portal buggy 4 link

[reclineaholic]

I'm building a portal buggy and I need to set up the 4 links, the lowers are in and really can't be changed much because they are flush with the bottom of the axle housings and the belly skid plate. The uppers have flexibility and I'm using a link calculator to help dial them in. A PDF of the calculator is attached and I'm looking for advice and opinions about the numbers on it and if I should make any changes. I don't understand what the "roll slope" graph is telling me, what good "roll slope" numbers would be, how to get them, and how it will affect the handling of the buggy so if someone could explain that to me in simple terms it would be much appreciated.

 

[vogelj]

I have no idea what that graph means! I think you might be overthinking it though. When I bought my portals from Jesse he gave me the advice listed below. I would start there and adjust it to fit your chassis.

- Typically 8° combined Caster and Pinion Angle
-Front: 6° Caster, 2° Pinion Angle
-Rear: 5° Caster, 3° Pinion Angle

- Keep links as parallel to the ground at ride height as you can.

- 8" of separation at the axle between the lowers and uppers

 

[vogelj]

This is the info that is given for the Hulse Cars.

 

[Ghetto Fab]

Roll axis slope is the tendency of the rear to rear steer as the body rolls over to one side. As the body rolls and the suspension flexes, the rear axle will no longer be square to the chassis and this will induce a steering effect. Usually you want roll understeer so its countering the direction the body rolls in a turn as that tends to feel more stable at speed. The graph I believe is just plotting the roll axis angle over suspension travel. As the suspension droops, or you raise the chassis, the roll axis will change from understeer to oversteer and get progressively more oversteer. That graph just shows that change. If you can you'd want to minimize or slow down that change.

In real life, roll over and understeer characteristics really apply to road going cars at speed. I would consider it for any build, but how fast is a portal, air shocked rig going to go? Honestly what you have looks really good as far as what little I know.

 

[Ghetto Fab]

Sorry duplicate post.

 

[reclineaholic]

Vogelj, Thanks for your response, I do have a tendency to overthink things. My vertical separation at the axle was going to be 8.5" but based on what Jesse and Richard are saying I think I'll change it to 8" and redo the frame ends to try to keep the anti squat around 30 and as flat as possible.

Getto Fab, thanks for the explanation of the roll slopes. I'm never going to go fast so I think I'll not worry too much about the roll slopes but keep an eye on the roll centers through travel and concentrate more on anti squat, anti dive numbers and packaging for tire clearances.

 

[reclineaholic]

This is the info that is given for the Hulse Cars.

View attachment 18014

It kind of looks like you're building a Hulse engineering chassis with JHF portals? Is this instead of the Iron man chassis? You don't need to comment if it's a secret, I appreciate your help.

 

[vogelj]

lol, I strongly considered building a Hulse chassis! I am definitely building the Ironman car. I have several friends building Hulse cars right now though.

 

[reclineaholic]

lol, I strongly considered building a Hulse chassis! I am definitely building the Ironman car. I have several friends building Hulse cars right now though.

View attachment 18023

Very nice! It looks like you're pretty far along too.

 

[vogelj]

It should be a roller very soon.