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Drag Setup

Started by LhMusL , Jan 31 2006 04:44 PM

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83 replies to this topic

#26 _Torana482HP_

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Posted 07 February 2006 - 04:51 PM

Well i want the car to handle real well, thats why i want hard springs + shocks, but if i go to the drags i dont want to be spinning the wheels all the time.

ive got some 15x10's with 275/50/15 tyres, the car we pulled them off had about 10mm to spare from the edge of the flare. probably will be similar on my car.

Cheers Chop

Devil, i might be in the wrong here but i think if you have softer springs + shocks on the back, the car will be at more of an angle while you accelerate so there would be more car weight on the back tyres, but i might be taking shit here. :tease:

Thanks for the info Devil. :spoton:

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#27 _CHOPPER_

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Posted 07 February 2006 - 06:30 PM

Let's take the extreme angle here. If you cross the 60 foot light with the front wheels off the deck, I'd say ALL the weight would have been transferred to the rear wheels. And with a correctly modified 4 link rear suspension, the effective load can be far greater than that. I'm not one for explaining how it all works, but I have a refference source on how a modified 4 link can work.

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#28 _devilsadvocate_

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Posted 07 February 2006 - 09:50 PM

Devil, i might be in the wrong here but i think if you have softer springs + shocks on the back, the car will be at more of an angle while you accelerate so there would be more car weight on the back tyres, but i might be taking shit

Thanks for asking!
Perhaps this will help, picture a plank hanging from its ends by two pieces of string so that one end is higher than the other. Despite the angle the weight is still shared equally between the two supports. Its a good one to ask people, which support is holding the majority of the weight?
In short, the angle that the plank is at doesnt shift the position of the centre of mass , it is still in the centre. Same thing with the car, if you put larger wheels on the front, making the front higher it doesnt shift any weight to the back.

Or perhaps this: if with standard springs the load on the rear axle is 600kg and 200kg of bricks are loaded directly over the rear axle the load will be 800kg on the axle. If this is repeated with soft springs the load on the rear axle will still be 800kg except the rear will be sagging.
As I posted b4, Im a bit out of my depth if you want to know more about drag racing suspension and ideal setups for getting the power down.

Edited by devilsadvocate, 07 February 2006 - 09:59 PM.

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#29 _Jewboy_

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Posted 07 February 2006 - 10:23 PM

Your forgetting about the dynamic force which is applied to the rear wheels as the front raises it does increase the load on the rear wheels (ie weight transer) if this doesn't happen why do the rear wheel become unweighted when braking hard (negative acceleration). Your right about if the car were just sitting on an incline (static) then they would be the same. Therefore a softer spring allows greater force to be placed on the rear as the spring doesn't resist as much.

Edited by Jewboy, 07 February 2006 - 10:24 PM.

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#30 _devilsadvocate_

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Posted 07 February 2006 - 10:35 PM

Therefore a softer spring allows greater force to be placed on the rear as the spring doesn't resist as much.

Jewboy, perhaps go back to this and incorporate Newton's 3rd law into your thinking.

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#31 _Jewboy_

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Posted 08 February 2006 - 10:26 AM

I thought of a better explaination. Force = Mass x Acceleration. At rest A=gravity so force on both front and rear are the same. when torque is applied to the car it accelerates the front up (negatively) so A= gravity - torque applied acceleration so A is less on the front. On the rear its opposite A= gravity + torque applied acceleration, so now rear force is now greater. As Newtons 3rd law states that an action has an equal and opposite reaction, the force on the front of the car will be smaller by the same amount it is greater on the rear but Net force (at balance point) is the same on the whole car. This is a very very simple explaination that doesn't include the fact that the springs are also playing a part in fighting gravity, so if they are softer the force as a product of time means it will react quicker to the change in force ie greater down force on the rear. Hopefully this made sense.

Edited by Jewboy, 08 February 2006 - 10:29 AM.

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#32 _devilsadvocate_

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Posted 08 February 2006 - 12:55 PM

jewboy: Im not in dispute that the vertical force on the rear wheels increases during acceleration and the force on the front wheels becomes less, Im just saying its not dependent on the stiffness of the rear springs.

If the car doesnt have springs, there will be still effects you talk about, except no one will see any visible changes of down force on the axles unless it gets to the point where the front actually lifts.

Edited by devilsadvocate, 08 February 2006 - 12:56 PM.

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#33 _MAWLER_

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Posted 08 February 2006 - 03:50 PM

You guys are using too many words with multiple syllables for me but I think you have both managed to agree that there is a greater downforce on the rear axles than the front. What the rate of the spring/shock does in my understanding is to more effectively transfer that downforce to holding the tyres on the ground. Ie. a softer spring/shock would absorb some of the force through its compression/travel while a harder spring/shock would put more downforce on the axle and therefore stick the tyre to the road??

