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Eric · 6th February 2009, 12:47 AM

i've gotten my front a arms modeled for my custom chassis, and i'm starting to get rather concerned when looking at the models. the a arms are insanely short...

i'm trying to remember my dimensions off the top of my head right now, but i know the lower a arm mounting points are 18.75 inches from the center of the car and 5.75 inches below the wheel centerline where it passes through the chassis. the upper a arm mounts are 19.25 inches from the center and 5.75 inches above the centerline. and well, the pivot point between the lower a arm and front spindle is about 26 inches from the center, and the arm itself is a few degrees lower than horizontal. do the math (as best as you can understand my description without a drawing), and the lower arm is very short and the upper arm is even shorter.

right now, i'm planning on a 7 degree king pin angle, 5 degrees positive caster, 80mm scrub radius, the roll center about an inch below the ground with the car at ride height, and the reaction point for the a arms about 130 inches out from the center or the wheel (away from the car). part of my concern here is that i plan to use heim joints with 14mm threads (hopefully not too over the top) for adjustability, and there seems to be a lot of risk of binding.

i've read up, but am still new at suspension design, and i really want it right before making anything. should i try tweaking the chassis design for lower a arms first off? depending on my wheels, i'm wondering if also perhaps trying a design with the reaction point 130 inches from the wheel toward the car since the current setup looks like a really flat version of a dune racer suspension in my opinion.

i'm terrified to think of the torrent of information that may come my way, but it's all for the better.

6th February 2009, 12:47 AM	#1 (permalink)
Eric 700west Rookie Join Date: Aug 2006 Location: Central Indy GT40: none, sadly Posts: 58	suspension geometry i've gotten my front a arms modeled for my custom chassis, and i'm starting to get rather concerned when looking at the models. the a arms are insanely short... i'm trying to remember my dimensions off the top of my head right now, but i know the lower a arm mounting points are 18.75 inches from the center of the car and 5.75 inches below the wheel centerline where it passes through the chassis. the upper a arm mounts are 19.25 inches from the center and 5.75 inches above the centerline. and well, the pivot point between the lower a arm and front spindle is about 26 inches from the center, and the arm itself is a few degrees lower than horizontal. do the math (as best as you can understand my description without a drawing), and the lower arm is very short and the upper arm is even shorter. right now, i'm planning on a 7 degree king pin angle, 5 degrees positive caster, 80mm scrub radius, the roll center about an inch below the ground with the car at ride height, and the reaction point for the a arms about 130 inches out from the center or the wheel (away from the car). part of my concern here is that i plan to use heim joints with 14mm threads (hopefully not too over the top) for adjustability, and there seems to be a lot of risk of binding. i've read up, but am still new at suspension design, and i really want it right before making anything. should i try tweaking the chassis design for lower a arms first off? depending on my wheels, i'm wondering if also perhaps trying a design with the reaction point 130 inches from the wheel toward the car since the current setup looks like a really flat version of a dune racer suspension in my opinion. i'm terrified to think of the torrent of information that may come my way, but it's all for the better.