Any one have the weight dist for a PWC S197??

[Drlee50]

http://racingcardynamics.com/weight-transfer/

You ever read this info? I really appreciated the exact math calculations of his work. Not that I can follow them totally! Lol Have a look, it's very educational. Long story short, he agrees with me on how you reduce that load on the front tires. Changes in CG are a last ditch effort and would be on a very dynamically odd racecar. Obviously he adds in the importance of anti roll bars as well which I would agree on too but maybe you would not.

If just moving weight to the rear of a nose heavy car was always the fix, why are there not multiple vendors selling the $1000 rear ballast kit for our mustangs? You could calculate the exact amount you would need and make a nice kit that fits in the spare tire well and give your car the perfect 50 50 weight distribution and the guarantee that you lap times will drop by seconds! Maybe that's the next million $ idea! Lol. Kidding but seriously there is a reason we have so many tools to alter how the chassis perform on track and allow adjustability for driver technique, track design, tire grip differences, engine power output , weight distribution etc etc. Assuming this guys lower control arms are aligned properly, a torque arm and proper sway bar adjustment would allow him to get around that track faster that ballast alone would. On top of that the car would brake better accelerate better and be under better control over all due the the improved rear grip and chassis dynamics.

That's about all I have to contribute on the subject. I agree, the lateral acceleration is why the car loads up the outside tires, not body roll alone. What im saying is the torque arm will transfer that load to the rear tires despite the car being nose heavy resulting in a more balanced car. Add in proper sway bars to load the inside tires as well as balance out the overseer condition a nose heavy car can have , and we have a very balanced (nose heavy) car thru the corner.

Sent from my LG-H932 using Tapatalk

 

[stuntman]

That is a nice overview of what is covered in Milliken's book Racecar Vehicle Dynamics -the Bible of Vehicle Dynamics.

Where did the author agree with you, other than saying that moving the CG forward will put more load on the front tires which will hurt braking performance and front grip by transferring more weight to the front tire? -which is EXACTLY what adding anti-lift from your recommended torque arm will do (thus agreeing with me).

Cg should never be a last ditch effort. It's a hugely powerful tuning tool that professional teams in Nascar, F1, Prototypes and Sports Cars use in the setup of their cars. It's so powerful that some sanctioning bodies limit the weight distribution limits in attempts to cut costs.

Why don't club racers and hpde guys play with or are concerned about Cg & weight distribution? Because they don't know any better, don't understand the importance it plays, because it's more complicated to put a battery relocation kit in the car, more expensive to lower the Cg, etc...

You continue to confuse body motion with load transfer. Body roll is NOT weight transfer. Reducing body roll does NOT inherently reduce weight transfer. That's a very common misconception so don't feel too bad.

If you replace all the springs and shocks with solid rods so there is zero suspension travel and then go around a corner, you'll have zero body roll (ignore tire deflection), but do you think that means there will be zero load transfer?

Again, body roll is NOT weight transfer.

I agree, the lateral acceleration is why the car loads up the outside tires, not body roll alone. What im saying is the torque arm will transfer that load to the rear tires despite the car being nose heavy resulting in a more balanced car. Add in proper sway bars to load the inside tires as well as balance out the overseer condition a nose heavy car can have , and we have a very balanced (nose heavy) car thru the corner.

This is another very common misconception, and goes to your (typical) misunderstanding of weight transfer.

Swaybars INCREASE load transfer to the outside tires, they DO NOT 'load' the inside tires more, but rather unload them, reducing the total tractive effort of that tire pair, which is why generally stiffer swaybars on one end of the car reduce grip on that end of the car.

Quoting your link:

If you analyse figure 2, you will see that an increasing fraction load transfer will come together with a decreasing lateral force potential for the axle.

In figure 3 the effect is repeated, but from a different perspective. Here, the load transfer is increased by means of the lateral load transfer parameter, instead of the FLT. Notice the smaller cornering potential (less grip) for higher values of the lateral load transfer parameter.

