Weight Bias and Handling

[Vettezuki]

Branched off the Cool C3 (http://motorgen.com/forum/showthread.php?t=13604) thread.

Putting a C5 trans in the back would make it more like 46/54.

That's actually closer to a race car ideal. It would help a lot with planting power as the weight is right over the drive axle.

[Ultraperio]

That's actually closer to a race car ideal. It would help a lot with planting power as the weight is right over the drive axle.

More weight in the back can actually make the car more tail happy, overloading the rear tires in a turn.
The main reasons you want a more rearward center of gravity is you are giving the front wheels more leverage authority over the cars moment of inertia, i.e. the car wants to change direction easier.

And having a rearward center of gravity allows more equal tire loading under braking allowing more total braking force to be applied.

[BRUTAL64]

That's actually closer to a race car ideal. It would help a lot with planting power as the weight is right over the drive axle.

My C2 is 43/57 from the factory.:drink:

[BRUTAL64]

More weight in the back can actually make the car more tail happy, overloading the rear tires in a turn.
The main reasons you want a more rearward center of gravity is you are giving the front wheels more leverage authority over the cars moment of inertia, i.e. the car wants to change direction easier.

And having a rearward center of gravity allows more equal tire loading under braking allowing more total braking force to be applied.

Your front tires have enough to do with sharing friction with both turning and braking.:boggled:

[Ultraperio]

Your front tires have enough to do with sharing friction with both turning and braking.:boggled:

Giving the front tires more leverage authority allows a greater change in direction with less tire loading.

Shifting your center of gravity rearward allows the rear tires to account for a greater percentage of total braking force. Offloading the front tires.

[Vettezuki]

More weight in the back can actually make the car more tail happy, overloading the rear tires in a turn.
The main reasons you want a more rearward center of gravity is you are giving the front wheels more leverage authority over the cars moment of inertia, i.e. the car wants to change direction easier.

And having a rearward center of gravity allows more equal tire loading under braking allowing more total braking force to be applied.

Thank you for the additional wholesome goodness of rearward COG bias. I was going for the simple dumb answer of launch traction. :mullet:

[enkeivette]

2010 Viper ACR: 49.5/50.5.
2005 Corvette: 51/49

:leaving:

Sorry guys, I believe the makers of these front engine rear drive supercars over yall when it comes down to what's best for a front engine rear drive car.

Seems simple enough to me, more weight in the front, more load on the tires, more understeer. More weight on the back, more load on the rear tires, more of a tendency to oversteer.

Equal weight distribution, neutral steer. Front engine rear drive cars always have slight oversteer. Putting more weight in the back would... make it worse. :nuts:

Yes, Ferraris and Porsches have a rear weight bias, but they also have the engine and your fat ass back there. I'm surprised they don't have more of a rear bias.

[Vettezuki]

. . . Sorry guys, I believe the makers of these front engine rear drive supercars over yall when it comes down to what's best for a front engine rear drive car. . .

These are street cars home slice. I was talking about idealized race cars. Ultraperio described it in more detail. And here's still some more.

Center of gravity forward or back

In steady-state cornering, because of the center of gravity, front-heavy cars tend to understeer and rear-heavy cars to oversteer, all other things being equal. The mid-engine design offers the ideal center of gravity.

When all four wheels and tires are of equal size, as is most often the case with passenger cars, a weight distribution close to "50/50" (i.e. the center of mass is mid-way between the front and rear axles) produces the preferred handling compromise.

The rearward weight bias preferred by sports and racing cars results from handling effects during the transition from straight-ahead to cornering. During corner entry the front tires, in addition to generating part of the lateral force required to accelerate the car's center of mass into the turn, also generate a torque about the car's vertical axis that starts the car rotating into the turn. However, the lateral force being generated by the rear tires is acting in the opposite torsional sense, trying to rotate the car out of the turn. For this reason, a car with "50/50" weight distribution will understeer on initial corner entry. To avoid this problem, sports and racing cars often have a more rearward weight distribution. In the case of pure racing cars, this is typically between "40/60" and "35/65." This gives the front tires an advantage in overcoming the car's moment of inertia (yaw angular inertia), thus reducing corner-entry understeer.

In short, if you need/want a car that will easily change direction, you want a rearward weight bias. You'll also tend to get oversteer in steady state cornering, but that's not the reason for the rearward bias.

[enkeivette]

These are street cars home slice. I was talking about idealized race cars. Ultraperio described it in more detail. And here's still some more.



In short, if you need/want a car that will easily change direction, you want a rearward weight bias. You'll also tend to get oversteer in steady state cornering, but that's not the reason for the rearward bias.

Your bold text says race cars and sports cars. Further, I don't see the difference. Still siding with Chrysler and GM on this one, sorry. :judge:

[BRUTAL64]

Giving the front tires more leverage authority allows a greater change in direction with less tire loading.

Shifting your center of gravity rearward allows the rear tires to account for a greater percentage of total braking force. Offloading the front tires.

Thus allowing the front tire to use most of it friction capabilities for stopping and turning the vehicle.:)

[Vettezuki]

Your bold text says race cars and sports cars. Further, I don't see the difference. Still siding with Chrysler and GM on this one, sorry. :judge:

Of course there cars work just fine. But if you give a pencil and blank piece of paper to a race car (hyper sports car) designer and say, make this handle as well you can on a course without restrictions, you're going to get a rearward bias NOT a 50/50 bias. Fin.

