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Old 01-10-2017, 09:40 PM   #1
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Swaybar suggestions?

So I've been thinking about sway bars recently. I track and autocross a lot and last year, my car definitely had a tendency to understeer and I'd like to neutralise that a bit.

About my setup, I have HKS Hipermax IV GT coilovers with the standard spring rates of 6k/4k and stock sway bars. Alignment is -2.2f/-1.7r. I was running old 245/40r17 original Rivals last year and next year I'll be on new 225/45r17 RS3s.

I spent a lot of last year adjusting the suspension and ended the season at 11 clicks from soft in front and 16 clicks from soft in the rear. I liked this setting at first because I felt the car was predictable and still mostly willing to rotate but on my last 2 track days, I could feel the cars lack of willingness to rotate was holding me back. Corner entry was fine but mid corner to corner exit would understeer pretty badly. It was something that could be fixed with additional throttle when the car was OEM but now I could be flat and the car would just push more.

While I know there is more to be tried with playing with the damping settings and alignment, I think adding some thicker sway bars are in order, especially a thicker rear bar but I wonder if anyone has any suggestions or thoughts.
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Old 01-10-2017, 09:50 PM   #2
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Can you get more camber up front? I bet you're not fully utilizing your front tires mid-corner-exit with that static camber, try -3.0, maybe even more.
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Old 01-10-2017, 10:45 PM   #3
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Yeah I would guess you are not getting everything out of the front tires and they are getting hot on the outsides (although there is only one way to know for sure: actually measure).

In addition to extra front camber I would suggest stiffer rear springs. So instead of fixing an imbalance with a big swaybar get closer to the right place with spring rates instead.
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Old 01-10-2017, 10:50 PM   #4
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I agree with the previous two posts. Also, can you either decrease your front spring rate or increase the rear rate?
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Old 01-10-2017, 10:55 PM   #5
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Remember this: compromise.
You are running relatively low rate rear springs so any anti-roll bar is going to contribute more anti-roll than a higher rate spring. The more the anti-roll bar contributes to the total anti-roll of the car (sway bar plus springs) the more cross talk (read less independent suspension) you are going to have.

Given the rear motion ratio you have a lot less spring rate at the rear wheel than the front. As @jamal has suggested a better fix would be higher rate rear springs but then there is the question of damping/valving for the new springs.
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Old 01-11-2017, 12:15 AM   #6
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Thanks for the suggestions everyone!

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Originally Posted by strat61caster View Post
Can you get more camber up front? I bet you're not fully utilizing your front tires mid-corner-exit with that static camber, try -3.0, maybe even more.
The coils come with camber plates and I've got a set of bolts so -3 should be no problem although I'm not certain this will really fix my problem. It is my understanding that camber helps more with initial turn in than corner exit which is where I am having problems so I have my doubts that going from -2.2 to -3 is going to make a huge difference. As it was, when I went from -1 to -2.2, I didn't feel like the difference was huge although it did really help my tire wear. Either way, I am looking at increasing front end camber in the spring and I'll play around with my damping settings but I'm just not confident that it will resolve my issues alone.

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Yeah I would guess you are not getting everything out of the front tires and they are getting hot on the outsides (although there is only one way to know for sure: actually measure).

In addition to extra front camber I would suggest stiffer rear springs. So instead of fixing an imbalance with a big swaybar get closer to the right place with spring rates instead.
Regarding changing spring rates, obviously that is optimal but it's just not feasible for me right now. I'd either be sending my existing coils to HKS USA for revalving or buying a new set with more neutral rates and either way, I can't afford that this year.

But I can afford a sway bar or two

I think that between additional front end camber, more damping adjustments and a better sway bar setup, I can get closer to a neutral handling car without the need to resort to blowing my wad (of cash) on upgrading my coilovers. The problem is that I don't know anything about sway bars and so I am wondering what I should be looking for to address the weaknesses I have found in the car.
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Old 01-11-2017, 01:53 AM   #7
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Well, you have adjustment left on the damper, I expect you could get away with a mild bump in rear rate without having to worry about the valving. Like 6 or 7k which would help a lot. Chances are valving doesn't vary much between different hks products with different spring rates anyhow...

