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Discussion Starter #21
I don't follow- what causes the jacking? I'm not following what you are referring to, either that or I disagree. Caution: I may need a diagram.

If I have 250# linear springs and a 250# equivalent sway (both connected at the same location on the A-arm for simplicity), how will this behaving any different than a 500# springs in a smooth, steady sweeper? I contend that there is no difference whatsoever. The sway bar transfers load to the other spring, but this behaves no differently than if that other spring were firmer to begin with.
 

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stretch said:
I don't follow- what causes the jacking? I'm not following what you are referring to, either that or I disagree. Caution: I may need a diagram.

If I have 250# linear springs and a 250# equivalent sway (both connected at the same location on the A-arm for simplicity), how will this behaving any different than a 500# springs in a smooth, steady sweeper? I contend that there is no difference whatsoever. The sway bar transfers load to the other spring, but this behaves no differently than if that other spring were firmer to begin with.
This is not correct. When the tire pushes on the 500 lb spring, the suspended mass of the car pushes the other way and the spring compresses.

If you have a 250 lb spring and an arb with an effective rate of 250 lb/in, the tire pushes on the spring which compresses in the same manner (against the suspended mass), but some of the load pushes on the leaf (arm) of the arb, which is resisted by the leaf/arm on the inside of the car. So some of the weight on the inside wheel is used to resist the force coming through the arb from the outside tire.

This promotes inside wheel lift by reducing the normal load on the inside tire.
 

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stretch said:
I don't follow- what causes the jacking? I'm not following what you are referring to, either that or I disagree. Caution: I may need a diagram.

If I have 250# linear springs and a 250# equivalent sway (both connected at the same location on the A-arm for simplicity), how will this behaving any different than a 500# springs in a smooth, steady sweeper? I contend that there is no difference whatsoever. The sway bar transfers load to the other spring, but this behaves no differently than if that other spring were firmer to begin with.
The sway bar is an anti roll bar. It trys to keep the inside and outside suspension at the same hieght. If you compress the outside the sway will want to compress the inside, or lift it off the ground. With a certain amount of grip or spring, the car will roll enough to make the sway bar pull the inside wheel up. If you were to disconnect the sway bar the outside wheel may have enough travel to get back in touch with the ground, which is nice.

Getting back to my helper springs... They have allowed me to increase my droop travel. If I were to sit the car down on 700 lb springs with out the helpers, the suspension would only compress about 1.5 inches up front and 1 inch in the rear. That would mean that if the inside picked up more than 1.5 inches only two wheels would be on the ground. This isn't because I have run out of spring, I have run out of strut travel. With the helpers, the cars sit much lower on the strut and I have 3.5" of droop up front and 2.5 in the rear.

When the car is rolled over and you have plenty of droop the car doesn't have much contact patch. I suspect this is why you have stated "if the main spring is extended then it doesn't matter".... the car has unloaded the inside tire a good bit. However, even a small amount of force or contact patch on the tire will help the car go faster and make the front and rear differentials settle down.
 

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To clear up some confusion on helper springs....I think stretch has them confused with tender springs. Not uncommon, considering they look exactly the same...:)

stretch said:
Increasing droop travel beyond the spring travel and adding a helper spring in the rear does not improve the situation. A helper spring simply makes your linear springs progressive; they work the same as a very progressive coil spring. It makes the end of your suspension travel very soft, and while this suddenly soft rear suspension may keep a tire planted, it'll only do so by changing the car's handling bias towards understeer. Progressive springs are not good for performance as they create jacking forces and can lead to unpredictability. The weight shift of the car has not changed because the center of gravity has not changed (it will have risen, if anything, due to the progressive spring rate).
A helper spring does nothing more then keep the main spring from unseating from the perch, thus allowing more droop travel. It has no real overall effect on spring rate, as it's just strong enough to keep pressure on the main spring (like 10-20 lbs/in). At normal load it is completely compressed and fully bound anyway.

A tender spring will make the overall rate more progressive and IIRC, is not usually fully bound at normal load. It also has a low rate, but enough to make the overall spring rate behave a little more progressively. Still very common on a lot of racecars. A little bit of progression is not the end of the world. That said i wouldn't run tenders on a street car....too damn complicated!



Great discussion! Maybe Arnie can get the techies from Whiteline to chime in here....


My logical idea is to increase the front spring rate to improve cross loading (and then the rear SPRINGS to maintain the balance of the car). Of course keeping in mind your tire choice when selecting rates to keep everything in check (more grip = need more spring). And making sure that you have enough droop travel and not too much sway bar.