[jedhead]

Front engine Ferraris also have the engine behind the front axle. This not only shifts weight to the rear but reduces the polar moment of inertia allowing the car to respond to steering inputs better. If you do any driving in a Porsche or a Corvair, it can be difficult to get the car to turn especially when you are accelerating and if the rear does come around too much, oversteer, it is difficult to get the rear end from swapping very quickly. Mid engine cars have both low polar moment and some rear bias to help with accelerating and stopping.

Bob

[enkeivette]

Of course there cars work just fine. But if you give a pencil and blank piece of paper to a race car (hyper sports car) designer and say, make this handle as well you can on a course without restrictions, you're going to get a rearward bias NOT a 50/50 bias. Fin.

Fin? :sm_laughing: Going to try that in front of a judge someday. IMHO, if GM can put the motor up under the dash in a van, they can move the motor as far back as they want in the Vette. And they do have a blank piece of paper, they're GM.

[Vettezuki]

Fin? :sm_laughing: Going to try that in front of a judge someday. IMHO, if GM can put the motor up under the dash in a van, they can move the motor as far back as they want in the Vette. And they do have a blank piece of paper, they're GM.

I'll plead the 5th to a judge. :smack:

BTW, you may recall that ZAD, peace be eternally upon him, argued almost violently for a rear engined Vette back in the 60s. Just say'n. The marketing boys rightly or wrongly, insisted on sticking to the formula. Fiberglass. Front Engine. RWD. Two Seats.

[enkeivette]

That Vette looked stupid. They tried to keep the hood longish and it just looked retarded. They also tried to put a rotary in it, doesn't mean it was a better engine than the piston engine.

[Vettezuki]

That Vette looked stupid. They tried to keep the hood longish and it just looked retarded. They also tried to put a rotary in it, doesn't mean it was a better engine than the piston engine.

You're thinking of the Aerovette. It was much earlier.

[Chuck]

Can't we all just get along?

[enkeivette]

Can't we all just get along?

Nnnnnnnnno!

[Chuck]

Oh good times!! :laugh:

[Ultraperio]

2010 Viper ACR: 49.5/50.5.
2005 Corvette: 51/49

:leaving:

Sorry guys, I believe the makers of these front engine rear drive supercars over yall when it comes down to what's best for a front engine rear drive car.

Seems simple enough to me, more weight in the front, more load on the tires, more understeer. More weight on the back, more load on the rear tires, more of a tendency to oversteer.

Equal weight distribution, neutral steer. Front engine rear drive cars always have slight oversteer. Putting more weight in the back would... make it worse. :nuts:

Yes, Ferraris and Porsches have a rear weight bias, but they also have the engine and your fat ass back there. I'm surprised they don't have more of a rear bias.

"Sorry guys, I believe the makers of these front engine rear drive supercars over yall when it comes down to what's best for a front engine rear drive car."

Street cars, even spots cars, are full of compromises and may not be setup for absolute cornering performance in the name of stability and safety for their generally less than capable occupants. Compromise wise, front/rear weight balance is a trade off between passenger compartment space, car size, and available/designated engines. Safety wise, all street cars are built with a focus on under-steer because an under-steering car is safer and more controllable/recoverable than an over-steering car.

Sure you could jam the motor under a sports cars dash van style, but where are your legs going to go? how difficult is it going to be to service that motor? How are you going to deal with the added height needed for the clearance?

"Seems simple enough to me, more weight in the front, more load on the tires, more under-steer. More weight on the back, more load on the rear tires, more of a tendency to over-steer."

Obviously a cars over/under-steering tendencies are based on more than its CoG location. What the CoG's location dictates, and is harder to tune in with tires and suspension tuning, is its turn in behavior and how quickly it will rotate about tis center of gravity. This is mainly dictated by the cars weight and where that weight is carried relative to the the force used to rotate it (the deflection of the front tires)

"Yes, Ferraris and Porsches have a rear weight bias, but they also have the engine and your fat ass back there. I'm surprised they don't have more of a rear bias."

You have to consider the reason these 'money no object' sports cars are designed with the motor in the mid/rear. Its because of the ideal weight distribution for high performance handling and the easiest way (car design wise) to attain that distribution.

Porsche is kind of the oddity, they rear mount their motors just as much (possibly more) for nostalgic reasons as for performance.

[enkeivette]

You already have to drop the motor out of the bottom of the car and dismount it to install long tubes, so how much more difficult can it get?

And no, all street cars are not built with understeer. Most are, yes. But the two examples that I've been leading with both have an oversteer bias from the factory.

Your philosophy sounds intelligent, but any way you slice it, with a front engine rear drive car that already has a tendency to oversteer, putting more weight in the back is just going to make that worse. Bet on it.



I'm not making any claims about rear engine cars.

[Ultraperio]

You already have to drop the motor out of the bottom of the car and dismount it to install long tubes, so how much more difficult can it get?

And no, all street cars are not built with understeer. Most are, yes. But the two examples that I've been leading with both have an oversteer bias from the factory.

Your philosophy sounds intelligent, but any way you slice it, with a front engine rear drive car that already has a tendency to oversteer, putting more weight in the back is just going to make that worse. Bet on it.



I'm not making any claims about rear engine cars.

