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Old 12-01-2004, 01:03 PM   #1 (permalink)
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Front 3-link design

After hours of reading and asking questions here and there I think Ive decided the best design for the front of my truck will be a 3 link with a panhard. Now time to clear up some of the technical questions. I will be running coilovers and its a HP 60. I think ill be running 2 lowers and a single upper on the passenger side. This is also a daily driver and needs to be street friendly, so the less bump steer the better.

1) How do you calculate antidive for the front?

2) where should I build in adjustability in the mounts. I would like to be able to adjust antidive from 80%-120% or so.

3) to get a flatter drag link is it ok to run the stock steering block under the crossover arm?

4) should I run a straight drag link or the bended one I have from ORD now.

5) does the upper link have to be parallel with the lower when looking from the top?

6) Should I run heims at one end and poly busgings at the other of the links? Heims at both?


Im sure Ill have more as these are answered.
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Old 12-01-2004, 02:59 PM   #2 (permalink)
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1. I dont have the time to get into that right now, maybe later or hopefully someone else can explain it simpler than I could

2. I would make the frame end of the UCA adjustable

3. I dont know

4. I dont know either

5. I would try to make the UCA parrallel to the chassis, and the lowers close together at the chassis and go out to the axle, keeping tire clearance when turning in mind. I built mine with all three front links the same length.

6. I would run heims at the axle and bushing at the chassis.

with a single upper link on the passenger side, you want the link to slant down from the chassis to the axle, but if on the driver side, you want it to slant up from the chassis to the axle. The horizontal location is important, once you get the side view geometry figured out with the anti-dive you want, you can get the optimal horizontal placement using the link geometry, tire size and gear ratio, but I'm probably splitting hairs here, you probably wouldnt know the difference.
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Old 12-01-2004, 03:58 PM   #3 (permalink)
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Quote:
with a single upper link on the passenger side, you want the link to slant down from the chassis to the axle, but if on the driver side, you want it to slant up from the chassis to the axle.
That's interesting. Could you try to explain to me why? Seems like a link slanting up from the chassis to the axle would be a pretty hard thing to do on most rigs including buggies, unless you got really radical with the design and built the chassis to fit that. A radius arm setup would fit MUCH easier, maybe that's what your saying? So I wouldn't want a radius arm on the passenger side?
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Old 12-01-2004, 06:58 PM   #4 (permalink)
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Radius arms suck. You can fit an UCA from the chassis up to the axle, I think tiny and the tiny knock offs do that. The reason Tiny works so well is because of the 3 link goeometry, if done right it will give you equal tire loading when climbing and not lift the front left link a triangulated 4-link does. The same is true for a front suspension. with proper link placement, the front tires will have equal traction when climbing, and can also have equal traction when braking.
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Old 12-01-2004, 08:05 PM   #5 (permalink)
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Thanks for explaining. I have a passenger side diff, so I was going to put the upper on that side anyways. Shouldn't be to hard to keep the upper angling down from the chassis to the axle. My a-arm design didn't work out so well(Bent), so I'm switching to a three link with panhard.
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Old 12-01-2004, 08:40 PM   #6 (permalink)
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anyone else have answered to the first questions?
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Old 12-01-2004, 08:52 PM   #7 (permalink)
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Wait, you have a bent drag link? Maybe you ment a bent panhard/tracbar. I would think that a straight tracbar would be stronger.
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Old 12-01-2004, 09:52 PM   #8 (permalink)
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no i mean drag link as in



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Old 12-01-2004, 10:09 PM   #9 (permalink)
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I would build a straight drag link....looks pretty easy to bend that thing farther.
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Old 12-01-2004, 11:38 PM   #10 (permalink)
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its .25" wall dom - dont think it will be bending....
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Old 12-02-2004, 01:50 AM   #11 (permalink)
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if you want to run that bent draglink you need to remember the panhard-trackbar has to follow the imaginary line from point a to b not the angle of your draglink...but you probably know that
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Old 12-02-2004, 04:17 AM   #12 (permalink)
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Quote:
Originally Posted by GOAT1

with a single upper link on the passenger side, you want the link to slant down from the chassis to the axle, but if on the driver side, you want it to slant up from the chassis to the axle. The horizontal location is important, once you get the side view geometry figured out with the anti-dive you want, you can get the optimal horizontal placement using the link geometry, tire size and gear ratio, but I'm probably splitting hairs here, you probably wouldnt know the difference.
Does this change with respect to what side the diff is on? ie a driver side diff would be the opposite?
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Old 12-02-2004, 05:06 AM   #13 (permalink)
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No, it does not matter what side the diff is on, the link configurations above when designed right will counteract a chassis tendency to load one side (or give one side more traction) when under power.
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Old 12-02-2004, 07:56 AM   #14 (permalink)
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1) pretty sure it's the same as anti-squat for the rear, but just remember there will be some amount of difference in anti-dive per side depending on which side the upper link is on. mine is on the driver's side and i get a little dive while stopping, but it could also be due to my panhard and/or alignment.

2) make about 3-4 sets of holes at the frame end of the upper link as well as a threaded adjustable end at the frame end mount of the upper.

