Hi

I was just wondering about one thing concerning the GTRs... it always occurred to me that their top speed seemed to be a little low, taking into account their absolute power of ~500 bhp.
On the longer straights, the GTRs seem to have only a minor advantage over the much heavier and less powerful FZ50. In the end of the Aston National start/finish straight, the difference is only 20-25 Km/h - of course with 0 downforce on the FZR.

Shouldn't it be possible for those monsters to hit the 300 Km/h-barrier quite easily or am I missing something? It seems they're completely lacking the "oomph" above 250 Km/h...
I didn't want to post this in the bug reports section because I was merely wondering and maybe there's something I didn't take into account.

See the attached screenshots for demonstration.

biggie

Even with zero wing angle, the GTR's are still generating significantly more drag than the FZ50 with no wings at all.
If you look at the aero section, set both wings to zero, you can see that the undertray and both wings are still generating a fair bit of drag over and above the body drag.
Also, the power to top speed relationship is exponential, so to acheive 25kph higher top speed once you are already up at 250kph requires a lot more extra power than increasing the top speed from 150-175kph for example.

well when you consider a Ferrari 550 Maranello road car has a top speed of 199MPH, and the race car will probably only do a little over 200 if even that.
it's not about top speed in race cars, more about acceleration and corner speeds.

He's talking about km/h.

Vain

for Vain:

Quote from nikimere :

well when you consider a Ferrari 550 Maranello road car has a top speed of 320.2Km/h, and the race car will probably only do a little over 321.8 if even that.
it's not about top speed in race cars, more about acceleration and corner speeds.

:P

Quote from biggie :

HOn the longer straights, the GTRs seem to have only a minor advantage over the much heavier and less powerful FZ50. In the end of the Aston National start/finish straight, the difference is only 20-25 Km/h - of course with 0 downforce on the FZR.

And two stupid questions from me:
1. Is this tested with no wind?
2. Have you tinkered with the gear ratios of the GTR?

EDIT
Never mind - just noticed that you have the hotlap record on Aston National with the FZR...

Quote from Vain :

He's talking about km/h.

Vain

km/h is just a unit. that doesn't affect my point!??

I thought you mistook km/h with mph and justified the achieved speeds as good-as-it-is.
Nevermind.

Vain

Well, the cars on Brazilian stock car championship have about 450hp and 1200kg, and their speed at the end of main straight on Interlagos track (where F1 takes place on Brazil, a track with tight curves but very long straights) is around 240km/h, so I think that the final speed of the GTR class cars (except FXR) is pretty on par with reality

Quote from colcob :

Even with zero wing angle, the GTR's are still generating significantly more drag than the FZ50 with no wings at all.
If you look at the aero section, set both wings to zero, you can see that the undertray and both wings are still generating a fair bit of drag over and above the body drag.
Also, the power to top speed relationship is exponential, so to acheive 25kph higher top speed once you are already up at 250kph requires a lot more extra power than increasing the top speed from 150-175kph for example.

Yes, I am aware of the undertray force. But I wasn't thinking that the drag would be so excessive that almost twice of the power/weight-ratio would result in only 25 Km/h more topspeed.

Quote from nikimere :

[...] it's not about top speed in race cars, more about acceleration and corner speeds.

True, but I was just wondering because I kept imagining that GTR-like cars could achieve higher top speeds. Guess I might have to reconsider

Quote from biggie :

But I wasn't thinking that the drag would be so excessive that almost twice of the power/weight-ratio would result in only 25 Km/h more topspeed.

If you look at the formula for calculating drag you see that the value also includes the velocity of the object (car in our case) squared...

Stolen from a physics-related site:
F_drag = 0.5 c p v^2 A
c = drag coefficient
p = density of air
v = terminal velocity
A = frontal area

Heres some real life downforce/drag figures for comparison to LFS cars(at 80.5m/s = 290km/h, 180mph)

1999 Ferrari Modena (street car) = -1892N downforce, 2570N drag

1997 McLaren GTR (long tail, Le Mans) = -7927N downforce, 3602N drag

2001 Penske-Reynard-Honda (Indycar, road setup) = -17680N downforce, 5941N drag

And for fun: 1992 Allard J2X (IMSA GTP) = -35352N downforce, 5892N drag (!!!)

And the LFS S2 cars:

LFS S2 GTR class (min/max) = -7154/14074N downforce, 3292/5238N drag

Formula XR(min/max) = -5541/11639N downforce, 2365/3965N drag

Formula V8(min/max) = -7387/15519N downforce, 3046/5179N drag

As you can see the LFS cars have realistic drag figures for the downforce they are generating.

The GTR class have high max. downforce for a GT style car, probably similar to the old JGTC cars when they had underbody tunnels(before 2001 iirc).

Quote from biggie :

Yes, I am aware of the undertray force. But I wasn't thinking that the drag would be so excessive that almost twice of the power/weight-ratio would result in only 25 Km/h more topspeed.

Power to weight is irrelevant, I'd say it's the most useless statisitic you can have about a car IMO.

Why?
Top speed can be judged by power vs. aerodynamics
Low speed acceleration is all about torque-to-weight (well, and grip)

Power to weight tells you nothing really.

It is the ~35% hike in power that you need to look at. Tuning the FZ50 to give the same output as the FZ50 GTR would give it a top speed of about 190mph. The FZ50 GTR can only manage about 180mph with wings at zero (no high nose cheat), so about 10mph is being lost to the undertray.

