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chassis gurus!!!

Posted By: maximum entropy

chassis gurus!!! - 04/25/13 03:48 PM

my buddy got a nice chassis car, and he's gonna run it for the first time on saturday. he scaled it, and it was heavy on the left rear corner. shouldn't it be the right rear? it's a four link car. idk if he has a roll bar- i assume he does.
Posted By: rickseeman

Re: chassis gurus!!! - 04/25/13 03:53 PM

Right rear should be the lightest
Posted By: maximum entropy

Re: chassis gurus!!! - 04/25/13 03:55 PM

interesting. i thought the left rear gets planted. is that in a leaf spring car only?
Posted By: rickseeman

Re: chassis gurus!!! - 04/25/13 03:58 PM

Well, a chassis car is normally coilovers. The driver sits on the left. The engine is in the front. So the right rear has the least weight on it.
Posted By: MR_P_BODY

Re: chassis gurus!!! - 04/25/13 04:05 PM

I disagree.. but you have to base the weights on how
much torque the car has.. any chassis car I have seen
wanted the RR a bit heavier as in 10 to 30 lbs... but
I would start out at zero and if it goes to the right
on the launch I would add weight to the RR by shortening
the upper right bar a 1/4 turn at a time
Posted By: Eric

Re: chassis gurus!!! - 04/25/13 04:06 PM

Generally the right would get the preload making the right side have more weight...BUT...some cars like to be set up neutral and some..like mine.. like negative preload. I set the anti-roll up neutral and make the adjustments with the 4-link. Some people use the anti-roll for preload also.
Posted By: Eric

Re: chassis gurus!!! - 04/25/13 04:09 PM

Here is a recent pass...made a slight move to the left so I lengthed the bar a hair...straight as an Arrow now..

http://www.youtube.com/watch?v=E5ocT5f7iss
Posted By: rickseeman

Re: chassis gurus!!! - 04/25/13 04:10 PM

I am talking about static weight. No preload.
Posted By: MR_P_BODY

Re: chassis gurus!!! - 04/25/13 04:10 PM

Quote:

Generally the right would get the preload making the right side have more weight...BUT...some cars like to be set up neutral and some..like mine.. like negative preload. I set the anti-roll up neutral and make the adjustments with the 4-link. Some people use the anti-roll for preload also.



I keep the anti roll at neutral all the time.. I load
it with the upper right bar(or negative if needed)
Posted By: maximum entropy

Re: chassis gurus!!! - 04/25/13 04:27 PM

sounds like there is no set rule- start neutral, and adjust as necessary? neutral with the driver in the car? or without? please pardon my ignorance, but i've raced nothing but leaf spring cars.
Posted By: rickseeman

Re: chassis gurus!!! - 04/25/13 04:59 PM

Start with neutral with the driver in the car. Fuel. Race air pressure in tires. -2 degrees pinion angle. Ready to make a pass. No preload. Horsepower will dictate if you need preload. Buy Jerry Bickel's book and Rick Jones book. Best money you can spend if you want to learn about chassis cars.
Posted By: Slingshot383

Re: chassis gurus!!! - 04/25/13 05:03 PM

Car needs to be on the scales just like it would be on the starting line, fuel, water, oil, driver (fully suited up), air pressure in the tires set. Set everything neutral and square (distances, front to back, and left. front to .r rear, and r. front to left rear) for the start, and adjust from there.
Posted By: MR_P_BODY

Re: chassis gurus!!! - 04/25/13 06:46 PM

Quote:

sounds like there is no set rule- start neutral, and adjust as necessary? neutral with the driver in the car? or without? please pardon my ignorance, but i've raced nothing but leaf spring cars.



No there is no set rule as to pre load... that is
determined on which way the car goes on launch...
and that means at the line to maybe 50-60 ft out...
really anything beyond that can be alignment or brakes
or other factors.. like Erics car likes a touch of
negative pre load, my car likes about 10# of +pre load..
so you get the idea.. and once you take the play
out of the bar (upper right) it doesnt usually take
much unless something is wrong... all this is based
on the zero of the car at race weight...
Note... if you go to square up the car like slingshot
said make sure what the front end is.. my car has
3/4" of stagger built into the front end(right tire
is set back 3/4" to give me a longer roll out) and
a lot of chassis shops do the same thing
Posted By: rickseeman

