Sorry, 2Fast_Fiero here is the best I can do from your post.

4WS - Unlike the Nissan Hicas (spelling) system, which was electronically controlled, the Prelude used a simple (relative term) mechanical arrangement which was dependent entirely on steering wheel angle and not speed. At small wheel angles the rear tires steered with the front, this would stabilize the car but did cause some understeer. Larger steering wheel angles caused the rear wheels to turn the other way, counter to the front, this would increase manoeuverability at low speeds. The problem arises when you turn the wheel far enough to invoke the counter steer mode at a higher speed. The result is almost definitely a spin unless you can catch it with opposite lock (which may invoke countersteer again, in the other direction, result - car spins but in the opposite direction).

Nowadays companies design multilink rear suspensions which "steer" as a reaction to certain forces (passive steering), the Porsche 928 used a system which worked that way, the Weissach (spelling again) axle. The only four wheel steering (active steering) is on monster trucks and GM pickups. (Please, if there are any other 4WS systems feel free to correct me).

Maybe, on the dirt road, you were exceeding the steering angle and getting the "wrong way" steer which caused your spin.

4WS just gets in the way, which is probably why Honda let their system quietly dissappear from the North American market.

BTW, test out the Prelude and let me know the results, follow this simple procedure:
- park the car on a low friction surface like dirt or grass.
- while you watch the rear wheels, have someone turn the steering wheel through its complete range of motion.
- As the wheel nears its limit, do the rear wheels start to turn the other way?

Ira

[This message has been edited by Monza76 (edited 07-26-2003).]

Great over view Monza. The one thing to remove bump steer in the rear is goto solid control arm mounts on a 84-87. Per Herb Adams this removed almost all of it. The solid mounts are no longer offered By Moroso but I am working on locating 3 sets. If I can I will post where to find them. I think we may be able to get them for around $100.00 This is a lot cheaper than they use to be.

Well 2Fast_Fiero, did they knock it out of the park for you, get a base or three, or swing and miss?

Dr. Ira gave his usual, great classroom dissertation, and California Kid actually took his car out and put in knee deep in the gravel trap to illustrate it for you

I'll take a really Neanderthal-istic stab too. The thread and main topic of discussion is about taking a Fiero to its absolute limit in a corner and having the rear wheels lose traction and the rear end come around so fast and intently that it is virtually impossible to correct it. The result is an unwanted and uncontrollable spin.

The main discussion has been what causes it. Some suggested bumpsteer, some forward weight transfer (due to braking or throttle lift), and a good bit of discussion about tires sizes and the effect thereof.

The Fiero, with most of it mass (engine/trans) near the back is harder to collect once it does "step out".

If I have been too simplistic don't be offended. I was a straight line junkie, and handling theory moron, before I came to PFF and these guys have edjumicated me. If not you, I know there could be others out there like me, who even experimented with handling but had no real clue what was actually going on. Someone else have to start in Handling Kindergarten and work their way up too

Check out Ira's site too - great stuff!

Hey Ira what do you teach?

perk

[This message has been edited by perkidelic (edited 07-27-2003).]

"why does the Fiero rear step out so unpredictably?"

Inexpierence

There are literally a million reasons why, they range from the ground and end at the drivers head and every tangable thing in between and even the intangable thought process of the driver.

Ultimatly it is the responsibility of the driver to recognize and prevent it from happening.

[This message has been edited by 84Bill (edited 07-27-2003).]

quote Originally posted by hyperv6: Great over view Monza. The one thing to remove bump steer in the rear is goto solid control arm mounts on a 84-87. Per Herb Adams this removed almost all of it. The solid mounts are no longer offered By Moroso but I am working on locating 3 sets. If I can I will post where to find them. I think we may be able to get them for around $100.00 This is a lot cheaper than they use to be.

Are you talking about the original H.A. bushings? If you find them I'll take a set.
Also, the rear control arm UHMW solid bushings from 8shark are excellent, quiet and rock solid. www.8shark.com ,along with West Coast Fieros aluminum engine cradle bushings the rear now "keeps up" with any steering input immediately. This is the race car feel. Of course all basic suspension parts have been replaced. ty-rod ends, lowering springs, struts etc. Yea, hard bushings in the back are a must and did'nt change my comfort level at all. JD

[This message has been edited by vse1fiero@cox.net (edited 07-27-2003).]