Quote from Bob Smith :

Low speed acceleration is all about torque-to-weight (well, and grip)

:huh:

Perhaps if your gearing is off...

Power limits the acceleration of the car. Not torque. 1500Nm of torque does you little good at 400rpms.

Last I checked, F1 cars get off the line in a serious hurry despite a tall first gear, an on/off clutch, and less torque than my road car. 200-250lb-ft

The venerable PT6 is another great example. The little PT6a produces
(depending on rating) 675ish hp and more than 1600lb-ft of torque at the output shaft at 2200rpm. At 30000 rpms at the input shaft of the planetary reduction box, its producing 118lb-ft of torque. Honda territory.

Unless fuel efficiency or ultra-longevity is important, engine speed doesn't much matter. Therefore, torque doesn't matter. The only thing that matters is the product of torque, a constant, and engine speed....horsepower.

So I would say that it is torque to weight thats an unbelievably useless figure. Its rarely published, perhaps because its pointless.

Sorry but I think you're wrong. Currently delivered torque absolutely dictates your acceleration.

Torque/effective wheel radius = delivered linear Force at contact patch.

Acceleration = Force/Mass

Therefore as weight = mass*g

torque/weight is directly analogous to force/mass which equals acceleration.

Therefore torque to weight is the most accurate way of defining a cars acceleration potential. The reason its never quoted is perhaps because people dont understand it.

Mass is irrelevant in the equation of top speed. The only thing it affects is how quickly you get to the top speed of the car, but mass only really affects low speed acceleration because power is what helps you overcome drag and accelerate at high speed. Here is an article that might explain everything, although a bit technically - The Physics of Racing

My god I know that. We were talking about acceleration just then.

Mass might have a very small effect on the top speed in the sense that a heavier car will put more load on the bearings, increasing rolling resistance.

I think I agree with Bob and Colcob about torque being more important than power for low-speed acceleration but I can't quite convince myself why.
Since engines tend to produce peak torque and peak power at different RPM, which point gives the best acceleration? If a car had constantly-variable transmission, would it be better to hold the engine at peak torque or peak power while accelerating?

Quote from skiingman :

Last I checked, F1 cars get off the line in a serious hurry despite a tall first gear, an on/off clutch, and less torque than my road car. 200-250lb-ft

This would only apply to the FO8, all the other engines are production based.

Hmm...

I understand the reasoning behind the favor of Torque : Weight,

But perhaps the rate at which the torque is being applied gives a better idea of how much energy is being put into the system, therefore HP: Weight should be more important....

Who cares if you've got all the force in the world if it takes a vast amount of time for it to be applied?

Drag cars are built for HP which probably says something.

My 2 cents

How about just saying how fast a car accelerates if you want to tell someone how fast a car accelerates?

An engine will always accelerate fastest at the torque peak in any given gear. Horsepower comes into play when you factor in gearing. Lets say you have engine a and engine b. They are similar but engine a makes 200lb-ft of torque at 2000 rpm and then suddenly drops off and engine b makes 200bl-ft up to 4000 rpm. So, engine b makes twice the hp of engine a because hp = torque/rpm. They are put in the same car with the same gearing. They will both accelerate off the line the exact same, until engine a has to shift because it got to 2000rpm. Engine b will pull ahead because it can continue to accelerate in 1st until it reaches 4000, and the car with engine a will be behind because it is in 2nd. Kapiche?

So really, since we can change the ratios in the lfs cars, to achieve the highest top speed it's all about hp.

Edit: another thing to think about. You can run a twice as short gear ratio in the car with engine b and reach the same speeds as engine a, ( since b can reach twice the rpms) but since engine b's ratio's are so short it will accelerate almost twice as well because torque to the wheels is twice as much.

The force at the wheels is simple:

F = (Torque * RPM * Transmission Efficiency)/Dynamic radius of driven wheels

As we know Acceleration is Force/Mass. So now we can work out how fast something accelerates. And in each gear it will be accelerating hardest at peak torque.

This doesn't take into account drag (of any sort), tyre slip or a few other things, so is a bit simplified, but will get good enough results for 99% of people.

Quote from biggie :

Hi

the difference is only 20-25 Km/h

That is a big difference actually. The extra horsepower required to add 25kph to a car's top speed would be much more than it may first seem. Adding a lot of extra horsepower would only give a tiny gain in performance for a car at the GTR's level of engineering. So horsepower by itself is no great measure of performance.

It may also be useful to find out out how quickly it takes the GTR to reach the FZ50's top speed. If the GTR car reaches the FZ50's top speed quicker than the FZ50 does, then the performance gap is widened even more than just a top speed rating would suggest.

I understand what you're saying but I'm still not convinced that the actual force at the wheels is all that's important, although by the equations that seems to be the case. Forgive my unreasonable questionng, but please help me understand this:

If MORE WORK is done on an object will it not accelerate faster because the total amount force exerted on it OVER GIVEN TIME is greater?

Being able to twist a steel axle with 300ft/lbs of rotational force is a lot less relevant than twisting the same axle with 300ft/lbs over any said amount of time. One could take all day, and one could happen in 1 second which would require more POWER, although the net force is the same. Isn't that correct? Where am I going wrong?

Isn't HP basically the rate at which Torque is applied (550 ft/lbs/sec iirc)? When talking acceleration - wouldn't being able to apply any given torque only be meaningful in the context of how fast it is applied?

Seems reasonable but show me where I am wrong... Yes I know F=MA etc...