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How much does link separation matter?

RunningProblem

RunningProblem

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I know the standard ‘four times link separation at the axle equals max tire size’ rule. I also know the limits of where stuff can fit. With the ‘4 times’ side rule someone would be limited to 28s and with 9” it’s 36” tires. What I’m looking for is an explanation, or understanding, of how much this matters overall. What’s going to happen if I run 38” tires on 7” of separation or 42” tires on 8” of separation? Is it just a matter of so much more torque being applied to the brackets, and axle, with larger tires causing so much more risk?
 
I've never heard the 4 times rule. 9-10" is hard to do on most rigs and 36-40s are basically every rig.

You kinda nailed the rest, 10" is "better" but not always practical with a full frame and whatnot.

Honestly just kinda package it in there where it works and try to get ~7" if you can. But also don't loose sleep over 5.5" unless you plan on rock bouncing.
 
Definitely NOT rock bouncing an XJ.

I phrased it weird. Actually, this website has a ton of info on it already explaining what I was wanting to know.


For vertical separation at the axle end of your rig, try for at least 25% of your tire size. For example, a 40” tire should have at least 10” of separation. Note: This isn’t always possible and installing links will require compromises.
 
Link separation/tire size is nonsense.

The less vertical separation on the axle, the more stress being applied to the link mounts. Build beef into the mounts and worry about other more important stuff.

Separation F&R does come into play when setting up the overall geometry of the suspension.

Milliken RCVD book says nothing about tire size/link separation.
 
RunningProblem said:
Definitely NOT rock bouncing an XJ.

I phrased it weird. Actually, this website has a ton of info on it already explaining what I was wanting to know.


For vertical separation at the axle end of your rig, try for at least 25% of your tire size. For example, a 40” tire should have at least 10” of separation. Note: This isn’t always possible and installing links will require compromises.
Click to expand...

I'd bet very few people with non rock bouncer/U4 ect type rigs are running 10" of separation.

It's just like the upper links should be 70% of lowers or lowers should be the same length as tire diameter. They're mostly BS. Especially when working around a body and frame.
 
gt1guy said:
Link separation/tire size is nonsense.

The less vertical separation on the axle, the more stress being applied to the link mounts. Build beef into the mounts and worry about other more important stuff.

Separation F&R does come into play when setting up the overall geometry of the suspension.

Milliken RCVD book says nothing about tire size/link separation.
Click to expand...

The only other thing I could think of being more important was the bolt length.
 
it's a simple rule of thumb to make it easy to put something together which will handle the stress without having to "design" or really beef up link mounts.

there are no hard and fast rules in suspension design.

even all the math and numbers are wild ass guesses at where moments will be and when and what weighs in where, because, at the end of the day, there are a thousand ways that it can be set up and work very well and about a thousand it can go poorly. doing what fits and striving for what's "best" will get you close enough to be good.
 
10" of link separation on the axle is pretty easy unless your running the bottom mounts horizontally off the axle tube for ground clearance. That cuts out about 4" by itself.

Lower link length, I always shoot for at least double your travel number. Less than that and your driving a forklift.
 
All i gotta say is watch a old s&n no seperation at chassis car. Even better drive one, you can belly out, then front/rear dig the whole car up and then drive away. Idk what axle sep was but the car could crawl like no other.
 
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I think Goat1 helped Fred on an magazine article way back in the day before anyone really knew what they were doing and before the suspension calculators. He and Fred just outlined some simple concepts to get people going. People have been repeating it ever since.

Yes, more separation is better, but geometry and where things fit is more important. Its always a compromise and that's what makes every design unique.
 
bunk said:
All i gotta say is watch a old s&n no seperation at chassis car. Even better drive one, you can belly out, then front/rear dig the whole car up and then drive away. Idk what axle sep was but the car could crawl like no other.
Click to expand...
That basically just gets you a radius arm car with the effective pivot point being a foot or whatever forward of where the links themselves actually end.

Yes you can use torque to jack up the front/rear but there's tradeoffs to everything.
 
arse_sidewards said:
That basically just gets you a radius arm car with the effective pivot point being a foot or whatever forward of where the links themselves actually end.

Yes you can use torque to jack up the front/rear but there's tradeoffs to everything.
Click to expand...
A triangulated radius arm with no panhard is pretty interesting though.
 
arse_sidewards said:
That basically just gets you a radius arm car with the effective pivot point being a foot or whatever forward of where the links themselves actually end.