So many opinions... so little time

Bottom line is that the wheel base is short, the weight is packed into a distribution that is rear bias and the majority of the folks driving these cars haven't figured out yet that the net effect is a PENDULEUM.

The mass if the car wants to rotate just behind the front wheels so, if pushed beyond adhesion, it WILL rotate.

I have read a few things that caught me off guard and are probably the biggest reasons why people DO loop their cars...

1 - The stock Fiero is NOT rear bias under braking. It's very much FRONT bias as with all cars. The more bias to the front under braking the LIGHTER the rear end is under braking which means, the LESS traction you have. Stepping over the rear traction threashold under braking is VERY easy becuase of this. Once it gets loose, the Tight Moment of Inertia (short wheel base, rear bias penduleum effect) takes over.

2 - "Bigger bars fix the problem" I hope nobody completely believes this. Any tuning done properly will help sure... but under it all the tight moment of inertial still lurks, waiting to be let out.

3 - Wider Tires... True to a point. Just be wary of on throttle UNDERSTEER which quickly jumps to off throttle OVERSTEER when you get into the corner to deep and deside a quick brake-n-steer is the best way out

4 - Power... Yes, more power will allow you to ride out a slide more effectively but just remember... this is NOT a drift car nor will it ever be. It CAN be done but even in the hands of a skilled and experienced driver the Fiero will loop 50% of the time. That line of minimal adhesion versus push is SO THIN... it's really easy to loose. And you WILL end up backwards.

The one point that everyone does have in common is that you will not know where that limit is unless you go out and FIND it. There is a place for that and it is called your local SCCA Club or Driving School. They will help you push your car and get experience at where your limit is. Yes, the earlier Fieros will find that limit sooner than the 88 but it IS out there and every fiero has it and once found, they ALL react the very same way.

Once you find it, you know where to stay away from. Unless you getting paid mega bucks to drive a car and take those risks... don't bother. I've seen to many dead race car drivers this year.

DKOV -

[This message has been edited by DKOV (edited 07-27-2003).]

The common element in the thread is experience. Find a safe way to learn how your Fiero handles near the limit (and beyond). Low polar moment cars with rearward weght bias are not tossable cars, as DKOV states, they would not make good drifters because once they let go the greater mass of the rear causes inertia to take over.

The point I was making is that with the stiffer rear bushings and solid cradle mounts the 84-87 cars behave a little closer to the 88s, bump steer is reduced since there is no longer as much uncontrolled motion (it cannot be eliminated since the suspension design hasn't been changed) and the breakaway characteristics are now determined more by the tires you use because again, we have eliminated the unnecessary compliance of the big rubber bushings.

As for the big rear sway bar, I think that is up to individual driver style, I don't mind a little understeer,(you can always use more caster to reduce that a little) and I am not looking for "ultimate road holding", I just want a predictable, fun car that feels good in daily driving and will not be embarassing in an occasional autocross (I don't care about being slow, as long as I don't loop it, get lost or plow over cones). I want a fun car, not a race car.

Ira

A fiero is rear bias even under braking and very much more so than a front engined car.

In theory, a perfectly balanced car the weight will be equal at both the front and rear wheels in a turn. The problem is that when decelerating that weight will shift causing an imbalance

Then there is the fact a body in motion will want to stay in motion and in a straight line. The heavy engine will effectively PULL the rear end out, it's that simple. Turning and braking in a fiero will not only take ground holding wieight off the rear but it will also pull it around.

Also worth mentioning is the "center of pressure" is ahead of a fieros "center of gravity" making it sensitive and snappy to directional changes. Put it this way if a fiero were a rocket it would be very unstable. The drag on the rear tires in a turn help it maintain it's stability but lessen the drag by moving the weight off and the force of inertia will take firm control of the situation.

Yel = CP
Red = CG during deceleration
Green = Static CG

Since the center of pressure is closer to the rear wheels and the CG is much further away from the directional wheels it makes this car much harder to take back control from the inertial forces acting on the rear.

