I don't think that would work. The car would roll towards the center of the corner, but the actual weight would still load the outside tires. When a car goes around a corner it is accelerating INWARDS, it's the car's inertia that loads the outside wheels. So despite the car rolling on its suspension and tilting inwards, the outer tires would still be loaded. In your circumstance, the only effect you'd create is that the passengers in the car would feel more downward force due to the tilting of the cabin. It's the same idea as a plane turning, when it banks the forces are transferred down on the passengers, instead of across them.

So it would seem you're always going to have some lateral weight transfer to the outside wheels.

quote Originally posted by Yellow-88: Roll angle has everything to do with weight transfer. If there is no roll, there is no weight transfer. Yes…..it is “G” forces working on the CG that causes the roll. It’s the roll that causes the weight transfer.

You're backwards. Weight transfer causes roll.

Go karts have weight transfer, but not roll.

As has been pointed out, a car with CG below roll centers would roll inward, but still transfer weight outward. No way around weight transfer. It's physics.

quote Originally posted by 88gtNewb: It's the same idea as a plane turning, when it banks the forces are transferred down on the passengers, instead of across them. So it would seem you're always going to have some lateral weight transfer to the outside wheels.

The plane in a banked turn is loading both wings equally, and balancing all the inertial forces against gravity. If it slows too much, it will begin to slide toward the inside wing, and the passengers will begin to feel force across them. Soon after, things will get nasty.

I think the comparison between aeronautical and automotive dynamics is a subject for another thread. As I recall, this started with… what will a rear roll bar do for….. I stand by the statement that, increasing rear roll stiffness will increase oversteer.

picture a train on a track, that is clear between the rails. the train has a ballast hanging down below the rails. the ballast is heavier than the train, and the train pivots/tips on the axles. when it goes into a turn, the ballast being heavier than the train will be what gets tipped outwards, while the train will tip inwards. the train wants to tip outwards, but is overwhelmed by the ballast. also, this is not gravity, it is centrifugal force.

also, banked turns are another thing to drive you crazy trying to imagine the weight shift forces.

anyways, back to sway bar. you will never know, untill you slap it on. every Fiero should have one. how big depends on to many things to just say bigger in front, bigger in rear, whatever. driving style, tire size & tire size stagger being the big variables. all you can do, is put it on, and see what happens. then you will know if you need more in front or more in back.

quote Originally posted by Yellow-88: Do karts really have noticable wight transfer? If so, is it from inside tires being compressed, and the outside one being lifted, because of the laterial force pushing sidways against the center of gravity? That would be a very tiny roll angle, but karts have very high CG's because most of the wieght is in the driver.

Of course they have weight transfer. Ever had one on 2 wheels? That's 100% weight transfer.
It's just hard to notice at amounts less than that as the frame flex and tires are the only suspension.
I don't know for sure though weither it's due to roll or not though.

quote increasing rear roll stiffness will increase oversteer

I 100% agree.

[This message has been edited by 88gtNewb (edited 06-24-2005).]

quote Originally posted by Yellow-88: I did really good in physics, and I'm having trouble imagining how the force of gravity can change direction. On a level road, gravity will always be pulling perpendicular to the road surface. If the chassis is square to the road, the CG will be centerd between the wheels. When it is levered left or right by laterial acceleration, the CG is rotated around the roll axis. Chassis wieght is shifted because the CG is no longer diretly above the roll axis. Do karts really have noticable wight transfer? If so, is it from inside tires being compressed, and the outside one being lifted, because of the laterial force pushing sidways against the center of gravity? That would be a very tiny roll angle, but karts have very high CG's because most of the wieght is in the driver. NOTE: This is just for livley dissusion, not to be a ....

Gravity is just a force. In fact, a gravitational field is indistinguishable from an accelerated frame of reference (Einstein).

A brick on a merry-go-round will have weight transfer. As I said before, it's a function of track width, CG height and lateral G. IOW, weight transfer is simply the result of the couple formed by the centripetal force exterted by the tires at the elevation of the pavement and the inertial tendencies of the car's mass exerted at the height of the CG. Weight transfer puts more load on the outside tire/suspension and unloads the inside tire/suspension. The outside suspension compresses and the inside extends... body roll.

