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Old 04-02-2006, 03:41 PM   #1 (permalink)
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4 link Calculator 101 please?

Sorry if I sound like a dumbass but can someone do a nice writeup for the tech section on how to use the link calculators, something pretty detailed that you don't have to be an engineer or a suspension expert to read and figure out how to use them. I was messing around with it the other day and would really like to know what anti-squat is, not only what it is but what percent is the goal, like higher or lower. roll over angles? whats that? also RC slope, height, angle? no clue. instant center? Vector? roll point?
or if there already is some kind of training link, please post it! thanks!
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Old 04-02-2006, 04:10 PM   #2 (permalink)
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can of worms.
There is no single answer.
Your best bet is to start reading.
To get started do a search for Gordon and read what he says.
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Old 04-02-2006, 04:14 PM   #3 (permalink)
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Here's how to get the values to plug into the calculator..

http://www.pirate4x4.com/forum/showp...3&postcount=21
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Old 04-02-2006, 04:17 PM   #4 (permalink)
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I got time so here is a quick summary of what you are going to find:


anti-squat - how much the chassis lifts or squats on acceleration. Common range is 0-125%. My feeling is that you should stay under 80%. Also look at how it changes with compression and droop

RC height - Your chassis is rolling about the roll center. The higher it is the less body roll you will have. Down side to a high roll center is that your axle will move weird (side to side under articulation) because your axle rotates about it also. Downside to low roll center is lots of body roll. Can be aided by a sway bar

RC angle - Effects over steer and under steer. Also can be seen as roll steer (axle moves forward and back as it articulates). The front can angle up as it goes back but the rear should be flat or angle down.

I think that is all you really need for definitions. If you really want to know what is going on start reading.
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Old 04-02-2006, 04:27 PM   #5 (permalink)
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yeah dude big can o worms. read the god of suspensions thread and the 4 link 4 dummy's thread and there are a couple other good ones.

or if your around this way swing by and ill explain it one day im out in the garage.
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Old 04-02-2006, 06:10 PM   #6 (permalink)
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4 Bar Link Calculator Version 3.0 Tutorial

This is one that I started working on a while ago and never finished...
Any comments are welcome (post here or email to triaged at gmail dot com)
Quote:
4 Bar Link Calculator Version 3.0 Tutorial

Let's start with the Vehicle Specifications.
Most of these should be obvious. If they aren’t don’t read any farther.
Vehicle CG Height: To measure this you will need access to some accurate scales. See www.jeepaholics.com for the procedure. A quick guestimate is to measure the top bell housing bolt height from the ground. This way however, is an approximate of the Sprung Mass CG Height (2nd tab).
Unsprung Mass: With the wheels on the ground this is everything that does not move if you bounce the body of the vehicle up and down. Some parts will have one end that will move up and down and one end that will not (like shocks or the links themselves). These parts are generally considered with half of their mass as unsprung mass. The best way to measure this is to unbolt the parts (tire/wheel, rear axle, shocks, etc.), weigh them individually, and add them all up.

Park your vehicle on level ground
Remove the rear tires and support the axle with jack stands at operating height if you need the clearance to climb under the vehicle
Use a plumb bob from the center of the axle tube to the ground on each side of the vehicle. Mark these points with chalk on the ground and draw a line between them.
Measure the distance between the marks, divide by two and mark the center. Now use a large square to mark a line under the center of the vehicle or do the same thing in the front and connect the dots.

Now start looking for places to put your links. When you find places you like drop the plumb bob from there. Measure from the transverse line (the one under the rear axle) to where the plumb bob meets the ground. This is your “X” value. Now measure from the longitudinal line (front to back down the center) to where the plumb bob meets the ground. This is your “Y” value. Now measure the length of the plumb bob from the point you picked for the suspension to mount to the ground. This is your “Z” value. Do this for both ends of both links on one side of the vehicle.