The same thing works on a front engined car but the because the center of pressure is behind the CG it makes this car much more stable and seem lethargic since the weight is over the directional wheels. Inertia will still pull the rear around but since the CG is so far forward the rear wheels are more sensitive to inertia than to a shift in CG.

The center of pressure and CG is much closer to the directional wheels in a front engine car making it easier to overcome inertia should it take control of the rear.

I am thoroughly enjoying this thread. I can only speak from first hand experience in my 88GT. When the car was virtually new I got into an impromptu race with a Pustang -- it was night time, the road was badly lit and I was unfamiliar with the nuances of the asphalt. I was travelling at some 100km (~60mph) and leading -- the Pustang all of a sudden was braking and slowing down rapidly; then I quickly realized why -- the road took a very abrupt near 90 degree turn to the right -- no warning signs and the bank on the road was reversed -- "Holy it-shay" the only thing that I could think of as I cranked the wheel over was "Stay on the gas, keep your foot off the brake" -- miraculously the back end never came round -- but I swear that my passenger side wheels left the ground for an instant and I felt this awesome force coming back through the steering column (like I was carrying the full weight of the car in my hands!).

Needless to say I survived the potential disaster -- and you should have seen the face on the Pustang driver when he finally pulled up beside me...

[This message has been edited by Garethster (edited 07-27-2003).]

Well, since I started this great debate I'll share what I have learned.

It is obvious that the greatest factor is driver skill and experience. I have only spun twice in a Fiero. Once was because I feel asleep at the wheel, after having been up for 72 hours straight. I woke up in the grass spinning, so I can't tell you what caused the spin. Can't remember whether it was dry or wet outside but the grass was most likely at least very damp because it was early morning in the springtime. Driver error regardless.

The second loop-de-loop was totally my fault. I did one of my favorite exit ramp, which is sort of like a chicane, and came through the end a little too hot. It was wet and I found the limits of the rear tires' ability to adhere in those conditions. I always thought that I hadn't lifted, but in retrospect it is entirely possible that I did lift slightly when I felt the back stepping out a bit. Since most of the vehicles I had owned, up to that point, had been front-engine/rear drive it would have been a natural reaction.

On to the conclusions.

While the driver is the biggest factor, it is still evident that it is possible to raise the threshold. Basically what a good driver must do is find the fine line and consistently drive just on the safe side of it. That is all well and good, but I prefer the idea of significantly rasing the bar first.

perk

The only thing that will "raise the bar" is to make that rear end "stick" to the ground.
The fiero is by design unstable in a turn there is no way to make it more so unless the CP were behind the CG and that would mean moving the CG forward alot! A more powerfull lighter engine will go a long long way to achiving this.
The CP would be closer but still ahead of the CG which will still give you a responsive feel and because the inertia is lower at the rear it will reduce the pull and not require as much drag to keep things pointed in the proper direction.

Basicly get rid of as much weight from the rear as possible. Maybe can those big heavy cast knuckles for machined billet aluminum replacements. Maybe even have a shop create an aluminum engine cradle. Take out the sound profing and trunk carpet! remove the A/C compressor anything to reduce the weight on the rear and get the CG closer to the CP in a turn. You will still need alot of drag to make the rear stay under you but it will significantly raise the speed at which the car will swap ends.

84Bill, no problem with the graphics, I don't mind people using my pictures as long as they give credit, which you did.

I have a question about sway bars, tires and centre of pressure. When you add larger rear tires exactly what impact will it have on centre of pressure, will it move it forward or backward? Now the same question for a rear sway bar, will the addition of a rear bar move the CP forward or backward?

Ira

Thanks Ira
First I must say the CP is a very complicated creature and finding out where it is exacly on a fiero is no simple task.

My statement about the CP changing with the addition or removal of bars was not entirely accurate. What it does do is increase the effective (sideward) drag on the tires.

Because the CP is in front of the CG the only way it will remain realitivly stable is to increase drag on the rear in a turn. Just like on a rocket with a CP ahead of the CG requires larger stabilizing fins to keep it pointed straight. Drag is drag weather it is (erodynamic) air pushing on a fin or the (friction) tire dragged sideways across the ground.

