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 Post subject: Front-End Body Roll
PostPosted: Sun May 28, 2017 6:22 pm 
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Joined: Thu Nov 06, 2014 5:12 pm
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Location: north bergen nj
Car Model*: 68 dodge dart 270
68 Dart 270--My sweet slant has alot of front body roll. Beacuse i bought new 14" tires and rims..then installed 4" front disc breaks-(unbelievable inprovement!!) ..i cant go with a sway bar. Question: Could i purchase x heavy duty shocks to lessen my crazy roll? OR?..... As always-any info is greatly appreciated for this awesome Slant 6 Forum.
HAPPY MOTORING


Last edited by suurthing on Fri Jun 09, 2017 6:57 am, edited 1 time in total.

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 Post subject:
PostPosted: Sun May 28, 2017 7:05 pm 
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Supercharged

Joined: Thu May 12, 2005 11:50 pm
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Car Model*: 64 Plymouth Valiant
Why can't you install a sway bar?

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 Post subject:
PostPosted: Sun May 28, 2017 9:44 pm 
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Another way to reduce body roll is to install larger diameter torsion bars. You could go to 0.890", 0.920", or 0.990" and still have nice handling and ride for the street. Better shocks make a big difference too. IMHO, Hotchkis makes the best ones these days, if you can afford them ($150/corner). Bilstein makes nice ones too, I hear. However, probably the largest single change you can make to how your car behaves is better/wider wheels and tires. Stock 13" and 14" limit performance quite a bit compared to newer cars

Hope this helps and happy building.

Lou

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 Post subject:
PostPosted: Wed May 31, 2017 9:38 am 
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emsvitil wrote:
Why can't you install a sway bar?


Addco and most other aftermarket bars bolt to the shock mounts, so even with a brake swap, they'll fit fine.

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 Post subject:
PostPosted: Wed May 31, 2017 4:02 pm 
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Using shocks to control body roll is a poor choice. Although you might be able to effect an improvement in your body roll observations, you likely will make many other handling sacrifices, most not good. Shock choice is best left towards the end of your upgrades: tires/rims, weight balance, TB selections, TP, swaybar choices, and finally application. A Roll/sawybar really is just a bandaid to fix something else in your suspension choices that is not giving you your preferred balance, nothing wrong with that and it is very common low cost simple fix, but not a must have, unless you are a flavor of the month candidate. A swaybar converts an independent suspension into a straight axle in degrees, defeating the original purpose of a IFS. I would first go with a TB change,and don't be timid, most/many say they like their choice, but always have in the back of their mind, "should i have gone bigger"? They will never know. After that an adjustable shock opens many options, and a custom sway bar a last piece to the puzzle, if really needed. Also a swaybar mainly corrects the tire road surface contact patch favorably, but the price paid is it lifts the inside tire, transferring a lot of cornering weight/force to the outside tire, the opposite of what most think is going on.


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 Post subject:
PostPosted: Thu Jun 01, 2017 7:43 am 
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Some tuners like to use springs to set both wheel rate and roll stiffness, but I personally prefer the school of tuning where one sets the springs to be as soft as they can to avoid bottoming out at your preferred ride height, then use sway bars to dial in body roll and oversteer / understeer balance.

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 Post subject:
PostPosted: Thu Jun 01, 2017 8:16 am 
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That's a common counter. The problem is as I see it, that line of thinking is often derived from the pro racing circuits, and makes sense for that application, where a circuit's needs are targeted for that track. In street applications, with a much wider range of variables, fuel, passengers, speed, conditions, road surface/bumps/railroad tracks/etc, and what is considered "soft" on the racetrack i suspect is still pretty stiff on the street. Additionally, "pitch" under hard braking/acceleration, is still mainly controlled by the springs only. Back to op, my thinking is for shocks their main purpose is to control speed of suspension movement, ie transitions, not the amount, which serves to a large degree to define the perceived handling characteristics for the driver.


Last edited by jcc on Thu Jun 01, 2017 8:40 am, edited 3 times in total.

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 Post subject:
PostPosted: Thu Jun 01, 2017 11:53 am 
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I'm with Matt.

I live in a rough and tumble part of the world. I like soft/stock torsion bars with the best shocks I can afford and a mild swaybar.

Of course as much tire on the road as possible is a part of that.