Resisting body roll whether its through swaybars or geometry (raising roll centers) puts more load on the outside tires and unloads the inside tires. This is why cars with heavy front swaybars and high Cgs (Mustangs, BMWs, NASCARs on road courses) lift the inside front tire in corners. Due to the lateral and diagonal load transfer, and soft rear suspension, the rear tires are more-evenly loaded (and rolls more than the front), while the stiff (swaybar) front attempts to reduce body roll by transferring more load to the outside front tire, unloads the inside front tire, and eventually picks the inside tire off the ground because of this load transfer.

Look into the mathematics a little more to understand how you want to REDUCE load transfer as much as possible to load both tires as evenly as possible in a corner. Lowering the Cg is one of the hardest, but best ways to do this. Unfortunately due to inherent challenges of street cars, especially big, heavy, strut-suspension Mustangs, you need to make the sacrifice of increasing load transfer and running more camber to optimize the grip of the outer tire (which is greater for that platform than the losses from reducing grip from the inside tire) compared to a better platform with a lower Cg, better suspension geometry, that does not need as big of a swaybar or as much camber.

I'd suggest picking up a copy of Racecar Vehicle Dynamics. If you're truly interested in this stuff and are serious about making your car faster and performing better on track, it's a must-have. There are also a few mathematical examples of how Cg and weight transfer affects grip that make it easier to understand than just looking at an equation by itself like in the somewhat plagiarized link you sent.

.

 

[Drlee50]

That is a nice overview of what is covered in Milliken's book Racecar Vehicle Dynamics -the Bible of Vehicle Dynamics.

Where did the author agree with you, other than saying that moving the CG forward will put more load on the front tires which will hurt braking performance and front grip by transferring more weight to the front tire? -which is EXACTLY what adding anti-lift from your recommended torque arm will do (thus agreeing with me).

Cg should never be a last ditch effort. It's a hugely powerful tuning tool that professional teams in Nascar, F1, Prototypes and Sports Cars use in the setup of their cars. It's so powerful that some sanctioning bodies limit the weight distribution limits in attempts to cut costs.

Why don't club racers and hpde guys play with or are concerned about Cg & weight distribution? Because they don't know any better, don't understand the importance it plays, because it's more complicated to put a battery relocation kit in the car, more expensive to lower the Cg, etc...

You continue to confuse body motion with load transfer. Body roll is NOT weight transfer. Reducing body roll does NOT inherently reduce weight transfer. That's a very common misconception so don't feel too bad.

If you replace all the springs and shocks with solid rods so there is zero suspension travel and then go around a corner, you'll have zero body roll (ignore tire deflection), but do you think that means there will be zero load transfer?

Again, body roll is NOT weight transfer.


This is another very common misconception, and goes to your (typical) misunderstanding of weight transfer.

Swaybars INCREASE load transfer to the outside tires, they DO NOT 'load' the inside tires more, but rather unload them, reducing the total tractive effort of that tire pair, which is why generally stiffer swaybars on one end of the car reduce grip on that end of the car.

Quoting your link:



Resisting body roll whether its through swaybars or geometry (raising roll centers) puts more load on the outside tires and unloads the inside tires. This is why cars with heavy front swaybars and high Cgs (Mustangs, BMWs, NASCARs on road courses) lift the inside front tire in corners. Due to the lateral and diagonal load transfer, and soft rear suspension, the rear tires are more-evenly loaded (and rolls more than the front), while the stiff (swaybar) front attempts to reduce body roll by transferring more load to the outside front tire, unloads the inside front tire, and eventually picks the inside tire off the ground because of this load transfer.

Look into the mathematics a little more to understand how you want to REDUCE load transfer as much as possible to load both tires as evenly as possible in a corner. Lowering the Cg is one of the hardest, but best ways to do this. Unfortunately due to inherent challenges of street cars, especially big, heavy, strut-suspension Mustangs, you need to make the sacrifice of increasing load transfer and running more camber to optimize the grip of the outer tire (which is greater for that platform than the losses from reducing grip from the inside tire) compared to a better platform with a lower Cg, better suspension geometry, that does not need as big of a swaybar or as much camber.

