Ball joints and roll centres
03-06-2003, 11:04 AM
#1
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Ball joints and roll centres
A few of use have been looking to adjusting our roll centers. A roll center is the imaginary point about which our cars turn. I am just trying to understand this. You have to be able to adjust your Instantanous center to control your roll center. A car with a proper roll center turns better, the tires bite better, the whole car feels more nimble.
Anway our spindles, the thing the wheel is bolted to is too short and non adjustable. A simple upper ball joint change to a mono ball joint allows the spindle length to be increased by up to 1.5 inches longer. They are only about $36.00American each, cheap enough.
Anyway we need to adjust the instantanous center. We need it about 2 inches inside the opposite tire. An instantanous center is a line drawn between the upper ball joint and the inner upper A arm pivot point on the frame . This is the upper line. The lower line is through the lower ball joint and the inner A arm mount. The intersection of these 2 line is the instantanous center. There will be one on either side.
Now the roll center is a spot that we really want and we want it about 4 inches above the road and in the center of the car , not off to one side.
The iroll center is a line drawn from the center of the tire to the instantanous center on the opposide side. Do this from both sides and you have the roll center where they meet.
I know this sounds a little far fetched but It is very important for a good handling car.
If the angle formed between the upper and lower A arms does not meet inside the opposite tire but might meet well beyond the car and this is the case with the C3 you roll center is all wrong and the car will not turn.
You need to angle the upper A arm down towards the inner A arm mount and not have the upper A arm level. One solution is redrill the inner mount on the frame and lower the inner mounting point so the upper A arm points down OR make the spindle longer by using extension ball joints. I was told the 1/2 inch of ball joint extension or reduction if you went too far makes all the difference.
While at a race shop where the owner really stressed to me the importance of the correct roll center he laid it all out on the board. He was really into the roll center to make the car handle.
When I call the supplier of race parts he also stressed the importance of roll center. It makes the difference between 2 cars of equal horsepower and driver ability of one comming in 1st and one comming in last.
The owner of the shop sent me home with the book STOCK CAR SETUP SECRETS BY BOB BOLLES.
I have just started reading the book to try and understand this principle.
I did quickly read about roll bars and the biggest rule in the book is that the arms bending back to attach to the lower A arms MUST be at right angles for the bar to work properly. Factory arms come off on a angle and this really screws up the effect of the bar. They stress the need for right angles. Monty has the nices settup I have seen.
While in the shop I also saw piles of brake rotors, the quick replaceable screw on type. Makes you mouth water to see all the parts lying around.
Most impressive was a nascar block with massive splayed main caps and heavy solid steel skirts to contain blow ups with damaging the block itself and hollow cranks for light weight. The blocks all have roller cam bearings also.
Anyway guys don't be too hard on me with this discussion. I am trying to learn more about setup.
In particular I need to know which upper ball joint to buy. There are two, a full size and a mid size. I went to the shop yesterday with a lower believing it would have the same tapper as the upper but I learned they are not the same on the olds spindles they use and might not be the same on our vets.
I will keep reading the book for the next week then go back and let the race shop explain it to me agian. Hopefully in this time I will know more.
Anway our spindles, the thing the wheel is bolted to is too short and non adjustable. A simple upper ball joint change to a mono ball joint allows the spindle length to be increased by up to 1.5 inches longer. They are only about $36.00American each, cheap enough.
Anyway we need to adjust the instantanous center. We need it about 2 inches inside the opposite tire. An instantanous center is a line drawn between the upper ball joint and the inner upper A arm pivot point on the frame . This is the upper line. The lower line is through the lower ball joint and the inner A arm mount. The intersection of these 2 line is the instantanous center. There will be one on either side.
Now the roll center is a spot that we really want and we want it about 4 inches above the road and in the center of the car , not off to one side.
The iroll center is a line drawn from the center of the tire to the instantanous center on the opposide side. Do this from both sides and you have the roll center where they meet.
I know this sounds a little far fetched but It is very important for a good handling car.
If the angle formed between the upper and lower A arms does not meet inside the opposite tire but might meet well beyond the car and this is the case with the C3 you roll center is all wrong and the car will not turn.
