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Discussion Starter #1
Quick background
Building my first truck, 1937 Dodge cab(body) on a custom built frame all kinds of new stuff under it.
I am a newbie when it comes to building trucks so I am stumbling my way through this. Hopefully have something fun to drive at the other end. So please excuse my dumb question.

I am at the point of setting up my Tri 4 link and I am running the calculator to make sure I have all my mounting locations correct.
Below is what I have come up with.



My question is when I go through the travel of the rear using the calculator the pinion angle changes,

UpTravel


DownTravel


I assume this is normal? again please excuse the newb.

Will this setup work? This is all based on measurements and mounting locations I can use.

Thanks for the help.

Scott
 

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Lower your antisquat 25-50%

Your pinion angle change is due to longer uppers than lowers, you want your uppers about 75% the length of your lowers (or at least just shorter some and not longer)

Much longer lowers would help a ton, also move the axle side mount up to get your AS down.

Uppers don't need that much triangulation, this will help shorten them up.

You want your roll axis angle negative a couple degrees, if you lower your frame upper link mount this will help, then adjust the rest of your mounts to get the AS back in the 50-75% range
 

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Discussion Starter #3
ok I will look at what options I have.

couple of questions:

Why would I want my anti squat so low?

This is general purpose vehicle and from the calculator website it says that 100% is a good default starting point.

Thanks for your help.

Will update when I have some new link positions.

Scott
 

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Depends on what you are building for. Is this a crawler? Or just a show rig?
Pinion change will also be dependent on how far the frame side mounts are from the output shaft. I try and get the lower frame mounts as close to the output shaft as possible. Uppers 70-100% of the uppers. I personally would drop the upper axle mount down a bit. You have plenty of separation and it would raise your instant center. It should drop your anti-squat down just a bit. Its personal preference but I like to be between 80-100% because I use rather soft coils.
 

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Looks like you are going for very modest travel numbers, but why not make the links a little longer? Maybe leave the uppers and make the lowers closer to 32-34"?
 

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Discussion Starter #6
not a rock crawler,

More general purpose off/on road vehicle for now.

Looking at the options I have for mounting the links so I can get the uppers shorter than the lowers.

If it is general purpose should I be shooting more 80-100% AS?


Thanks

Scott
 

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Anti squat/brake dive is a personal preference. It is just a measurement of how weight is transferred from the front to the rear under acceleration. The lower the anti squat the more the ass end will drop when you step on the gas. The rear will also rise more during braking. Its nice to use frame side brackets with multiple mounting holes in the so you can easily adjust the links up and down to change the anti-squat. Typically the lower the separation at the frame the higher the anti-squat.

The calculator is only a guide and the end result may require some fine tuning to get the ride results you want for what you are doing.
 

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Is the custom frame already built? If not you shouldn't have any problem putting links anywhere you want.

Longer links make geometry changes through suspension movement happen slower. This is always a good thing.

Is your CG really at 27"? That seems a bit low and will change all the numbers the calculator spits out.
 

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100% AS is a guideline derived from performance suspension on street cars and drag racers, where you have very limited travel and are trying to keep the suspension as flat as possible while launching the car and slamming on the brakes into the corner, you are essentially designing the system to bind up which is great for a track car. Most of that doesn't translate to offroad and especially rock crawling. If you are setting up for lower travel shocks and general purpose you can shoot for 70%AS. The main problem with most people setting up 100% AS on rock crawlers/jeeps/etc is that they have minimal up travel and massive amounts of droop and they're suspension usually has drastic raising AS rate so at full droop the suspension is actually over 150% AS and cause major suspension jacking and binding
 

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I have never heard anyone explain that high anti squat causes binding in the suspension. What exactly binds? I agree too many jeeps and crawlers design with too little up travel and have an unbalanced set up.
 