So to answer the question I don't think it so much moves the CP but it creates more drag force on the rear tires and makes it harder for inertia to pull it out from under you. It may infact move the CP aft but this would only be speculation on my part.

BTW
I have never attempted to calculate the CP because it requires more brain power than I cam capable of mustering. It will be somewhere between the front and rear wheels since the CG is not very far from the center of the rear wheel it would be safe to assume it is ahead of it..

[This message has been edited by 84Bill (edited 07-27-2003).]

I understand the complexity of the concept, I would say that most of the successful modified Fieros probably grip well in the rear because the combination of wide tires and a rear sway bar increases the effective rear contact patch, as you put it, increasing drag.

The danger I see in this is that it would seem to imply that if you did unload these wheels by sudden throttle lift (or even braking) the breakaway would be more abrupt. Yet it seems that V8 engine swaps with SBCs or Northstars (both fairly heavy relative to stock engines) seem to benefit from the stiff rear, I guess the additional power on tap will catch the car more effectively than a weaker engine.

When I can afford it I will definitely do the rear bushings and mounts, and the wider rear tires. I have a Fiero front sway bar so I may mount it at the rear and go experiment with it to see what effect it will have with a stock powertrain. If I had enough money I think I would go with a Quad 4 swap and front mounted battery along with the suspension mods. I think that would be an effective way to get a more powerful, but still good handling, Fiero without extensive modifications.

Ira

The V8 does add to the gripping power of the rear wheels for sure and from what I understand it is offset by the battery in the front. Like a seesaw with a fat guy on one end close to the fulcrum and the thin guy way down the end can balance him out. Like I said in the very beginning getting a car to corner well can cost about as much as a shuttle launch and be as equally complex. That is to say that the battery helps slow the rise of the front end and cause even more downward force on the rear wheels. Or maybe the weight increase is just enough that it takes longer to shift faward fast and far enough to remove sufficient drag. I duno, but V8 fieros still swap ends.

Personaly I would like the ass end to stay planted as much as possible before I change the CG by moving weight from the rear and putting it in the front. If anything I'd just want to remove weight from the rear and see what effect it has on cornering.

[This message has been edited by 84Bill (edited 07-27-2003).]

quote Originally posted by 84Bill: The only thing that will "raise the bar" is to make that rear end "stick" to the ground...Basicly get rid of as much weight from the rear as possible. Maybe can those big heavy cast knuckles for machined billet aluminum replacements. Maybe even have a shop create an aluminum engine cradle. Take out the sound profing and trunk carpet! remove the A/C compressor anything to reduce the weight on the rear and get the CG closer to the CP in a turn. You will still need alot of drag to make the rear stay under you but it will significantly raise the speed at which the car will swap ends.

Exactly 84Bill, I will have:
> no sound proofing
> no A/C
> and no trunk to have any carpet in!!!
(actually no sheetmetal behind the rear firewall other than the factory main frame rails and then the down strut tubes from the cage.)

My rear suspension will be SLA with aluminum coil-overs so there will be a significant weight loss there, and I have been looking into billet uprights as well. There is a double benefit in that, as it will simultaneously reduce unsprung weight. I have even considered the aluminum cradle idea before, I may eventually fabricate one. The stock cradle is pretty light (I think 54lbs was posted in a thread once)so there isn't a ton of weight to lose for the money.

I will have an aluminum LS1 and something a little different for a drivetrain, which should all work out to about the same weight as a V6 Fiero. The rear end of the car will be lighter though because of all the other weight saving measures, and my transmission will be much further forward for a little better distribution.

Because of the need for increased "drag", as you put it, and the need for a little more traction for the larger more powerful motor the rear tires will be significantly wider.

perk

I don't know about you perk but I find that the Fiero, in well maintained stock form, is a very manageable car. The trailing throttle oversteer can be caught by getting back on the gas and the bump steer unsettles the driver more than the car. However, as we are seeing more and more big engined swaps we are seeing far more handling issues arise.