I did Ok in physics, too.

Yellow-88: What the car guys call "weight transfer" is actually the relationship between the car's inertia and the direction of travel. When inertia pushes one way, and traction pushes another, you get "weight transfer". Obviously, the force of gravity remains constant.

Does that help?

[This message has been edited by Blacktree (edited 06-24-2005).]

Ok, imagine this... a rectangle that is absouletely rigid with no flex connected to the four wheels and holds them perfectly upright (no suspension)... and tires that are rocks with no sidewall flex (look out Fred Flinstone). Now, push the rectangle exactly sideways (like the cornering force acting on the CG of the car). If it slides exactly sideways, then there will be no weight transfer.

That said, there is no such thing as "absolutely rigid" and our tires are not rocks. Even a go cart has frame flex and the tires also act like springs. So in the "real world" cornering force causes the outside suspension to compress and the tires to deflect... along with the resulting weight transfer.

Another thing that is not being discussed here is tire pressure. Changing tire pressure does two things; it changes the "footprint" of the tire and the "spring rate" of radial tires. If tires are over inflated the middle will bow out like a baloon... if under inflated, the middle will bow in. The result of over/under inflation is less than the entire "footprint" of the tire making 100% contact along with the resulting loss in traction. In terms of "footprint" radial tires are not particularly sensative to over/under inflation. A pound one way or the other doesn't make a very big difference However, a pound difference makes a large difference in the "spring rate" of the tires. (Watch the NASCAR guys... they adjust the handling of their guys with tire pressue changes as often as any other adjustment.)

In the case that started this discussion, front tire pressures that are considerably off from ideal could indeed cause understeer (but not the chatter). It would certainly be worth a few tests with air pressure to see what the results are... and it's virtually free. Just don't go way low or way high on the pressures.

Oh yea, one other thing. Yellow-88 said "increasing rear roll stiffness will increase oversteer". That is absolutely correct. Roll stiffness can be increased with either springs or anti-roll bars.

so, you don't want to go to poly? i pollied the whole front of my car, and it handles like a dream. all the specs and numbers don't mean sh**. all i know, is it goes great and it hasn't spun out yet. and i've hit some corners pretty fast. it has let loose on wet roads, but nothing i couldn't handle.

quote Originally posted by GT Racer: Ok, imagine this... a rectangle that is absouletely rigid with no flex connected to the four wheels and holds them perfectly upright (no suspension)... and tires that are rocks with no sidewall flex (look out Fred Flinstone). Now, push the rectangle exactly sideways (like the cornering force acting on the CG of the car). If it slides exactly sideways, then there will be no weight transfer.

Well... this isn't entirely correct either. There will sill be "weight transfer" as long as the push (CG height) is not at the same elevation as the friction holding the car (contact patches).

Try visualizing this same rock tired car on a gimbal. Tilt it 30 degrees. Gravity still points down, but relative to the car, the force is down and to one side. This is the same way the acceleration looks to someone in the car. The acceleration vector now passes closer to the downhill wheel, which means that this wheel carries a greater portion of the vehicle's weight. Weight transfer without body roll...

Better yet, take your rock-tired car model and perch it on top of 2 weight scales. Orient it so the two left wheels are on one scale, and the two right wheels are on the other. Now push the model to the right (but not enough to make it slide). The right side scale will register more weight, whereas the left side scale will register less weight.

The higher the car's center of gravity, the more pronounced this effect will be. The principle is very similar to the mechanical advantage of a lever.

Well, yes and no. If you construct the "flinstone car" the way I did rigid frame/rock tires, center of mass at the same point as the roll center)... then no. However if the center of mass is say, 9 feet above the center of the wheels (9 feet above the roll center), then when you push on the center of mass, it will try to pick up the "inside" tires and weight will be transfered to the outside. But if Fred Flinstones car had 20 feet diameter tires with the same rigid frame (at the center of the tires) but the center of mass was 9 feet below the the center of the tires (and below the roll center) then when you push on the center of mass, then weight will be transfered to the "inside" tires. So you can see that weight transfer also has to do with the roll center. Now we are getting down to some serious handling stuff.

