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javid said:
I'm not sure what the hollow 32 works out to in solid...
IIRC 29.xx-30.xx, basically the same as the whiteline or close to it.
 

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Discussion Starter #42 (Edited)
javid said:
When I ran track days on the stock spring and WL bars, the car felt 'good' with 24 front and 22 rear, it felt a little quicker at 24 R but you had to be a little smoother with the car. So matching the bar front to rear or a slightly smaller bar in the rear should work well.... I'm not sure what the hollow 32 works out to in solid...
It works out to be similar to a 29.7mm solid bar, IIRC. To keep the bar rates roughly equal to the weight distribution (I would think this I would want this at minimum), I would need the 27mm bar in the rear. That's why I'm leaning towards the 27mm bar. Not many people run it though, so information on it is scarce.

(I haven't measured the car yet, are the motion ratios the same front and rear? I know the're close.)
 

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stretch said:
It works out to be similar to a 29.7mm solid bar, IIRC. To keep the bar rates roughly equal to the weight distribution, that would put me at a 27mm bar in the rear.

(I haven't looked at the car yet, are the motion ratios similar front and rear?)
Yes, they are about .9 at both ends.
 

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stretch said:
It works out to be similar to a 29.7mm solid bar, IIRC. To keep the bar rates roughly equal to the weight distribution, that would put me at a 27mm bar in the rear.

(I haven't looked at the car yet, are the motion ratios similar front and rear?)
Yes, they are about .9 at both ends. IIRC
 

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needforspeed said:
word.

Most cars with ARB motion ratios that high are track only.
OT: I was chatting with some PRO IT honda racers at the last RoadA national event and heard different chassis's were running up to 18k springs in the rear with big 20-25mm bars. I couldn't believe it untill they explained they had a strut and bar motion ratio of like 0.50. :lol:
 

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javid said:
OT: I was chatting with some PRO IT honda racers at the last RoadA national event and heard different chassis's were running up to 18k springs in the rear with big 20-25mm bars. I couldn't believe it untill they explained they had a strut and bar motion ratio of like 0.50. :lol:
Forgive my ignorance... but could you explain what this means?
 

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What the OP doesn't understand is that springs and swaybars do not even remotely work like each other. A spring works in compression, while a swaybar works in rebound. A spring prevents one end of the car from leaning over, while a swaybar pulls up on the other end of the car to prevent this side from leaning. Having a stiff swaybar is like having lots of rebound damping and will PULL the inside tires off the road while its preventing lean on the other side of the car.

The reason that people don't want to lift inside rear wheels on an *STi* is that it prevents them from getting on the gas as early as they want. With a rear wheel up in the air, the stock rear differential on an STi is open. With this, the inside wheel will receive all the power and result in a) no acceleration until it comes down, and b) a giant clunk when the wheel does come down and all the power transfers.

If you apply your ideas to a WRX or an STi with aftermarket differentials, then yes, having a inside rear tire in the air is absolutely inconsequential. On a WRX I would run a 27mm rear swaybar all day long. In fact, that is the bar that I ran on the car when I won the Solo 2 National Championships in STX. On Javid's STi on the other hand, we don't run a rear bar, as we want to be able to put te power down.

Having said all this, if you look at the motion ratios of the suspension and the corner weights of a stockish STi, you will want somewhere in the 1000ish lb front wheel rate and 600ish lb rear wheel rate. If you calculate the swaybar motion ratios, you will be looking at a 650ish front spring with a 22-24mm bar or a 1000ish front spring with no bar. In the rear, a 650lb spring will require no rear bar and work well on a track car, while an autox car might opt for some more rear rate for oversteer.

None of this matters really on a "street car" with "street tires" as for that, you will never be getting to point of wheel lift anyways and you should be free to adjust your suspension with springs AND bars.

-Tom Hoppe (trhoppe on nasioc)
Javid's 6 Gun Racing partner in crime
 

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Discussion Starter #52 (Edited)
What the OP doesn't understand is that springs and swaybars do not even remotely work like each other. A spring works in compression, while a swaybar works in rebound. A spring prevents one end of the car from leaning over, while a swaybar pulls up on the other end of the car to prevent this side from leaning. Having a stiff swaybar is like having lots of rebound damping and will PULL the inside tires off the road while its preventing lean on the other side of the car.
I understand this perfectly, but what I'm trying to get accross is that for a given wheel rate, the end result is the same. First, a sway doesn't pull-up per se in that there is no extra motion that reduces load on that corner; it merely prevents the spring from unloading in the first place. The total spring rate increases in turn. A firm spring unloads in a shorter distance, too. Either way you have exactly the same amount of load unloading in exactly the same distance, so they DO behave similarly.

The places the forces originate from is somewhat irrelevant, because the amount of weight on that corner is not affected by where the forces originate. A sway bar cannot lift a wheel off the ground if there is still weight on it, obviously. It doesn't just magically make the wheel float because the forces originate from a different place. The weight shift due to forces on the center of gravity is completely unchanged regardless of your spring and sway setup. Do we agree on this? If there is any weight on that corner, the wheel, thanks to a thing called gravity, will fall to the road, even if a sway is preventing it from extending.

Someone mentioned earlier getting both inside wheels airborn. Sway bars nor springs could influence that whatsoever! A wider track, lower center of gravity, lower cornering forces, or downforce would do it- nothing else.