Re: chassis gurus!!! - 04/25/13 07:03 PM

Hopefully the car will go straight the way it is already set up. My car is 150 lbs heavier on the left front than the right rear. Do I care? No. All I care about is if it goes straight when I let go of the button. And it does. I have some buddies that think you are supposed to put it on scales and crank the preload into it until it has the same weight on the rear wheels. I don't know why. There are experts somewhere who could take your wheel weights and horsepower and set the car preload before you go to the track but they don't live next door to you, so you have to learn this yourself. Set your 4-link heim joints up where the left hand thread joints are in the front. You didn't say how much horsepower you have, lets say you have 800. If you set it up with no preload it will probably drift to the right after the launch. Put a half a flat of preload in it and make another hit. Keep working it until it goes straight, then life will be good.
Posted By: cudaman1969

Re: chassis gurus!!! - 04/25/13 09:03 PM

Remember the engine rotates chassis clockwise and rearend c-clockwise. I put 30 pounds more on left front and rest equal then take slack out of top right bar. Went straight and no burnout just clean tires and go. Every car is different just how flexible it is.
Posted By: B1KILLER

Re: chassis gurus!!! - 04/25/13 10:58 PM

Quote:

Hopefully the car will go straight the way it is already set up. My car is 150 lbs heavier on the left front than the right rear. Do I care? No. All I care about is if it goes straight when I let go of the button. And it does. I have some buddies that think you are supposed to put it on scales and crank the preload into it until it has the same weight on the rear wheels. I don't know why. There are experts somewhere who could take your wheel weights and horsepower and set the car preload before you go to the track but they don't live next door to you, so you have to learn this yourself. Set your 4-link heim joints up where the left hand thread joints are in the front. You didn't say how much horsepower you have, lets say you have 800. If you set it up with no preload it will probably drift to the right after the launch. Put a half a flat of preload in it and make another hit. Keep working it until it goes straight, then life will be good.




That would work for me
Posted By: Quicktree

Re: chassis gurus!!! - 04/25/13 11:04 PM

I wouldn't touch a thing until i seen what it's going to do
Posted By: Cab_Burge

Re: chassis gurus!!! - 04/26/13 05:31 AM

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
Posted By: MR_P_BODY

Re: chassis gurus!!! - 04/26/13 05:46 AM

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



Pretty simple Cab.. when people talk about changing/adjusting
pre load its the upper right bar on the 4-link system...
when you shorten that bar it pushes the right rear
tire downward.. which adds weight on that scale...
if you lengthen it its lifting that tire.. taking
weight off that scale.... if the car goes to the right
off the line that means the left tire is doing more
work pushing the car to the right... in that case
you ADD pre load(shorten the bar).. if the car is
going to the left.. the right tire is working more
so you take pre load out... (lengthen the bar)
EDIT
when we say positive = ADDING pre load... negative
= going negative from the zero point...everything on
preload is from the upper right bar starting at zero
(zero pre-load) then you add or subtract a FLAT or more
from that point... a flat is the hex flats on the
adjuster bar....I hope I said it simple enough ...
but it is very simple
EDIT 2
Also Cab... each bar has a certain job assigned to
it... the 2 lower bars are for setting the length
of the axle housing AND squaring the housing...
remember that the tire is out past the bars so if
you turn the lower right bar out to lengthen the
axle it will pivot on the left bar so the left tire
just got closer... so you need to use BOTH lower bars
to set the length and square the axle housing...
next is the upper left bar... this bar is to set the
pinion angle... then the upper right is the pre load
bar... if you use each bar in this manner you can
talk to anyone and talk the same language
Posted By: B G Racing

Re: chassis gurus!!! - 04/26/13 11:48 AM

With any ladder bar or four link chassis,with the car race ready,start at neutral and adjust if necessary for 20 to 30 pounds heavy on the passenger(right) rear wheel.Make any fine adjustments after you test run the car at the track.
Posted By: gregsdart

Re: chassis gurus!!! - 04/26/13 01:44 PM

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!

Attached picture 7683231-Dartpics+others105.jpg
Posted By: gregsdart

Re: chassis gurus!!! - 04/26/13 01:46 PM

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!

Attached picture 7683234-Dartpics+others066.jpg
Posted By: Quicktree

Re: chassis gurus!!! - 04/26/13 03:52 PM

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
Posted By: rickseeman

Re: chassis gurus!!! - 04/26/13 04:27 PM

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.
Posted By: MR_P_BODY

Re: chassis gurus!!! - 04/26/13 04:59 PM

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
Posted By: Cab_Burge

Re: chassis gurus!!! - 04/27/13 02:21 PM

I'm off to the races today with no changes to the chassis, I hope it goes straight 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
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