I guess the best way I can explain roll center is to imagine a pig on a barbeque spit. The roll center is the shaft that goes through the middle of the pig. Push on the pig above the shaft and it will roll one way (to the outside in our case)... push on the pig below the shaft and it will roll the other way.

Roll center is established by our suspension geometry. The front suspension establishes the front roll center, and the rear suspension establishes the rear roll center. An imaginary line betweek the two roll centers establishes the roll center of the car. If you raise the rear roll center, then more weight will be transfered to the outside front during cornering... and vice versa. (This is another area where the NASCAR guys adjust handling. They can raise or lower the rear panhard bar to change the roll center) Also, note that in the real world case of our cars, the roll center will always be blow the center of mass. Thus, If you push on the center of mass, weight will always be transfered.

So, back to the case at hand. You can see that if you screw up the roll center... by lowing the car without relocating the suspension pick-up points, you can seriously screw up the roll center. This can be most pronouced with McPhearson Struts. Lowering the rear of a Fiero too much could even make the roll center go BELOW GROUND! ... an understeer (greater than the factory designed in understeer) could be caused by rear roll center that is too low.

I have a sophistocated suspension analysis computer program that will give roll center information (along with camber change, bump steer and a lot of other stuff.) When I get a chance, I'll measure everything on my '88 and report back what I find. (It may be a while before I get back on this because it is not a trivial task. Every suspension point has to be very carefully measured in both the horizontal and vertical dimensions... even 1/4" off in a couple of measurements could screw up the results.)

this is very entertaining reading! I have a pretty good idea on the subject as most of you do. the hard part is trying to get it across...

quote Originally posted by GT Racer: Well, yes and no. If you construct the "flinstone car" the way I did rigid frame/rock tires, center of mass at the same point as the roll center)... then no. However if the center of mass is say, 9 feet above the center of the wheels (9 feet above the roll center), then when you push on the center of mass, it will try to pick up the "inside" tires and weight will be transfered to the outside. But if Fred Flinstones car had 20 feet diameter tires with the same rigid frame (at the center of the tires) but the center of mass was 9 feet below the the center of the tires (and below the roll center) then when you push on the center of mass, then weight will be transfered to the "inside" tires. So you can see that weight transfer also has to do with the roll center. Now we are getting down to some serious handling stuff.

No and no. Weight transfer does not depend on suspension geometry. A car with CG below roll center will transfer weight exactly the same as a car with CG above roll center; it will just experience body roll in the opposite direction.
Think about the car on the gimbal example.
Also, when the rock tired car accelerates, it transfers weight to the rear boulders, correct? It obviously does this without suspension movement because it doesn't have suspension. Cornering is no different. Weight transfer is the result of any G force other than straight down. Body roll or dive or squat are the RESULT of weight transfer, NOT the cause.

Weight transfer also happens during acceleration. A RWD car will have more accelerating traction than a fwd car due to weight transfer. Might be an easier example to invision.

When all the physica lessons are over;
do we use the rear swaybar or not?

I think it should be clear by now that adding a rear anti-sway bar... or any other modification changes should not be done without first figuring out all of the suspension variables. Everything is a matter of ballance. Too much rear "bar" (too much addition of roll stiffness) will make the car oversteer. If you are able to come up with a ballanced package including front & rear springs, as well as front & rear "bars" will improve handling. Just adding a rear "bar" is a shot in the dark.

[This message has been edited by GT Racer (edited 06-27-2005).]

Now back to the physics for a second...

Will,
Consider this. You said, "it will just experience body roll in the opposite direction.". To experience body roll in the oposite direction (toward the inside), the inside springs would have to compress and the outside springs would have to extend. The only you can compress a spring is to add weight to it and a spring will extend when weight is removed... and that's the only way a car could roll to the inside.