You have to separate over-steer due to chassis setup and oversteer due to which wheels are driven.

When I talk about over-steer and under-steer I'm talking about steady state cornering tendencies with no throttle influence. Sure you can get any reasonably powered RWD car to over-steer very easily, but that is an entirely separate issue from the chassis tendencies. I haven't driven a viper so i cant speak from experience, but i do know at the limit(however high) late model corvettes tend to under-steer. You're not going to get a corvette to over-steer unless you give it some power, turn in under hard braking, or give it a scandinavian flick.

You are making blanket statements about over-steer. A rear biased car will not always over-steer more than a front biased car. For instance again under hard braking in a turn a front biased car can unload the rear wheels to the point of loss of traction. In a rear biased car the additional weight over the rear wheels might keep them loaded up and prevent over-steer.

Another example on the other hand is what jedhead alluded to. A rear heavy car will tend to under-steer on corner exit under power. This is because of the weight transfer unloading the front wheels. A front heavy car will plant more effectively on corner exit under power. This is actually the current GT2's achilles heel as it has too much power and too little weight in the front causing near loss of control(due to under-steer) under hard acceleration in a turn.

[enkeivette]

No blanket statements. Statements from reading motor trend magazine for years. They tested all the hot cars a few years ago and published a report. Vipers and Vettes had slight oversteer. And I'm pretty sure they know the difference between breaking the tires loose with the motor and breaking the tires loose with lateral g force.

So, yes, a Corvette will oversteer in neutral. Wanna go for a ride? I'll show ya. And as physics would have it, more weight in the rear would make that bias worse.


The Corvette frame has been completely transformed 3 times since my frame was conceived in 1963. The front end is about 2 feet shorter now and the transmission is in a different spot. I don't believe that maintaining a 50/50 weight distribution again and again was an accident. Too much has changed and the weight distribution is no accident. The fact that the other American front engine rear drive supercar has almost the exact same weight distribution with a different frame, engine, and transmission location is no coincidence either.

I'm not saying they got it exactly where they wanted it, I agree there is always a need to compromise. But I'll bet 50/50 was and always has been their goal.

[BRUTAL64]

:popcorn:

[BRUTAL64]

Another example on the other hand is what jedhead alluded to. A rear heavy car will tend to under-steer on corner exit under power. This is because of the weight transfer unloading the front wheels. A front heavy car will plant more effectively on corner exit under power. This is actually the current GT2's achilles heel as it has too much power and too little weight in the front causing near loss of control(due to under-steer) under hard acceleration in a turn.

Well, I'd like to agree-- but my C2 may have it own ideas. It goes into the corner with a little under steer and goes to OVER STEER in the middle and neutral out.

That's with a 47/53 weight. Over the years it has always been this way.:boggled:

[Ultraperio]

No blanket statements. Statements from reading motor trend magazine for years. They tested all the hot cars a few years ago and published a report. Vipers and Vettes had slight oversteer. And I'm pretty sure they know the difference between breaking the tires loose with the motor and breaking the tires loose with lateral g force.

So, yes, a Corvette will oversteer in neutral. Wanna go for a ride? I'll show ya. And as physics would have it, more weight in the rear would make that bias worse.


The Corvette frame has been completely transformed 3 times since my frame was conceived in 1963. The front end is about 2 feet shorter now and the transmission is in a different spot. I don't believe that maintaining a 50/50 weight distribution again and again was an accident. Too much has changed and the weight distribution is no accident. The fact that the other American front engine rear drive supercar has almost the exact same weight distribution with a different frame, engine, and transmission location is no coincidence either.

I'm not saying they got it exactly where they wanted it, I agree there is always a need to compromise. But I'll bet 50/50 was and always has been their goal.

50/50 may have been the goal. 50/50 weight distribution may indeed be the best compromise for a street car but this does not make it ideal. What i am saying is in terms of outright performance a rearward weight bias allows for quicker changes in direction and better braking performance which is proven time and again by purpose built race cars and very high performance street cars.

[Ultraperio]

Well, I'd like to agree-- but my C2 may have it own ideas. It goes into the corner with a little under steer and goes to OVER STEER in the middle and neutral out.

That's with a 47/53 weight. Over the years it has always been this way.:boggled:

Again, over/under steering tendencies are not just effected by weight bias. Suspension setup/alignment, damper and spring rates, and relative tire sizes pressures and compounds all greatly effect a cars tendencies around a corner.

Besides, 47/53 isn't exactly what I'd call 'tail heavy' ;)

[enkeivette]

50/50 may have been the goal. 50/50 weight distribution may indeed be the best compromise for a street car but this does not make it ideal. What i am saying is in terms of outright performance a rearward weight bias allows for quicker changes in direction and better braking performance which is proven time and again by purpose built race cars and very high performance street cars.

The Viper broke the lateral G record in 97 with its 50/50 weight distribution, not sure who has it now. Probably the Mosler, but that's not really a fair take since the Mosler comes factory with slicks.

I won't argue your point about race cars, because I really don't know. And maybe a rear weight bias works better with Porsches and Ferraris, I really don't know. But it doesn't with Vettes and Vipers, so I really can't agree that your theory has been proven time and time again with very high performance street cars. Unless you can provide examples like I've been doing. :p

IRAC-RAFADC! :suicide:

[Chuck]

I am with Brutal on this one!