3) don't know about this, but if the bolts are strong enough and the surfaces are large enough, i don't see why not.

4) straight as possible is always best.

5) no, mine aren't and it steers just fine, if you mean drag-link and tie-rod. if you mean links- again, no, they do not need to be parallel from the top, but they need to be close to it from the side or, because one will be offset to one side, that anti-dive will get worse the more of a difference in verticle separation you have. between the frame and axle mounts.

6) if DD, then yes, heims and bushings, just makes the heims last longer and gives a better road ride, not to mention, a little softer in the boulders. if trail rig, as long as there is no bad binding, heims all around will be fine.

here's mine:

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Old 12-02-2004, 01:47 PM   #15 (permalink)
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before you all rip me apart, this is a 10 second job to help me understand things.


http://homepage.mac.com/darketernal/...c/DSCN8603.jpg

with that in mind, pretending the light blue is my COG line, would where that IC produce lots of antidive? Am I looking at things totally wrong?
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Old 12-02-2004, 03:59 PM   #16 (permalink)
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just use the 4 link calculator. dive and squat are the same effect. there is also a slight effect that I think isn't accounted for, the cog rotating around the tire. Not sure it isn't in there, but if not, fast stopping could have a tiny bit more dive than estimated. I wouldn't worry about it, as it feels normal to have a tiny bit of dive.
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Old 12-02-2004, 04:22 PM   #17 (permalink)
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Quote:
Originally Posted by DarkEternal
before you all rip me apart, this is a 10 second job to help me understand things.


http://homepage.mac.com/darketernal/...c/DSCN8603.jpg

with that in mind, pretending the light blue is my COG line, would where that IC produce lots of antidive? Am I looking at things totally wrong?
Draw a line from your front tire contact patch through the instant center. Take the height of where that line cross the rear axle (about at the gutter between the windows in your pic) and divide by the COG height. multiply by the % of front braking and that is your % anti-dive.
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Old 12-02-2004, 07:32 PM   #18 (permalink)
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note trying to thread heist but i am also in process of same set up...........question is is there anything wrong with heims at both ends of links for ease of adjustability?
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Old 12-02-2004, 07:54 PM   #19 (permalink)
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Nothing wrong with heims at both ends, it's just harsher and may contribute to faster wear on a daily driver. I'm running heims at both ends of all my links on my buggies.

Bent vs. straight drag doesn't matter. For tierod end angle reasons, bent may be better. Just keep the imaginary straight line thing as mentioned above, in mind, for trackbar setup.

I'm drawing a complete blank as to what a "stock steering block" is. If it was strong enough to survive between the stock push-pull arm and the knuckle, it's probably fine between the crossover arm and the knuckle.

I think everything else asked, has been answered with the same things I'd add.
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Old 12-02-2004, 08:06 PM   #20 (permalink)
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Quote:
Originally Posted by GOAT1
The same is true for a front suspension. with proper link placement, the front tires will have equal traction when climbing, and can also have equal traction when braking.

I can understand how traction is equalized. The driveshaft torque tries to lift one tire and push down the other. With the right geometry, the offset upper link puts equal and opposite forces on the tires so thier contact pressure stays the same. But how can this happen under brakeing, when there is no torque on the driveshaft?? Equal traction under braking would mean zero "brake lean". If this is possible, what determines upper link placement ??
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Old 12-02-2004, 08:17 PM   #21 (permalink)
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The stock steering block as in this:




Also as far as coilovers Ive been looking at the king 2.5s - any comments on them? Other sugestions?
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Old 12-02-2004, 08:32 PM   #22 (permalink)
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Quote:
Originally Posted by GOAT1
Radius arms suck.

I know some people say this but why? I have never heard an explination of why.
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Old 12-02-2004, 09:18 PM   #23 (permalink)
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Originally Posted by tanzuki
I know some people say this but why? I have never heard an explination of why.
variable roll resistance = bind
to allow the suspension to move they use compliant bushings = sloppy
if you want more travel you have to use sloppier bushings

they were so close to a great thing, just had to add a 3rd link
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Old 12-02-2004, 09:26 PM   #24 (permalink)
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Quote:
Originally Posted by mj
variable roll resistance = bind
to allow the suspension to move they use compliant bushings = sloppy
if you want more travel you have to use sloppier bushings

they were so close to a great thing, just had to add a 3rd link

So are you talking about the frame end of the radius arm? I could understand why that style of bushing would suck, but if a radius arm bushing was replaced with a heim joint, jonny, etc does that fix variable roll resistance?

I understand radius arms on both sides don't work. Maybe that's what you explaining. But how about the pic Fledging666 posted eairlier with a radius arm on only one side?

Here's the pic from earlier:

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Last edited by tanzuki; 12-02-2004 at 09:39 PM.
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Old 12-02-2004, 09:37 PM   #25 (permalink)
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Quote:
Originally Posted by mj
variable roll resistance = bind
to allow the suspension to move they use compliant bushings = sloppy
if you want more travel you have to use sloppier bushings

they were so close to a great thing, just had to add a 3rd link
Thats not true. There are many ways to increase travel on a Radius arm without touching the bushings. Move the link mounts closer together for one.
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