It is really a moot point since our cars all have their center of mass well above the roll center and all weight transfer will be to the outside. The important point I want to make with my example is the importance of the car's roll center and that changing your suspension without doing it right could screw it up.

quote Originally posted by GT Racer: Just adding a rear "bar" is a shot in the dark.

yeah, but its easy to do & cheap.
and untill someone puts out a formula with all the variables, thats all you can do.
every Fiero should have a rear sway bar.
and you'll never know how big or small a bar you need untill you take the "shot in the dark".

quote Originally posted by Will: Gravity is just a force. In fact, a gravitational field is indistinguishable from an accelerated frame of reference (Einstein). A brick on a merry-go-round will have weight transfer. As I said before, it's a function of track width, CG height and lateral G. IOW, weight transfer is simply the result of the couple formed by the centripetal force exterted by the tires at the elevation of the pavement and the inertial tendencies of the car's mass exerted at the height of the CG. Weight transfer puts more load on the outside tire/suspension and unloads the inside tire/suspension. The outside suspension compresses and the inside extends... body roll. I did Ok in physics, too.

I forgot to combine the forces, and got hung up on the word weight. The “weight force” has changed direction, and is now pointing more toward the outside tires. Roll is a manifestation of that new direction.

I think you did better than me in physics, Will.
I stand corrected.

quote Originally posted by GT Racer: ....So, back to the case at hand. You can see that if you screw up the roll center... by lowing the car without relocating the suspension pick-up points, you can seriously screw up the roll center. This can be most pronouced with McPhearson Struts. Lowering the rear of a Fiero too much could even make the roll center go BELOW GROUND! ... an understeer (greater than the factory designed in understeer) could be caused by rear roll center that is too low. I have a sophistocated suspension analysis computer program that will give roll center information (along with camber change, bump steer and a lot of other stuff.) When I get a chance, I'll measure everything on my '88 and report back what I find. (It may be a while before I get back on this because it is not a trivial task. Every suspension point has to be very carefully measured in both the horizontal and vertical dimensions... even 1/4" off in a couple of measurements could screw up the results.)

I’d love to see that printout. I’ve done it the hard way, and can see very clearly how lowering a strut suspension can really screw-up the roll center height. It looks to me like lowering the nose a bit more than the tail of a 88 Fiero will result it a roll axis parallel to the ground. It also looks like more than an inch in the rear is too much. Your printout is worth waiting for.

quote Originally posted by Yellow-88: I forgot to combine the forces, and got hung up on the word weight. The “weight force” has changed direction, and is now pointing more toward the outside tires. Roll is a manifestation of that new direction. I think you did better than me in physics, Will. I stand corrected.

it's easy if you sketch it out on a dry erase board

quote Originally posted by Pyrthian: yeah, but its easy to do & cheap. and untill someone puts out a formula with all the variables, thats all you can do. every Fiero should have a rear sway bar. and you'll never know how big or small a bar you need untill you take the "shot in the dark".

A “shot in the dark” is sometimes called "testing". Adjustable end links are just normal end links with a stiff little coil spring between the upper and lower ends. By starting with an overly stiff rear bar, you can adjust the stiffness by changing the coil spring. You only need the adjuster on one end.

Smooth, damp parking lots are good, safe places for testing.

quote Originally posted by Yellow-88: A “shot in the dark” is sometimes called "testing". Adjustable end links are just normal end links with a stiff little coil spring between the upper and lower ends. By starting with an overly stiff rear bar, you can adjust the stiffness by changing the coil spring. You only need the adjuster on one end. Smooth, damp parking lots are good, safe places for testing.

you need the adjustable link on both sides unless you are only making turns in one direction -

you can usually fine tune the sway bar system by simply changing out poly and rubber end links and pillow blocks -- ideally someone would make adjustable sway bars (that have multiple mounting points for the end link changing the distance of the link from the bar centerline) then you could easily change settings in a matter of minutes.

quote Originally posted by Kohburn: you need the adjustable link on both sides unless you are only making turns in one direction - you can usually fine tune the sway bar system by simply changing out poly and rubber end links and pillow blocks -- ideally someone would make adjustable sway bars (that have multiple mounting points for the end link changing the distance of the link from the bar centerline) then you could easily change settings in a matter of minutes.

I got my bar from a big pile of them at a swap meet, and I have no idea what it came off of. It is considerably thicker that a stock 88 bar. It’s mounted in poly blocks with very little resistance to rotation. I have a coil spring adjuster on one end, and it definitely affects both sides equally. There is 2” of movement before the spring bottoms, and I’m not sure if it ever has. I do know that with solid links, it was too stiff.