It has always been true that if you increase power you must upgrade the suspension for the extra power. If you do a good job of upgrading then you can add more power until you need to upgrade further. Eventually you will reach the design limitations, at which point the entire suspension must be reengineered. It is obvious from your post that this is where you are, redesigning the whole rear section of the car.

Personally I would rather have an underpowered car with excellent handling than a straight line car, that is because I like it that way. The next guy might be quite happy with a car which is slower in the turns but has the acceleration to scorch the straights. Who is right, both!!! The more powerful car will probably have better lap times around a road course (unless it handles really bad) and will be undoubtedly quicker on the drag strip. It will also draw the biggest crowds of admirers. The handling car should be quicker on an autocross course and may be more fun on twisted back roads, rewarding for the driver who likes that.

I know it is possible to have both but let me point out that people like Will and California Kid have cars that have had extensive, and expensive modifications done in order to achieve both. My budget barely allows for gas, so I can only look at maintaining my car, replacing worn parts like shocks and struts, and making small improvements like bushings. Therefore I tend to look at handling from a more frugal perspective. The stock Iron Duke behind my head makes handling a different issue, I must look for grip and stability and allow for a little more understeer since I may not have the engine to power out of a tail out slide. I can also make do with the stock braking system since my lower powered car is also fairly light and will not overwhelm the brakes with me driving. This means I have less unsprung weight, and can use 14" wheels (or even 13s) with low profile tires to keep unsprung weight even lower and effectively increase my gear ratio. The result is a pleasant, unintimidating car which is definitely not everones cup of tea.

I dearly love twisty roads and hopefully I can get this Fiero into shape so that I can truly enjoy those roads again.

Ira

Oops, I seem to have drifted away from the purpose of this post, I am sorry. I think the Herb Adams approach, a very stiff rear, seems to work best for most of these swaps, that is basically what Will is using, though not with the VSE parts. I may head in that direstion over time, the UHMW rear bushings look like a distinct possibility for the future, I like the look of larger tires on the rear (I was planning on eventually doing this anyway) and, as I have already said, I will be willing to try the "front bar on rear", at least until I see how it behaves.

[This message has been edited by Monza76 (edited 07-27-2003).]

[This message has been edited by Monza76 (edited 07-27-2003).]

This is one of the most educating threads I have ever read. I am truly thankful and impressed by the knowledge presented here. Although it feels like I've been driving my car for so long, I really only have about 5 months of driving experience with my Fiero. I must say that I really never gave much thought to the major handling differences between the Fiero and all the FWD cars I had driven previously.

The only times I have ever spun my car were during wet weather. Basically I did the dumbest thing possible and went around a turn, not accelerating into it, and then hammered the gas midway through. Basically with the force already heading into the turn, the wet road did not allow me to just pull straight out of the turn, instead the spinning tires basically created a frictionless surface for my car to spin around on. I understand that now and much more thanks to these posts.

quote Originally posted by DKOV: this is NOT a drift car nor will it ever be.

You are definately right about this. So many times I have put the Fiero into a drift (mainly for entertainment purposes) but from what I have now read, this makes perfect sense.

In conclusion, my driving habits will change in accordance with my new knowledge. Thank you to all who have given great input, you all deserve a positive rating.

------------------
Alex

1987 GT 2.8 V6

quote Originally posted by perkidelic: Exactly 84Bill, I will have: > no sound proofing > no A/C > and no trunk to have any carpet in!!! (actually no sheetmetal behind the rear firewall other than the factory main frame rails and then the down strut tubes from the cage.) perk

Did you notice a difference in the way the car cornered after removing the rear end weight??

Does it seem to hold the road any better?

quote Originally posted by Monza76: I know it is possible to have both but let me point out that people like Will and California Kid have cars that have had extensive, and expensive modifications done in order to achieve both.

Yep...I sure do have some bucks tied up in the "Kid"!!! But more importantly, the knowledge of all who have worked on this car since 1993. A 'light weight' SBC conversion with the right suspension treatments will corner better than most peoples abilities on this Forum (myself included). You have to learn how to manage this performance to be completely safe (preferably on a race track). My spin out experience at Waterford was an extreme careless mistake, because I didn't remember exactly where turn 1 was in order to get on the brakes early enough (and I was paying attention to too many other things during the pass). My error was so bad, that even if I had a car that would pull 2 G's I would still be going to the pit.

