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Author Topic:   Front Roll Centers
Strokin3
Member
posted August 12, 2001 07:36 PM
Does raising the front roll center from lets say 3" to 4" require stiffer front springs? I
raised mine and am experiencing much more travel at the RF than before I changed it.

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Artie Perilloux


bbracer17
Member
posted August 12, 2001 09:47 PM
When I checked my roll centers on my old car they were actually below ground ( yes that is possible), when I raised them to 3 1/2 inches above ground I had to go up 200 lbs on the right front spring. I'm not sure how much 1 inch change would make but i'm sure you would probably need to go up a little.


wfoondirt
Member
posted August 13, 2001 02:08 PM
Raising the roll center actually increases roll resistance, so everything else remaining the same you would be able to go softer. The problem arises in how you raised your roll center, if you just raised the front ride heights, dependant upon the geometry of your suspension, you could have changed the amount of anti-dive which is why you are experiencing the increased shock travel. There are alot of factors that apply to front suspension but from the information you gave that would be my best guess.


Strokin3
Member
posted August 13, 2001 06:16 PM
WFO, I actually lowered the inner mounting points of my upper control arms. The pivot shaft is parallel to the ground. Should the rear hole be slightly lower than the front hole to put the upper control arm shaft at an angle downhill to the rear of the car?

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Artie Perilloux


bbracer17
Member
posted August 13, 2001 08:40 PM
I also lowered the inner mounting points of the upper control arms. My upper arms did angle down to the spindle but when I was done they angled up to the spindle and my shock travel increased drastically. It must have been more from the geometry change of the arms rather than raising the roll centers because you would think that it would roll less.


LITTLEMAN
Member
posted August 13, 2001 10:00 PM
Moving the inner mounting points down will raise the roll center but it can also move it left or right of center and if you move it closer to the left of center the car will behave like it has a stiffer right front spring moving it to the right will result in the car behaving like it has a softer right front spring also where the roll center ends up at full roll is more important than the static setting.


wfoondirt
Member
posted August 14, 2001 08:46 AM
I wouldn't say that the terminal position of the roll center is most important but the movement of the roll center through roll is important.
Also i'm not sure if there is a misunderstanding of termonology here but typically (i say this because there are alot of variables in front suspension geometry) lowering the upper control arm mounts will lower the roll center especially if they were angled up to the spindle to start with. But it is possible is some cases to raise the roll center that way. So for clarification what suspension are you running (stub, spindle, control arms etc) and how are you determining the roll center.
Typically (again it varies alot) on chevelle stubs the upper control arm shaft is angled slightly down and to the rear.


Strokin3
Member
posted August 14, 2001 09:20 AM
The front stub is a camaro. I instaled W5
front spindles and it lowered my ride height so I compensated by turning down on the jack bolts and lowering the upper arm inner pivots down. I have computer software that calculates the roll center heigth above the ground as well as lateral location. I didn't pay close enough attention to the lateral location and I will recheck this.I do understand that the dynamic lateral location of the front roll center is important. Thank you for waking me up. There is just so much to remember.

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Artie Perilloux


wfoondirt
Member
posted August 14, 2001 02:18 PM
Strokin, have you read the section on front suspension in Milikins race car vehical dynamics? Front suspension is too complex to analyze on a forum like this and that book has a very good section on front suspension and will help in taking all factors into account when working on front geometry.
as a side note, early 70's cameros actually have pretty good geometry to start with and it doesnt take alot to get them to work well on a race car, i wish we could run on mods them around here. I have a few aquaintaces that use them on a sportsman type car and we ended up using all the stock mounts.


Strokin3
Member
posted August 14, 2001 07:48 PM
WFO, you are correct. The Cameros are easier
than most. I have to remove the stock upper arm mounts to install the tubulars. I use the stock drag link but I run 5/8 tubes with rod ends in place of the stock stuff. The bump steer is never too hard to get right either with the Camero stub. I run a Sportsman car but you mod guys got it going on when it comes to seting up and tuning your cars. Thanks for the input.

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Artie Perilloux


dirtsquirt
Member
posted August 20, 2001 10:05 PM
You can get it from the sae website http://www.sae.org/servlets/productDetail?PROD_TYP=BOOK&PROD_CD=R-146
or i believe amazon.com or barnes and noble have it too


dirtsquirt
Member
posted August 22, 2001 04:10 PM
Thanks for the info.


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