Help a nOOb set up his Coil-Overs in Winston

I'll throw a theory out there as a placeholder for future thought.

Ryan, Matt, and others smarter than me please chime in with your thoughts.

With such a light spring rate, spring mass begins to nearly be the same as unsprung mass.

Never had this issue myself, I imagine you have to get creative in order to get the unsprung mass to be compliant.

If they were equal masses, I would think it would be tough to get suspension to work well without upsetting the chassis.

Definitely don't intend to hijack Dave.

Just peeking into the rabbit hole.
 
mcutler said:
Yes please keep posting your progress.

I feel like your going to need a rear sway bar, if you don't already have one. A stiff one. The front is really going to put that light ass to work, (rear always does more work than the front anyway) no weight back there for the shocks to work from.

Keep posting, we're paying attention...[emoji106]

Matt
Click to expand...

It needs a rear sway BAD! I'm thinking of going with this kit ROCK CRAWLER KITS

Problem is, as you can imagine. I already have 10lbs of shit in 5 pound bag. Placement is going to be tough with out getting really creative.


 
I'll give the height some consideration. It has a 117" wheel base, so break over isn't great as is. I'm not crazy about the link placement, especially the rear uppers, but that's the way it came. That may be something else I change before all is said and done.

When do you want me to drop it off for you to put the sway bar on? lol
 
Oliver's said:
I'll give the height some consideration. It has a 117" wheel base, so break over isn't great as is. I'm not crazy about the link placement, especially the rear uppers, but that's the way it came. That may be something else I change before all is said and done.

When do you want me to drop it off for you to put the sway bar on? lol
Click to expand...
I have and still run a less than 20" belly, previously 117" wb, and now on 115" with closer to 18.5 now. Looks like yours is close to 24". Your link points geometry would likely be better, with a lower belly. Your instant center now looks to be almost above the engine.

Let me check my schedule...

Matt
 
Oliver's said:
I'll give the height some consideration. It has a 117" wheel base, so break over isn't great as is. I'm not crazy about the link placement, especially the rear uppers, but that's the way it came. That may be something else I change before all is said and done.

When do you want me to drop it off for you to put the sway bar on? lol
Click to expand...


If you start moving link locations, get your instant center as far out in front of your rig as possible.

The line of action drawn through the contact patch of the tire, to the instant center dictates how much force, bumps in the terrain act on the springs vs the links.

The steeper the slope of this line, the more force is seen through the links and straight to the chassis.

The flatter this line, the more force that goes through the springs and shocks, to get to the chassis.

Awesome buggy. What I seen on Face space looked awesome. Haha. Looked like you were hammering on it, and having fun.
 
Mac5005 said:
If you start moving link locations, get your instant center as far out in front of your rig as possible.

The line of action drawn through the contact patch of the tire, to the instant center dictates how much force, bumps in the terrain act on the springs vs the links.

The steeper the slope of this line, the more force is seen through the links and straight to the chassis.

The flatter this line, the more force that goes through the springs and shocks, to get to the chassis.

Awesome buggy. What I seen on Face space looked awesome. Haha. Looked like you were hammering on it, and having fun.
Click to expand...


Draw me a picture. Crayon is fine. lol
 
Just to extrapolate on what mac threw down... directing more force through the shocks- TUNABLE hardware, is a good thing. The force directed through the links is NOT tunable (and handicaps the suspension for having to band aid less than desirable geometry) without serious fabrication changes. Great example of how your suspension geometry goes hand in hand with the tunability/drive ability-handling of the entire car.


For those following along; when you build something, especially a buggy with no body and frame constraints; start with the geometry and suspension and build your design and style from that point.


Sorry we've turned your thread into suspension/Coil over 101 Dave.[emoji481]

Matt
 
Don't apologize, this is good stuff!
 
I hope these help. These are quick and dirty as I'm working in the shop, but get the overall idea across.

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4d02667da83911c37a5aa7f1c8c406d3.jpg


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As Matt said, the forces sent through the links to the chassis are not tuneable with shocks and springs.

Calculating the actual force is irrelevant, as it is a function of the slope of the line of action and the square of ground speed.

The thing to remember: the faster you go or plan to go, it becomes more important. It also becomes more important the steeper the slope of the line of action.

With any design you have to compromise all aspects, and build for what's important for you, and where you are riding.

You have to compromise the slope of the line of action, with desired antisquat, pinion angle change, and ground clearance.

If you are moving stuff, you just do the best you can, to help all that you can for tuning the shocks.

Please forgive if my terms are generic and not the correct engineering terms.

I'm no engineer, just a hack in a dirty shop trying to keep up.

HTH.
 
I'm no engineer, just a hack in a dirty shop trying to keep up.

@Mac5005 are you sure?
That's like @mcutler calling himself only a recycler...
 
I'll just leave this here.
 
Oliver's said:
I'll just leave this here.
Click to expand...


That's mostly accurate. Yes what I call the line of action, is also the Antisquat line.

When I think of side view instant center, Im just looking at where the IC is hortizontally, in front of the rear axle.