So the spring and shock setup is about most effectively getting the acceleration force to the ground.

Cheers,

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#34 _355lxss_

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Posted 08 February 2006 - 04:36 PM

diff setup also plays a small part in traction. If you have adjustable upper trailer arms you can set the pinion gear/yoke 2-3 degrees negative camber (pointing more towards the ground) which will make it bit harder of the line.

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#35 _devilsadvocate_

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Posted 08 February 2006 - 05:35 PM

So the spring and shock setup is about most effectively getting the acceleration force to the ground.

Cheers,

Yes Liam, its all about getting traction, from what I can fathom its a bit of mystical science getting the right combo of tyres, springs and shocks and other links to get the tyres to bite just right.

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#36 _CHOPPER_

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Posted 08 February 2006 - 06:37 PM

So the spring and shock setup is about most effectively getting the acceleration force to the ground.

Cheers,
Yes Liam, its all about getting traction, from what I can fathom its a bit of mystical science getting the right combo of tyres, springs and shocks and other links to get the tyres to bite just right.

alltora, do you have a time slip to show us how fast your 6 cyl beast travels down the 1/4 mile? Can you tell us how many cars you've modified for drag racing? Or are you just reading from books? My primary school age children can read from books, but that doesn't mean they know what they are talking about.

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#37 _Torana482HP_

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Posted 08 February 2006 - 07:14 PM

Lol,

Well Chopper, im interested in hearing some more info that you have to offer. Ill tell you a bit more about what my setup will have and you can tell me if my car will just be doing douhnuts on the drag strip starting line.

I want my car to handle well so thats why id prefer hard suspension.

LH torry,
about 450HP,
9in with probably 3.75 gears,
the rims and tyres i told you about,
turbo 350,
3500 or 4200 stally.

Thanks for your help chopper :spoton:

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#38 _devilsadvocate_

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Posted 08 February 2006 - 08:18 PM

So the spring and shock setup is about most effectively getting the acceleration force to the ground.

Cheers,
Yes Liam, its all about getting traction, from what I can fathom its a bit of mystical science getting the right combo of tyres, springs and shocks and other links to get the tyres to bite just right.
alltora, do you have a time slip to show us how fast your 6 cyl beast travels down the 1/4 mile? Can you tell us how many cars you've modified for drag racing? Or are you just reading from books? My primary school age children can read from books, but that doesn't mean they know what they are talking about.

Go easy Chopper, Ive clarified I believe some Physics that is applicable whether its a ride on lawn mower or drag car. If you can reason as to why it is incorrect, lets hear it, dont stand back, but otherwise dont be such a timewaster.
I think I answered your other questions ^, perhaps get one of your children to go through it carefully.

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#39 _Torana482HP_

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Posted 08 February 2006 - 08:27 PM

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#40 _Torana482HP_

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Posted 08 February 2006 - 08:28 PM

^lol, i love that smiley

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#41 _Jewboy_

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Posted 09 February 2006 - 10:48 PM

My understanding of the spring rates is that it does 2 things, firstly a soft spring allows greater movement which increases down force and it acts as a delay for the tyres to get traction. This probably is one of the easiest experiments that anyone can do to prove that it works (would only be a fraction of a second, unless the car wasn't getting grip before). I personally wouldn't bother as i will go by what others say, whom have done the rigorous testing. No point trying to argue against proven formula.

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#42 _devilsadvocate_

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Posted 09 February 2006 - 11:31 PM

Jewboy, I think you theory about the possibility of the delay factor having some bearing on when and how much grip is attained sounds good, which will be also spring/shock and tyre pressure factors (of which I would have no idea which works best or what driving/throttle control techniques would prevent a full out wheelspin at takeoff!)

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#43 Struggler

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Posted 10 February 2006 - 06:50 AM

This is the way I see it.....

You mash the pedal and unleash all your torque on the rear tyres. A stiff spring allows no give at all and makes it harder for the tyre to get traction, a softer spring takes that shock and slows it down, making it easier for the tyres. Think of your tyre as a fishing line and the fish as your engine power. See how some guys can land a 20lb fish on 2lb line when other guys can't land a 1lb fish on 2lb line. The fish weighs the same, just the application of force is different.

This does not take into consideration weight transfer. To make it easier for your rear tyres it helps to put more weight on them. 90/10s and long soft front springs will throw some of the front mass onto the rear wheels. This makes it easier to get traction.

In a perfect world the best vehicle reaction time comes with no suspension - look at a dragster. The sad reality of a street car is you need bandaid fixes like springs and shocks to counter the weight distribution and lack of tyre.

If you want to run firm springs and shocks and go drag racing you can, you just need a huge tyre to get the traction you need. In fact, as stated earlier the stiffer the suspension, the quicker the car will react, but in reality the shock on the tyres will be too much and they will likely go up in smoke.