:popcorn:

[Vettezuki]

. . .

Your philosophy sounds intelligent,

Actually, it's called physics. Different discipline.

but any way you slice it, with a front engine rear drive car that already has a tendency to oversteer, putting more weight in the back is just going to make that worse. Bet on it.



I'm not making any claims about rear engine cars.

Out of curiosity, what mystical life force differentiates a FRWD with say 45/55 and RRWD with 45/55 all other things being equal? We're controlling for weight bias (and punting on mass centralization a bit).

[Vettezuki]

I don't think this thread has enough hostility yet. I'm inviting Carlos. . . stand by. (I may regret this. It's sort of like releasing the Kraken.)

[BRUTAL64]

Again, over/under steering tendencies are not just effected by weight bias. Suspension setup/alignment, damper and spring rates, and relative tire sizes pressures and compounds all greatly effect a cars tendencies around a corner.

Besides, 47/53 isn't exactly what I'd call 'tail heavy' ;)

Ok, I was wondering when we would get to this. First with all the aluminum I have up front --heads, intake (plus stuff removed) I would have even less on my front tires.(all the stuff I removed lifted my spring height 1 inch)

Ok, slightly positive camber in front with as much caster I could get into it.

Negative camber in back, plus over size tires and a sway bar.

Yep, this all makes a difference in an OLD C2 that gives the newer cars a real bad time on the twists!

Now, if I only had some brakes.:boggled::inout:

[BRUTAL64]

I don't think this thread has enough hostility yet. I'm inviting Carlos. . . stand by. (I may regret this. It's sort of like releasing the Kraken.)

I like Carlos. I welcome his input.:thumbs_up:

[enkeivette]

Actually, it's called physics. Different discipline.



Out of curiosity, what mystical life force differentiates a FRWD with say 45/55 and RRWD with 45/55 all other things being equal? We're controlling for weight bias (and punting on mass centralization a bit).

I totally agree, although his philosophy sounds great, physics is what really matters. :p

[enkeivette]

I don't think this thread has enough hostility yet. I'm inviting Carlos. . . stand by. (I may regret this. It's sort of like releasing the Kraken.)

I feel like I'm in a trench and you just announced that you're throwing a grenade in here. We may learn a valuable lesson, but at what cost? At what cost Ben?

[enkeivette]

Adam posting on Motorgen at 4 am, it could only mean one thing... paper due tomorrow!

[BRUTAL64]

Adam posting on Motorgen at 4 am, it could only mean one thing... paper due tomorrow!

Glenn posting at 3:48 am, it could only mean one thing... X Box!:boggled:

[enkeivette]

Glenn posting at 3:48 am, it could only mean one thing... X Box!:boggled:

I went to bed at 7:03, then still had to wake up for class. Beat that!

[BRUTAL64]

I went to bed at 7:03, then still had to wake up for class. Beat that!

Better you than me.:lmfao:

I went to school at one time. I know how tough it can be.:hail:

Unlike me, I know it will do YOU some good.:bigthumbsup:

I know you will make the best of it.:drink:

[BADDASSC6]

There is a lot of miss information here. I'm on my blackberry so bear with me. There are obviously a lot of factors, but let's focus on the ones that are most pertinent. Let's talk about center of gravity, polar momentum, and corner weights. The center on gravity of a car is actually three dimensional. It is a point in the X Y Z axis of the car. For this discussion I will be referring to X or longitudinal axis. The moving the center of axis forward or aft will change the ratio of effort that the front and back wheels must do to rotate the car around it's COG. Polar momentum is a function of how hard to rotate the car the closer the mass of the car is to the COG the easier it is to rotate. Corner weights are affected by the COG and the overall car weight. Corner weight are the amount of force applied to the tires. As more weight is applied the greater they grip. let's apply this to a corvette. It has a slightly forward COG with relatively high polar momentum and has perfect weight distribution. Read a magazine and you would believe that it oversteers, that's flat out wrong. C6 understeer! They have tons of torque so if you rape the pedal it will step out, but driven correctly you can go flat out very early. Most vettes races run almost square tires. I run 275 fronts and 295 rears. The car is corner balanced 50/50, but before my new rims (245 fronts old) I Rand slight front heavy for more front end grip. Remember that changing corner weights changes the force applied downward to the tire, but does not change the polar momentum or the amount of grip required to move the front or rear. if you can drive then you are consiously managing the shifting weight of the car to make it turn in track out slide whatever.

[enkeivette]

There is a lot of miss information here. I'm on my blackberry so bear with me. There are obviously a lot of factors, but let's focus on the ones that are most pertinent. Let's talk about center of gravity, polar momentum, and corner weights. The center on gravity of a car is actually three dimensional. It is a point in the X Y Z axis of the car. For this discussion I will be referring to X or longitudinal axis. The moving the center of axis forward or aft will change the ratio of effort that the front and back wheels must do to rotate the car around it's COG. Polar momentum is a function of how hard to rotate the car the closer the mass of the car is to the COG the easier it is to rotate. Corner weights are affected by the COG and the overall car weight. Corner weight are the amount of force applied to the tires. As more weight is applied the greater they grip. let's apply this to a corvette. It has a slightly forward COG with relatively high polar momentum and has perfect weight distribution. Read a magazine and you would believe that it oversteers, that's flat out wrong. C6 understeer! They have tons of torque so if you rape the pedal it will step out, but driven correctly you can go flat out very early. Most vettes races run almost square tires. I run 275 fronts and 295 rears. The car is corner balanced 50/50, but before my new rims (245 fronts old) I Rand slight front heavy for more front end grip. Remember that changing corner weights changes the force applied downward to the tire, but does not change the polar momentum or the amount of grip required to move the front or rear. if you can drive then you are consiously managing the shifting weight of the car to make it turn in track out slide whatever.

