Roll Centers

[let-r-eat]

The position of the upper mount/lower mount and tie rod inner pivot point is what your looking for. These guys are talking but are not taking into account the steering pivot points. You can't talk suspension geometry without talking steering/upper/lower pivot points. These softwares are berries and cream but you have to understand what your looking at. If you change the offset on a front wheel your changing suspension geometry. The center of the contact patch is where its at. Visualize a line through the lower inner pivot/upper inner pivot and inner steering pivot. You need to be able to draw a straight line threw them. Then worry about the arm angles and placement of the tie rod end on the spindle. Where are they measuring the 6" ride height?

[Ghopper]

Dirtrunner35 -
If you are mentioning force-based roll centers, with calculation of a virtual swingarms. Unless you know another way? I am a believer in weight jacking term (you also mentioned) as described in my previous post and a component of the force-based RC. Looking at normal force change during a parallel lateral force test, checking this at a few roll and pitch angles give. If you iterate the solution on each side of the test body and load condition, calculate the virual swingarm by the point that the 3 force vector cross, then look for the intersect of results of the two sides.

Static Margin is difficult to bring into a discussion on increasing roll stiffness as it is usually described with 2D bicycle models and lumped front/rear axle tire cornering stiffness. However a good way to explain understeer gradient with respect to CG fore/aft placement.

I am drawing a blank on elastic conjugate points. Can you explain further?


Let -r -eat -
If 7up just changes upper ball joints, he will not have to worry much about steeringing geometry changes....it may bump out a little more. I would just bolt on new upper and lower ball joints. He may have to add some shims on the outer tie-rod to lower the pivot point.



Ghopper

[7uptruckracer]

I have to be careful what I do because of the rules. I was told I can get bump back by moving steering components. I know adding the joints can cause me to bump out more. I just have to make sure I can get it back within spec the others cars I have are no problem but this one has gearbox steering so its going to be more a hassle while skirting the rules (using that favorite color of racers) I just needed clarification because I was told the outer lower control are pivot point should be mounted BELOW the Inner pivot point and that goes against what I thought because wouldn't that have implications on my camber curves that are undesirable? And being it has a 6" lowest point ride height rule I can get to 6" but geometry is more important so i'm trying to maximize my heights, raise my RF and shift it to the right of the CL. Being this particular car is a G body metric car and has a already way low roll center I know I want to up it. and it does have drop spindles which has lulled the competition into thinking it rolls less but it hasn't changed the RC Just the Center of gravity height so they seem to think it doesn't roll less persay but they are still running the huge bars for a 2700lbs car and they are cutting arms and doing unsafe things to run them id rather run a smaller bar which should also compensate for might RC shift to keep the car balanced and maybe even add some balance to it! sorry for the rambling

[Dirtrunner35]

I was just giving that example for different things that effect front end geometry, I have bob bolles program about getting the roll center the same front and back, to many questions you need to guess at in the program. I have 3 programs from Auto-ware.com and they work great.

Since you are limited on what changes you can do to your car, I would put the inner control arm points a little lower than the ball joints. Can you elongate the upper control arm mount holes or cut them off and make them lower ?

I ran a stock sway bar on my metric clip car for 2 years on dirt.

[drtrkr244]

I was just giving that example for different things that effect front end geometry, I have bob bolles program about getting the roll center the same front and back, to many questions you need to guess at in the program. I have 3 programs from Auto-ware.com and they work great.

Since you are limited on what changes you can do to your car, I would put the inner control arm points a little lower than the ball joints. Can you elongate the upper control arm mount holes or cut them off and make them lower ?

I ran a stock sway bar on my metric clip car for 2 years on dirt.

Yea, I agree. You have to call Bob to get too many inputs. It needs to be more user friendly.

Have you compared the two sftwares results, were they close or totally different?

[Dirtrunner35]

Yes I agree, roll center height , left to right, center of gravity height. The program is about roll angle and not weight transfer. I guess if you know how a car works you could use it with success but then why would you buy it? I have his set-up secret book and bought his newer one and 2/3rds is the old book so I returned it. He contradicts himself in his book, I did learn some things from his book but more at Auto-ware.

Have you compared the two software results? Were they close or totally different? I did years ago and that's why I quit using the roll angle program. My computer crashed and I don't have the measurements for Bob's program, if I did I would tell you what was different. I would hate to see the roll angle on my dirt mod, lol.

[drtrkr244]

Yes I agree, roll center height , left to right, center of gravity height. The program is about roll angle and not weight transfer. I guess if you know how a car works you could use it with success but then why would you buy it? I have his set-up secret book and bought his newer one and 2/3rds is the old book so I returned it. He contradicts himself in his book, I did learn some things from his book but more at Auto-ware.

Have you compared the two software results? Were they close or totally different? I did years ago and that's why I quit using the roll angle program. My computer crashed and I don't have the measurements for Bob's program, if I did I would tell you what was different. I would hate to see the roll angle on my dirt mod, lol.

Im sure its not the "end all' software, but i do feel it helped my racing program.Its a little difficult to use, but i think its a good investment for $150.At least, it gets you measuring every suspension pick up point, and thinking how they work together. I do know i used it on a homemade car, built on a garage floor and it turned into an unbeatable car. Good thing it had bolts instead of ball joints as i used about one foot of 3/4 tubing for spacers on the front end.I do believe it will get u in the ballpark...JMO

[7uptruckracer]

NO we can't cut anything or elongate holes other then a repair issue, Kinda a catch all thing and way of ruling they use....Nascar what can ya say......I have a gameplan I'm going sunday to set my arm angles and heights with stock ball joints and see where I end up height wise with the right geometry then see how much more i can adjust. I was going to get extended lower Ball joints but after looking tonight my outter pivot points on my lowers are already lower then my inners and I only have an Inch till I'm at the minimum allowable ride height so I might only be doing my upper ball joints. I might use a .500 inch longer stud on the RF and .100 on the LF thoughts? If i can get what i want outta the lowers i can do up to 1" lower ball joints and get them up right and get my 6" minimum.......input? right track here?

[drtrkr244]

NO we can't cut anything or elongate holes other then a repair issue, Kinda a catch all thing and way of ruling they use....Nascar what can ya say......I have a gameplan I'm going sunday to set my arm angles and heights with stock ball joints and see where I end up height wise with the right geometry then see how much more i can adjust. I was going to get extended lower Ball joints but after looking tonight my outter pivot points on my lowers are already lower then my inners and I only have an Inch till I'm at the minimum allowable ride height so I might only be doing my upper ball joints. I might use a .500 inch longer stud on the RF and .100 on the LF thoughts? If i can get what i want outta the lowers i can do up to 1" lower ball joints and get them up right and get my 6" minimum.......input? right track here?

Definitely, putting longer balljoint studs on a "stock" car is necessary.They generally have too low of a roll center for circle track racing.Putting longer stud on rf wii shift rc to the right.Technically, you can draw out your pickup points on graph paper, but if you need to make changes , youll have to start over.To start changing things without knowing where you are at might cost you more in the long run.

[cgs]

does anyone have a geometry program laying around the want to sell at a reasonable price?

[1Blacksheep]

Chassis pivot point should always be lower than the the outer pivot point JMO !!! Increasing the upper A angle moves the (theoretical ) RC closer to that corner and raises it at the same time with No other changes. RC ht and lateral location walks hand in hand with front spring rates and rear wt %. To answer original Question .