You need to angle the upper A arm down towards the inner A arm mount and not have the upper A arm level. One solution is redrill the inner mount on the frame and lower the inner mounting point so the upper A arm points down OR make the spindle longer by using extension ball joints. I was told the 1/2 inch of ball joint extension or reduction if you went too far makes all the difference.
While at a race shop where the owner really stressed to me the importance of the correct roll center he laid it all out on the board. He was really into the roll center to make the car handle.
When I call the supplier of race parts he also stressed the importance of roll center. It makes the difference between 2 cars of equal horsepower and driver ability of one comming in 1st and one comming in last.
The owner of the shop sent me home with the book STOCK CAR SETUP SECRETS BY BOB BOLLES.
I have just started reading the book to try and understand this principle.
I did quickly read about roll bars and the biggest rule in the book is that the arms bending back to attach to the lower A arms MUST be at right angles for the bar to work properly. Factory arms come off on a angle and this really screws up the effect of the bar. They stress the need for right angles. Monty has the nices settup I have seen.
While in the shop I also saw piles of brake rotors, the quick replaceable screw on type. Makes you mouth water to see all the parts lying around.
Most impressive was a nascar block with massive splayed main caps and heavy solid steel skirts to contain blow ups with damaging the block itself and hollow cranks for light weight. The blocks all have roller cam bearings also.
Anyway guys don't be too hard on me with this discussion. I am trying to learn more about setup.
In particular I need to know which upper ball joint to buy. There are two, a full size and a mid size. I went to the shop yesterday with a lower believing it would have the same tapper as the upper but I learned they are not the same on the olds spindles they use and might not be the same on our vets.
I will keep reading the book for the next week then go back and let the race shop explain it to me agian. Hopefully in this time I will know more.
03-06-2003, 10:00 PM
#2
Melting Slicks
Re: Ball joints and roll centres (norvalwilhelm)
All too often the fix to handling has become a set of 20" billet rims with elastic bands for tires.I personally don't like that look on a C-3,and look forward to an engineered suspension upgrade that will make improvements to the handling,without detracting from the classic muscle car look of the C-3.
Keep me informed on gains made Norval.
I've already baught and installed the VetteBrakes 550lb springs,poly strut and 360 glass rear spring,front and rear swaybars,a set of rims and 50 series tires in an effort to crispen up the handling.Works quite well,but there's always room for improvement. :cheers:
Keep me informed on gains made Norval.
I've already baught and installed the VetteBrakes 550lb springs,poly strut and 360 glass rear spring,front and rear swaybars,a set of rims and 50 series tires in an effort to crispen up the handling.Works quite well,but there's always room for improvement. :cheers:
03-06-2003, 10:23 PM
#3
Drifting
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St. Jude Donor '05
Re: Ball joints and roll centres (The Money Pit)
Norval, I will be unavailable for the next week. I look forward to a lot of new information on this subject upon my return.
I think most of us will be basing our suspensions on either the VPB 460#/550# front springs or the front monospring conversion. Many other variations of shocks, balljoints, A-Arms etc. will enhace the system to even higher degrees. Then there is the frame stiffing mods that we will hopfully achieve soon also.
I would like to achive a car that will run and handle with a new C-5. And if it doesn't? Well, I'll have a lot of fun trying. Jim
I think most of us will be basing our suspensions on either the VPB 460#/550# front springs or the front monospring conversion. Many other variations of shocks, balljoints, A-Arms etc. will enhace the system to even higher degrees. Then there is the frame stiffing mods that we will hopfully achieve soon also.
I would like to achive a car that will run and handle with a new C-5. And if it doesn't? Well, I'll have a lot of fun trying. Jim
03-07-2003, 09:01 AM
#4
Team Owner
Re: Ball joints and roll centres (norvalwilhelm)
Norval, damnit man, here I thought olf Zora would have had that pretty well figgered out.....I have heard of this roll center stuff, buddy of mine races pretty heavy.....but never thougt much of it in the vette....
so to extend the upper ball joint stem about an inch or so??? raising the upper ball joint more??? interesting...by how much??? I got calipers, and can snoop around....what's easiest way to do this?? I would imagine maybe mounting the stock ball joint on the underside of the A arm, instead on top the way the factory does it...and if it's not enough add a shim between BJ and A arm...lowering joint even more...keeping stem in place....
not sure what this does for the grease boot though....