Ok, you have a C6 and you race it. I won't argue, if you say they understeer, they understeer.

So do you think it would be better to have more of a 47/53 46/54 weight balance?

[Vettezuki]

There is a lot of miss information here. I'm on my blackberry so bear with me. There are obviously a lot of factors, but let's focus on the ones that are most pertinent. Let's talk about center of gravity, polar momentum, and corner weights. The center on gravity of a car is actually three dimensional. It is a point in the X Y Z axis of the car. For this discussion I will be referring to X or longitudinal axis. The moving the center of axis forward or aft will change the ratio of effort that the front and back wheels must do to rotate the car around it's COG. Polar momentum is a function of how hard to rotate the car the closer the mass of the car is to the COG the easier it is to rotate. Corner weights are affected by the COG and the overall car weight. Corner weight are the amount of force applied to the tires. As more weight is applied the greater they grip. let's apply this to a corvette. It has a slightly forward COG with relatively high polar momentum and has perfect weight distribution. Read a magazine and you would believe that it oversteers, that's flat out wrong. C6 understeer! They have tons of torque so if you rape the pedal it will step out, but driven correctly you can go flat out very early. Most vettes races run almost square tires. I run 275 fronts and 295 rears. The car is corner balanced 50/50, but before my new rims (245 fronts old) I Rand slight front heavy for more front end grip. Remember that changing corner weights changes the force applied downward to the tire, but does not change the polar momentum or the amount of grip required to move the front or rear. if you can drive then you are consiously managing the shifting weight of the car to make it turn in track out slide whatever.


What's the primary design reason for the purpose built race cars (formula whatever) and high end exotics for having rather strident rearward weight biases? Or is that just a function of some other design requirement? (I understand the goal of mass centralization around the COG to optimize PMI.) Obviously for one thing they're using aero to create down force for grip which changes what they can do in the first place.

Obviously the ZR1 and ACR do pretty well stock to stock against the exotics at the Ring, so they certainly manage :) Though, while I have no experience, the thing that seems to be repeated as an observation comparing say a 430 to a ZO6 is that it is much harder to drive the ZO6 at its limits. The Ferrari requires less controlling ability. This is comparing relatively similar levels of non-driver assistance. (i.e., it's not a GT-R that drives itself.) :huh:

[BRUTAL64]

There is a lot of miss information here. I'm on my blackberry so bear with me. There are obviously a lot of factors, but let's focus on the ones that are most pertinent. Let's talk about center of gravity, polar momentum, and corner weights. The center on gravity of a car is actually three dimensional. It is a point in the X Y Z axis of the car. For this discussion I will be referring to X or longitudinal axis. The moving the center of axis forward or aft will change the ratio of effort that the front and back wheels must do to rotate the car around it's COG. Polar momentum is a function of how hard to rotate the car the closer the mass of the car is to the COG the easier it is to rotate. Corner weights are affected by the COG and the overall car weight. Corner weight are the amount of force applied to the tires. As more weight is applied the greater they grip. let's apply this to a corvette. It has a slightly forward COG with relatively high polar momentum and has perfect weight distribution. Read a magazine and you would believe that it oversteers, that's flat out wrong. C6 understeer! They have tons of torque so if you rape the pedal it will step out, but driven correctly you can go flat out very early. Most vettes races run almost square tires. I run 275 fronts and 295 rears. The car is corner balanced 50/50, but before my new rims (245 fronts old) I Rand slight front heavy for more front end grip. Remember that changing corner weights changes the force applied downward to the tire, but does not change the polar momentum or the amount of grip required to move the front or rear. if you can drive then you are consiously managing the shifting weight of the car to make it turn in track out slide whatever.

Good stuff!:thumbs_up:

[Ultraperio]

The Viper broke the lateral G record in 97 with its 50/50 weight distribution, not sure who has it now. Probably the Mosler, but that's not really a fair take since the Mosler comes factory with slicks.

I won't argue your point about race cars, because I really don't know. And maybe a rear weight bias works better with Porsches and Ferraris, I really don't know. But it doesn't with Vettes and Vipers, so I really can't agree that your theory has been proven time and time again with very high performance street cars. Unless you can provide examples like I've been doing. :p

IRAC-RAFADC! :suicide:

A cars cornering limits (what a lateral G on a skidpad tests) are dictated by far more than the cars CoG and is a separate discussion to the current one. We're discussing a cars tendencies approaching and past its limits, due to the location of its CoG. An under-steering or an over-steering car can post very good lateral G numbers but it 's lateral G numbers aren't necessarily a function of its under/over-steering tendencies or its CoG location. And its lateral G numbers aren't necessarily a good indication of how well handling a car it is (tho lateral road holding is definitely a contributing factor to a well handling car).

