result after the 2.08 update.

Ferrari F10 '10
Downforce/ v.2.07/ v.2.08/ Change
Min............ 223.6.... 235.6.... +12.0 mph
Default....... 215.0.... 215.0.... same
Max........... 210.5.... 199.9.... -10.6 mph