GENE
GENE
so to extend the upper ball joint stem about an inch or so??? raising the upper ball joint more??? interesting...by how much??? I got calipers, and can snoop around....what's easiest way to do this?? I would imagine maybe mounting the stock ball joint on the underside of the A arm, instead on top the way the factory does it...and if it's not enough add a shim between BJ and A arm...lowering joint even more...keeping stem in place....
not sure what this does for the grease boot though....
GENE
GENE
03-07-2003, 09:15 AM
#5
Re: Ball joints and roll centres (mrvette)
I have a book called How to make your car handly, by Fred Puhn. It does a very good job of explaining this stuff, a definite must read for everyone intersted in this subject.
The longer upper balljoint is pretty common, especially among the camaro crowd so it seems (I first learned of the availability of longer ball joints and spacers there)
As for mounting the upper arm lower on the frame, it seems like that's kind of har to do without chopping the whole frame upp (since the mounting surface is not flat lower down), another option would be to use shorter arms and mount them on the outsude of the frame, like C4's but then you'd have to choose is the right legth to be able to set proper minimum camber, too long and you can only set it so much.
The longer upper balljoint is pretty common, especially among the camaro crowd so it seems (I first learned of the availability of longer ball joints and spacers there)
As for mounting the upper arm lower on the frame, it seems like that's kind of har to do without chopping the whole frame upp (since the mounting surface is not flat lower down), another option would be to use shorter arms and mount them on the outsude of the frame, like C4's but then you'd have to choose is the right legth to be able to set proper minimum camber, too long and you can only set it so much.
03-07-2003, 12:01 PM
#6
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Re: Ball joints and roll centres (mrvette)
mrvette. Our spindles are tooooo short. In the camaro and later the corvette they went to a longer spindle. The easy way to extend our spindles is with a special ball joint that gives us up to 1.5 inches extension in the upper ball joint, you can also do the bottom. A line projected by the angle of the lower A arm and the line projected by the lower A arm must meet about 2 inches inside the opposite wheel. Ours meet well beyond the car. A line projected from the center of the tire to this imaginary point in both directions , one from the left tire and one from the right where they intersect is the Roll center. This in our cars is below the ground. I want it up about 4 inches directly under the center of the car.
The major problem we see is the outside wheel in a hard turn goes positive camber and we want negative camber. Increase the spindle length and this happens.
Our cars share upper ball joints with 55-82 BelAir Biscayne, Capric, impala and get this Corvair.
We have full size ball joints and Coleman sells extended ball joint #833-110-R You want the flat one not the angled. They are $36 AM.
They also sell a lower extension ball joint that can lower a car but to 1.5 inched without touching the spring. The spindle is just moved higher up the car so the car sits lower without modified springs. They are also adjustable.
I am also finally breaking down and installling 460 pound springs. My ball joints should be in Monday or Tuesday so I will see if they will fit.
The major problem we see is the outside wheel in a hard turn goes positive camber and we want negative camber. Increase the spindle length and this happens.
Our cars share upper ball joints with 55-82 BelAir Biscayne, Capric, impala and get this Corvair.
We have full size ball joints and Coleman sells extended ball joint #833-110-R You want the flat one not the angled. They are $36 AM.
They also sell a lower extension ball joint that can lower a car but to 1.5 inched without touching the spring. The spindle is just moved higher up the car so the car sits lower without modified springs. They are also adjustable.
I am also finally breaking down and installling 460 pound springs. My ball joints should be in Monday or Tuesday so I will see if they will fit.
03-07-2003, 12:13 PM
#7
Re: Ball joints and roll centres (Twin_Turbo)
The ball joints Norval (and myself and a couple of other guys) are looking at are designed to fit most other Chevy's so they are not bolt in (they are four hole as opposed to our 3 hole), but they simply have an adjustment built in that allows you to force the tapered shaft farther down (or up) thru the pivot ball, thus effectively extending the length of the spindle. Bolting them onto our A-arms is a matter of either drilling a couple of new holes in the A-arm, or in the mounting plate of the ball joint! Simple. And, they are cheap, about $35 per side. Very common among the circle track set.
