Physics of an automobile, suspension, and weight transfer?

  • Thread starter Magnus
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  • #76
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Originally posted by Mr. Robin Parsons
Clearly wimms the problems here are, you don't read what I am writing, or, it is a comprehension problem, or, you are simply ignoring the facts and fishing me
Funny, I thought this about you. What I don't comprehend is why all disagreements in this site must develop into unpleasant confrontation.

I stated a car with an automatic tranny, you come back with popping the clutch stalls out the motor!
chill. We talked about torque, not tranny. Effect you implied would have to manifest with any tranny. And of course I meant manual tranny when I said clutch.

So wimms, 1 (one) horsepower equals 33,000 lbs/ft/minute, or 550 ft/lbs per second. The rails engine has 6000 HP, so 3,300,000 ft/lbs per sec, or 1650 TONS/ft/sec, or 165 tons/ft/tenth of a second.
Have it occured to you, that moving 1 lbs 3M feet in one second and moving 1650 tons 1 feet has a difference?
Engines generate torque. Horsepower is product of torque and rpm:
Horsepower = Torque x 2 pi x rpm / 33000 which simplifies to:
Horsepower = Torque x rpm / 5252
Torque = Horsepower x 5252 / rpm
for 6000hp @8200rpm this is 3842 lbs.ft of torque, meaning 3842 lbs of force at arm length of 1 ft, at tangential velocity of 858ft/sec, which is achieved only at the end of drag run with chassis speed of over 200 mph. Sure, if you had gearing ratio of 858:1, you'd have 858x3842 = 3M lbs x 1ft /sec, but your gearing ratio is 3.2:1 !
So gimme a break with this 1650 TONS of lifting force. This is not heavyweight lifter crane, its a vehicle. Max HP is developed only when vehicle is speeding. At low speed you have nearly no HP, and only torque.

If you want launch forces, talk about torque. I specially searched for you and found a spec with 6,250 lbft of torque, which is more than is produced at 8200rpm, normal for any engine.
I spent time to find the calculations needed. You obviously didn't read anything. You see 6000HP -> boom - 1650 tons of lifting force.

P.S. You seem to wish to use the "5 G" figure for the cars acceleration, it does not develop that 5 G immediately, first tenth of a second, but it does lift it's wheels
Interesting. What is the supporting reaction force? Surely not inertia of car to acceleration, right? Some magical 'sticking' to the ground. Wheels spinning, producing 50000nm of traction torque, and for the first 10th of a second vehicle instead of accelerating, opts to spend some fun time on lifting its fronts instead.
In first 1/10 seconds, 5Gs produces 25cm displacement. Calculate. 5Gs all the way! I can agree that 5Gs aren't achieved immediately, because of engine reving up and tires warming up, but I can't see how lifting can be independant from acceleration.

You're arguing wrong thing. So far angular moment of inertia of rear wheels haven't been discussed, but spinning up rear wheels takes considerable amount of energy. That might be your first 10th of a second you are seeking for.

Sooo, PLeeease Explain to everyone here how cam radius is related to wrist pin pressure!
(Don't know much about engines do you?)
English is not my language. I meant crank. If you'd not mean disrespect you'd not try to make fun of it. Or, is it that I'm having personality comprehension problem here?
 
  • #77
VeeP
first post :D

hey yall


just to clear something up (and help some of you understand this particular idea).

Softening the rear suspension (to a limit) on a RWD car in a drag launch situation is there to help provide the rear subframe recieve as much of the cars weight as possible (giving the nose up tendency).
As the nose lifts, it removes wieght from the front wheels (which serve no purpose other than to steer the vehicle) to the rear wheels. More wieght over the rear wheels means that the tire contact patch grows (and u still have the same amount of pressure per square unit) - which means that your tire can generate more traction, which means that you can apply more force to the ground without the tire lighting up - which means you can accelerate harder. . . .

However - this does NOT apply to certain types of cars (specifically dedicated drag cars) - particularly rail cars - why?
Becuase in rail cars, most of the weight is already over the rear tires. Same goes for funny cars, alot of the weight already sits over the back wheels.
Oh, rail cars dont even have suspension actually. . . its just the wheels directly bolted to the chassis (obviously through very low friction means) - the tire provides most of the suspension. . . .

FWD cars are a completely different story, maybe if someone specifically requests it i will explain.


oh. . . btw, i hope i can positively contribute to these forums and learn much from yall too :D
 
  • #78
Originally posted by MRP
Clearly wimms the problems here are, you don't read what I am writing, or, it is a comprehension problem, or, you are simply ignoring the facts and fishing me (ends HERE!)
wimms, did you read this?? (above and below)

Originally posted by wimms
So gimme a break with this 1650 TONS of lifting force. This is not heavyweight lifter crane, its a vehicle. Max HP is developed only when vehicle is speeding. At low speed you have nearly no HP, and only torque.
Where did I call it lifting force, I simply stated force, aside from that, listen to the car's engine at the start line, revvvvvving up, well past 2000 rpm, as it is engine speed that counts, NOT the cars speed.

Originally posted by wimms
English is not my language. I meant crank. If you'd not mean disrespect you'd not try to make fun of it. Or, is it that I'm having personality comprehension problem here?
Should have told me it wasn't your first language from the start, it would have helped. No. I am not making fun of you, simply pointing out, from your posting the appearance YOU created of NOT knowing what you are talking about. Sorry if it caused you any negative emotive, it was NOT my intention.

Once again,
Originally posted by MRP(ends HERE!)
 
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