Looks like 65mm id and 170mm long, which is also close enough to 2.5" that you can use those.
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Old 01-11-2017, 12:09 PM   #8
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Those rear springs are too soft as mentioned.

A small bump in rear sway bar size will help. Try a 16mm rear.

It's not the "best" solution but it will be an improvement and they're not a lot of money.


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Old 01-11-2017, 02:04 PM   #9
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Quote:
Originally Posted by Lynxis View Post
So I've been thinking about sway bars recently. I track and autocross a lot and last year, my car definitely had a tendency to understeer and I'd like to neutralise that a bit.
I have the opposite problem. My rear springs are stiffer, so i keep getting oversteer. I'm trying to get a 22mm whiteline front swaybar, but i'm not sure if that is over kill and shift the balance the other way.
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Old 01-11-2017, 03:06 PM   #10
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Originally Posted by Lynxis View Post
Regarding changing spring rates, obviously that is optimal but it's just not feasible for me right now. I'd either be sending my existing coils to HKS USA for revalving or buying a new set with more neutral rates and either way, I can't afford that this year.
Are you sure you need revalving? Do you have shock dynos of the various adjuster settings?

If the answer is yes, the plots should tell you everything about whether you need a revalve or not.

If the answer is no, call up HKS and ask them how high of a spring rate they feel their rear shocks will support. Softer rears than fronts is very much the wrong way with this car IMO. Most are running square, some are running with higher rates in the rear.
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Old 01-11-2017, 06:57 PM   #11
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According to hks you can change things by 2k.

http://www.hks-power.co.jp/en/produc...ermax/db/13673

So 6k rears would be no problem, and would really help. In non-metric a 2.5" ID, 6" long, 350lb spring would probably be about right.
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Old 01-11-2017, 08:58 PM   #12
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Quote:
Originally Posted by jamal View Post
According to hks you can change things by 2k.

http://www.hks-power.co.jp/en/produc...ermax/db/13673

So 6k rears would be no problem, and would really help. In non-metric a 2.5" ID, 6" long, 350lb spring would probably be about right.
I had kind of just guessed that revalving would be required considering increasing spring rate to 6k would be a 50% increase which is pretty massive. The JP manual advising that you can do so almost sounds crazy to me.

I e-mailed HKS USA about it and they said they don't recommend increasing spring rates more than 20% without revalving but noted that they do not offer revalving services for the Hipermax series of coilovers and suggested that they would need to be sent to an independent shop.
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Old 01-11-2017, 09:13 PM   #13
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+1 I've also heard +/- 100 lbs is possible on good dampers, have done it myself as well. It will feel under/overdamped (in this case underdamped) but may be worth it.

I'd still do the alignment first, I don't think you realize how much lean the car has on corner exit, it doesn't feel like it, but that doesn't mean you're not rolling on the outside edge of that tire.

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Old 01-12-2017, 10:35 AM   #14
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Quote:
Originally Posted by Lynxis View Post
I had kind of just guessed that revalving would be required considering increasing spring rate to 6k would be a 50% increase which is pretty massive.
Worth noting that to maintain the same %critical damping with stiffer springs, you only need to increase by the *square root* of increase in spring rate. 1.5X stiffer springs only require 1.22X increase in damping. Could be that this is within the dampers' adjustment range.

6k front/4k rear makes zero sense on this car. Assuming motion ratios of 0.95 front and 0.75 rear, your wheel rates are:
6kg/mm * .95^2 = 5.4 kg/mm front
4kg/mm * .75^2 = 2.3 kg/mm rear

If lengths are similar I'd consider swapping them front/rear to get 3.6 kg/mm front, 3.4 kg/mm rear wheel rates.

Last edited by ZDan; 01-12-2017 at 01:02 PM.
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