The front suspension of the C3 was originally designed in the early 50's and was a basically a take-off of a large Chevy sedan. It was marginally redesigned for the vette, but it was designed with positive camber gain (wheel leans out in a curve) so that the tires wouldn't be pulled off the wheels in a corner. Not much of a problem unless you are funning F70 Bias ply tires. But definitely not the ideal setup for for keeping an optimum patch of tire in contact with the ground. This is gonna be a sweet sweet improvement and am so looking forward to testing this out. I still can't imagine while nobody else has hit on this in the las 50 years, but I suspect a vast conpiracy amongst the racing elite :skep:
Chris
The front suspension of the C3 was originally designed in the early 50's and was a basically a take-off of a large Chevy sedan. It was marginally redesigned for the vette, but it was designed with positive camber gain (wheel leans out in a curve) so that the tires wouldn't be pulled off the wheels in a corner. Not much of a problem unless you are funning F70 Bias ply tires. But definitely not the ideal setup for for keeping an optimum patch of tire in contact with the ground. This is gonna be a sweet sweet improvement and am so looking forward to testing this out. I still can't imagine while nobody else has hit on this in the las 50 years, but I suspect a vast conpiracy amongst the racing elite :skep:
Chris
03-07-2003, 01:02 PM
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Re: Ball joints and roll centres (71roadster)
Chris actually got me going on this about a week ago with his posting on all the ball joint options. I have off and on talked about the extended ball joints without really planning to do anything with it for now but with Chris asking questions, sending me information I got on the train and started to really look into it. The more I read, research and talked to knowledgeable people the more I kept looking at our front ends and wondering why we had these old things.
Anyway after alot of help I ordered Coleman Upper Mono Ball Joint GM Full size number 33-110-L YES L not R The L is a left FLAT mount .
Like Chris said I hope with a slight bit of drilling to be able to bolt them right in. I will have them by Monday or Tuesday and hopefully before the week is up know if they will work. $36.50 AM each.
So Chris are you going to let me try installing them first? I will post pictures of how it goes.
I will remove the upper A arm this weekend.
The spring does NOT have to come out, Just place a good floor Jack under the lower control arm.
Anyway after alot of help I ordered Coleman Upper Mono Ball Joint GM Full size number 33-110-L YES L not R The L is a left FLAT mount .
Like Chris said I hope with a slight bit of drilling to be able to bolt them right in. I will have them by Monday or Tuesday and hopefully before the week is up know if they will work. $36.50 AM each.
So Chris are you going to let me try installing them first? I will post pictures of how it goes.
I will remove the upper A arm this weekend.
The spring does NOT have to come out, Just place a good floor Jack under the lower control arm.
03-07-2003, 01:30 PM
#9
Drifting
Re: Ball joints and roll centres (norvalwilhelm)
Norval,
I am very interested in hearing about your results. On the Camaro boards, everyone was talking about a spacer that did the same thing. The only negative anyone mentioned was increased tire wear. In fact, it was said that several people removed the spacers because of this. Here is a link to a pro-touring site where they talk about these changes a lot. Look in the suspension area, and do a search.
http://www.pro-touring.com/forum/forum.htm
I would also recommend buying "How to Make Your Car Handle" by Puhn. This is a great book that covers all types of suspension issues. Good luck.
Ken
I am very interested in hearing about your results. On the Camaro boards, everyone was talking about a spacer that did the same thing. The only negative anyone mentioned was increased tire wear. In fact, it was said that several people removed the spacers because of this. Here is a link to a pro-touring site where they talk about these changes a lot. Look in the suspension area, and do a search.
http://www.pro-touring.com/forum/forum.htm
I would also recommend buying "How to Make Your Car Handle" by Puhn. This is a great book that covers all types of suspension issues. Good luck.
Ken
03-07-2003, 01:57 PM
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Re: Ball joints and roll centres (bb69)
bb69 The spacer blocks do do the same thing but they cost about $195 American VS $36 American each for complete new ball joints. The spacer blocks take the stock ball joint and add a spacer between it and the a arm. I know the extended ball joints are race proven while 1/3 th the price.
