Front Geometry mods for extreme ride height

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Front Geometry mods for extreme ride height

Postby NixVegaGT » Wed Feb 25, 2015 11:48 am

Unlike most of our GM cousins (bigger cars of the same era), our front geometry is designed for some positive 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 + 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.
- Nic '73 Vega GT "DogBoxx" Batwing LS1
http://www.cardomain.com/ride/2357894
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Re: Front Geometry mods for extreme ride height

Postby Monza Harry » Wed Feb 25, 2015 8:13 pm

NixVegaGT wrote: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.

Well Nick the more I read the less clear the answers get! So I am going to do what you are suggesting and start with the parts "everybody is doing" (and I already have) Bigger sway bars, Energy Susp. Polyurethane bushings, I will start with Good (? I hope) replacement shocks (I am Jonesing for a set of those "Viking" shocks that a link was posted awhile back for, http://magazinevolume.com/12765BF/#/1/ just more than I can spend as I already have a set of WAY lesser shocks) and as much tire as I can get/fit with the combo I end up with and try and improve it if I am unhappy with the results. I will end up doing the "Rick Racer" LS1 brake upgrade and probably 17" wheels and 225R/45-17 (I hope) tires are around 24/24.5" (depending on Mfg.) which by being short(kind-of/right height, for our cars anyway) I am hoping that I can fit that width with out an excessive amount of BFH work. So I think that last statement of yours, is a good plan for your car as you are way deep in the "MODS", a little test and tune will be probably be the order of the day I am sure! Harry
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Re: Front Geometry mods for extreme ride height

Postby cjbiagi » Wed Feb 25, 2015 8:24 pm

Ok, we have two threads going on the same thing, anyway:


Umm, why is positive camber gain lucky? You want to have negative camber gain on the outside wheel for maximum grip. 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.
Last edited by cjbiagi on Sat May 14, 2016 5:07 pm, edited 1 time in total.
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Re: Front Geometry mods for extreme ride height

Postby tinsfci » Thu Feb 26, 2015 2:17 pm

cjbiagi wrote:Ok, we have two threads going on the same thing, anyway:


I saw there were two threads too, but Nic claims H-bodies have "positive camber gain" in this thread and "negative camber gain" in the other thread...? :?:

I´m not sure, but I think H-bodies have positive camber gain, which is NOT good for performance (stable grip in corners)
But I think most cars (especially american cars) from early 70s has positive camber gain?
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Re: Front Geometry mods for extreme ride height

Postby jdascout » Sat May 14, 2016 12:59 pm

H bodies came with a factory setting of -.5 to -1.5 being factory recommended caster setting. for quicker steering response a more positive caster angle is preferred. your K.P.I. is preferred King Pin Inclination Angle. Why do you think BMW's handle so well? they come with a +4-5 degrees of caster. So if swapping out the upper control arms is a quick easy gain of 2 degrees. I would jump om it. I am building a 1974 base model hatchback. I found a 1964 Buick 300 V8, it only weighs in at 405 lbs. Iron block/aluminum heads and intake. Factory rated at 335 ft lbs@3000 and 250h@ 4000, as a budget build I picked up some GT control arms w/poly bushings and S10 spacers. to get the handling I want I am thinking. Moog V8 Cargo Coils, S10 2" drop spindles. I bought some sway bars, one of my neighbors friends was over so I held my front sway bar up to his front bar. It looks just about 1" wider each side at the link eyelets. S10 Extreme ZRQ58 uses a 1 5/8 ft sway bar. get my drift? (no pun intended) So with the stiffer progressive rate Moog cargo coils, relative lite weight of the 300. this should stiffen it up, and drop it down to an even ride height or rake a bit.

any thoughts on this train of thought?
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Re: Front Geometry mods for extreme ride height

Postby cjbiagi » Sat May 14, 2016 5:10 pm

Swapping the upper arms results in about 9 degrees of caster, not 2 degrees. So, that is a bunch of caster on a street car. Ideally 4 to 5 degrees would be great, it's just pretty much impossible to get that with the stock components, especially while trying to get a reasonable camber angle as well.
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