I think calling 50/50 the "perfect" distribution is a misnomer or possibly a bit vague as to what it is "perfect" at. I will not argue that several of the best handling road cars were designed with 50/50 weight distribution as a goal. However you only hear this as a goal for front engine, rear drive cars. I've never heard of Ferrari putting mass forward to try to 'correct' its rearward biased cars. My personal favorite, the 3rd gen RX-7 (one of the best street/track cars of the 90's), was even marketed with its 50/50 weight distribution (also another under-steering car) as one of its main selling points. 50/50 weight distribution may be "perfect" in that it is balanced front to rear and it may be "perfect" in that it is the best compromise between stability/safety and and good responsive handling but It is not "perfect" when building a car for maximizing its handling potential.

Another interesting thing to consider is most/all 'exotic' mid/rear engined sports cars either have a base AWD option (Gallardo, Mercialago, 911 turbo), have a plethora of electronic nannies (every Ferrari out there) to keep the car stable, or try to kill you at every less than perfect attention opportunity (aforementioned Mosler). Possibly because the additional responsiveness comes at the price of less predictable, more dangerous handling characteristics at the limit (i.e. snap over-steer, something that has plagued Porsche's for years) which would be acceptable on a race track with a savvy driver but unacceptable on public roads with your typical driver. Thus requiring either a more deft driver, some under-steer inducing AWD, or little black box to keep your foot out of it and the nose pointed in the direction you're traveling.

Remember the trouble they had with keeping MR2's on the road?

Another thing that I would contest is the idea of "add weight receive grip" in regards to corner weighting. I think its a little more complicated than that but that might be beyond the scope of this thread.

[BRUTAL64]

"snap over-steer"--the first time I heard that was in the 60s. It was in reference to a Porsche.:boggled:

C2 and C3 Vettes can get the same problem because of great camber and toe out changes at full travel. That why I limited my rear travel with a sway bar.:crutches:

[Vettezuki]

"snap over-steer"--the first time I heard that was in the 60s. It was in reference to a Porsche.:boggled:

C2 and C3 Vettes can get the same problem because of great camber and toe out changes at full travel. That why I limited my rear travel with a sway bar.:crutches:

How bout stopping in a straight line? C3s in stock form can do some mighty exciting things if you hit the brakes at high speed.

[BRUTAL64]

How bout stopping in a straight line? C3s in stock form can do some mighty exciting things if you hit the brakes at high speed.

Yep, the same changes in toe and camber can happen with the rear suspension under braking load. BUT, the rear suspension does not move as much as it does on hard cornering.

The front suspension has it bump steer quirks to. But not quite as bad as the rear. Limiting travel helps there also.

[Ultraperio]

"snap over-steer"--the first time I heard that was in the 60s. It was in reference to a Porsche.:boggled:

C2 and C3 Vettes can get the same problem because of great camber and toe out changes at full travel. That why I limited my rear travel with a sway bar.:crutches:

I'm not familiar with C3 suspension. Is the toe change due to changes in geometry through its travel or load induced bushing deflection?

[BRUTAL64]

I'm not familiar with C3 suspension. Is the toe change due to changes in geometry through its travel or load induced bushing deflection?

C2 an C3 have basically the same chassis.

It actually both. But. most comes from the toe change as the rear moves in an arc from lowest to highest. The camber change can be as much as 5 degrees also.:rolleyes2:



Over that last 35 years I learned to use the snap over steer to my advantage.

At any time over 120 mph (road pitch change) you can end up 180 degrees different than you wanted-- yep, did that on Mar Vista in Whittier / 1976.:smack:

[Ultraperio]

RX-7's and possibly 300zx's if i remember correctly had 'passive rear steer' where strategically placed bushings allowed passive toe out on the outside rear under load when in a corner giving the car over-steer like behavior without loss of traction. Problem is, when the bushings inevitably wear out you have some wacky toe situations which unsettle the car.

Solution is delrin or urethane bushings to stiffen up play or aftermarket solid toe links to eliminate the setup entirely.

[BRUTAL64]

RX-7's and possibly 300zx's if i remember correctly had 'passive rear steer' where strategically placed bushings allowed passive toe out on the outside rear under load when in a corner giving the car over-steer like behavior without loss of traction. Problem is, when the bushings inevitably wear out you have some wacky toe situations which unsettle the car.

Solution is delrin or urethane bushings to stiffen up play or aftermarket solid toe links to eliminate the setup entirely.

For C2 and C3 trailing arms--the best is a "johnny Joint".:)

[Ultraperio]

This reminds me, I have a model of the majority of a C4's rear suspension/differential in accurate dimensions in solidworks if anyone is interested and dabbles in that sort of thing.

Credit goes to the creator, unfortunate i cant remember who or where.

http://img715.imageshack.us/img715/5103/43665032.jpg

[BRUTAL64]

This reminds me, I have a model of the majority of a C4's rear suspension/differential in accurate dimensions in solidworks if anyone is interested and dabbles in that sort of thing.

Credit goes to the creator, unfortunate i cant remember who or where.

http://img715.imageshack.us/img715/5103/43665032.jpg

You have drawings to use a C4 diff in an C2/3??

[Ultraperio]

You have drawings to use a C4 diff in an C2/3??