I will do a complete alignement after the change. Regardless of what you do to the suspension if you set it back to normal setting after the modifications it should not increase wear on the tires.
I thank you for the link and will look at it.
I will also let everyone know how it turns out.
I will do a complete alignement after the change. Regardless of what you do to the suspension if you set it back to normal setting after the modifications it should not increase wear on the tires.
I thank you for the link and will look at it.
I will also let everyone know how it turns out.
03-07-2003, 02:30 PM
#11
Re: Ball joints and roll centres (bb69)
The spindle extenders everyone on the camaro boards refer to increase the spindle a fixed 1 - 15/16". Thats a lot. The adjustable ball joints have a much more workable range.
Norval, yep, I'm waiting for your report on fit, but I wont wiat on results. I understand the geometry and have a lot of faith it will work. Beside, I want to ge tmy car running and I only want to align it once!
Chris
Norval, yep, I'm waiting for your report on fit, but I wont wiat on results. I understand the geometry and have a lot of faith it will work. Beside, I want to ge tmy car running and I only want to align it once!
Chris
03-07-2003, 04:49 PM
#12
Drifting
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St. Jude Donor '05
Re: Ball joints and roll centres (71roadster)
And just what happens if you put the lower joints in the front suspension that drops the car 1 - 1.5 inches? If you are intending to lower your car will this help retain a better suspension position? Will the extra length below the spindle create a better or worse situation or does it even matter? Jim
03-07-2003, 05:19 PM
#13
Team Owner
Re: Ball joints and roll centres (norvalwilhelm)
Norval, NOW I"m all confused....
at first you said you wanted to basically raise the outer tip of the upper A arm in ralationship to the inner pivot point.....ok, we can't LOWER the inner pivot point without modifying hell....so we elect to raise the outer tip of the A arm...
which is making a taller spindle, effectively....
so, the stock ball joint is bolted on top of the arm, with stud and boot and body of joint joining the spindle....
SO to raise the a arm tip...why can't we just reverse the monting location??
and add a spacer if necessary???
would that work??? I hope you aren't considering adding a spacer between ball joint and A arm in the stock configuration...joint on top of arm....
that to me would effective make for a shorter spindle I presume...NO???
now much longer are these ball joints??? now much is that a arm raised???
somehow, I like the idea of a shorter ball joint stud...just for lateral support, and putting a spacer with joint mounted UNDER the A arm ...somehow i'ts gotta be mechanically superior....
GENE
at first you said you wanted to basically raise the outer tip of the upper A arm in ralationship to the inner pivot point.....ok, we can't LOWER the inner pivot point without modifying hell....so we elect to raise the outer tip of the A arm...
which is making a taller spindle, effectively....
so, the stock ball joint is bolted on top of the arm, with stud and boot and body of joint joining the spindle....
SO to raise the a arm tip...why can't we just reverse the monting location??
and add a spacer if necessary???
would that work??? I hope you aren't considering adding a spacer between ball joint and A arm in the stock configuration...joint on top of arm....
that to me would effective make for a shorter spindle I presume...NO???
now much longer are these ball joints??? now much is that a arm raised???
somehow, I like the idea of a shorter ball joint stud...just for lateral support, and putting a spacer with joint mounted UNDER the A arm ...somehow i'ts gotta be mechanically superior....
GENE
03-07-2003, 06:40 PM
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Re: Ball joints and roll centres (mrvette)
Norval, NOW I"m all confused....
at first you said you wanted to basically raise the outer tip of the upper A arm in ralationship to the inner pivot point.....ok, we can't LOWER the inner pivot point without modifying hell....so we elect to raise the outer tip of the A arm...
which is making a taller spindle, effectively....
so, the stock ball joint is bolted on top of the arm, with stud and boot and body of joint joining the spindle....
SO to raise the a arm tip...why can't we just reverse the monting location??
and add a spacer if necessary???
To move the ball joint from mounting on top of the A arm to the underside would gain you very little. Yes you could add a spacer block and it should work but I am not planning that. They sell them for about $195.