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Mine is a multipurpose street, crawler, go fast. I run around 80% as with 1 degree of oversteer and it performs great. 70 mph off road, Flexes like crazy, drives and corners awesome on the road. 16" of travel up front (6 up 10 down)and 21" in the rear (9 up 12 down). I don't think I have ever had to stomp on the gas with the rear fully drooped out though. Normal braking is flat but if I really stomp on the brakes I can get the rear to pop up. Same on acceleration but I do run some low coil rates.
 

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Anti-squat isn't a binding in the links, as we generally think of binding. Even with 100%AS, the suspension is free to move. Think of it this way, if you have 150% AS, the rear would lift when it sees the longitudinal load transfer, it can't be in a bind if it can also move to lift. AS is just the links carrying the load instead of the springs.
 

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Discussion Starter #14
Some really great info guys. Did a bunch more reading over weekend and staring at the truck and calculator.

Yes this is a custom frame, initially I had it in my head where the links would fall and was really clinging to that placement. Your help pushed me to look at other options.

Here is attempt number 2:



UpTravel - I could go higher with my frame setup.


DownTravel - wasn't sure how far I should be pushing this.


Thoughts? Concerns? weld it up?

Thanks again for all the help.

Scott
 

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I have never heard anyone explain that high anti squat causes binding in the suspension. What exactly binds? I agree too many jeeps and crawlers design with too little up travel and have an unbalanced set up.
Anti-squat isn't a binding in the links, as we generally think of binding. Even with 100%AS, the suspension is free to move. Think of it this way, if you have 150% AS, the rear would lift when it sees the longitudinal load transfer, it can't be in a bind if it can also move to lift. AS is just the links carrying the load instead of the springs.
Yes as gt1guy stated its technically not a bind, its the suspension forcing a load on your suspension to counteract forces induced by weight transfer/gravity/drivetrain torque. It's just easier for most people to understand it as a "bind" rather than technical description. The problem is everything works great and the suspension is free to move on flat ground where you have gravity acting against the car like normal. Now place the on a 45deg incline and you all of the sudden lost 50% of the effective gravity acting against the suspension that you designed the suspension to have 100% AS against, this is where you will literally see the suspension "bind" or resit free movement due to the load the links are now supporting with the external forces of 100% of the gravity to counteract it back to neutral. If you combine that 45deg incline with a 45deg sidehill now you've just lost even more gravity effecting the downward normal orientation and things get even worse. These are the extreme illustrations, but it helps most people understand why in any offroad situation your typical street car suspension design isn't ideal. On my buggy I have the AS/AD set at 30% front and rear with only 4" of uptravel, this lets the suspension be free to move no matter what incline or angle I'm at without any additional forces being applied that might induce the car to roll over. Plus with only 4" of uptravel on ORI's there isn't mush of any suspension that it can squat or dive into anyways.
 

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Some really great info guys. Did a bunch more reading over weekend and staring at the truck and calculator.

Yes this is a custom frame, initially I had it in my head where the links would fall and was really clinging to that placement. Your help pushed me to look at other options.

Here is attempt number 2:



UpTravel - I could go higher with my frame setup.


DownTravel - wasn't sure how far I should be pushing this.


Thoughts? Concerns? weld it up?

Thanks again for all the help.

Scott
Overall that looks better except for your roll axis, you want that at least zero and preferably negative a few degrees. Having a positive roll axis, especially +5deg is going to make the car what to swap ends at the slightest loss of traction in the rear end and make you spin out and be very unpredictable at speed on dirt roads.
 

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any suggestions? (will start moving mounts around again)

Thanks

Scott
Mostly just play with the mounts and see what change makes what numbers different, then you can see where you can actually move stuff to that fits and go back and forth of the calculator and realistic mounting spots.

You should be able to add a little triangulation to your lowers and get the roll axis to start dropping down.
 

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Discussion Starter #19
Ok try number 4? 5?... gah lost count.




This seems to check all the boxes. .. Although not sure about dipping the upper links like I am.


Thanks

Scott
 
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