When I think of Antisquat, Im looking at the height of the IC from the ground, and where the line of action (antisquat line) cross a specific vertical line. This specific vertical line represents the torque/traction split front vs rear.

If the line of action, cross the torque/traction vertical line, at the COG height, That will represent 100% AS.

The AS percentage changes base on torque/traction F/R, but the slope of the line of action does not change. This is why any specifc AS value is less important, but must consider the other variables.

That image doesn't account for traction split front vs rear.

If you are on flat ground and in 4wd, with 50/50 torque and traction split,
The 100% antisquat line moves rearward by 50% the wheelbase.

2a62957ad8554406e8437d05d6da9863.jpg


The orange line represents the 100% AS line, for 50/50 torque/traction split.

The blue dotted line represents the 100% AS line for 100% rear torque/traction.

The older 4link calculator, and most engineering books use this model and formula.

Whatever the split for front/ rear torque or traction split, moves the vertical lines front or rear, illustrated by the blue or the pink vertical lines.

Now, where it begins to get clear as mud:

Depending on link location, you could have over 100% AS while in 2wd, yet 75% antisquat while in 4wd on flat ground.

This would move your instant center to between the orange and blue dotted line. This is shown below with the green lines and green IC.

7458fa41d3e26cded9e2a912c1960909.jpg


Another complication to consider:

When going uphill, on 45% degree obstacle,

50% of the sprung weight is now on the links and not the springs.

This is because the vehicle pitch is 45% yet gravity direction remains constant.

This moves your suspension position towards droop.

As well, you are moving towards 75% rear torque/traction, and 25% front.

Now you want to consider your link locations at droop, with differing torque/ traction splits.

Sorry for the hijack again Dave.
 
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So after doing some measuring this morning for Mac, I applied the small amount of 4 link knowledge I have to my rig to discover just how un-ideal it is.

With a 43" tire I should have 25% of that as my vertical separation axle side. Ideal is 10.75" , I have 8".
I should have 50% of the vertical separation at the rear frame side. 5.375, I have 7"

Lower link length is 37.5. Upper is 31.5. Ideally the upper should be 70% of the lowers length, In a perfect world my upper should be 26.25"

I'll let Scott post his findings to see if anything can be changed relatively easy help some of these numbers.
 
Oliver's said:
So after doing some measuring this morning for Mac, I applied the small amount of 4 link knowledge I have to my rig to discover just how un-ideal it is.

With a 43" tire I should have 25% of that as my vertical separation axle side. Ideal is 10.75" , I have 8".
I should have 50% of the vertical separation at the rear frame side. 5.375, I have 7"

Lower link length is 37.5. Upper is 31.5. Ideally the upper should be 70% of the lowers length, In a perfect world my upper should be 26.25"

I'll let Scott post his findings to see if anything can be changed relatively easy help some of these numbers.
Click to expand...

Is the lengths of your links the physical measurement from heim to heim- or is it the distance from A-B viewed in a side profile? Reason I ask, i don't always subscribe to the 70% rule. I prefer a longer distance of the uppers (when viewed from the side) by an inch or so. (They may or may not be longer physically, depending on triangulation). This helps to keep the pinion pointed at the output throughout travel, and doesn't change your static AS.

Just at a glance from the pics you posted: were this my recently purchased rig, I would make these changes to the rear; (can't see the front of the car well enough to know the clearances and what I would change on the front, but they would be similar. ) I'm basing these changes on trying not to make changes to the chassis side mounting points of the suspension; easier from a fabrication point of view.

*Hard for many to grasp this, but I would lower the whole car. *

1. With 43's, I would set the belly at 20-21". This would do two things; one it gives your lowers a near flat position and your uppers a downward slope to the chassis; key to this is wheel recession (COMPLIANCE) in up travel. Two, lowers the center of gravity. Helps the Instant Center.

2. I don't see a problem with your frame side separation, but would change the axle side, but also make the uppers a tick longer. For reasons stated earlier. (This would require the building of new towers/ truss.) This would help put your instant center out in front and lower relative to the COG.

3. Cut all the upper shock mounts from the chassis. (After the belly is moved to height mentioned above) set the bypasses at half travel and reattach. (BP are position sensitive due to the location of the bypass tubes, must always use the entire stroke; coilovers are speed sensitive, they don't require use of the entire stroke. I wouldn't attach the CO until I was ready to set the car at bump) obviously this would require building all new upper shock attachments points. **If you only had coilovers, at this point I would attach them at half travel provided you had enough clearance at full bump. **

-keep in mind, during this process you would need to constantly be able to raise and lower the axle to check chassis clearances; Both up and down and in articulation.

4. Add a sway bar; attach to the lower links if necessary.


I have a propensity to use a lower ride height to the advantage of suspension compliance. If you drag your belly, pic a better line or drive faster!

Like I said, just my observation from the limited view I've had of the car. YMMV.




Matt
 
I'm not a fan of the TK1 bars. I break enough of them I keep a spare. I could probably be one and done with a PAC by now:rolleyes:
 
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