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I figured this is where I will get the best response. I'm looking to raise my Roll Center and shift it laterally as well. The car has slotted lowers on both sides and I can get Upper Ball Joints with taller studs in a few increments as well. I have also been told different things as to how the lowers should be angled. Should the lower outer ball joint be higher or lower then the inner pivot point if its anything other then level and what happens if its both ways being I have slotted lowers and not sure where to start with ride heights.
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Do you want to move it static or dynamic ? -
Lets start with static and save dynamic for later after testing! Help me with each effect. The lower arm positions as far as the outer ball joint in relation to the inner pivot point. Which way is correct. and adding longer ball joints on LF upper LF Lower and the RS etc.Comment
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Google "Bob Bolles" and read some of his articles.Comment
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any of the google stuff just sends you to links to buy his books......that's why I posted here for a good breakdown.Comment
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Why? I have been working with front end design and designing my own frt. ends and assisting in designing and testing race car frt. ends for builders for over 4 years now. The more I learn the more I find out how little is know by people who have studied this in depth from an engineering problem stand point most of their lives. With an engineering and racing background of over 30 years I have also taken classes specifically about frt. end suspension design and worked with several car designers and several engineers.
First of all get yourself a couple of computer programs and see what cars that run well have for readings. Now I am sure I will be told I don't know what I am telling you by someone but at my age I really am getting used to that and don't care. Roll center is a theory. While it is an indicator it is not the do all answer, all that and a bag of chips some people think, in MHO. Moment arm length, center of gravity location and instant center locations along with camber gain in roll plus initial camber settings AND their complex relationship can be more important in MHO. In other words roll center is in my OPINION an average of ALL those factors. I have built and adjusted suspensions with all sorts of roll centers and roll center movements BUT it is all at the cost of the other factors I listed. This weighing of importance or prioritizing which are most important to handling is what makes a car consistent or inconsistent under all driving circumstances IMHO. Now with that said I have found in MOST cases a roll center from 2" to 4" off the ground and slightly right of center seems to be a good starting, static point. Then again when you start the dynamic changes or increasing the roll center movement you WILL have to sacrifice other things.
Mark Bush designed the Rocket Black frt end that has won a ton of races and it's roll center has almost NO movement on roll, or dynamically. I have built and raced frt ends that would send the roll center over 20 inches to the right and maintained the roll center at 2" above ground through out roll BUT it was at the expense of camber gain and instant center locations. Ok so with all that said unless you are ready to get into spindle design and the compromise in that design factor you are limited by whatever spindle you use also. Compromise is what it is all about. So with all this going on you have bump steer that needs to be as close to 0 as you can keep it, IMHO. In closing welcome to the deep dark hole.Last edited by hpmaster; 02-13-2012, 12:21 PM.Comment
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I'm very familiar with all of this and before i spend the money on the programs i'm looking for some more general answers. I run both dirt and asphalt and they both require a different package. Dirt we ran about 8" left of the centerline and 4 inches off the ground with my lowers level and the uppers at around a 6 degree split. etc etc. what I'm working on now is a G body Metric. we are limited to what we can do I can't modify mounts it is running a drop spindle. we have a 6" ride height rule. My question is should i run my lowers level or should the inner pivot point be higher or lower. I need to ultimately raise my roll center and shift it to the right it I know has a low low roll center as it is and it might not even be offset right with its current setup which make it lay over really hard on the RF and i don't want to go the Big Bar route like the rest it makes it too tight and causes clearance issues but regardless I just am looking for a general lower control arm rule of thumb and what running extended ball joints in my lowers will do I plan on running an extended upper on the right upper arm to help shift my RC to the right as it is now i could run a shorter but still extended upper of the Left upper if it also helps raise me RC just need some guidance being I don't want to spend if it isn't neededComment
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That's the problem without the programs you are in for a lot of time plotting this on paper. For me to suggest anything would be a shot in the dark not taking into account all the other measurements. I would spend the $100.00 to $200.00 for a program and plot your frt end and then make theoretical adjustments until you get what you need. I still believe plotting a good car's frt end is where I would start then adjust yours close. From that starting point your experiments will have a repeatable base line to go back to when things do not work out. Racewise, Mark Bush's company, has a frt. end program that is 3-d and seems pretty cool, Auto Ware is one of the ones I have and seems ok to me. If you want to talk about it message me and I will try to help more.Comment
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Bob Bolles has written tons of articles for Circle Track and other publishers its on the net you just have to look a little harder.
