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Re: chassis gurus!!!
[Re: maximum entropy]
#1425303
04/26/13 09:44 AM
04/26/13 09:44 AM
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Joined: Jan 2003
Posts: 10,011
Frostbitefalls MN (Rocky&Bullw...
gregsdart
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,011
Frostbitefalls MN (Rocky&Bullw...
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As I understand it, there are two places that twisting forces come from that load or unoad each rear tire at the hit. The one that can't be changed is engine torque against the chassis. You can see it on a top fuel car on launch. The other is the twisting force produced by the instant center of the chassis components. The second one can be anywhere from mild to wild depending on the setup of the chassis combined with the starting line torque available to act on it.
IMHO the best setup is just enough preload to counteract the first force at the hit, and use an anti roll device to counter the suspension forces. Any preload that is in the car will also be there down track, which can affect handling and traction.
What I have seen on my ladderbar car is if I go to the front mounting hole at the neutral line, on the hit the left bar will gain leverage over the right bar because of chassis roll induced by engine torque at the instant of the hit. The problem builds on itself instantly, because as the car roll rotates the left bar instant center gains leverage, and the right one loses it. I have had my car literally leave on one tire because the twisting got so violent the left rear suspension ran out of travel and the tire came off the track.
A fourlink car could also get this messed up if it is set up wrong, because it is so much more adjustable.
On a fourlink car, these forces can be reduced by moving the instant center away from the neutral line and moving it further forward to reduce leverage.
Most ladderbar cars never experience this problem to the severity that I did because the instant center is high enough to not let the twisting get out of hand before the shocks and springs can stop the suspension movement.
But if you try and put 850 + hp through a set of 30 inch ladderbars things can happen quickly.
The photo shows chassis twist before the anti roll, and before I got it totally screwed up!
Last edited by gregsdart; 04/26/13 09:45 AM.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: chassis gurus!!!
[Re: gregsdart]
#1425305
04/26/13 11:52 AM
04/26/13 11:52 AM
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Joined: Jan 2003
Posts: 32,394
Quicktree
I Win
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I Win
Joined: Jan 2003
Posts: 32,394
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Quote:
I built an anti roll bar, and the twist you see in the bar is after one pass. The tube is 1 1/8 by .125. I went to 1 3/4 by .134 and it can't hurt that one!
if mild steel try CM
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Re: chassis gurus!!!
[Re: Cab_Burge]
#1425306
04/26/13 12:27 PM
04/26/13 12:27 PM
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Joined: Jan 2012
Posts: 2,652
Stuttgart, Arkansas
rickseeman
master
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master
Joined: Jan 2012
Posts: 2,652
Stuttgart, Arkansas
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Quote:
I'm in a similar situtaion as Carls freind, new to me, tube chassis car and no good chassis books in my poccession, yet. Not to hijack this tread but when you guys use the word "negative" or "positive" preload would you please explain which bar and which way to adjust it to get that and what to look for on a scale when adjusting it those two ways   
As Mr P Body said, preload is in the top passenger side bar. Let's forget for a moment about positive and negative, shorten and lengthen, that stuff is too complicated, you will learn about that in the books you are about to order. Let's forget about the scales, you just want the car to go straight. A normal chassis car, with under 1000 hp, set up neutral, is probably going to pull to the right. (It is asking for positive preload but that doesn't matter.) If your 4 link bars are in where the left hand heims are to the front, this is easier. Imagine using the top passenger bar as a steering wheel. If it is drifting to the right, you will be turning the top right bar to the left to bring it back. Put a piece of masking tape on the bottom of the bar. Take a magic marker and draw a line on the masking tape. Loosen the jam nuts. Turn the top bar the same way you would turn it if it was the steering wheel to bring it back to the left. Turn it 1/2 a flat. (Thirty degrees, 1/12 of a turn). Lock the jam nuts. Now make another hit. It should not be going to the left as bad. Keep adjusting until it goes straight. Steer with the top right bar. (If you have alot more than 1000 hp it will most likely drift to the left, asking for negative preload.) Sorry for the long winded answer.
2011 Drag Pak Challenger
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Re: chassis gurus!!!
[Re: rickseeman]
#1425307
04/26/13 12:59 PM
04/26/13 12:59 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Cab... one of the factors some forget is that the rear end is trying to spin around the drive shaft... if you could hold the drive shaft with the rear end not in the car the rear end housing would spin in circles... its trying to do the same in the car.. the RR tire is trying to go up and the LR tire is trying to go down... thats why the LR tire tends to do more work and tends to drive the car to the right... so you need to help equalize the tire loads by adding the pre-load to the RR.. the amount of torque and the chassis flex dictate the pre load 
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I didn't get to rewiegh it with me in the car so that is next on the list to do. Sorry Carl for hijacking this 
I hope he is at the races todya, I thnk I know the car he talking about, if so it is brand new one so it will be interesting to see what it does 
More tonight on a seperate post, off to the races 
