I have a Brunton Stalker (Lotus 7 type car) with LS-3 power and need to hook up better out of the corners. I am looking for basic generalities as I know there are sooooo many factors involved.
Looking all over the internet for 4 bar-link set up info for road racing and finding next to nothing. Now I am not looking for perfection just want to be in the ball park............parking lot.
Right now I am planning on top bar 10 degrees front up with the bottom bar horizontal.
Is there any information that covers road racing/4-link set ups available?
Thanks
Scott
When I was designing the suspension on my Locost, it was recommended to not angle the bars at all, as this can make it less optimal in corner exit when you get on the throttle and the "anti-squat" kicks in. As far as I remember the conversation, anyway.
I'm not traction limited like a V6 Stalker might be, but I certainly have had no complaints or regrets with what I did.
I would make it adjustable, so I can have zero, and then some extra holes for more anti-squat.
YES to leaving the lower bar horizontal.
Lower the roll center if possible and increase the antisquat, preferably with changing the angle of the upper links. The lower links should stay parallel with the ground or slightly up at the rear to prevent weird roll steer issues. If the front of the lower bars points down, you get roll understeer, which feels nice and progressive. If the front points up, you get roll oversteer, which feels like a CJ-5.
Stalker_LS3 said:
Right now I am planning on top bar 10 degrees front up with the bottom bar horizontal.
If I'm reading that right, you would be putting pro-squat into the suspension. I haven't looked into it for a long time, but I seem to recall that for road racing setups the general recommendation was something in the range of 50-65 percent anti-squat recommended. The AS percentage is the relative intersecting height at the front axle centerline vs the 100% line which connects the contact patch to the CG height at the front axle. So the upper example looks like maybe 40-ish percent of the lower (100%) example shown here: https://www.jalopyjournal.com/forum/attachments/anti-squat-gif.3653435/
Roll understeer is generally preferred to roll oversteer.
Additionally, 3-link plus lateral locator or triangulated 4-link (with 3 DOF joints) will fully constrain a rear axle without over constraining (binding) it. However, a traditional parallel (in plan view) 4-link plus lateral locator will inherently over-constrain the system without additional compliance, including if also (typical of Locosts) parallel in side view, which does lead to binding. Careful attention to angles on a traditional 4-link can still mitigate the binding though, as seen here: https://www.locostusa.com/forums/viewtopic.php?f=5&t=13741
If you really want to dive deeper into the detailed design, rather than just using rules of thumb to get good enough, this is a good (free) 4 link calculator: https://irate4x4.com/resources/4-link-calculator.4/
Also keep in mind that triangulated 4-links are highly susceptible to bind if all the joints aren't free to move and rotate - ideally you'd want spherical bearings at both ends of every linkage, and a regular cylindrical bushing would actually be a very bad choice. So improving the fittings could eliminate bind and improve traction. Land Rover used a torus-and-hourglass bushing arrangement on the old Defenders that was a decent compromise.
After posting I realized I was looking at dirt track info as they mentioned a bird cage. That was the only hint it was dirt track info..... So I will be angling the top bar down at the front not up as mentioned (face palm here). Really need to separate out the dirt track stuff from the drag race as this was quite confusing and I now have a much better understanding.
Speaking of dirt track racing, the rear end set up is so fascinating, just watch a few videos on you tube of the rear axle on track doing its thing, incredible what they have come up with.
Thanks for the comments
Scott
I went through all the same looking for info before deciding on a 3 link setup. The theory is pretty much the same between the 3 and 4 links
The bird cage definitely throws a wrench in things and changes the dynamics a lot because the links don't get the rotational forces from acceleration and braking.
I did my best to explain the basic stuff in this video
It doesn't sound to me like the problem is cornering geometry, it sounds like your LS3 is just blasting past traction and sending the butt end faster than the nose? Is that what I'm hearing?
If so, you need the lower bars angling up as they go forward. You'll sacrifice a little bit of roll center but the acceleration will cause rear lift and increased traction as it loads the rear tires. This was always the draw of "truck arms" in Nascar. If you were on a tight, technical track, you could drop the front arm mounts down for max handling. If you were on a long track with fewer tight turns, you moved the front arm mounts up, so the more your foot went to the floor, the more the arms would lift the rear and add weight to the tires. This was also why some drag cars went to truck arms. You can angle the crap out of the rear arms and generate enough upward force that you not only lift the rear, but also lift the front. Watch some drag launch videos and you'll see when they release the trans brake, the trunk AND the hood both go up meaning you're not only adding rear weight to the tires, but transferring front weight to the rear.
If the arms angle down at the front, the force from the axle pushes the frame down on accel which unloads the rear and compounds the problem.
I think the secret here is finding a happy balance between cornering and being able to plant the torque you have
In reply to Asphalt_Gundam :
I saw your video(!) while doing my home work. Very helpful. Dont you just love that Garage Fab guy, hilarious!
Thanks
Scott