I'd suggest picking up a copy of Racecar Vehicle Dynamics. If you're truly interested in this stuff and are serious about making your car faster and performing better on track, it's a must-have. There are also a few mathematical examples of how Cg and weight transfer affects grip that make it easier to understand than just looking at an equation by itself like in the somewhat plagiarized link you sent.

.

Thanks for the reply. I don't have the time to reply in detail at this moment cuz I gotta swap header on a Cayman S tonight. But real quick:

Im talking about manipulating sprung weight. The rear end, the frame and control arms are under the springs and they are influenced by the torque arm.

I know for sure that you don't think that the only thing needed is 50 50 weight distribution. But im gonna ask anyway:
If I have a 50 50 weight car and it is pushing thru the corner or over steering or it is washing out the outside front tire in a turn....what do you do ?

Sent from my LG-H932 using Tapatalk

 

[stuntman]

Thanks for the reply. I don't have the time to reply in detail at this moment cuz I gotta swap header on a Cayman S tonight. But real quick:

Im talking about manipulating sprung weight. The rear end, the frame and control arms are under the springs and they are influenced by the torque arm.

Yes the wheels, tires, brakes, and axle is unsprung. Technically only half of the weight of springs, dampers, control arms/torque arms, panhard bars is unsprung.

The positioning of the torque arm affects the instant center of the suspension as does the angle of the control arms. You can change the Ic by changing the locating points of either, on the chassis or axle.

I know for sure that you don't think that the only thing needed is 50 50 weight distribution. But im gonna ask anyway:
If I have a 50 50 weight car and it is pushing thru the corner or over steering or it is washing out the outside front tire in a turn....what do you do ?

Of course not, that would be absurd. Heck, when possible, most front-engine cars would still perform better with less than 50% front weight. Vipers & AMG GTs are actually rear-heavy. Trans-Am cars and some of the front-engine tube-frame GT cars that raced in Grand-Am were also rear-heavy.

That is way too opened ended to answer. At the end of the day, a car with 50/50 weight distribution will fight inherent understeer tendencies better than a car with 52/48 distribution. Likewise a rear heavy 48/52 would fight understeer less than a 50/50 car (assuming everything else is the same).

In attempts to answer your question, you would first need to look at your tire temps. If you're overheating the front tires, or if you don't have a proper tire temp and temp spread across all 4 tires, that is your indication to work on the chassis and make the necessary adjustments to make the tires work effectively. All suspension setup is focused on is making the tires work effectively. If you're not checking your temps and pressures, you might as well be blindfolded.

 

[Drlee50]

The car I have tracked for the past 7 years was a 2002 dodge viper with twin turbo and 980 rwhp and I ran a 335 square slick setup. I'm gonna say it was very fast around every Track I was on. I recently bought a boss 302 and it's Actually fast as well. More of a momentum car vs my viper. But still I csn drive this car fast. Previously I have had many mustangs including an outlaw car running 1200 hp out of a 331 ci 88mm turbo motor with a powerglide . others were track cars and I have used watts, torque arms, altered k members and arms to change geometry etc etc. What I can tell you through my actual track experience, having run both high hp and low hp and heavy front and heavy rear weighted cars in both drag racing and road course racing platforms is this: you can tune suspensions to make a car handle differently. Weight transfer is far more than being 50 50 distributiontion. You can make a car that is out of front to rear balance be far faster than a 50 50 car with power and tire sides being equal . I have done it and so have many many other racing teams. The point is, using these techniques, you can overcome the inherent design flaws produced from the factory design. Ill post more tomorrow.
Thanks

Sent from my LG-H932 using Tapatalk

 

[stuntman]

Cool list of cars. I really like Vipers.

Of course you can have multiple different setups and weight distributions perform very similarly. Just look at Gat4 & GT3 cars, front engine, mid, & rear engine cars all turning the same laps on almost identical tires.

Heck, two teams were racing FWD cars professionally, one car ran 600/1,800lb spring rates while the other ran 1,500/700. Both cars drove completely differently but turned the same laps and we're class leading cars.

Weight transfer is far more than being 50 50 distributiontion.

I have no idea what you're trying to say here. Weight transfer happens whenever a force acts on the CG of the car. Weight distribution is part of the cars Cg location. The name of the game is maximizing the performance of the tire with your setup for what the CG is.