These are replacement ball joint that are totally adjustable up to 1.5 inches greater then stock. I effect lengthening the spindle.
If you project the angles of your upper and lower A arms inward towards the opposite tire they should meet about 2 inches in from the opposite tire. If both A arms are parallel they will never meet. So lets put the bottom A arm parallel to the ground and so we have to tip the upper arm down to meet the lower arms projected line.
These ball joints are race proven over tens of years with slicks under extreme braking and turning conditions without a problem.
Your upper A arm does not carry load, the lower does. The upper maintains alignment of the wheel both in and out and backward and forward. The car will not fall down if you remove the upper ball joint. The wheel will flop over and then the car will fall but it is because the wheel has fallen over.
Put a jack under the lower control arm and the upper A arm can be safely removed.
I will find Chris's original post on these ball joints and show you pictures.
at first you said you wanted to basically raise the outer tip of the upper A arm in ralationship to the inner pivot point.....ok, we can't LOWER the inner pivot point without modifying hell....so we elect to raise the outer tip of the A arm...
which is making a taller spindle, effectively....
so, the stock ball joint is bolted on top of the arm, with stud and boot and body of joint joining the spindle....
SO to raise the a arm tip...why can't we just reverse the monting location??
and add a spacer if necessary???
To move the ball joint from mounting on top of the A arm to the underside would gain you very little. Yes you could add a spacer block and it should work but I am not planning that. They sell them for about $195.
These are replacement ball joint that are totally adjustable up to 1.5 inches greater then stock. I effect lengthening the spindle.
If you project the angles of your upper and lower A arms inward towards the opposite tire they should meet about 2 inches in from the opposite tire. If both A arms are parallel they will never meet. So lets put the bottom A arm parallel to the ground and so we have to tip the upper arm down to meet the lower arms projected line.
These ball joints are race proven over tens of years with slicks under extreme braking and turning conditions without a problem.
Your upper A arm does not carry load, the lower does. The upper maintains alignment of the wheel both in and out and backward and forward. The car will not fall down if you remove the upper ball joint. The wheel will flop over and then the car will fall but it is because the wheel has fallen over.
Put a jack under the lower control arm and the upper A arm can be safely removed.
I will find Chris's original post on these ball joints and show you pictures.
03-07-2003, 06:46 PM
#15
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Re: Ball joints and roll centres (norvalwilhelm)
This is the ball joint, maybe not the exact one but one like it http://www.colemanracing.com/section/index.htp?id=1191
These are the bolt in spacers. The long spindles do the same thing
These are bolt on, but arent adjustable and are a little pricey. http://www.drgas.com/promotor/spindleex.html http://www.hotrod.com/howto/50358/index.html
Hope this works
71 rodster did the searching and provided us with information. I just followed it.
These are the bolt in spacers. The long spindles do the same thing
These are bolt on, but arent adjustable and are a little pricey. http://www.drgas.com/promotor/spindleex.html http://www.hotrod.com/howto/50358/index.html
Hope this works
71 rodster did the searching and provided us with information. I just followed it.
03-07-2003, 06:50 PM
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Re: Ball joints and roll centres (norvalwilhelm)
They also make these things for the lower ball joint so you can angle the lower A arm upwards to move the height of the roll center. The other thing they can be used for is to adjust the ride height. With lowers installed you can lower the car up to 1.5 inches with just turning the adjustment on the ball joint.
There are alot more knowledgable fellows on this forum then me and they are not saying anything.
Help me out guys. Redvetteracer?
There are alot more knowledgable fellows on this forum then me and they are not saying anything.
Help me out guys. Redvetteracer?
03-07-2003, 07:23 PM
#17
Re: Ball joints and roll centres (norvalwilhelm)
Don't blame me! PROSOUTH started this years ago! If anything, blame my high bandwidth connection. Makes it to easy to research every little thought that pops into my head.
03-07-2003, 07:33 PM
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Re: Ball joints and roll centres (71roadster)
Chris, Coleman has a whole list of upper tubular A arms very reasonably priced. A whole page and all under $50. :) :)
Think about that.
Think about that.