One of the reasons I posted requesting any pictures taken of my car at Waterford, was get a look at how the chassis was performing in turns. One of the things I wanted to do prior to going to Waterford was to re-torque the front urethane sway bar bushing, but didn't (they haven't been touched in 3 years). "Old Lar" posted one picture that showed me the suspension was holding pretty well, photo was taken just as I had turned into the apex of the turn (road is crowned a little but the car is staying pretty flat on both front and rear).

Later that aftenoon I had learned enough about the track to put the "Kid" into turns with either front tire singing a song, and the back end remained solid. I really enjoyed the experience as I would never attempt pushing those limits on the street.

[This message has been edited by California Kid (edited 07-27-2003).]

quote Originally posted by Monza76: Sorry, 2Fast_Fiero here is the best I can do from your post. 4WS - Unlike the Nissan Hicas (spelling) system, which was electronically controlled, the Prelude used a simple (relative term) mechanical arrangement which was dependent entirely on steering wheel angle and not speed. At small wheel angles the rear tires steered with the front, this would stabilize the car but did cause some understeer. Larger steering wheel angles caused the rear wheels to turn the other way, counter to the front, this would increase manoeuverability at low speeds. The problem arises when you turn the wheel far enough to invoke the counter steer mode at a higher speed. The result is almost definitely a spin unless you can catch it with opposite lock (which may invoke countersteer again, in the other direction, result - car spins but in the opposite direction). Nowadays companies design multilink rear suspensions which "steer" as a reaction to certain forces (passive steering), the Porsche 928 used a system which worked that way, the Weissach (spelling again) axle. The only four wheel steering (active steering) is on monster trucks and GM pickups. (Please, if there are any other 4WS systems feel free to correct me). Maybe, on the dirt road, you were exceeding the steering angle and getting the "wrong way" steer which caused your spin. 4WS just gets in the way, which is probably why Honda let their system quietly dissappear from the North American market. BTW, test out the Prelude and let me know the results, follow this simple procedure: - park the car on a low friction surface like dirt or grass. - while you watch the rear wheels, have someone turn the steering wheel through its complete range of motion. - As the wheel nears its limit, do the rear wheels start to turn the other way? Ira [This message has been edited by Monza76 (edited 07-26-2003).]

Incorect on my dads prelude...I have altho seen the 4WS you are talking about on Preludes. What I meant by MIMICING is that it mimics 4WS. You can park the car on a flat surface and turn the wheel hard over in any direction and the rear wheels do not move. If the car however leans in one direction, the suspension is setup to make the wheels turn. I have a brake program and brought up the pictures of the Lude Si, and it had the steering your talking about, not the one my dad has. Its held together by an arm which is bolted to the body, if the body starts to roll, the wheels will turn to comfensate. I've played with both the Fiero and the Prelude, and I can easily out manuver the PRelude with my Fiero if I was going up against myself. I was very impressed by the way the Fiero handles.

FWDs can have lots of cornering grip but the handling is usually not that interesting.

Ira

quote Originally posted by 84Bill: Did you notice a difference in the way the car cornered after removing the rear end weight?? Does it seem to hold the road any better?

Nope, but that may be because I haven't driven it yet

I said "will have" have because I haven't applied the weight savings to the real car yet. I have an 84 that I bought for $125 to use as a parts mule. I removed the trunk, and a bunch of other crap, from it to see how everything was put together and do a "dry run" before cutting my main car. All I have done to the "good car" (my 85) so far is gut the interior, and climate control system.

It was already lowered three inches, by the infamous method of clipping the factory coils. It had 225/50R-15 Hoosiers all the way around on Crager five spokes. It also has Moog problem solver adj ball joints, and new gas shocks, up front.

It had potential. Of course, cutting the springs made it race car stiff, but for what I used it for I kind of liked it. The ignition module went bad and I have been more interested in swapping the V8 in than getting the Duke running again.

