Front Geometry mods for extreme ride height

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Front Geometry mods for extreme ride height

Postby NixVegaGT » Wed Feb 25, 2015 11:51 am

Unlike most of our GM cousins (bigger cars of the same era), our front geometry is designed for some negative camber gain. Lucky for us. The challenge is when you are building something to get the chassis much closer to the ground and update to a rim choice that will offer some tire options. I don't know if others have been looking much but even 15" tires are much less common in the wider variety...

In my case, I've got the chassis ride height setup for around 4" at the pinch weld at the bottom of the rockers. (I've extensively modified the drive train to put everything scrap-able up above that point including the exhaust).

With 2" drop spindles I was able to at least get the LCAs to sit roughly level at ride height. The problem is that puts the UCA at a pretty aggressive neg. camber gain angle. I've run a few sims moving the UCA inboard mount up a bit but there's really not much change. I've also modified the tapers on the ball-joints to get roughly 1/2" shorter to mitigate this problem a bit. It's possible that with limited suspension travel that I will not have a problem but I wanted to spread out my thoughts to the collective and see what you all might think about it.

One other option I guess I'm considering is modifying both the upper and lower inboard mounting locations to raise them up. Perhaps that would solve my problem...

Since I fabricated everything in the rear for the Rx7/Miata rear IRS setup, I was able to set that geometry to be perfect at 4" for a really flat curve with a little + camber gain for roll...

The roll center seems to work out pretty well for the front. Perhaps I should just roll with what I've got and see if I encounter a problem, then fix it. Practical experience vs. theory/hypothesis. Make sense?


Thanks in advance for your thoughtful input.
Last edited by NixVegaGT on Thu Feb 26, 2015 2:21 am, edited 1 time in total.
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Re: Front Geometry mods for extreme ride height

Postby cjbiagi » Wed Feb 25, 2015 7:42 pm

Umm, why is positive camber gain lucky? You want to have negative camber gain on the outside wheel for maximum grim. Generally you want to have the lower control arm parallel to the ground and the upper control arm pointing slightly upward at normal ride height. A popular upgrade on other GM cars was to use a taller spindle (B body cars I believe) on some other GM intermediates which would result in raising the upper control arm angle to provide the preferred negative camber gain in a turn. There is a ton of info on the the net that can describe the benefits of negative camber gain, it basically counteracts the the lean of the car and helps keep the tire flat on the road.
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Re: Front Geometry mods for extreme ride height

Postby Monza Harry » Wed Feb 25, 2015 8:43 pm

Clyde/Nick as I posted in the other sub-forum (AutoX...) the more you read the less clear the answers become! Negative camber gain is good but can reach a point of diminishing (or even -ve) returns, and the shorter the sidewall the less you need, as the tire will deflect less (in theory any ways). Nick had explained that the taller spindles are the less desirable the roll centre became ( I hope I am remembering that correctly Nick[?]) So that brought me to another idea, and that was to use the early X-Body spindles which according to Kenova are about 1 1/2" taller than ours (with bolt on steering arms to deal with the Ackerman and turning ratio situation) we could shorten the upper control arms to tailor our Camber curve and flip the upper ball joint and hang it from the top spindle BJ mount,(a little fab needed and hopefully enough material to re-do the BJ taper upside down and make it all fit I doubt the mount is long enough for that plan anyway) and keep the UCA angle about the same with only a little inner pivot point adjustment( we hope?) Like I said in the other post I have given up on a "Magic Bullet" suspension and I will tune the ugly out as I go (that is all good in theory anyways) and as $$Money permits. Harry
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Re: Front Geometry mods for extreme ride height

Postby waybad » Wed Feb 25, 2015 8:58 pm

very interesting :th:
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Re: Front Geometry mods for extreme ride height

Postby cjbiagi » Wed Feb 25, 2015 9:08 pm

Obviously anything taken to an extreme is as bad as not doing anything at all. Once you start mixing and matching parts everything needs to be checked. I was speaking in general terms that compared most stock suspensions. Making changes that create a negative camber gain is a good thing. This allows you to maintain a reasonable static camber setting and then have the suspension build in the desirable negative camber gain as the car turns into a corner. The easiest way to accomplish this is to raise the outboard end of the upper control arm (where the balljoint is) by using a taller spindle or other means to adjust the angle. Ideally you would like to plot the curve as the suspension moves through its' range. However, my main point was that negative camber gain is more desirable than positive camber gain.
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Re: Front Geometry mods for extreme ride height

Postby NixVegaGT » Thu Feb 26, 2015 2:20 am

LOL! WHOOPS> I totally meant NEG. camber gain. Thanks dude. Yes, the L-body was setup to make NEG. camber gain with the geometry. I'm gonna go edit the post...

Now the more I think about it, it sure is weird to say it like that… Gaining something negative... I guess if you add a negative number to a negative number you DO get a lower number. I guess that's gain? LOL!

Thanks for posting to this thread so quickly, team. I'll be able to re-read this stuff in the morning.
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