An important factor in Torsion bar selection is getting the ride and handling you want at the target ride height .

Part of handling on rougher roads is having as much suspension travel as possible. A bar that is too stiff or (soft ) can lead to getting "bucked off" in corners.

Adding a swaybar to your car allows for the transferring of force from one wheel to the other. The addition of the bar to stock T bar suspensions makes the car feel stiffer . When 1 wheel gets a load a portion is transferred to the other wheel.

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 Post subject:
PostPosted: Thu Jun 01, 2017 1:03 pm 
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sandy in BC wrote:
I'm with Matt.
........................ When 1 wheel gets a load a portion is transferred to the other wheel.


We need to be very careful here, the load you are referring to, increases roll stiffness by lifting the less loaded wheel further(we really should be referring to tire contact patch, as that is all that is really important in handling). The reason that is ultimately important, a car sees less overall tire grip anytime tire contact patches are unequally loaded between tires(assuming same sized tires), period, that is one negative result of a swaybar in action.


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 Post subject:
PostPosted: Fri Jun 02, 2017 6:30 am 
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Any method of increasing roll stiffness will have that effect. The key to maximizing grip is having the roll stiffness properly balanced between both ends of the chassis.

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 Post subject:
PostPosted: Fri Jun 02, 2017 7:08 am 
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How do you explain, because an increase in say both front TB rates, and its then corresponding increase in roll stiffness, does nothing to reduce the inner tire patch loading in a normal cornering situation, whereas a sway bar actively further reduces the inner tire patch loading when the swaybar rate is increased? Am I missing something here?

The point of F/R balance is I agree very important, and why I am hesitant to suggest categorically a front swaybar by itself is end all/be all fix, ie balance is a greater goal. The racing soft spring stout swaybar solution I still feel is a tough theory to translate directly to the street, without getting caught up in semantics. A race car can be suspension tuned to not ever bottom out and have maximum suspension travel on a well known specific race track, on the street, bottoming out is to be avoided, and the potholes/surfaces/etc will always be unknown, to a large degree.


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 Post subject:
PostPosted: Fri Jun 02, 2017 10:05 am 
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For a given center of gravity height and a given lean angle it doesn't matter one bit how the roll stiffness is achieved. The car will transfer the same amount of weight from one side to the other. A sway bar essentially steals a spring rate increase from one side to give to the other.

I have had both soft spring, big sway bar A bodies and stiff-spring no-sway-bar A bodies. My '66 Dart was in the first camp, while street driven, and my '67 Valiant was in the second. The Dart ended up as a road racer with 1.04" torsion bars and a 1.125" front sway bar. Although the initial turn-in wasn't as sharp the Dart handled better balance-wise without the sway bar and this is why I tried going without a sway bar on the Valiant. With 1.04" torsion bars, QA1 shocks and big 17" tires the Valiant handled very well, but the floppy stud-mounted idler arm was the pits. The steering acted as if it had a big spring which required one to crank in a lot of steering to enter a corner and then back off to maintain the desired line.

For most folks it's easiest to slap on a sway bar and do no more. It will feel a lot better and will drive fine so long as you don't drive so hard you find that you've increased understeer substantially. With 13 or 14" tires it's hard to generate a lot of grip and it tends to make noise and be uncomfortable so most people never get to the massive understeer place. Then you have people like Lou and me. :D

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 Post subject:
PostPosted: Fri Jun 02, 2017 6:48 pm 
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Joshie225 wrote:
For a given center of gravity height and a given lean angle it doesn't matter one bit how the roll stiffness is achieved. The car will transfer the same amount of weight from one side to the other. A sway bar essentially steals a spring rate increase from one side to give to the other.


I suspect I'm starting to beat a dead horse here:D , but I feel this an important often misunderstood point, maybe not by you, but your description could be easily misunderstood IMO. I agree the weight on the front axle doesn't change, the amount a corner transfers is consistent based on the parameters you mentioned, BUT the loading L/R of the tire contact patches is dependent on the swaybar rate in this example. The inside tire sees less loading, because the bar lifts that wheel, the outer tire patch sees more loading, the result, among other things, less roll, and likely greater understeer, due to the fact the outside tire now has greater loading per sq in. By lifting the inside tire, there is less force pushing on the roadway to "roll" the body. The two big upsides are, improved driver handling perception, and maybe a better improved tire contact patch because the tire(s) are leaning less and have a more favorable tire contact patch..


