I'm writing a car racing computer game.
In order to simulate the cars, I need some values for the car's
parameters.
Some are fairly easy, such as size and weight, but others are more
difficult.
If we assume a high performace touring car, say a 7 series BMW or
the like:
What is an approx valuse the thrust force/ acceleration? (I realise
this will vary with rpm).
What is the approx co-efficient of friction, for the tyres?
What is tha approx braking force?
What is the approx areodynamic drag?
What is the approx areodynamic downforce.
I realise that thes parameters will often not be constants, but vary
with speed, or some other parameter, but an approx descrption and
value would help.
I've looked around various websites, and got a lot info, but another
problem i have is this info is often expressed in a specialised units
that are difficult to interprete. For instance, the thrust of an
engibe is often expressed in terms of ft/lbs Torque. How does this
translate to simple F? Or the performace of tyres is expressed ar Load
Index. How does this relate to co-effficient of friction?
Any help appreciated.
Jim Williams
The Bosch Automotive Handbook answers pretty well all of your questions.
It's available from either Bosch directly or from good automotive
bookshops.
Julian Edgar
>I'm writing a car racing computer game.
>In order to simulate the cars, I need some values for the car's
>parameters.
Lots of luck; I believe that 99% of the people who start this task
vastly underestimate its scope and fail to complete it. Not to
discourage you, but do have a realistic look at whether you are
skilled enough and have ENOUGH TIME to complete it.
Look in Road and Track, or the equivalent magazines, or go to a BMW
dealer. The sales pamphlets for the car will often have a horsepower
or torque curve for the motor. From this, you can derive pretty good
estimates. For a street car, assume 30% loses in the drivetrain.
I'll answer your question, but if you use the first part of my answer,
you'll REALLY be wasting your time. 1.1 or so, but could probably
range for 0.9 to 1.4. This varies far more by factors that you are
probably unaware of (slip angle, % slip, unit loading, etc.)
You really need to read a lot about tires, for the tire/road interface
is probably the most complicated part of getting the whole simulator
to feel "right." The only simulator released to date that has even
close to the right feel is [Hard | Race] Drivin' by Atari. Even the
Papy sims (to date :-) ) don't really get it completely right, despite
plenty of effort. GPL on the other hand...
1.0 G of deceleration. Thus, whatever the mass of the car is
multiplied by acceleration due to gravity in your chosen units. This
is largely independent of speed, but quite dependent on wheel loading.
Cd of somewhere around 0.33, but this is likely in the sales pamphlet
and in the car mags. This is quadratic with speed.
This is likely to not be in the mags, but might be (unlikely) in the
sales pamphlet. Most street cars probably generate negative downforce
at speed, as an accident of their streamlining. In any event,
aerodynamic loading for a street car is probably not much of a factor
until speeds of 75mph or so. This is quadratic with speed.
I've taken a shot at it, but you need to know a lot more than it
appears you do. It's not insurmountable, but it's a hard climb if you
don't have a solid math and engineering background.
Uhoh, long, hard road ahead...
Those are the natural (English) units for torque. Divide by the radius
to get the force in lbs. (300 ft-lbs operating at a radius of 2 feet
provides 150 lbs of force.) This question indicates a lack of
mechanical engineering background. To get a good simulator, you're
going to need some mech E background, or at least have access to a
patient person who does...
Load Index is a term that I'm not familiar with without the benefit of
the surrounding context. It probably covers the fact that a tires
coefficient of friction DECREASES with increasing unit load, but
again, with no context, it could be an English term for something I
know about, or it could well be one of the many things I still don't
know about tires...
---Jim
Quoted text (34 lines)
>I'm writing a car racing computer game. >In order to simulate the cars, I need some values for the car's >parameters. >Some are fairly easy, such as size and weight, but others are more >difficult. >If we assume a high performace touring car, say a 7 series BMW or >the like: >What is an approx valuse the thrust force/ acceleration? (I realise >this will vary with rpm). >What is the approx co-efficient of friction, for the tyres? >What is tha approx braking force? >What is the approx areodynamic drag? >What is the approx areodynamic downforce. >I realise that thes parameters will often not be constants, but vary >with speed, or some other parameter, but an approx descrption and >value would help. > I've looked around various websites, and got a lot info, but another >problem i have is this info is often expressed in a specialised units >that are difficult to interprete. For instance, the thrust of an >engibe is often expressed in terms of ft/lbs Torque. How does this >translate to simple F? Or the performace of tyres is expressed ar Load >Index. How does this relate to co-effficient of friction? >Any help appreciated. >Jim WilliamsQuoted text (35 lines)
> I'm writing a car racing computer game. > In order to simulate the cars, I need some values for the car's > parameters. > Some are fairly easy, such as size and weight, but others are more > difficult. > If we assume a high performace touring car, say a 7 series BMW or > the like: > What is an approx valuse the thrust force/ acceleration? (I realise > this will vary with rpm). > What is the approx co-efficient of friction, for the tyres? > What is tha approx braking force? > What is the approx areodynamic drag? > What is the approx areodynamic downforce. > I realise that thes parameters will often not be constants, but vary > with speed, or some other parameter, but an approx descrption and > value would help. > I've looked around various websites, and got a lot info, but another > problem i have is this info is often expressed in a specialised units > that are difficult to interprete. For instance, the thrust of an > engibe is often expressed in terms of ft/lbs Torque. How does this > translate to simple F? Or the performace of tyres is expressed ar Load > Index. How does this relate to co-effficient of friction? > Any help appreciated. > Jim WilliamsQuoted text (10 lines)
>How realistic do you want your simulation to be? You can reduce it down to >a simple point mass simulation (search the web for RARS as an example) or >you can do something with a full suspension, including sprung and unsprung >masses, tire load sensitivity, engine torque curves, etc. >If you have a decent math background, an excellent reference book is "Race >Car Vehicle Dynamics" by Milliken & Milliken. You can purchase it through >SAE (I haven't seen it anywhere else) for about $80. This book covers all >aspects of simulating a vehicle, and includes some real tire performance >data supplied by Goodyear, something I haven't seen in any other book. >Good luck, and let us know how it goes!>Have a look at Cartest...It simulates the performance of cars from a
>whole bunch of
>variables....and its surprisingly accurate....
>My Website has a copy......http://www.users.bigpond.com/byronl
Thanks. I'll do that.
