Right front ball joint

[45mod]

I run a long ball joint in the lf and a short ball joint in the rf upper as I know a lot of people do. My buddy who is a very successful driver runs the long ball joint in the lf AND the rf. He got this car from another very successful driver. What does this do? How does this affect the car long ball joint versus short ball joint in the right front (upper)? Thanks

[HEAVY DUTY]

Long LF upper will raise roll center and move it to the right. More importantly it will add camber gain. You will have to reset the bump steer.It is probably a good thing unless the roll center gets too high. It might create shock clearance problems.

[MasterSbilt_Racer]

I believe HD mistyped and meant to describe the RF.

[Fraley Racing Ent.]

always remember if your changing ball joint lengthe to adjsut roll centers that it affects caster, camber and bump steer. you have to check and/or rest all of these things

[HEAVY DUTY]

Your right Mastersbuilt, I did mean RF. Glad you caught that

[45mod]

Thanks for the info guys. One more thing will this make my spring act stiffer or softer or no affect?

[HEAVY DUTY]

RF spring should act stiffer, because the roll center will be higher and farther right, which will resist body roll some.

[Fraley Racing Ent.]

it will make it "stiffer" but it wont be that much of a change. dont start changing springs to compensate for the movement of the roll center .... you will end up back a square one or not knowing what made the change in the car.

[Lizardracing]

Is the wheel rate and roll center location linear?

[HEAVY DUTY]

The wheel rate is linear, but the roll center will probably move right, and maybe up more with the long balljoint than the short one. Raising the roll center will shorten the moment arm causing the car to roll less. ( will act like lowering weight in car)

[Lizardracing]

Does the RC move right in linear fashion to the increase in RF spring rate? Do the front springs affect RC at all? Where does the RC go is I take out the RF spring and replace it with a solid spacer?

How can graph paper and a ruler on current theory accurately calculate RC if the springs are partly responsible for RC migration using just mechanical attachment points without springs?

[HEAVY DUTY]

I do believe springs play a part in the roll center. If you had a solid bar, the roll center would be at the contact patch of the tire with the solid spacer I am assuming. I personally believe that the roll center is one of the least important things in a front end. Camber curves, caster gain, and bump steer all are more important than where the roll center is. There are a lot of theories on roll centers, and a lot of money being spent on programs that tell you that roll centers are the most important thing in a front end. What are your thoughts Lizardracing?

[jsf74]

That's funny I've talked to several very good drivers and a few chassis builders and they say the same thing. While it's good info to know the roll center its not the be all end all. It's more of a tuning tool and helps sell magazines.

[speedbuggy]

I don't think a stiffer spring changes roll center (if you agree that roll center is just a geometric expression of suspension behavior). Roll centers are calculated without regard for spring stiffness. For any given suspension configuration. there is a path that the roll center will migrate along. The spring just helps dictate how far along that path the roll center travels.




......Camber curves, caster gain, and bump steer all are more important than where the roll center is. There are a lot of theories on roll centers, and a lot of money being spent on programs that tell you that roll centers are the most important thing in a front end......
?

I agree with this.


That's funny I've talked to several very good drivers and a few chassis builders and they say the same thing. While it's good info to know the roll center its not the be all end all. It's more of a tuning tool and helps sell magazines.

and this...

[Lizardracing]

Lets say I get 4" of up travel on the RF and 4" of down travel on the LF as measured from the end of the spindle. For theory discussion, this was quantified by data acquisition during testing day. If I took my car home put my car on jack stands and took the springs out, lowered the LF 4", raised the RF 4", remeasure the mechanical pivots points to come up with a RC location and migration pattern, does that change when I place the spring back in the car while still on jack stands?
RC location theory is usually referred to in about two dimensions as viewed from the front/back. Measurements are noted from the upper ball joints, lower ball joints, inner mounting points and the tire contact patches. The vectors are to be averaged of the front and rear inner mounting points of both upper and lower controls arms.

Does the front roll center have to be located in two dimensions or can it migrate front to rear as well? If I have a car that gains/loses caster and the Instant Centers now move forward, does that change the Roll center and the moment arm lenght? If a line is drawn from the CG of the front and rear and that line is a angle is not parallel to the ground but slants downward toward the front(front is lowe) does that also mean wheel base lenght is a factor in where the RC/ Moment arm lenght should be located?

Maybe I think too much.....

[HEAVY DUTY]

I see what you mean about the roll center moving front to rear. I have a 3 dimensional front end program that should account for that somewhat. I heard that Larry Moore once said," if you bolted a solid bar with hiems in place of the lf shock, where would the roll center then be?" The car would have to rotate around the shock mount on the LF a frame, or the LF tire patch, regardless of where the instant centers of the front a arms were. What about the roll center when the lf tire lifts off the ground? Most of the good roll center programs are figuring a force based (loaded) suspension and taking jacking forces into account, and assume that the car is semetrical side to side, with the spring rate and weight equal from side to side. I personally don't believe that the roll center is a solid pivot point that the front end moves around, like a lot of people teach, and that the spring rates have to play a part in the front roll centers.

[Lizardracing]

Tires act like springs too so how does that adds to the complexities of calulating RC's

Because dirt track surfaces are generally pretty eratic in the terms of calculating RC locations(bumps, banking, car attitude) are constantly changing than I surmise that RC locations are more of a generality with some useful info but by far any absolute. Finding practical application for the knowledge will be needed.

Maximizing the average contact patch and wheel loading to balance the car front and rear for driver preference and tire wear through Camber, Caster, and Bump Steer has much more impact on the common racer than current RC theory in my opinion. Maximizing the drivers ability to feel the car traction limits and provide quality feedback for adjustment purposes is probably even more important than anything else.

[1Blacksheep]

Back when we raced solid front axle Micro sprints we adjusted Dynamic turn ability with Springs and left the front pan alone. We could not give a Ratts Azz where the MOMENT Center was especially when the Left front tire was only for getting the car to the green flag and the first 10 ft of entry to the corner. The rest of the time it hung there for ballast .You can safely bet your Hiney springs effect the SAID MC ! Which is just a Thought Guide to start with . IMO

[Lizardracing]

I got to studying an Indy car the other day my local University builds in the engineering dept and I pondered the question. How do they calculate RC and MC when the upper and lower control arms are parallel and don't intersect to create the IC to map the RC?

[1Blacksheep]

I got to studying an Indy car the other day my local University builds in the engineering dept and I pondered the question. How do they calculate RC and MC when the upper and lower control arms are parallel and don't intersect to create the IC to map the RC?

That's some canti lever stuff that when you connect all the lines the IC points to the RC which falls somewhere between the Big and Little Dipper ! LOL just kiddin

[speedbuggy]

I got to studying an Indy car the other day my local University builds in the engineering dept and I pondered the question. How do they calculate RC and MC when the upper and lower control arms are parallel and don't intersect to create the IC to map the RC?

Do you really want an answer to this or you just joking around?

Smart as you are, I think you already know the answer. Just consider that the IC's are infinitely distant from the contact patches. At least, that's how I would look at it.