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 Post subject:
PostPosted: Fri Jun 02, 2017 7:46 pm 
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jcc wrote:
I suspect I'm starting to beat a dead horse here :D


Agreed.

jcc wrote:
but I feel this an important often misunderstood point, maybe not by you, but your description could be easily misunderstood IMO.


Yes, and I don't believe you fully understand my point.

jcc wrote:
I agree the weight on the front axle doesn't change, the amount a corner transfers is consistent based on the parameters you mentioned, BUT the loading L/R of the tire contact patches is dependent on the swaybar rate in this example.


Weight transfer is dependent upon center of gravity height, mass, lateral acceleration and track width. Spring rate isn't even a part of the equation. The spring rate, suspension motion ratio and sway bar rate determine the wheel rate. And it matters not one bit if that wheel rate is achieved with or without a sway bar, the body roll will be the same.

https://en.wikipedia.org/wiki/Suspension_(vehicle)#Weight_transfer

jcc wrote:
The inside tire sees less loading, because the bar lifts that wheel, the outer tire patch sees more loading...


You have the exact same result in wheel loading will occur if the same wheel rate is achieved through springs alone.

jcc wrote:
...the result, among other things, less roll, and likely greater understeer, due to the fact the outside tire now has greater loading per sq in.


The understeer happens because the outside front tire is loaded more as the roll couple has been changed and the front suspension is effectively propping up the rear suspension. If the rear roll rate were increased to achieve the previous front/rear split then understeer would not increase.

jcc wrote:
By lifting the inside tire, there is less force pushing on the roadway to "roll" the body. The two big upsides are, improved driver handling perception, and maybe a better improved tire contact patch because the tire(s) are leaning less and have a more favorable tire contact patch..


The forces which cause body roll do not include the presence or absence of a sway bar.

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 Post subject:
PostPosted: Sat Jun 03, 2017 8:27 am 
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Joshie225 wrote:
jcc wrote:
but I feel this an important often misunderstood point, maybe not by you, but your description could be easily misunderstood IMO.


Yes, and I don't believe you fully understand my point.

I am trying.

Joshie225 wrote:
jcc wrote:
I agree the weight on the front axle doesn't change, the amount a corner transfers is consistent based on the parameters you mentioned, BUT the loading L/R of the tire contact patches is dependent on the swaybar rate in this example.


Weight transfer is dependent upon center of gravity height, mass, lateral acceleration and track width. Spring rate isn't even a part of the equation. The spring rate, suspension motion ratio and sway bar rate determine the wheel rate. And it matters not one bit if that wheel rate is achieved with or without a sway bar, the body roll will be the same.

https://en.wikipedia.org/wiki/Suspension_(vehicle)#Weight_transfer

Not sure I agree with that, as a swaybar adds to outer wheel rate by reducing inner wheel rate, springs (TB) alone do not receive any contribution or conversely any reduction in spring rate from the opposing wheel, the point of a sway bar.
jcc wrote:
The inside tire sees less loading, because the bar lifts that wheel, the outer tire patch sees more loading...


Joshie225 wrote:
You have the exact same result in wheel loading will occur if the same wheel rate is achieved through springs alone.

Not sure what result you are referring to, are you saying tire patch loading will not change with the use of a swaybar?

jcc wrote:
...the result, among other things, less roll, and likely greater understeer, due to the fact the outside tire now has greater loading per sq in.


Joshie225 wrote:
The understeer happens because the outside front tire is loaded more as the roll couple has been changed and the front suspension is effectively propping up the rear suspension. If the rear roll rate were increased to achieve the previous front/rear split then understeer would not increase.

We agree on the marked bold above, which is what I thought I clearly stated, and we aren't really focused on rear bars according to the OP's question.

jcc wrote:
By lifting the inside tire, there is less force pushing on the roadway to "roll" the body. The two big upsides are, improved driver handling perception, and maybe a better improved tire contact patch because the tire(s) are leaning less and have a more favorable tire contact patch..



Joshie225 wrote:
The forces which cause body roll do not include the presence or absence of a sway bar.
You are talking forces,I''m talking tire contact patch loading, which directly relates to understeer characteristics, we are not focusing on the forces that cause body roll, more what reduces body roll, ie a swaybar, and the price paid for that reduction, to stay on track.


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