But it will always be the same, moving weight to the rear (rearward cg) puts less load on the front tires and improves braking and front grip entering corners. If the car does not have a braking or front grip problem, then moving the CG rearward might not be a benefit. But a 54/46 Mustang will always improve as you move the CG towards 50/50.

 

[Fair]

So... the OP's mechanic wants to add weight to his car to make it better? That's not good advice. Maybe on some dirt track car or whatever back in the day, but he likely had a set of CLASS RULES that required a minimum weight, so achieving minimum weight using ballast additions was common. Almost all forms of racing do this. And in that case, sure, put the ballast rearward to improve the front to rear bias as much as possible. But we don't ever want to add weight to "go faster" in track cars. Bonneville (skinny tires + low grip surface) and some other rare exceptions exist, but not road course use. Weight is the enemy.



The dirty little secret is that most OEM based chassis turned into race cars are nearly impossible to get to a "perfect" 50% front / 50% rear bias. That's not even the goal that race engineers shoot for in RWD cars... they want to hit about 53-54% rear bias, if rules and layout allows. Which really isn't possible in a front engined/rear drive car without mountains of ballast. Most prepped Mustangs are still 53-55% front weight biased, even with rear mounted ballast.



And on the internet people will argue about exact placement of ballast, start throwing around "polar moment" and other $5 words, and have no data to back up their claims. But that's the internet - endless debate over useless minutia.



Sure, we want to see a 50/50 cross weight, which is relatively easy to adjust for with 4 corner ride heights. Do this with your normal fuel load (or half the load for longer stint cars) and with the driver (or simulated weight) in place. How this thread swerved off into torque arms and weight transfer... ??

 

[Grant 302]

But that's the internet - endless debate over useless minutia.

Endless when threads are resurrected after a month? Timeliness would have made that a great post.

 

[Fair]

Endless when threads are resurrected after a month? Timeliness would have made that a great post.

Yea, I missed it. But uinlike Social Media pages, where all posts are gone within 48 hours... and asked again! Here on the TMO forum, the subjects (and tech answers) tend to stick around for a while...

 

[smallblock]

Yea, I missed it. But uinlike Social Media pages, where all posts are gone within 48 hours... and asked again! Here on the TMO forum, the subjects (and tech answers) tend to stick around for a while...

At least until photobucket holds your photo documentation for ransom...

 

[Grant 302]

At least until photobucket holds your photo documentation for ransom...

Crossing my fingers that there isn't an issue with flickr being acquired by smugmug...

 

[Norm Peterson]

Just stumbled across this thread.

http://racingcardynamics.com/weight-transfer/

You ever read this info?

Not that I know of. Thanks for the link, I'm going to print it out and read it at a more leisurely pace.

the lateral acceleration is why the car loads up the outside tires, not body roll alone.

You're missing something pretty basic here. All of the various body inertial motions - whether it's roll, squat, dive, lift, heave, or anything else - are merely the visible evidence that some sort of load transfer is happening. It's the inertial force that's the independent variable here (due to lateral, longitudinal, or vertical g's), not the subsequent displacements. The displacements happen because the car's suspension (and its tires) are not rigid components rigidly fixed to the chassis, which would be a go-kart with wheels but no tires.

Do try to separate the idea of mass distribution from load transfer. You can move the distribution of load transfer around by playing with spring and bar stiffnesses (and dynamically with shock tuning), but that does not change the mass distribution or its rotational inertia that's opposing yaw (that desired change in direction).

Add in proper sway bars to load the inside tires

Stabilizer bars actually UNload the inside tires. You're still insisting that roll is causing lateral load transfer and trying to imply that less roll = less lateral load transfer. As a now-retired structural engineer/analyst with a long-time personal interest in vehicle dynamics topics, I just can't let that go unchallenged.

Norm

 

[ArizonaBOSS]

Swaybars definitely unload the inside. Experimented with an OEM LS bar in 2016 and it would blow the inside tire off in 50-60mph corners at Buttonwillow, even with at T2 diff. Made the car very squirrely with the setup at the time. Ended up going back to a smaller bar with stiffer springs to alleviate that issue.