Yeah….different stiffness rubber end links, or blocks would work to fine tune a bar.

Yeah….changing the distance to the end link would be nice. How about finding one with long arms, and fabricating movable end links?

they do make sway bars with adjustable ends. roughly 1" movement. to much deflection if you go to far. also, just switching between rubber, poly & solid end links, you get MUCH adjustablitiy also. the bar size is only one variable. what shocks/struts you use affects what size bar. what spings you use affects what size bar. what size tires you have. you cannot plainly say "bigger in front" or "bigger in rear". you are forced to take the initial "shot in the dark". and as long as you have a good guess where to start, (which for many is just a front bar in back, or a Fiero store front & rear combo) you should be fine.

and also - lots of people dont actually race their car, or even approach hazardous speeds, they just like the "flat" go-kart feel.

quote Originally posted by jeffndebrus: When all the physics lessons are over; do we use the rear swaybar or not?

It sounds pretty unanimous. Yes. (??)

quote Originally posted by GT Racer: Now back to the physics for a second... Will, Consider this. You said, "it will just experience body roll in the opposite direction.". To experience body roll in the oposite direction (toward the inside), the inside springs would have to compress and the outside springs would have to extend. The only you can compress a spring is to add weight to it and a spring will extend when weight is removed... and that's the only way a car could roll to the inside. It is really a moot point since our cars all have their center of mass well above the roll center and all weight transfer will be to the outside. The important point I want to make with my example is the importance of the car's roll center and that changing your suspension without doing it right could screw it up.

Think about the force on the suspension links. The springs aren't taking it all...

Roll center front vs. rear will change the front to rear weight transfer during cornering. The higher the roll center in the rear, the more weight will be transfered to the front... less understeer, more oversteer. The same approach for the front... higher in front -> more weight transfers to the rear. Also, the roll center at each end moves up and down as well as side to side. So it is not nearly as simple as locating the line between the front and the rear along the center of mass of the car.

A picture will be worth 1000 words. A demo version of computer suspension analysis program I use can be downloaded. It has examples you can use to see how suspension changes affect the roll center along with camber, caster, bump steer, ackerman and a whole lot of other stuff. The web site is: http://www.performancetrends.com/SuspAnzr.htm

Note in the first example on the web page that the "model" has simultaneous roll, dive and steer inputs and that the roll center roll center has moved to the far right of the "model". (Also note all of the precise measurements that need to be entered into the program).

quote Originally posted by Will: Roll axis should be parallel to centroid axis, not necessarily level.

Centroid axis..??

quote Originally posted by Yellow-88: Centroid axis..??

Slice the car in the vertical-lateral plane into lots of thin slices. Find the CG of each slice. Draw a best-fit line through all the CG's... That's the centroid axis.You can see that in the Fiero it is higher in the rear of the car than in the front. The car will be most predictable with front and rear roll moments proportional to the car's weight distribution, which happens when the distance from the centroid axis to the rear roll center is the same as the distance from the centroid axis to the front roll center.

quote Originally posted by Will: Slice the car in the vertical-lateral plane into lots of thin slices. Find the CG of each slice. Draw a best-fit line through all the CG's... That's the centroid axis.You can see that in the Fiero it is higher in the rear of the car than in the front. The car will be most predictable with front and rear roll moments proportional to the car's weight distribution, which happens when the distance from the centroid axis to the rear roll center is the same as the distance from the centroid axis to the front roll center.

With that being the case, a traditional front engine rear drive live axle setup, would have a roll axis crossing the centriod axis.

In my crude analysis of the Fiero chassis, it seems that lowering the rear, lowers the roll center much faster than lowering the front. A 2” drop puts the rear just about on the road, and the front still well above it. The stock ride hide puts the front roll center lower than the rear.

So how many angels CAN dance on the head of a pin..??

