Alternate spinle idea - Chevy Impala SS Forum
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post #1 of 5 (permalink) Old 04-12-2004, 04:00 AM
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While figuring I came up with an alternate way to fix the front end camber gain. This idea involves another issue besides camber gain: Roll Center Height. The roll center height is calculated by trangulataing the upper control arm to the lower.

This is done by drawing a straight line from the lower ball joint to the lower frame mount and doing the same for the upper control arm. Where these two lines meet makes a convergence point.
Draw one line from this convergence point to where the tire center line meets the ground. Draw another from the center of gravity to the ground. The point where the two meet is the roll center height.

All this being said, if you make the angle between the upper and lower arms more obtuse the roll center height will be raised, making the angle more acute will do the opposite.

My idea is to space both upper and lower ball joints 1". Doing so would net the same spindle length as spacing just the upper, but would be more effective in raising the roll center height.

Making the roll center height closer to the center of gravity will result in less body roll, and more lateral acceleration will be the result.

This fix would also solve any clearance issues.
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post #2 of 5 (permalink) Old 04-12-2004, 07:18 AM
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Sounds like you are doing the same exact thing as the spacers, roll-center wise, but if you are talking about spacing stock ball joints from the CAs rather than the spindle, you'll lose the roll-camber benefits, which you should not sell short.

If you plan on spacing the stock ball joints away from the spindle one inch, I have to ask, how? The Pro Motorsports spacers are the height that they are, because that's about as short of a spacer as you could make, and still retain a long enough spindle bolt in the spacer, and a long enough ball joint stud to retain the cotter pin.

There is a longer upper ball ball joint that might be made to work, but I don't know of any OEM style lowers that are longer, and I would be VERY hesitant to use any type of spacer there, as the majority of the suspension load is carried there.

I am comming more and more to the conclusion that the longer upper ball joint, in combination with a lowered UCA mount, is probably the next avenue to explore.
post #3 of 5 (permalink) Old 04-12-2004, 08:20 AM
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I meant to use extended length ball joints. It is not so much that the spindle needs to be longer, but that the space between upper and lower ball joints needs to be longer. In review of some of the math the lower ball joint would only need to be extended about .5". With and inch top and bottom it would raise the roll center height too much, and like you said you would lose all camber gain benefits. I do agree though that the "GM" mod and a one 1" extended ball joint is probably the way to go. Do you know if anyone makes a .5" extended ball joint?

Edit: I found a previous post saying our cars roll center should be 4-3 inches above ground. According to Herb Adams this is incorrect. The roll center height for any car should not be more than 1" below ground to 3" above gound other wise what was metioned above will happen.
post #4 of 5 (permalink) Old 04-12-2004, 10:45 AM
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Do you know if anyone makes a .5" extended ball joint?
For the stock balljoints, not that I know of.

I do know the Bill Harper (Navy Lifer) has found an 11/16" screw-in balljoint that he can use when rebuilding control arms (along with re-tapering the spindles to match, of course). One of the things this accomplishes is that it is longer.....not sure if it is 1/2", but if I remember right that is pretty close.
post #5 of 5 (permalink) Old 04-13-2004, 02:58 AM
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"If the roll center of the front suspension is raised, it has the same effect as increasing the front roll stiffness...Raising the front roll center height also reduces the amount of camber gain, which causes even more understeer. The combined effects of more roll stiffness, and less camber gain, can cause a considerable loss in front-end cornering power."ch.16 Chassis Engineering, Herb Adams

I guess this would make my concept for this mod incorrect. Well back to the drawing board. Anyone have the blue prints to our front end....?
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