MM Road & Track Springs

[Ivan 5.0]

Ivan, what is your sway bar setup? You got the stockers still? You take off the rear bar? How is the oversteer/under steer bias? You hit your bump stops any? Lets bring this thread back around to the topic.

I'm running Steeda's front and rear swaybar kit (35mm adjustable front/25mm non-adjustable rear). The front bar is set to the middle position. I haven't really pushed the car, but the current setup feels more "oversteerish" than my prior springs (Steeda Sports).

 

[sheizasosay]

My rear springs are very stiff (325lbs). I'm thinking about removing the rear sways to soften the rear for less "oversteer".

I'm running Steeda's front and rear swaybar kit (35mm adjustable front/25mm non-adjustable rear). The front bar is set to the middle position. I haven't really pushed the car, but the current setup feels more "oversteerish" than my prior springs (Steeda Sports).

Ok, I fought the urge earlier, but now it's too much to resist...TAKE OFF THE REAR SWAYBAR!!!!

 

[Ivan 5.0]

Ok, I fought the urge earlier, but now it's too much to resist...TAKE OFF THE REAR SWAYBAR!!!!

Wouldn't moving the front bar to the stiffest position reduce oversteer? Meh - who knows, it may feel just fine when pushed at the track...

 

[sheizasosay]

Wouldn't moving the front bar to the stiffest position reduce oversteer? Meh - who knows, it may feel just fine when pushed at the track...

You can and it would. That might also lower your overall grip though. If the rear rate is too high and you balance the front by increasing front wheel rate (which could reduce front grip) to get rid of oversteer would be an example.. I can tell you this: removing you're rear swaybar will almost certainly increase your rear lateral grip.

 

[claudermilk]

I'm thinking way ahead for my own car, but the question I think is relevant here.

In this case, would getting an adjustable rear bar and setting it to the soft position help? It seems like that would potentially balance the car without going to full stiff on the front and reducing overall grip. Educate me.

 

[Norm Peterson]

It would help as long as the soft position on the adjustable bar is softer than what you've got back there now.

A comparison of bar diameters will give you a hint, but since the arm length also matters (significantly!) you can't judge this based on bar diameter alone.


Norm

 

[Ivan 5.0]

Isn't the stock 2011 GT bar 25mm?

 

[Norm Peterson]

Fred Puhn's formula for sway bar stiffness of a solid steel bar (How To Make Your Car Handle)

Ignore all the leading decimal points. I grabbed this from a forum that allows multiple blank spaces and it's the simplest "fix" I could come up with.



. . . . . . . . . . . . . . . . 500,000 D^4
K (lbs/in) = _______________________________________________
. . . . . . . . . .(0.4244 x A^2 x B) + (0.2264 x C^3)


. . . . . . . . . . . . B
. . . . . . ._____________________
. . . . A| / . . . . . . . . . . \ C
. . . . .|/ . . . . . . .. . . . . \


A - Length of end perpendicular to B (torque arm - inches)
B - Length of center section (inches)
C - Length of end along arm (inches)
D - Diameter of bar (inches)

For a tubular bar, substitute [Outside Diameter]^4 - [[Inside Diameter]^4 for D^4


Edit - there are several other things that affect sta-bar stiffness, but the above formula seems to be about 95% accurate in most cases - close enough for most peoples' purposes.



Norm

 

[DRock]

Ok, I fought the urge earlier, but now it's too much to resist...TAKE OFF THE REAR SWAYBAR!!!!

Best advice i have heard yet.

Took mine off and never looked back

 

[sheizasosay]

Best advice i have heard yet.

Took mine off and never looked back

What rates were you running?

 

[DRock]

What rates were you running?

8K front and 5k rear. Coilovers.

Honestly without the rear sway it rides better, handles better and feels as if the rear end doesnt want to come around as soon.

I feel with a solid rear the sway really isnt as important

 

[Whiskey11]

8K front and 5k rear. Coilovers.

Honestly without the rear sway it rides better, handles better and feels as if the rear end doesnt want to come around as soon.