Yes you can use torque to jack up the front/rear but there's tradeoffs to everything.
Click to expand...
IMO a important observation for a thread titled like this. If you ever get a chance to wheel with one of those old s&n cars DO IT. I was lucky enough to borrow one for a few years.
 
bunk said:
IMO a important observation for a thread titled like this. If you ever get a chance to wheel with one of those old s&n cars DO IT. I was lucky enough to borrow one for a few years.
Click to expand...
Do you have any pictures or video of it?
 
Treefrog said:
Do you have any pictures or video of it?
Click to expand...
Not anymore. Killed my google (youtube) account when i found out they meddled in the election. I do know there are a group of guys in texas who have a bunch of them. IMO its just a interesting piece of old school buggy history, there are way better designs now.
 
My guess is there are probably better ways to accomplish the same effect. I've heard that Jessie is playing around with hydaulics on top of his air shocks to get essentially the same thing. I was just looking at pics of another build that looks to be doing the same.
 
gt1guy said:
The less vertical separation on the axle, the more stress being applied to the link mounts.
Click to expand...

Yep, what gt1guy said.

Think of it like a breaker bar, a long bar being better.


gt1guy said:
Milliken RCVD book says nothing about tire size/link separation.
Click to expand...

He may have not said it, but it would affect it.

A bigger tire is a longer torque arm from the centerline of the axle. Then it will depend on how heavy the vehicle is, how much traction it has, etc.


Ghetto Fab. said:
I think Goat1 helped Fred on an magazine article way back in the day before anyone really knew what they were doing and before the suspension calculators. He and Fred just outlined some simple concepts to get people going. People have been repeating it ever since.

Yes, more separation is better, but geometry and where things fit is more important. Its always a compromise and that's what makes every design unique.
Click to expand...

That was a great article for the time and I still recommend it to people as a primer when they are just starting to play with link suspension.
 
8-10” axle side
3-5” frame side
Link length at least twice shock travel
Links as flat as possible at ride height (same for panhard)
Equal length links (pinion will follow the longer link on droop)
As much triangulation as possible (for 4 link)

I’ve built dozens of rigs following those simple rules of thumb. No funky handling characteristics out of any of them. Building within a full body rig you have to compromise, I feel like people way over think their numbers when most of us weekend rock donkeys wouldn’t be able to tell the difference between a “perfect” setup and one that “fits”
 
Ghetto Fab. said:
My guess is there are probably better ways to accomplish the same effect. I've heard that Jessie is playing around with hydaulics on top of his air shocks to get essentially the same thing. I was just looking at pics of another build that looks to be doing the same.
Click to expand...
We did this on Dave Cole's old pro mod buggy back in 07 or 08. Covered quite a bit on the old site. I could probably dig it up if you're interested.
 
Im4yotas said:
We did this on Dave Cole's old pro mod buggy back in 07 or 08. Covered quite a bit on the old site. I could probably dig it up if you're interested.
Click to expand...
Jesse is running Different than the easy button shocks.
The easy button using the inside of the shock shaft as another shaft, Jesse has an IFP in the main shock, and a hydro port above it, and can force articulate within the existing travel of the shock.

Further off topic - what driveshafts were in Dave Coles for cruiser buggy to take the 24" travel?

Back on topic - the total layout is far more important than the separation at the axle. You can step up the link and heim size with smaller separation and achieve the same thing. Looking at the instant center / roll axis / roll center of both ends as a package is far more worth worrying about than separation at the axle alone.
 
Opiebennett said:
Further off topic - what driveshafts were in Dave Coles for cruiser buggy to take the 24" travel?
Click to expand...
I have no idea what Dave Cole's buggy has, but my buggy has 24" of travel at the wheel and a standard spicer 1410 driveshaft works great with no binding.

Trophy Trucks run 1480 u joints and get more than 30" of travel in the rear.

Geometry plays a role in there.
 
Byro said:
8-10” axle side
3-5” frame side
Link length at least twice shock travel
Links as flat as possible at ride height (same for panhard)
Equal length links (pinion will follow the longer link on droop)
As much triangulation as possible (for 4 link)

I’ve built dozens of rigs following those simple rules of thumb. No funky handling characteristics out of any of them. Building within a full body rig you have to compromise, I feel like people way over think their numbers when most of us weekend rock donkeys wouldn’t be able to tell the difference between a “perfect” setup and one that “fits”
Click to expand...
i just looked at my numbers and hit all your tips spot on,
8.25 separation at axle
4.5 at frame
14 in Coil and 39 inch links
flat lower links
equal link length, my rear drive shaft only moves in and out 3/4 of a inch when cycled/ flexed out
lots of triangle top to bottom.

all i have to say is this is sound advice, i think my set up works amazing, no crazy side roll action, no crazy dive or squat. flat out super pleased.
 
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