A lot of the time it's not quite that easy, and simply not possible with the parts you have. I think you can get by with the big sway bars and a little wheel lift, but of course it's not the "ideal" solution. But still a good compromise, and cheap!


- Andrew
 

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GTWORX.com said:
A lot of the time it's not quite that easy, and simply not possible with the parts you have. I think you can get by with the big sway bars and a little wheel lift, but of course it's not the "ideal" solution. But still a good compromise, and cheap!


- Andrew
Which I think is why sways are so popular. That and they typically give you more roll resistance with out increased NVH. They have there place in the world of improved handling but they also have limitations.
 

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javid said:
Which I think is why sways are so popular. That and they typically give you more roll resistance with out increased NVH. They have there place in the world of improved handling but they also have limitations.
exactly! If vehicle dynamics is anything, it's a collection of 1000 estimated guesses and 2000 approximations.
 

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Discussion Starter #29
Man, replying in these threads takes quite a time commitment. Not complaining. :)

needforspeed said:
This is not correct. When the tire pushes on the 500 lb spring, the suspended mass of the car pushes the other way and the spring compresses.

If you have a 250 lb spring and an arb with an effective rate of 250 lb/in, the tire pushes on the spring which compresses in the same manner (against the suspended mass), but some of the load pushes on the leaf (arm) of the arb, which is resisted by the leaf/arm on the inside of the car. So some of the weight on the inside wheel is used to resist the force coming through the arb from the outside tire.

This promotes inside wheel lift by reducing the normal load on the inside tire.
I don't believe this is correct.

Just imagine that your sway bar connects directly to the shock/spring assembly (which it nearly does on some cars) and any distribution of loads from the A-arm can be taken out of the equation. The sway acts directly on the springs.

If your theory was correct, this would prevent inside wheel lift since the load transfered through the sway bar would not be as efficient at compressing the inside spring.

I had meant to draw a force vector graph out on paper this morning before work and scan it in, but got distracted and ran out of time.


javid said:
The sway bar is an anti roll bar. It trys to keep the inside and outside suspension at the same hieght. If you compress the outside the sway will want to compress the inside, or lift it off the ground. With a certain amount of grip or spring, the car will roll enough to make the sway bar pull the inside wheel up. If you were to disconnect the sway bar the outside wheel may have enough travel to get back in touch with the ground, which is nice.
But if you were to disconnect the sway bar, you are changing the roll resistance (probably dramatically) on that end of the car and would need an equivelant spring rate increase in order to maintain the same handling bias.

That's my point (which NeedForSpeed is arguing!), that the firmer springs leave you in a very similar situation. Problem not solved. And, getting back to my original point, this means that a big rear bar isn't a bad thing!

(I realize that big springs > big bars for a track car as there are numerous other benefits, but I don't think the compromise is worth it on even an aggressive street car.)


Getting back to my helper springs... They have allowed me to increase my droop travel. If I were to sit the car down on 700 lb springs with out the helpers, the suspension would only compress about 1.5 inches up front and 1 inch in the rear. That would mean that if the inside picked up more than 1.5 inches only two wheels would be on the ground. This isn't because I have run out of spring, I have run out of strut travel. With the helpers, the cars sit much lower on the strut and I have 3.5" of droop up front and 2.5 in the rear.

When the car is rolled over and you have plenty of droop the car doesn't have much contact patch. I suspect this is why you have stated "if the main spring is extended then it doesn't matter".... the car has unloaded the inside tire a good bit. However, even a small amount of force or contact patch on the tire will help the car go faster and make the front and rear differentials settle down.
But this is the same as having a very progressive spring rate, no different than a very progressive coil spring. We agree on that.

What this accompishes is a change in roll resistance towards understeer as cornering forces increase (and you get further into the soft coils). Once the inside wheel is into the helper spring area, your average spring rate for the rear drastically decreases. This raises your center of gravity as the car is now lifting a far greater distance on the inside than it is compressing on the outside, and creates a potentially large shift towards understeer. Is understeer worth keeping a rear wheel planted? I take it you would say yes, since you like your setup, but if the car isn't turning at its peak potential then you haven't really solved the problem of needing to get on the throttle as early as possible.
 

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"But if you were to disconnect the sway bar, you are changing the roll resistance (probably dramatically) on that end of the car and would need an equivelant spring rate increase in order to maintain the same handling bias."

