I've decided I'd like to have a little sports prototype (well not that little really) racer for myself, partly because the existing attempts were pretty but rubbish when it got to the gritty bits and partly because I don't want to follow the rules. I've decided to make the car with a low drag body option and no wings or winglets to provide just enough downforce to reduce highspeed lift for a bit of fun with roughly 1000bhp/ton as well as additional high downforce bodes that I'll work on later.

I've gone for a de-restricted Judd GV4 (4 litre V10, 700bhp @ 10500rpm) and am planning to have a weight (less fuel) of 750kg.

Rather than guessing everything I've built what I want in a CAD program (mainly because my 3ds Max skills need a bit of work) with simplified double wishbone suspension.

From my model I've established:

Wheelbase: 2861
Track (f/r): 1730/1627
Length: 4600
Width: 2000
Height: 1021

So on the fat side for a modern sports racing prototype.

Anyway I started putting in the values for Car Factory and it wants the height of the centre of mass of the car, I have absolutely no idea what would be roughly right for a sports racing car and can't find anywhere with suggested values so any ideas?

Try Mr I converted LFS racers to rTracktor calculator

Which CAD program are you using? I think Solidworks can calculate the center of mass. You'll just need to add the driver. Other programs I've got no idea, TBH.

Quote from JTbo :

Try Mr I converted LFS racers to rTracktor calculator

I think it's time to download open office again

Quote from MAGGOT :

Which CAD program are you using? I think Solidworks can calculate the center of mass. You'll just need to add the driver. Other programs I've got no idea, TBH.

ProDesktop 2000 only because I get it free through school. I think it does have facilities to calculate mass but the model is no where near detailed enough to get meaningful results at the moment.

Quote from ajp71 :

I think it's time to download open office again

Some use this, don't know if there is windows version.

But that Niels's spreadsheet is really must to have when working with such things, especially for dampers as that is part I have done something for

Quote from ajp71 :

ProDesktop 2000 only because I get it free through school. I think it does have facilities to calculate mass but the model is no where near detailed enough to get meaningful results at the moment.

If you know rough values of the engine, drivetrain, suspension and driver you can get an approximate which you can then tweak to your liking for rF. I don't think you'll get any sort of exact value no matter what you do, though, so I wouldn't bother trying too much.

Nobody knows of any RL values for reference, anything would be useful and any prototypes ball park figures would be perfect. AFAIK this value is only used by CarFactory so can't be extracted from the standard rF cars, but I have found a value of 365mm for the Caterham mod so I'm guessing about 250mm would be a sensible guess for now for a prototype.

Quote from ajp71 :

Anyway I started putting in the values for Car Factory and it wants the height of the centre of mass of the car, I have absolutely no idea what would be roughly right for a sports racing car and can't find anywhere with suggested values so any ideas?

Before or after suspension deflection? Or without suspension at all? I have all the values used in LFS, I just need to know specifics.

Quote from ajp71 :

Nobody knows of any RL values for reference, anything would be useful and any prototypes ball park figures would be perfect. AFAIK this value is only used by CarFactory so can't be extracted from the standard rF cars, but I have found a value of 365mm for the Caterham mod so I'm guessing about 250mm would be a sensible guess for now for a prototype.

In car factory it is real world value, in HDV it is real world value minus ride height.

So add first ride height, add then 30-40% of engine height top of that and I believe you are pretty close?

Also you might find attachment interesting, hsss, don't tell anyone that I attached it here :shhh:

Why? I have that document too, found it while googling a couple of months back. I assumed it was free anyway?

Quote from Bob Smith :

Why? I have that document too, found it while googling a couple of months back. I assumed it was free anyway?

Where I got that, it said that do not spread it, but it was really long time ago on another forum

Quote from Bob Smith :

Before or after suspension deflection? Or without suspension at all? I have all the values used in LFS, I just need to know specifics.

I suppose without suspension, anything you've got on the FO8 and GTRs would be brilliant

I've managed to get the centres of mass out of LFS with VHPA, which puts it all nicely into perspective. One thing I couldn't find though was whether there's anyway to get the roll centres out of VHPA (particuarly for the FO8 and that Ultima).

Nope, nothing to do with roll centres in there. Nothe the Ultima was made by me from little in the way of factual data, so it's mostly guesstimates.

I've made the car in rF (physics only) and it's a bit of a beast. I originally made it with the stock tires from Neil's Corvette and no downforce which produced a completely undrivable car. Then swapped inertia values from CarFactory's out put to Neil's tool which nearly doubled lat and long values. Then the car became more how I expected it to be, in fact despite complete guesswork for a lot of the values a bit of tweaking in CarFactory went a long way, the resulting car would still loose control upon too hard a throttle application at 150mph.

I decided 1000bhp/ton was a bit excessive for road tires so put it on realistically sized big slicks (Avon 320/690 R18, 365/690 R18) and changed compound to match (Neil's F3k curve and long/lat CoF of 1.8 for those interested). Then I quickly shoved a rear wing on it (mostly a copy and paste of the Sauber wing) producing a car that will switch from catastrophic understeer to power oversteer on a dab of the throttle. I think I'll have to give in and give it a bit of front downforce to make it raceable but I'm aiming for cornering forces under 2G for the low downforce/drag version. It also currently does a Mercedes CLR impression over the hump at LeMans

1/10th of Sauber wing downforce is still going to be plenty

When I'm making some test cars, I use Niels's spreadsheet for most things, Carfactory for suspension.pm bits only and bit of own creativity for rest

When doing road car physics, I use inertia calculator I found from RSC forums, I think it was in Racer section and very long time ago.

I've put the rF3 engine into the car to try and sort the handling of the car. It seems that it's still suffering from a lot of low speed (as in non-aero related) oversteer my guess is something needs fairly radical changing in the suspension. Guess I'll just have to solve it by experimenting.

One thing I'm not certain about is whether I've got the weight bias (F/R) set right in in car factory, I'm trying to set it to 45/55 (F/R) so from what I can gather I enter the front value (45) in car factory the other thing I'm not certain about is what I should enter as the TLLTD I've currently got 58.9% and the CarFactory documentation said it should be at least 5% in front of CoG for stability and the further forward the more understeer would be produced so I'll try bumping that up to see if it helps rid me of the low speed handling issues. I've attached the CarFactory settings if anyones interested