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Car Accelerationby VMail
Tags: acceleration 
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#1
Jan904, 06:58 AM

P: 11

Hi Im making a racing game for the XBox, I need some info on the following Gears, Gear Ratio and Acceleration, basically I want to know how a real car moves, if you are insteasted in testing the PC version then let me know
Car Spec air density = 1.29kgm3 mass = 1550kg red line = 8500rpm drag coefficient (cd) = 0.34 (not an official number) height = 1.36m width = 1.785m frontal area = height × width = 2.4276m2 (only an approximation) wheelbase = 2.665m tire = 245/40ZR18 tire radius = 0.3266m (this number is calculated from the tire spec) torque = 392Nm@4400rpm power = 206000W@6800rpm 1st gear ratio = 3.827 2nd gear ratio = 2.36 3rd gear ratio = 1.685 4th gear ratio = 1.312 5th gear ratio = 1 6th gear ratio = 0.793 reverse gear ratio = 3.28 final drive ratio = 3.545 lateral acceleration = 0.94g on skidpad of 300ft radius weight distribution (front/rear) = 57%/43 minimum turning radius = 5.6m To make things simple, the throttle can only be up or down I want to know quickly the car will move, say like from 0MPH to 30MPH, staying in 1st gear (or KPH which ever is easy, I can always convert it later) (also i havent given the distance) also Ive been given torque = 392Nm@4400rpm, how would i find the torque at 5000rpm? 


#2
Jan904, 09:18 AM

P: 29

Torque in kilograms per meter  1kgm = 9.8 NM Horsepower in spanish CV unit (I think its more or less same as HP)  1KW = 1.36 CV/HP So you could calculate torque at 5000 rpm if you had the horsepower figure at the same egine speed. That engine has an output of 245.81 hp at 4400 rpm and 280.16 hp at 6800 rpm. 


#3
Jan904, 11:54 AM

Sci Advisor
P: 905




#4
Jan904, 06:58 PM

P: 11

Car Acceleration
most cars a FWD, so it a FWD now, and no traction I think (a lot of wheels spinning)



#5
Jan904, 11:34 PM

P: 28




#6
Jan1004, 03:05 AM

Sci Advisor
P: 905

Low speeds like 0 to 30mph are easy because air drag is negligible. Acceleration in g's is
[tex]{f_f\over {1\over\mu} + {h\over L}}[/tex] where [tex]\inline{\mu}[/tex] is the lateral g's (coefficient of friction), [tex]\inline{f_f}[/tex] is the fraction of weight on the front, h is the height of the CG (I estimate 0.5m), L is the wheelbase. Plugging in your numbers gives 0.45 g's or 14.4 ft/s/s. 30mph is 44 ft/s, so the time to get there is 3.05 seconds. The same specs for RWD give 2.76 s. 


#7
Jan1004, 01:36 PM

Sci Advisor
P: 674

This problem is a little involved for an online forum. People take courses on this stuff. Go to the library and pick up some books on auto engineering. Even that won't help you very much with tires, since real data on them is almost impossible to come by (krab's approximation isn't very good). You'll have to experiment, and see what feels right.
You'll also need a torque curve (which you can guess at from peak torque and power figures  just draw a reasonable looking graph which satisfies both conditions) at the wheels  not the usual net rating. Then you have to worry about how the differential(s) distributes torque, and the rotational inertia of the various driveline portions. Springs and shocks also affect how the car launches. If you're just making a simple arcade game (ie not a sim), then you can get away with less, but you didn't say. Ask more specific questions. 


#8
Jan1004, 04:01 PM

P: 11




#9
Jan1004, 05:41 PM

P: 1,528

I'd be interested in testing the game  phatmonky@yahoo.com



#10
Jan1104, 12:40 AM

Sci Advisor
P: 674

You should probably browse around this site a bit
http://www.racer.nl/ He's making a game that's supposed to do the physics "right," and has a lot of documentation on it (free source too I think). It might give you some ideas. 


#11
Jan1304, 08:55 AM

P: 11

I dont think krab formular is correct as there is nothing referanceing the gears



#12
Jan1304, 01:21 PM

Sci Advisor
P: 905

Anyway, I did the other calc.s for you. 1/4 mile: 14.11 sec @110.9 mph top speed: 163 mph 060: 6.86 sec 60 ft time: 2.89 sec A graph of driving force versus speed in each gear is here. The Green curve is your traction limit. Since the drive is FWD, this is rather low. The Red curve is air resistance. Where it crosses your white curves is top speed. The Blue curve is the performance you would get if you had an ideal gearbox which always kept you at peak power. 


#13
Jan1304, 01:50 PM

P: 11

Its a bit hard for me to explain this, 1st and 2nd gear gives different acceleration
eg 030MPH in 1st gear will take 3.05sec but what if you drive 015 in 1st gear and switch to 2nd from 1530MPH both will take different times to get to 30MPH 


#14
Jan1304, 02:02 PM

Sci Advisor
P: 674

Well 30 mph is only 5300 rpm is 1st gear, so there would be no point in shifting before then. Shifting near 7000 rpm would be optimal for the 1>2 shift if that doesn't hit the rev limiter.
If your torque curve is reasonably flat, you should be able to smoke your tires through almost all of 1st gear, so max acceleration is reached at the traction limit (part throttle). This is approximated through krab's formula. 


#15
Jan1304, 02:08 PM

Sci Advisor
P: 905




#16
Jan1304, 02:48 PM

P: 11

does the graph show that top speed in 1st is approx 40MPH
how would I determin how quickly the lbs goes up? 


#17
Jan1404, 01:07 PM

Sci Advisor
P: 905




#18
Jan1404, 01:17 PM

P: 11

In my car (Toyota Yaris) I can go 060MPH in 8.3sec, Toyota say 060MPH is 12.8Sec. I did it 8.3sec because I change from 1st to 2nd at 30MPH.
If I drove properly 1st 015MPH 2nd 1530MPH 3rd 3040MPH 4th 4060MPH the second way would take longer because Ive changed gears too quickly, so thats what I need the formula for 


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