Keep in mind that when I spec'd my setup about two years ago, not many folks were running equal spring rate front and rear (the fad was to run a higher rate up front reagardless of sway bars), nor were many running more than 8 or 10k springs. So I was in new territory. I went with 12k/12k based on Siegle's experiance with 12k/10k, the advice of Tom Hoppe (who won a solo II champinionship on 8k/10k IIRC), Joel Ferman (very competative autoXer, consistatn top 10 in the nation over the past few years, and a number of the motorsports folks on Nasioc. It was an educated guess.

Initially, on street tires the car was a little quicker than before. On race tires it was much quicker but was edgy on entry and transitions and was picking up both wheels mid corner. On street tires with more power, it will still pick up the front wheel on exit. Pulling the rear bar resolved this and didn't compromise the mid corner grip. To me this meant I was closer to an appropriate bias front to rear. I am certain it's not best, but closer.

At this point, if I did it all over I would probably go with a 12k rear and no bar, a 14 or 16k front, and a 18 to 20mm adjustable front bar for rain vs wet... thats just a "more educated guess". Of course I would go with a coilover that had a digressive valving and plenty of droop / compression for the ride hieght that I want.

Again, the nice thing about springs vs sway bars is that the wheel rate is the same for accel/dec vs cornering. When you brake with small springs and big bars your front suspension only has the spring's wheel rate. Your suspension will compress much more.

helpers:

I have to have droop travel; you do too. I have to have the wheel in contact with the ground when the car is loaded. When it is in contact with the ground the front and rear diff's will perform much better. Also, only rally suspensions are designed for cars to 'land'. Most suspensions doesn't react well to a wheel suddenly landing on the ground.

Mid corner with out helpers, a JIC or Tien Flex suspension (and many others) will only let the tire fall about 1.5" (with big springs and a given ride height). With helpers the strut can fall ~3"; this 1.5" of droop doesn't really effect the car's bias. By the time the car has rolled to let the inside raise 2" the inside wheels are not really effecting the cars handling so it isn't reasonable to compare the insdie rear rates to the out side front.

What rates and bars are you running? Want camber and toe are you running?

I'm not sure what you are saying about the sawy bar preventing lift on the inside wheel. If the outside wheel compresses the inside wheel will experiance compressive forces becasue the sway bar wants to resist twisting. Again, if you jack half your car up with bars the 'inside' wheels won't drop donw to full droop. If you jack both sides of the car up the 'inside' wheel will drop even further. The difference in height is roughly the amount of lift that the bar is causing at high g cornering.
 

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Discussion Starter #31
On street tires with more power, it will still pick up the front wheel on exit. Pulling the rear bar resolved this...
Pulling the rear bar should not resolve lifting a front wheel. This doesn't make sense. It'd cause it, and reduce rear wheel lift.

and didn't compromise the mid corner grip.
Seriously? This is good information- if a reduction in rear sway size does not actually compromise the handling bias of the car (I'm sure there are enough unknown variables at work for this to happen, even though it goes against conventional wisdom), then I undersand why you would run a smaller rear bar.
 

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stretch said:
Pulling the rear bar should not resolve lifting a front wheel. This doesn't make sense. It'd cause it, and reduce rear wheel lift.


Seriously? This is good information- if a reduction in rear sway size does not actually compromise the handling bias of the car (I'm sure there are enough unknown variables at work for this to happen, even though it goes against conventional wisdom), then I undersand why you would run a smaller rear bar.

Both the statement that you quoted are functions of the whole setup which was already in place when I pulled the rear bar.

The front is lifting cause I have a big bar up there and lots of power and grip. If I ran a little bit smaller rear springs with a sway bar the lift might reduce or increase depending on what rates and bar I went with. On one had the big rear springs are limiting rear compression under accel, however the lack of rear sway is letting the car roll more in the rear.

If I had more spring and less bar up front it wouldn't lift... hence my plan for my next setup (14 or 16k front with a small bar) however folks probably don't make an adjustable bar as small as I want.

Note that I stated grip and not bias with regard to the mid corner issue. The car still pushes a bit mid corner but is very well setup for entry, exit and transitions. Provided that I am going fast through a turn and I can exit quickly I don't really care if the front or rear washes out first. Also, I find that I spend very little time 'mid-corner' in my car, entry and especially exit seem to consume more of a given corner. This should be true of most STi's. We all get on the gas quicker than a miata or vette and our front LSD lets us dive into corners far faster than most other cars. Mid corner though, the STi is never going to behave like a well setup rwd car; we have too much weight up front and inferior suspension design for tarmac.
 

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can't use the wrx bars can you?

Probably have to go back to stock....
 