This is just a basic look at what happens, other factors such as HP and TQ and the force the tailshaft exerts on the diff housing (causing the left or pass. side of the car to lift, and the right or drivers side to dip) make getting a torquey street car to leave efficiently quite a challenge. There are many street cars in the 8-11 sec bracket with different shock/spring combos on each corner.

P.S. A soft spring does NOT increase down force. It just softens the shock on the tyre. The force is the same, it just gets applied differently. Bear in mind also, the drivers rear wheel is trying to LIFT upon acceleration. A soft spring on this corner will not help traction. This is why an auto car when linelocked spins the drivers rear wheel. The weight is coming off it and being applied to the pass. side wheel. The drivers side tyre gets lighter and spins easier. The pass. side wheel is pushed so hard into the road that that side of the car is lifted.

Edited by Struggler, 10 February 2006 - 07:01 AM.

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#44 _Jewboy_

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Posted 10 February 2006 - 11:02 AM

I do think that a soft spring does to a small degree increase the force on a car as it allows for more travel on the suspension which increases weight transfer plus it doesn't resist the shift in weight as much. It wouldn't be huge but any gain is a plus. Anyway that enough for me on this subject.

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#45 _devilsadvocate_

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Posted 10 February 2006 - 01:03 PM

The pass. side wheel is pushed so hard into the road that that side of the car is lifted.

The whole car tilts to the right because of the engine being rotated clockwise forcing it against the engine mounts due to it spinning(forcing) the tailshaft in the opposite direction. The left tyre doesnt move upwards, so it cant lift the car upwards either.

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#46 Struggler

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Posted 10 February 2006 - 03:07 PM

Then explain to me why when an axle breaks it is always the left or pass. side one ???????

The engine has some torque reaction but I can assure you the weight difference at the rear wheels is substantial. Try it. Put a car on corner scales and torque it up against the convertor and read off the corner weights.

Also the distance from the crankshaft to the engine mount is much less than the distance fron the pinion to the wheel. The axle is also subject to greater torque due to the gears in your box and diff. Think about it. Which do you think would lift the car easier ?

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#47 _devilsadvocate_

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Posted 10 February 2006 - 08:37 PM

not saying that the forces arent as you say they are.
Just that the whole tilting of the car towards the right is due to the engine pushing on the engine mounts, not due to any wheel that is stuck on the ground mystically pushing up. Take away the engine mounts and it wont happen, the engine would want to spin around the tailshaft if there was significant traction at the rear wheels.
Anyway, I know this goes against what most people who visit this forum think, and think Im just having a lend. Perhaps do a search and read it up, this link:
http://hotrod.com/techarticles/34238/
has some quite good info.
ie "The torque from the driveshaft imparts a torque to the rear axle in the same direction as the driveshaft is spinning. The chassis twists the other way as a reaction to the torque from the driveshaft and axle because the engine and transmission are fixed to the chassis", much the same as I put it?, it also has a nice little bit about weight transfer(front to back):
"Roll stiffness (provided primarily by springs and bars) affects the rate or speed at which weight is transferred. In other words, stiffer springs and anti-sway bars do not change the amount of weight transferred. They simple get it there quicker so the car responds quicker in proportion to the stiffness of the springs and bars."
I wouldnt take everything as gospel on that site(or anything I say either), but its not bad.

Something to try at home: Put the handbrake and or brakes on as hard as possible, try and take off in 1st gear giving it a lot of throttle, this will create a right lean on the car,with even a small engined car.

Edited by devilsadvocate, 10 February 2006 - 08:47 PM.

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#48 Struggler

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Posted 10 February 2006 - 08:47 PM

The chassis twists the other way as a reaction to the torque from the driveshaft and axle

Isn't this what I am saying ?

The whole car tilts to the right because of the engine being rotated clockwise forcing it against the engine mounts

If what you are saying is correct, you should get the same tilt from revving your engine in neutral.

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#49 _devilsadvocate_

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Posted 10 February 2006 - 08:58 PM

No this what you said, "The pass. side wheel is pushed so hard into the road that that side of the car is lifted"
In regards to spinning the engine in neutral, the engine will tilt to the right slightly in reaction to spinning the crankshaft and gearbox components against a little bitof friction.
Its like holding a drill in your hand and turning it on, not much twisting force is felt, but if you start drilling a hole and the bit starts to bite(like the tyres getting traction) it will exert a very large force reaction on your hands trying to hold it.
Youll only get the large tilt if their is significant traction or resistance at the wheels, thats why I suggested doing the static drive against the handbrake.

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#50 Struggler

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Posted 10 February 2006 - 09:31 PM

So what your saying now is that the force that lifts the car has an equal and opposite force that drives the pass. side wheel into the road ? I thought that is what I was saying........

You win, I give up.