03-07-2003, 08:38 PM
#19
Melting Slicks
Re: Ball joints and roll centres (norvalwilhelm)
Norval, let's see if I got this right. TO change the rool center you can change the upper or lower ball joint to give yourself an effectively longer spindle. Can you do both the upper and lower? It seems this would allow you to lower the car without cutting the springs which has always been a controversy and change the roll center at the same time. Would doing both be too much?
thanks
thanks
03-07-2003, 08:41 PM
#20
Re: Ball joints and roll centres (norvalwilhelm)
First off, Gene Coleman makes some excellent products for race cars. But just because they are made for race cars doesn't mean they are good for street cars. I have used those ball joints on my race car many times but I have also bent and broke them. Unlike a street car the suspension on a race car is dropped out of the car and inspected on a weekly basis to check for damaged parts. An open bearing design like that requires a lot of maintainance. Before I would use them on a street car I would call Gene and ask him his opinion.
That is not a correct statement. The roll center is the point at which weight will tranfer from one wheel to another during cornering. A high roll center will reduce weight transfer during cornering. A low roll center will induce weight transfer. The roll center is constantly moving during suspension movement.
The imaginary line drawn through the a-frames must go through the centerline of the inner pivot mounting point (a-frame bushings) and the centerline of the ball joint pivot. Just raising the a-frame without raising the pivot point can cause binding and will not accomplish what you want to do. Because of this spacers are not recomended. Longer ball joints or spindle must be used to raise the roll center.
There is no perfect roll center height. A high roll center with a low center of gravity (ie: small block car) can handle just as bad as a low roll center with a high center of gravity. (ie: big block car)
As far as no one hitting on this in the last 50 years, it is because for suspension to work everything has to be taken into account. Making a change in one thing will affect something else. Changing your roll center may require you to make changes in you center of gravity, ackerman angle, anti-dive, anti-squat, spring rates, shock tuning, caster gain, bump steer and sway bar rates. With 30 years of racing experience I still feel I know only a fraction of what is known on suspension geometry. Watch a Nascar race and you will see with just a few small adjustment you can turn a great handling car into an ill handling car.
Also not a completly correct statement. Straight arm sway bars are more responsive than a bent arm. But for a sway bar to be most effective it has to have the arm mounting as close to the end of the a-frame as possible. Some times this requires a bent arm. It become a trade off as to what is best for you application. If the arm is bent it will require a larger diameter bar or a more rigid arm as opppsed to a straight arm bar.
There are volumes of book on the fundementals of suspension geometry you can reference to get a basic understanding of how all these points work together. The best tip I can give is don't just focus on one thing (roll center) but try to understand how all of it works together to balance the car.
[Modified by Pete79L82, 7:43 PM 3/7/2003]
A roll center is the imaginary point about which our cars turn
The imaginary line drawn through the a-frames must go through the centerline of the inner pivot mounting point (a-frame bushings) and the centerline of the ball joint pivot. Just raising the a-frame without raising the pivot point can cause binding and will not accomplish what you want to do. Because of this spacers are not recomended. Longer ball joints or spindle must be used to raise the roll center.
There is no perfect roll center height. A high roll center with a low center of gravity (ie: small block car) can handle just as bad as a low roll center with a high center of gravity. (ie: big block car)
As far as no one hitting on this in the last 50 years, it is because for suspension to work everything has to be taken into account. Making a change in one thing will affect something else. Changing your roll center may require you to make changes in you center of gravity, ackerman angle, anti-dive, anti-squat, spring rates, shock tuning, caster gain, bump steer and sway bar rates. With 30 years of racing experience I still feel I know only a fraction of what is known on suspension geometry. Watch a Nascar race and you will see with just a few small adjustment you can turn a great handling car into an ill handling car.
I did quickly read about roll bars and the biggest rule in the book is that the arms bending back to attach to the lower A arms MUST be at right angles for the bar to work properly. Factory arms come off on a angle and this really screws up the effect of the bar. They stress the need for right angles. Monty has the nices settup I have seen
There are volumes of book on the fundementals of suspension geometry you can reference to get a basic understanding of how all these points work together. The best tip I can give is don't just focus on one thing (roll center) but try to understand how all of it works together to balance the car.
[Modified by Pete79L82, 7:43 PM 3/7/2003]