I HAD A GOOD ONE THISAFTERNOON
getting on the interstate on a big on ramp loop i was doing about 70 and holding it just fine when i came up on an explorer, and had do let off and when i let off the drivers side rear tire slipped and the a$$ arround came arround on me, i spun it arround twice on the on ramp/ just where the on ramp meets the interstate, the ass came out and i almost saved it but lost it big time, did a couple whoopdie doo's and whipped it all the away arround twice right on the interstate
it was fine until i let off then the weight transfer must been enough for me to loose it, if i wouldnt have had to let off the gas i woulda been fine

would a rear bar have made this not happen?

it is the First time i have ever spun out in a fiero, (on dry pavement and not on pourpose )

no a rear bar would have made it worse

wider rear tires would have helped

SOFTEN THE OFFENDING END! A rear "bar" would stiffen the offending end.

But as usual it is not that simple. Transitional handling is when weight is being transfered. In this case when you let off the gas, weight was transfered away from the rear wheels and you went for an "E-ticket ride".

Shock absorbers (dampers) have the most affect on transitional handling. In this case, your front shocks may be too soft (bad) in compression damping or your rears may be too soft (or bad) in rebound damping. But... since you said in the beginning that you have cut springs... lowered the car... still have old rubber bushings... understeers and chatters around a corner... it sounds to me like you should back off on the street until you get your suspension problems worked out.

As I said before, all of the parts of the suspension have to be in ballance. Changing one thing affects everything else. When you modify a suspension, it needs to be done as a complete package. If you are taking a "shot in the dark" and then testing it on the street, you're looking to bend up your car... and maybe a trip to the hospital

quote Originally posted by GT Racer: SOFTEN THE OFFENDING END! A rear "bar" would stiffen the offending end. But as usual it is not that simple. Transitional handling is when weight is being transfered. In this case when you let off the gas, weight was transfered away from the rear wheels and you went for an "E-ticket ride". Shock absorbers (dampers) have the most affect on transitional handling. In this case, your front shocks may be too soft (bad) in compression damping or your rears may be too soft (or bad) in rebound damping. But... since you said in the beginning that you have cut springs... lowered the car... still have old rubber bushings... understeers and chatters around a corner... it sounds to me like you should back off on the street until you get your suspension problems worked out. As I said before, all of the parts of the suspension have to be in ballance. Changing one thing affects everything else. When you modify a suspension, it needs to be done as a complete package. If you are taking a "shot in the dark" and then testing it on the street, you're looking to bend up your car... and maybe a trip to the hospital

If you were in an under steer steady state, you’re front slip angles would be bigger than your rears. By unloading the rears, and shifting some weight forward, I would think that the front slip angles would get smaller and tuck the nose in. If it was extreme enough, you could switch from under to over steer just by backing off. ( ? ? GT Racer )

If there is soft rubber stretching and relaxing under changing load, who knows what will happen.

I agree with GT Racer. "Testing" on the real road could give us a bad reputation.

quote Originally posted by $Rich$: I HAD A GOOD ONE THISAFTERNOON getting on the interstate on a big on ramp loop i was doing about 70 and holding it just fine when i came up on an explorer, and had do let off and when i let off the drivers side rear tire slipped and the a$$ arround came arround on me, i spun it arround twice on the on ramp/ just where the on ramp meets the interstate, the ass came out and i almost saved it but lost it big time, did a couple whoopdie doo's and whipped it all the away arround twice right on the interstate it was fine until i let off then the weight transfer must been enough for me to loose it, if i wouldnt have had to let off the gas i woulda been fine would a rear bar have made this not happen? it is the First time i have ever spun out in a fiero, (on dry pavement and not on pourpose )

I'll echo the above sentiments that you do not have enough done to your car to be consistent when pushing this hard on the street. You NEED bushings in order to establish controllability and consistency in your car before trying to increase its limits.

That being said... What you experienced was textbook Fiero lift-throttle oversteer.

This phenomenon is a combination of the car's natural lift throttle reaction with the vaguaries of worn out bushings and the inability to countersteer soon enough because of the Fiero's very slow steering ratio.

Bushings in the rear suspension will go a long way toward giving you the ability to cope with this reaction. Running MUCH wider rear tires than front will reduce the severity of the reaction to the point that you can use to slow the car down fast when you run up behind someone.

Don't go pushing that hard on public roads again until you install some more mods. Imagine what would have happened if there had been a car in one of the lanes you spun through...

[This message has been edited by Will (edited 06-30-2005).]