BTW- isn't the rear differential a clutch-type and active even if a wheel is airborn?
 

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Actually it does pull *up* on that corner :) For every bit of compression on the opposite end, the swaybar is pulling up on this end. Like I was saying, a swaybar acts *just* like a ton of shock rebound damping.

For a given wheel rate, the results is not even CLOSE to the same.

-Tom
 

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Discussion Starter #54
trhoppe said:
Actually it does pull *up* on that corner :) For every bit of compression on the opposite end, the swaybar is pulling up on this end. Like I was saying, a swaybar acts *just* like a ton of shock rebound damping.

For a given wheel rate, the results is not even CLOSE to the same.

-Tom
It doesn't pull up so much as prevent the spring from pushing down. The sway bar doesn't actually lift the wheel up mid-corner, it just prevents the spring from moving down. A firmer spring would be fully unloaded in its travel earlier than a soft one, so the effect is the same. That wheel becomes fully unloaded in a distance exactly equal to the wheel rate, regardless of whether the wheel rate is influenced primarily by spring or sway rates. Heck, isn't that the definition of a wheel rate?!

Could you show me a force vector graph showing how the forces are different? Every example I've seen is contrary to what you and the others here are saying.
 

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It doesn't pull up so much as prevent the spring from pushing down.
Modify this to "It pulls up TO prevent the other side spring from pushing down" and you are closer :)

While the wheel rate is going to be the wheel rate, the forces that are exerted on other sides of the car will be different if you attain that wheel rate with springs or swaybars.

When you are getting the wheel rate through the spring on a roll, the outside is compressing and the act of "compressing" isn't acting on any other corners of the car. Its independent, because the springs on each corner are independent and act on each other independently. When you are getting your wheel rate through the swaybar, the outside is compressing and that act is also removing the weight off the inside and trying to pull up on it. The swaybar is not independent as it affects the whole end of the car where its on.

For example, you are fully loaded on a left handed sweeper. Through the middle of this sweeper when shocks have no effect anymore, you hit a hole in the middle of the turn. This hole brings the left front wheel DOWN and with a swaybar, it affects the outside front right wheel by bringing it UP. With no swaybar in that situation and a fully independent suspension, the inside would just go down into the hole by itself and not affect the rest of the suspension.

-Tom
 

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Sorry but wanted to clear something up. The 24mm Bar (BSR37XZ) is the one you are refering to as being 22-24-26? Or is it the 22mm (BSR37Z) that you are refering to? Just trying to clarify.. sorry. :(

Great thread. Lots of information. Trying to decide which Rear Sway Bar to go with to compliment the 27-29 FSB on stock springs for now.
 

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Discussion Starter #57 (Edited)
trhoppe said:
While the wheel rate is going to be the wheel rate, the forces that are exerted on other sides of the car will be different if you attain that wheel rate with springs or swaybars.

When you are getting the wheel rate through the spring on a roll, the outside is compressing and the act of "compressing" isn't acting on any other corners of the car. Its independent, because the springs on each corner are independent and act on each other independently. When you are getting your wheel rate through the swaybar, the outside is compressing and that act is also removing the weight off the inside and trying to pull up on it. The swaybar is not independent as it affects the whole end of the car where its on.
Right, but that only means the wheel rate changes depending on whether you're going straight or turning. Assuming a steady-state, smooth sweeper, your wheel rate would be identical for a 250# spring and 250# bar compared to a 500# spring and no bar. (The big bar combo would only have a 250# wheel rate on straights, affecting a magnatude of other things, but I'm talking after the car has settled into a sweeper.) Both the inside and outside wheel would have the exact same 500# wheel rate once settled into a turn. Thus, as it pertains to lifting a wheel mid-turn, nothing changes unless the outside tire hits a bump. Your example example is valid, but assumes a bumpy track, whereas I am assuming a smooth track for this discussion.

For example, you are fully loaded on a left handed sweeper. Through the middle of this sweeper when shocks have no effect anymore, you hit a hole in the middle of the turn. This hole brings the left front wheel DOWN and with a swaybar, it affects the outside front right wheel by bringing it UP. With no swaybar in that situation and a fully independent suspension, the inside would just go down into the hole by itself and not affect the rest of the suspension.
I certainly agree that sway bars are not the best-performance option for the reason that they prevent the suspension from being independent, but that's a seperate issue from lifting the rear wheel unless you're on a bumpy course. I would agree that sways do not make sense for a rally car or even most dedicated race cars.
 

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Mykl said:
Forgive my ignorance... but could you explain what this means?
Motion ratios ratio the motion of the strut / spring to the wheel. The impreza's strut moves at almost the same rate as the wheel (0.9). On a honda the wheel moves 1" for every 1/2" of strut movement. So with 1000# (per inch) springs on a honda the wheel will only need 500# of force to move 1 inch.

Spring rate * motion ratio = wheel rate
 

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javid said:
Motion ratios ratio the motion of the strut / spring to the wheel. The impreza's strut moves at almost the same rate as the wheel (0.9). On a honda the wheel moves 1" for every 1/2" of strut movement. So with 1000# (per inch) springs on a honda the wheel will only need 500# of force to move 1 inch.

Spring rate * motion ratio = wheel rate
um, it's Ks * MR^2 (because you have to put both the force and the displacement in proportion).
 
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