I feel with a solid rear the sway really isnt as important

Or for those who don't do the whole "8k/5k" thing, 450lbs/in and 280 lbs/in. Definitely would not want a rear bar with that setup. I'm contemplating pulling my stock 2009 GT rear bar with 550/275.

 

[Arustik]

Or for those who don't do the whole "8k/5k" thing, 450lbs/in and 280 lbs/in. Definitely would not want a rear bar with that setup. I'm contemplating pulling my stock 2009 GT rear bar with 550/275.

I ended up going back to the 250 rear spring will see how it feels with stock rear bar, if oversteery will pull rear bar. I also have dampening and rebound adjustments. Remember talking to you about this!

 

[FR500GT]

8K front and 5k rear. Coilovers.

What coilovers are you running?

Or for those who don't do the whole "8k/5k" thing, 450lbs/in and 280 lbs/in. Definitely would not want a rear bar with that setup. I'm contemplating pulling my stock 2009 GT rear bar with 550/275.

Could you explain a little more about this? (I'm a newb when it comes to swaybars)

 

[NoTicket]

8kg/mm instead of ~448lbs/in

 

[Whiskey11]

Could you explain a little more about this? (I'm a newb when it comes to swaybars)

What would you like to know about more specifically? The reason why I would pull the rear bar? The reason why I would pull the rear bar is based on my experience at 550/275lbs/in spring rates on my car. I feel that at my current rates the car is plenty loose (oversteer) and I personally am contemplating pulling my stock rear bar off because my front bar is already full stiff. Until I get to an actual autocross event, I'm not going to pull it though. He has less front spring rate than I do but more rear spring rate. That would push the car heavily into the oversteer direction, further than my car and thus I'd want less rear bar.

As for how swaybars work, well if we think of how springs work with weight transfer (not technically the correct term), coil springs work by reducing weight transfer the stiffer they get. The stiffer your springs are side to side the less body roll right? Well swaybars reduce body roll in a different way They reduce body roll by pulling weight off the inside tires and transferring it to the outside tires. The extreme example of this is a car that picks up an inside tire while turning. Depending on where your tires are at in their load range more swaybar can be a good thing or a bad thing. Good if you are under that load range and leaving grip on the table and bad if you are already at the max and more load reduces grip.

 

[sheizasosay]

A good read? http://www.ozebiz.com.au/racetech/theory/wttrans.html

 

[DRock]

What coilovers are you running?




Could you explain a little more about this? (I'm a newb when it comes to swaybars)

IM running BC's and really wish i had a stiffer spring up front. I would not recommend going any harder out back unless your going for the whole Becauseracecar thing. ha

 

[sheizasosay]

IM running BC's and really wish i had a stiffer spring up front. I would not recommend going any harder out back unless your going for the whole Becauseracecar thing. ha

Maybe lower your car more. I've ran the same front rate before with no other change but ride height and could tell a difference in brake dive. That's if you don't feel like changing springs.

Spring rates are easily the most varied "Reccomendation" there is. Unless the car is prepped to run a particular track with a particular tire and particular geometries and particular everythig else, it's a compromise.

I'm not saying 280in/lb isn't stiff. But on a track it's a lot more at home than on the street. Dual purpose cars are a compromise unless you want to drive a race car on the street or an OEM car on the track; both are purpose built.

 

[Whiskey11]

Maybe lower your car more. I've ran the same front rate before with no other change but ride height and could tell a difference in brake dive. That's if you don't feel like changing springs.

Spring rates are easily the most varied "Reccomendation" there is. Unless the car is prepped to run a particular track with a particular tire and particular geometries and particular everythig else, it's a compromise.

I'm not saying 280in/lb isn't stiff. But on a track it's a lot more at home than on the street. Dual purpose cars are a compromise unless you want to drive a race car on the street or an OEM car on the track; both are purpose built.

Good coilovers really helps calm this down. I wont deny that my car is stiff, but the ride is not harsh. The only reason I wouldn't go with more rear spring rate is because I don't think it is necessary without a lot more front spring rate. For a DD 550/275 is probably the end of the road unless you get some silly pimpy dampers with regressive piston curves and all that jazz.