I will likely have it back on the road with this same basic suspension setup so that I can get a feel for how each new "bright idea" affects the whole. I will get an aggressive alignment too.

Just for the record I never had a problem with the way my Fieros handled. As I mentioned, my two end swaps were totally driver error, and neither made me afraid to push the car again. I just kept reading about it here on PFF so I figured I'd better ask some questions before building a monster - I'm glad I did.

perk

quote Originally posted by 84Bill: Also worth mentioning is the "center of pressure" is ahead of a fieros "center of gravity" making it sensitive and snappy to directional changes. Put it this way if a fiero were a rocket it would be very unstable. The drag on the rear tires in a turn help it maintain it's stability but lessen the drag by moving the weight off and the force of inertia will take firm control of the situation.

Ok, so you want to get in depth here...

I guess you're used to dealing with aerospace stuff, by your use of the term "center of pressure". Let's change things and call that "center of traction" because that's more applicable to automotive use.

If a car is floating in outer space, and you push on it with the line of force through the CG, the car will move without rotating.

If the same car is on pavement, and you push on it with the line of force through the center of traction in plan view, then the car will slide without rotating.

If a Fiero has equal tires all around, and you push it sideways halfway between the front and rear tires, then it will slide sideways. Obviously, the center of traction is halfway between the front and rear tires.

If you put larger rear tires on the car, you move the center of traction aft, because you're increasing the grip at the rear end. You compute the fore/aft position of the CT just like you would the fore/aft position of the CG.

If a car's weight distibution is 45/55, then the CG is 55/(45+55) of the wheelbase aft of the front axle CL.
The CT can be determined in the same way, by considering the available traction at each end.

The cornering forces on a car are exerted at the CT.

If the CT is forward of the CG, then the car departs via a spin, because the cornering forces extert an oversteering moment on the CG. Vice versa for a CT aft of the CG. If the CT is on the CG, then the car is neutral.

If you do the algebra, you'll see that when the tire width matches the weight distribution, the CT is coincident with the CG.

Then you can make the car do anything you want by transferring weight around via throttle and brakes.

[This message has been edited by Will (edited 07-28-2003).]

What a great thread! If I can contribute .02, I'd agree getting more of the on-board weight up front (the battery) would probably help. I forgot who advocated keeping the spare in the front because they got better track times. If you go wider with the wheels in therear, you'll need a sway bar. remember the Fiero didn't come with one originally. Gerald Stvorik's UMHW bushings in the rear a-arms would be good for dealing with torque-steer, since the twisting of the rear a-arms caused a lot of alignment changes. And cradle bushings are a good idea poly or aluminum. Bump steer is the sudden alignment changes that are basically the result of the Fiero design. If you get the RCC kit, be sure to specify the change in suspension height first. I guess coil-overs are a bad idea with the RCC setup since it isn't easily adjustable. The Held kit would be better for that, but man is that expensive! Once you install the RCC kit, you cannot change the height again. Wheels don't have the same affect in this application.

------------------
John DuRette
Black 85 SE, undergoing work as we speak!

quote I stated earlier I believe it was Will who once posted that the percentage difference in tire width must be at least that of the percentage difference in weight, so 10% to 15% larger rear tires.

and then

quote Will wrote If you do the algebra, you'll see that when the tire width matches the weight distribution, the CT is coincident with the CG.

I beat you to it but I gave you full credit.

Ira

Sounds good to me Will but whatever you call it the principal is the same. I used the aerospace term because it makes the most sense to me. If you put a fiero on a pole it would want to put is arse end into the wind where as a normal car would nose first into the wind.
The logic is sound and I think it goes a long way in explaining how and why a mid engine car is radicly different. Even if the CT (as you call it) were behind the CG it is a heck of alot closer together than in a traditional car and it is known that the closer they are together the more sensitive a vehicle will be to directional changes.

Obviously cars are nothing like airplanes but one might be surprised how related they can be in how design efects performance. Some of the best performing aircraft are short and stubby (like a short wheelbase car) and the CG is much closer to the CP than a more stable aircraft. Unlike airplanes cars can use both the ground and air for stability and it's much more preferable that just air.

quote Originally posted by 84Bill: The logic is sound and I think it goes a long way in explaining how and why a mid engine car is radicly different. Even if the CT (as you call it) were behind the CG it is a heck of alot closer together than in a traditional car and it is known that the closer they are together the more sensitive a vehicle will be to directional changes.