I don't have anything C2/3 related but that model does have all bolt holes. Would just be a matter of understanding the diff mount setup in the C2/3 and getting measurements. :thumbs_up:

[BRUTAL64]

I don't have anything C2/3 related but that model does have all bolt holes. Would just be a matter of understanding the diff mount setup in the C2/3 and getting measurements. :thumbs_up:

I have a little information on the swap--unfortunately it isn't that easy. TT at vettemod.com has all that info on the swap--if I remember correctly.:drink:

[Ultraperio]

I have a little information on the swap--unfortunately it isn't that easy. TT at vettemod.com has all that info on the swap--if I remember correctly.:drink:

Yea, I've been reading up on that guys project. Pretty impressive CAD/fabrication skills that guy has.

http://members.home.nl/m.b.p.jongman/reararm_1.jpg

[BADDASSC6]

Let me out it this way. C6 and c5 vettes have 50/50 distribution, but the run a 245 front with a 295 rear. Steady rate. Cornering the car pushes. As far as race cars and what's ideal there are a lot of other factors. In F1 engine packaging and aerodynamics dominate. Those cars are so light that the driver is a significant mass. They car more about overall weight and packaging. The tightest corners they are still doing 90mph. Aero is always in play. I red a great article about the development of carbon fiber transmission housings. They were lighter than the magnesium units, but the cars were already running ballast to make weight. The big gain was that the magnesium units got soft at something like 300c. They CF ones can run hotter which allowed them to use smaller heat exchangers. This resulted in a big top end gain and a big gain in fuel efficiency. The best advice I ever heard was to look at what the competive guysare running. GT cars have much more room for design levity and this you see much more varing competitive cars. In gt2 we see mid engine ferraris fighting with ass happy 911s fr M3 and Big bore Corvettes having very tight battles in long 24hr races. Ultimately you can make anything work. Vary tire sizes componds, suspension tuning, wings whatever. The key is to get out there and see what works.

[BRUTAL64]

Yea, I've been reading up on that guys project. Pretty impressive CAD/fabrication skills that guy has.

http://members.home.nl/m.b.p.jongman/reararm_1.jpg

I have met and talked with TT and his twin brother. Very impressive people!

[BRUTAL64]

Let me out it this way. C6 and c5 vettes have 50/50 distribution, but the run a 245 front with a 295 rear. Steady rate. Cornering the car pushes. As far as race cars and what's ideal there are a lot of other factors. In F1 engine packaging and aerodynamics dominate. Those cars are so light that the driver is a significant mass. They car more about overall weight and packaging. The tightest corners they are still doing 90mph. Aero is always in play. I red a great article about the development of carbon fiber transmission housings. They were lighter than the magnesium units, but the cars were already running ballast to make weight. The big gain was that the magnesium units got soft at something like 300c. They CF ones can run hotter which allowed them to use smaller heat exchangers. This resulted in a big top end gain and a big gain in fuel efficiency. The best advice I ever heard was to look at what the competive guysare running. GT cars have much more room for design levity and this you see much more varing competitive cars. In gt2 we see mid engine ferraris fighting with ass happy 911s fr M3 and Big bore Corvettes having very tight battles in long 24hr races. Ultimately you can make anything work. Vary tire sizes componds, suspension tuning, wings whatever. The key is to get out there and see what works.

Great stuff----again!

[Vettezuki]

This reminds me, I have a model of the majority of a C4's rear suspension/differential in accurate dimensions in solidworks if anyone is interested and dabbles in that sort of thing.

Credit goes to the creator, unfortunate i cant remember who or where. .

Betcha it's Twin Turbo (Marck) over in Europeland. BTW, the Guldstrand 5 Link is basically the same setup for C2/3 as the C4 suspension. In fact, as the story goes, GM got it from him practically over lunch. This is something I seriously consider for down the road.

http://www.guldstrand.com/ProdImages/5-Bar-Suspension.jpg

[Vettezuki]

Let me out it this way. C6 and c5 vettes have 50/50 distribution, but the run a 245 front with a 295 rear. Steady rate. Cornering the car pushes. As far as race cars and what's ideal there are a lot of other factors. In F1 engine packaging and aerodynamics dominate. Those cars are so light that the driver is a significant mass. They car more about overall weight and packaging. The tightest corners they are still doing 90mph. Aero is always in play. I red a great article about the development of carbon fiber transmission housings. They were lighter than the magnesium units, but the cars were already running ballast to make weight. The big gain was that the magnesium units got soft at something like 300c. They CF ones can run hotter which allowed them to use smaller heat exchangers. This resulted in a big top end gain and a big gain in fuel efficiency. The best advice I ever heard was to look at what the competive guysare running. GT cars have much more room for design levity and this you see much more varing competitive cars. In gt2 we see mid engine ferraris fighting with ass happy 911s fr M3 and Big bore Corvettes having very tight battles in long 24hr races. Ultimately you can make anything work. Vary tire sizes componds, suspension tuning, wings whatever. The key is to get out there and see what works.

:thumbs_up:

Or hire somebody who knows what they're doing from experience. ;)

[enkeivette]

I leave for two days and there are a thousand pages to read. I'm bored with this, did Carlos say 50 50 for front engine rear drive or what?

[Vettezuki]

I leave for two days and there are a thousand pages to read. I'm bored with this, did Carlos say 50 50 for front engine rear drive or what?

Carlos said (http://motorgen.com/forum/showpost.php?p=46370&postcount=57).