You are going to need to purchase a software program to locate and adjust your roll center. You can plot it out on paper but is a waste of time because you dont know whats going on with it dynamically you cant simulate roll and g-force on paper. I would buy either of those two programs they work fine, also if you like puzzles trying to design roll centers with stock parts will be fun.Comment
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Changing the kinematic roll center to decrease the car from "lay(ing) over really hard on the RF" adds a mechanical stiffness to the suspension during cornering. This stiffness is created by a sideforce applied to the tire acting through the instant center of the suspension. The resulting force vector has lateral (side) and vertical components. The vertical vector component is the force that resists movement of the suspension. Move the instant center, increase/decrease this force. The closer the IC is to the wheel the more effect it will have. Moving the roll center up or to the right is usually done by moving the IC closer to the wheel.Originally posted by 7uptruckracer View Post
Whether the car is "lay(ing) over really hard on the RF" or not, the Left to Right weight transfer is nearly the same. Front roll stiffness and rear roll stiffness will determine which tires are gaining the most weight. YOU are increasing the front roll stiffness when you move the roll center.
Roll center
- a cornering force dependent roll stiffness. The force vector that resists suspension movement is larger with a larger cornering force
- the same force vector resisting movement also effects ride-rate (ride stiffness)
- the car is usually tighter on exit with a rollcenter to the right (increased wedge)
Swaybar (front only)
- changes roll stiffness only WITHOUT any dependence on cornerning force at the tire.
- ideally the ride-rate is NOT effected
- the car is usually tighter on exit with high front roll stiffness (increased wedge)
So back to the sway bar option..... you said you dont want a front sway bar, because by its self the car is tighter, but if a rear sway bar is added at the same time the weight transfer could be the same.
Track banking will determine if you should change RC or swaybar. High banked tracks with have a large vertical acceleration and lateral acceleration, versus flat tracks that have large lateral accelerations. That will highlight the importance of ride-rate changes between RC and Swaybars.
GhopperComment
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No I said I didn't want to run the huge sway bar because there are to many clearance issues and the people run them to overcome the G-bodys low roll center so. I want to try to run a smaller bar and raise the roll center to something more normal. I need these questions answered. Which is the correct way for the lower arms to be mounted with the inner or outer pivot points higher. And what does running a longer lower ball joint from what's there now do? Will it do anything at the same ride height and my thought is I should not run it If my arms are flat now that would drop my lower below the inner pivot point and cause weird camber change issues if I lowered my heights to compensate the issue wouldn't that just lower my roll center? And does raising both upper angles raise roll center I know offsetting the angles changes my lateral location which I want to to just dunno if I should leave one stock or raise one and little and the other more so I still get my lateral shift but still raise itComment
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Originally posted by 7uptruckracer View Post
Ok, forget the golden ticket answer above of why and how to make this change.
Answer you seek -> Don't change ride heights and add longer ball joints to top/bottom - Done
GhopperComment
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I have used Bob Bolles software now for 3 years. It is spot on. I have used it dlm's, mods., tq late mods. On the tq setup , the driver has not lost a race in 2 years. It takes a little time at first, but it gets easier the more u use it. I talked to Bob last year at VSP, he told me every major dlm car builder is now using his software. Matching the roll angles front to rear only seems logical when u think about it. It will make your car more consistent. Beware, you still have to make the proper adjustments according to the track cond., but your car seems to stay consistent!!Comment
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Bob Bolles lol sorry i had to laugh. I have his program , a lot of dust on it. Auto Ware has great stuff, should attend his webinars. Ever seen any data from a Data acquisition ??
Great reading-- Auto Ware
Let me start by saying the RC is the result and not the cause of the motion or forces. So, it is best to think about RCs in reverse. Regarding force, lateral position of an applied force has no impact on the resulting vertical forces (thanks to Mr. Newton's Principle of Transmissibility) So, saying the lateral location of the RC changes the vertical loading in the tires is just not true. Chances are anyone that has observed a change in handling and attributed it to the RC location, just missed something else that really caused the change.
Again the RC is the result and not a solid object like a Heim joint. The RC is you are thinking is no doubt from the "wheel position analysis method" where lines are projected from control arms. The method is almost 100 years old and has many simplifying assumptions that have long been forgotten. A newer method roughly 25 years old is much more accurate, but somehow its popularity never caught on like the old method. But again many aspect of vehicle dynamics never flourished like RC (for example when was the last time you heard anything about static margin, elastic conjugate points or any of the dozens of other parameters)?
Granted if you want to think in terms of kinematics the RC is a convenient point to sum moments, and a higher RC does result in positive or negative jacking. However, shocks, springs, bars and even bushing all contribute to the resulting RC (that's why I like the new method better).
Okay, now that I went on about how to build an atomic clock and you just asked about the time
let me say, use your suspension geometry needs to net desirable dynamic camber and if you are un happy about weight transfer do something else, not mess up the alignment. imho
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