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dailydriversti said:
can't use the wrx bars can you?

Probably have to go back to stock....
I could / would try them but they would not be adjustable. Who knows though a bar might work well in the dry and then in the wet just disconnect the front bar rather than adjust it. On 10k/8k springs, no bars (front or rear) is 'perfect' on street tires in the wet. On race tires and stiffer springs it may work out too.
 

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stretch said:
Just imagine that your sway bar connects directly to the shock/spring assembly (which it nearly does on some cars) and any distribution of loads from the A-arm can be taken out of the equation. The sway acts directly on the springs.

If your theory was correct, this would prevent inside wheel lift since the load transfered through the sway bar would not be as efficient at compressing the inside spring.
I don't understand what you mean by efficiency. I also don't understand what packaging/MR has to do with arb jacking.


Ok so we'll take the situation you described above, ARB droplink mounted at the same place as the spring.

You go around a turn, boom WT. Outside spring compresses from load increase on outside tire, and the outside arb leaf goes up and puts arb in torsion.

At the same time, the inside spring is extending. Meanwhile, the inside arb leaf wants to go up the same amount the outside arb leaf goes up (more or less), BUT the inside spring resists this motion.

So the ARB compresses the inside spring, possibly taking it off of the ground.



stretch said:
That's my point (which NeedForSpeed is arguing!), that the firmer springs leave you in a very similar situation.
No they don't! With no rear ARB there can't be any rear ARB jacking promoting inside wheel lift.

Look at any fast F1 car and you will not see a rear ARB. This is one of about 1000 reasons why they don't have a rear arb.

Look at any fast Speed World Challenge car, and you'll see the same thing: no or very small rear ARBs. Realtime runs 5000lb/in rear springs, but they don't lift wheels too much.
 

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Discussion Starter #37 (Edited)
javid said:
Mid corner though, the STi is never going to behave like a well setup rwd car; we have too much weight up front and inferior suspension design for tarmac.
Both the suspension design and weight distribution are very close to that of the Mazda Protege, and that car had fantastic handling dynamics. My goal would be to make the STI as lively and intuitive as a modified Protege (which itself isn't far off older Civics, also fun cars), yet with all the corner exit potential inherent in an AWD car.

I'd still love to see a force vector graph explaining the forces you are referring to. I understand what you're talking about but don't believe those forces are meaningful. We'll have to resume this conversation after I buy one of those books or after you make some drawings for me. :)

So, last question, and getting less technical here (I think I'm done with the rest of this discussion for now): I'm going to keep a softly sprung STI with big sway bars. That's what my budget allows, and it's a daily driver so I like the compromise of big sways over firm springs. I am working on a conversion for WRX Koni Sports for the STI. I'm on stock springs now and may get Pinks or RCE springs in the future. Based on experience, would you recommend the 24 or 27mm rear sway to match a Strano 32mm hollow front bar? I'll run the 24mm if I can, but not if it is at the expense of rotation. I like a tossable car. My car will never (or rarely) see R-compounds as it'll be prepped for a street tire autocross class.
 

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Good read fellas :tup: However now I'm very hesitant to go with my swaybar choices as this seems to be a much more controversial topic than I realized. I had planned on getting the Whiteline 27-29 mm front and 24mm rear. I'd be running wide R-comps and Worx springs and doing auto-x and occasional track days. Should I reconsider?

Thanks,
Nate
 

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stretch said:
Both the suspension design and weight distribution are very close to that of the Mazda Protege, and that car had fantastic handling dynamics. My goal would be to make the STI as lively and intuitive as a modified Protege (which itself isn't far off older Civics, also fun cars), yet with all the corner exit potential inherent in an AWD car.

I'd still love to see a force vector graph explaining the forces you are referring to. I understand what you're talking about but don't believe those forces are meaningful. We'll have to resume this conversation after I buy one of those books or after you make some drawings for me. :)

So, last question, and getting less technical here (I think I'm done with the rest of this discussion for now): I'm going to keep a softly sprung STI with big sway bars. That's what my budget allows, and it's a daily driver so I like the compromise of big sways over firm springs. I am working on a conversion for WRX Koni Sports for the STI. I'm on stock springs now and may get Pinks or RCE springs in the future. Based on experience, would you recommend the 24 or 27mm rear sway to match a Strano 32mm hollow front bar? I'll run the 24mm if I can, but not if it is at the expense of rotation. I like a tossable car. My car will never (or rarely) see R-compounds as it'll be prepped for a street tire autocross class.
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...
 
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