To use an aircraft analogy, it's probably better to use center of lift as opposed to center of drag (Are these usually in the same location?) because lift is roughly perpendicular to direction of travel, just like cornering forces in a car. Drag is anti-parallel to the direction of travel.

quote Originally posted by Will: To use an aircraft analogy, it's probably better to use center of lift as opposed to center of drag

Center of Drag sound much more "gooder".

Man you guys are freakin awesome! The cream of the crop, the cat's meow, the pinnacle of intelligent life...

Seriously, this has turned out to be a great thread full of truly great wisdom. I can't wait to incorporate what I have learned here in the car.

84Bill I thought about it and decided that I am going to fabricate an aluminum cradle. I will start with the factory cradle, but will eventually replace it with my own creation. This, again, is to implement one change at a time and note the effects.

perk

What have you learned, perk?

Uh-oh pop quiz! I don't like you anymore

*One, there are no serious (read irreversible) design flaws which create the end swapping scenario. That was the main thing I wanted to know before investing mega bucks and hours into Project Lab Rat.

*Two, there are definite countermeasures that one can take which will raise the threshold at which the rear end will initiate the swapping procedure. I am going to an extreme in this regard, but I also understand the importance of a well thought out and executed suspension setup.

*Three, there is no substitute for driver competence, skill, and experience. To reap the full reward, and avoid the ultimate catastrophe, the monkey-in-the-middle must be up to the task.

*Four, even though it really fits within the second bullet's point, proper tire sizing is crucial.

*Five, I am going to get lost in the list of great automotive design and technical books made known to me here on PFF and get an even better undertanding of the theory behind the methods I plan to use. These threads help so much because I have at least a basic surface level of consciousness first, which makes comprehension much easier.

*Six, and this is gonna be a big one, I revised my build-up plan to allow me to test each "bright idea" one at a time and realize and document its effect on the whole, and make the appropriate "yea or nea" call on it; rather than do "the works" and then try to reverse engineer to find out what's actually doing what.

*Seven, thanks in great part to knowledgeable, patient, people like yourselves I am gonna have a BAADDDDDD Fiero!

Well, did I pass - huh did I did I??? Do I get to pick up a wrench now?

perk

Edit was to fix typos, for future junkies...

[This message has been edited by perkidelic (edited 07-29-2003).]

[This message has been edited by perkidelic (edited 07-30-2003).]

Well perk I think you definatly have enough information to be dangerous. I guess it would be safe to say your question was answered. Like I said before I love the way fieros handle even without modification, I relish the thought that my 90 hp bone stock coupe can out corner almost any car available to the general public. I will own a fiero until the day I go kicking and screaming to the great gig in the sky and if there is a way you can bet your arse I will take my fiero with me.

Anywho, keep us posted on your progress
Bill

PS
I was wondering if any of you guys take your car to a track. reason I ask is you could try putting a bag of concrete mix in the trunk and see what efect it will have on cornering. I would suspect that a 60lb bag will stiffen the rear suspension and if you have the battery up front and a healthy V6 on tap (just keep the revs up fairly high) the result may be quite interesting.

I like they way the Fiero handles. Kinda like the F-22. That thing cant actually fly on its own. Totally unstable. But thats what makes it so damn agile. I've heard people mention putting weight in the front. NO! never go for MORE weight. Take it out of the back. Maybe move wieght (the battery, great example) from the back to front, but do not add additional weight to the car. But anyways, the root of the thread - why does it step out so unpredictably? well, as we can see from all the posts - it isnt unprediactable - everyone knows it does! no, actually I'd say the short wheel base, and the even balance of the weight makes it seem that way. Take different cars at the same speed around the same curve, and see which rear steps out first. I will bet that our little fiero will be one of the last ones standing, and knowing this can tend make us stupid in the turns. Just because we can take turns better, doesnt mean we can take them twice as fast.