[BRUTAL64]

Betcha it's Twin Turbo (Marck) over in Europeland. BTW, the Guldstrand 5 Link is basically the same setup for C2/3 as the C4 suspension. In fact, as the story goes, GM got it from him practically over lunch. This is something I seriously consider for down the road.

http://www.guldstrand.com/ProdImages/5-Bar-Suspension.jpg

Very impressive hardware. I really want to talk to Dick before he's gone. I have talked to his son a number of times. Want to take a trip out there?

[BRUTAL64]

I leave for two days and there are a thousand pages to read. I'm bored with this, did Carlos say 50 50 for front engine rear drive or what?

Read my son and learn..........:drink:

[enkeivette]

Carlos said (http://motorgen.com/forum/showpost.php?p=46370&postcount=57).

I read that, it's not a direct answer. It means, it depends. And since the Americans have been able to produce front engine rear drive cars that can keep up with and even pass up the exotics, the 50/50 must not be an accident.

Regardless, your C3 oversteers, if it's anything like mine. And adding weight in the back is going to make that worse. I'm over this now. Fin. :)

[Ultraperio]

I read that, it's not a direct answer. It means, it depends. And since the Americans have been able to produce front engine rear drive cars that can keep up with and even pass up the exotics, the 50/50 must not be an accident.

Regardless, your C3 oversteers, if it's anything like mine. And adding weight in the back is going to make that worse. I'm over this now. Fin. :)

It also came out in this thread that the C2/3's overteer due to rear suspension geometry changes causing toe out. :jester:

[BADDASSC6]

Adam,
here is what I would do:
- research the c3 suspension and see if they are any major faults that cause the over steering. A good example of this would be the older mustang LCAs. They would flex them bins under load causing snap over steer. A simple parts swap would get you 90 percent there.
- next get the car corner balanced and try to get as close to 50/50 as possible. You cand do this by jacking up on corner and forcing it to carry more load.
-Then take the car for a ride with a friend that can drive. Maybe Ron. I'm not saying you can drive, but it helps to have someone with some track time there to make sure that the problem isn't a driver input issue.
Set your air pressure at 32 to start. Take it on a windy cruise. Every 20 minutes measure you tire pressure. When hot bleed them both to 36. Then adjust the pressure to make the car handle neutral. Go in half pound increments. Try to stay between 32 and 36. If you need to vary the pressure my more than 2# front to back then its time to start making other adjustments to sway bars or shifting weight. Easier still is to play with the tire sizes. If you can get your hands on a Pyrometer with a probe then you are money. I like to measure the temps in the inner center and outer part of the tire to make sure I'm using the whole contact patch. Also I check to ensure that the tires are getting to the manufacturers recommended temperature operating band. This way I know that In getting the most out of my tires. So I will go as far to say that is is best to start as close to 50/50.

[enkeivette]

I know about the toe out, when the halfshaft move above the 90 degree mark, and continues to compress, the wheel moves up the arc, pulling the back of the trailing arms in, causing toe out. If the car is high enough, compressing will result in toe in which is what you want. (The shaft will move up the arc approacing 90 degrees, pushing the arm out.)

I had my alignment guy set the car with toe in with this in mind. And my suspension is so damn stiff, I don't see it compressing all that much anyways. My car will slide before it dips too much. I've never noticed a problem with the geometry issue personally, after I lowered it to the point that it was technically an issue.

Carlos, thanks for the info. I'll keep those numbers in mind. As far as the oversteer is concerned, I like a little bit. I prefer it over understeer. And I'm no pro, as you know. My car can out perform my abilities as a driver both in a straight line and around a corner. So I'm really not too worried about it. It's fun for me, that's all I'm after. :D

That and proving to Ben that he's wrong. Hahahaha.

[enkeivette]

Adam,
here is what I would do:
- research the c3 suspension and see if they are any major faults that cause the over steering. A good example of this would be the older mustang LCAs. They would flex them bins under load causing snap over steer. A simple parts swap would get you 90 percent there.
- next get the car corner balanced and try to get as close to 50/50 as possible. You cand do this by jacking up on corner and forcing it to carry more load.
-Then take the car for a ride with a friend that can drive. Maybe Ron. I'm not saying you can drive, but it helps to have someone with some track time there to make sure that the problem isn't a driver input issue.
Set your air pressure at 32 to start. Take it on a windy cruise. Every 20 minutes measure you tire pressure. When hot bleed them both to 36. Then adjust the pressure to make the car handle neutral. Go in half pound increments. Try to stay between 32 and 36. If you need to vary the pressure my more than 2# front to back then its time to start making other adjustments to sway bars or shifting weight. Easier still is to play with the tire sizes. If you can get your hands on a Pyrometer with a probe then you are money. I like to measure the temps in the inner center and outer part of the tire to make sure I'm using the whole contact patch. Also I check to ensure that the tires are getting to the manufacturers recommended temperature operating band. This way I know that In getting the most out of my tires. So I will go as far to say that is is best to start as close to 50/50.

Being this hardcore I take it you're running some of those 3K mile tires on the street?

[BADDASSC6]

Yeah I do. I have two old set of R888s and one old set of Sport Cups. The R888s are good when they are new and when they are almost completely gone. They lose a lot of grip in between. The Cups I just didn't like and they were so fucking expensive. The same setup process works for street tires. Just be careful when pulling out the pyrometer probe because they tend to break in street tires.

Weren't you supposed to put your car on a dyno?