Front Suspension Design - Lateral-g Forums

GMracer · #1 03-10-2010, 08:12 AM

So I'm reworking my front suspension ideas in CAD currently. And what I've done so far is map out the points on my spindle, now these spindles are McGaughys 2" drop spindles for 99-06 silverados. I know I could just raise my suspension up, (like I did currently) which puts it at a stock stand point, but I'm curious if I could optimize this spindle to perform better and have better camber gain in the turns. Also since all the balljoints and tierod enter from the top I'm contemplating swapping the LCA and tierod to enter from the bottom. Which allows the LCA and steering rack to be mounted lower on the chassis, thus allow the engine to be lower.
I have the CAD file for my spindle, it's nothing crazy just a rough sketch with all my important points laid out from the front and side. As far as the caster angles I didn't lay it out with them, but stock is about 5*

the file is a dwg file. I'm interested in anyones thoughts and opinions.

Also the reason I'm sticking with this spindle (or my stock spindle, shorter in height) is because I want to run Wilwoods 16" rotors. I don't know of any other spindle that will allow me to do so. Besides the c10 I believe.

MtotheIKEo · #2 03-10-2010, 10:03 AM

Since the balljoints are tapered you cant really just stick them in the other side.

Are you using some kind of suspension analysis program to determine geometry or just eyeballing it?

GMracer · #3 03-10-2010, 10:12 AM

I can have the spindles machined, I already thought all about that. Plenty of people have done so in the past.

However I've been laying it out in CAD but I don't have a suspension analyzer, besides the free trial one.

B_Alley · #4 03-10-2010, 09:40 PM

I wouldn't shoot for stock geometry, it really isn't that great, but then again, if your not sure of what your doing, then its better than going in the wrong direction. The problem I see with the spindle now is that is has about 12 deg of KPI and only 5 of caster. We always designed our cars to have more caster than KPI since caster helps you with camber gain when turning the wheels on both sides of the car! I'm not sure what 10-15 deg of caster would do to your cross weight transfer though, may have to run some numbers. The biggest improvement would be made by altering your control arm mounting points. You can tweak your camber change in roll and not mess with crazy trail and scrub radius values. From a vehicle dynamics standpoint, anything you can do to get that motor lower, the better. What size of tire and wheel offset are you running?

GMracer · #5 03-11-2010, 07:19 AM

Yea I know my KPI isn't that great, and it's not that I dont know what I'm doing I'm just looking for some outside input.

My scrub radius is just over.5" which is great, I have 20x8.5" wheels, 9.5" lip to lip with 2.75" from outside lip to WMS

Also I don't think increasing my caster that much would be a benefit, I could see more issues than anything arising from that.

deuce_454 · #6 03-11-2010, 08:13 AM

Quote:

Originally Posted by GMracer

Yea I know my KPI isn't that great, and it's not that I dont know what I'm doing I'm just looking for some outside input.

My scrub radius is just over.5" which is great, I have 20x8.5" wheels, 9.5" lip to lip with 2.75" from outside lip to WMS

Also I don't think increasing my caster that much would be a benefit, I could see more issues than anything arising from that.

now since you have fabricated everything on that car anyway... wouldnt it be better to make a pair of spindles, possibmy mod teh ones you have to get the correct cambergain and kpi??

its not that much more work than changing the mounting point son the frame.. or mashining the spindle and changing the lower arm....

GMracer · #7 03-11-2010, 08:34 AM

That's a really good point, I could do that... I wasn't really aware that the KPI would hurt me that much. After the above post and some reading I've been doing I guess it would be beneficial if I adjusted it.

B_Alley · #8 03-11-2010, 06:44 PM

Yea you have too look at both KPI and Caster for your total SAI, they're both related, but all the tire thus camber cares about is SAI. It does make a difference, and is a hell of a lot easier than adjusting frame points, just make sure trail isn't to much where you start breaking stuff or jacking too much weight off your inside rear! One thing a lot of people surprisingly forget when they do kinematic analysis is with the roll the car for roll conditions, they forget to turn the wheels :/ I've seen it done way too much!