After you have these measurements (some basic and some far from it) enter them all into the light blue cells on the main page.
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Last edited by Triaged; 04-02-2006 at 06:12 PM.
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Old 04-02-2006, 07:42 PM   #7 (permalink)
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Quote:
Originally Posted by TRD
I got time so here is a quick summary of what you are going to find:


anti-squat - how much the chassis lifts or squats on acceleration. Common range is 0-125%. My feeling is that you should stay under 80%. Also look at how it changes with compression and droop

RC height - Your chassis is rolling about the roll center. The higher it is the less body roll you will have. Down side to a high roll center is that your axle will move weird (side to side under articulation) because your axle rotates about it also. Downside to low roll center is lots of body roll. Can be aided by a sway bar

RC angle - Effects over steer and under steer. Also can be seen as roll steer (axle moves forward and back as it articulates). The front can angle up as it goes back but the rear should be flat or angle down.

I think that is all you really need for definitions. If you really want to know what is going on start reading.
Where do oversteer and understeer play into this?
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Old 04-20-2006, 12:45 AM   #8 (permalink)
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I have a couple questons also, bear* with me here.

Is 0 to -1 the best roll axis angle for crawling? do u want roll over steer? or understeer? if u have like lets say 6 degrees is that going to effect it that much?

Should your roll axis be level as possible?

when measureing cog or cg is the easiest way to do this measuring from the top bellhousing bolt to the ground?

how high is too high for your roll center height? should it be above your upper links, etc. is there a standard go around on that.

I have read a litte bit on the suspension links for dummies thread, maybe i should get a red star.
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Old 04-20-2006, 05:49 AM   #9 (permalink)
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Quote:
Originally Posted by JackieTreehorn
Where do oversteer and understeer play into this?
it effects how a rig will track when its flexed out, like in a boulder field,, and on steep rutted out climbs where on side will fall into a hole or rut...A little is ok(id say no more then 6*, some might say more, but just as long as its not in the double digits its good), but alot is not good..
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Old 02-17-2009, 02:39 PM   #10 (permalink)
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Originally Posted by JackieTreehorn View Post
Where do oversteer and understeer play into this?
*yes yes I know holy 3 year old thread batman and the op prob won't read this but oh well some might*

But also another big part of how body roll can be felt in over/understeer, is say you are turning around a sharp corner at a fair amount of speed, weather it be you are driving your 4-linked DD on the streets, or you are in a rock racing tournament, or you are just chasing that bunny rabbit in your crawler...

If you have lots of body roll, it is felt the same as rear steer (say when like your flexing out on a rock.) So, when you turn around a corner at speed and your body rolls, your rear axle will change its square-ness to the frame. The outside tire (in the corner) moves towards the rear of the vehicle, and the inside tire moves towards the front of the vehicle. Make sense? (its all because your control arms follow an arc of a circle, rather than move straight up and down)...

When this happens, your rear axle will actually not follow in the exact same line as your frame, and so therefore it is felt as "Understeer" and you will not turn as sharp as you were origionally planning on.
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Old 02-17-2009, 03:53 PM   #11 (permalink)
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Originally Posted by ChocFlip201 View Post
...So, when you turn around a corner at speed and your body rolls...The outside tire (in the corner) moves towards the rear of the vehicle, and the inside tire moves towards the front of the vehicle. ...and so therefore it is felt as "Understeer" and you will not turn as sharp as you were origionally planning on.
What you describe is actually oversteer and it will turn sharper.
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Old 02-17-2009, 08:52 PM   #12 (permalink)
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What is the best percentage to shoot for on upper and lower lengths? I have been trying to lower my oversteer from 6* to 2* and to do this my uppers will be at 80%. 70% gives me more like 3* . I was almost content with 6* oversteer as my final result untill I started trying different numbers on the calculator. Is it going to be that much of a difference?
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Old 03-18-2009, 10:00 PM   #13 (permalink)
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What you describe is actually oversteer and it will turn sharper.
Yep you're right thanks for the correction... I was tired when I posted that...
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