 

[Norm Peterson]

I'm partway through that article - it printed out on 25 pages in Word even with the pictures downsized.

One thing I think needs mention is that when working with the K(phi) terms for the front and rear suspensions is that stabilizer bar stiffnesses need to be maintained as moment stiffness separate from the moment stiffnesses from the springs (rather than transferring bar end rates out to wheel rates and working back from there). Keep in mind that on the inside, the sta-bar is acting opposite to the spring, and I suspect that's what gets in the way by the time you're trying to calculate degrees of roll per lateral g when you work from wheel rates alone. Using the bar rates to wheel rates approach tends to give much lower figures for deg/g than reasonable (and I've baselined the other approach against a deg/g figure obtained from a K&C test discussed in a sidebar to a Car and Driver article.


Norm

 

[Drlee50]

Thanks Norm!
I don't think I typed what I was actually visualizing in my head when mentioning sway bay optimization.

When the inertia acts on the body in a corner, and it rolls over a certain amount, that takes a certain amount of time. To unroll and come back to "level" that also takes time. This amount of time has an effect on the drivers ability to get back to WOT and get through that corner. The shorter amount of time the body stays "rolled" , the faster you can get through the corner. Sway bar adjustment / optimization can help you redistribute grip to get through that corner faster. Obviously there is a balance between springs bars and tires and weight distribution etc.

If im wrong, then maybe my cars are weird because those adjustments have made my cars faster through corners and they end up a bit "flatter" feeling through the corners. Now if you don't have enough spring, then a bar can only take you so far. Im my experience with a torque arm, all 4 springs are compressed down while braking , not just the fronts and unloading the rear- which would be typical on a nose heavy car. As a result, I can brake later and do more than just initiate turn in while braking. I can brake further into the turn because the car is "flatter". It just works! Lol . maybe I'm not explaining it in the proper technical terms. But the original point was- how can you make a nose heavy car go around a corner faster, more like a 50 50 weight car? Im my experience, the torque arm helped do just that.



Sent from my LG-H932 using Tapatalk

 

[Grant 302]

Using the bar rates to wheel rates approach tends to give much lower figures for deg/g than reasonable

I tend to agree on this. I *think* the problem in general is the approach looks at it as a 'single' wheel rate and travel when this really isn't the way it 'works'.

 

[Norm Peterson]

A torque arm will unweight the rear axle via anti-lift (the braking side of anti-squat). Sometimes this effect is called anti-squat's evil cousin, if the percent is high enough to put the car into brake hop. Certain years of GM's F-body cars (torque arm equipped) were absolutely notorious for this.

I suppose if you've got enough anti-lift, the elastic component of resistance to lift might be downward out back (I haven't tried to logically verify this yet). But the forward load transfer (which always unweights the rear tires) still absolutely must occur, simply because the sprung mass CG cannot be below grade. Except, perhaps, in an amusement park ride where the "car" is suspended below its "road".

As soon as you mention the time it takes for these various effects to occur, you have to introduce the fact that they don't happen exactly in phase with one another. Kinematic (geometric) load transfer happens first (almost but not quite instantaneously), followed by load transfer through the dampers and springs/bars. Damper forces peak before spring/bar forces peak. This can be used to advantage, and normally is with a stick-axle RWD car


Norm

 

[Norm Peterson]

I tend to agree on this. I *think* the problem in general is the approach looks at it as a 'single' wheel rate and travel when this really isn't the way it 'works'.

I went through several iterations of a TLLTD spreadsheet, but it wasn't until I started taking a closer look at the amount of roll predicted that I stepped away from running force stiffnesses out to the wheel and doing Kt^2 calculations from that. I was finding only moderate bar stiffness changes - with no spring changes - cutting the deg/g almost in half. As a sanity check, that says "go back and look at that whole thing again", loud and clear.

I'll take being within about 0.2°/g of that sidebar value as good enough verification of the revised approach.


Norm

 

[blacksheep-1]

for your discussions, 4 different cars, 3 different classes, 1 on a bank