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Group A spring rate questions

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dirtbag240

New member
Joined
Feb 17, 2017
Location
vancouver canada
So i was just browsing through the group a 240 specs and read that they were running 800lbs front and 600lbs rear

Im running 300lbs front and 250 rears and its already pretty damn stiff, to the point where i can deffinetly feel a bit of skittering through highspeed corners in the front
,now if course race car vs hopped up station wagon

Though im still intetested how it wouldnt be super prone to over steer with springs that stiff

Does it just come down to wider taller tires and the 4 way adjustable dampers in the group A cars?
 
The fancy GrA dampers help, and race tracks are also much, much smoother than the average road that you drive on. I bet the car also ran a massive front sway bar, and a tiny or non existent rear.
 
mck1117 said:
The fancy GrA dampers help, and race tracks are also much, much smoother than the average road that you drive on. I bet the car also ran a massive front sway bar, and a tiny or non existent rear.
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So do the 240s benefit from having a large front bar and tiny rear? I would think that the different causes for massive understeer, but I've read of some people that remove their rear bar for autocross.
 
When you say Group A, I assume this is a reference to the actual Group A cars and not the standard cars with an intercooler that were sold in the US as a dubious way to get the homologation numbers up?

They ran on perfectly smooth tracks, ran slicks, had a rear diff/axle setup that was bent to provide “camber” despite being solid-rear-axle; it’s quite different to a road car.
 
GeneralBurrito said:
So do the 240s benefit from having a large front bar and tiny rear? I would think that the different causes for massive understeer, but I've read of some people that remove their rear bar for autocross.
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The rear roll center is so high and the front so low that you need a massive front and little to no rear to compensate. The roll center and sway bars both have the same effect on weight transfer, the only different being that the roll centers transfer weight immediately, and sway bars transfer weight proportional to roll, contributing to roll stiffness. While sway bars can help move the handling balance around, they are one part of the system that contributes to managing the front/rear distribution of weight transfer.

For example, I autocrossed my 240 sedan this past weekend with 550/225 springs, a 21mm front bar and no rear, and it still picked up the inside rear wheel in steady state cornering. The roll axis is so steeply inclined that when the car rolls, it also pitches nose down. This is why these cars need front roll center help if lowered, to help raise the front RC, balancing out the car.
 
mck1117 said:
The rear roll center is so high and the front so low that you need a massive front and little to no rear to compensate. The roll center and sway bars both have the same effect on weight transfer, the only different being that the roll centers transfer weight immediately, and sway bars transfer weight proportional to roll, contributing to roll stiffness. While sway bars can help move the handling balance around, they are one part of the system that contributes to managing the front/rear distribution of weight transfer.

For example, I autocrossed my 240 sedan this past weekend with 550/225 springs, a 21mm front bar and no rear, and it still picked up the inside rear wheel in steady state cornering. The roll axis is so steeply inclined that when the car rolls, it also pitches nose down. This is why these cars need front roll center help if lowered, to help raise the front RC, balancing out the car.
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Ah, I now see the need for the roll center correction from Kaplhenke.
 
Yep. It's not totally inaccurate to think of a high roll center as a "large sway bar" and a low roll center to be a "small sway bar". If you put the RCs at the height of the center of gravity, the car will have zero roll, but will also be incredibly hard to drive as you get no feedback (think go kart). Ever notice how soft, rolley-polley cars are really easy to drive at the limit? However if you put the RCs too low, the car will have excessive roll, making it difficult to manage camber on the outside tires.
 
So just to quickly understand,the reason our cars tripod in hard cornerd is becsuse the front is too soft with too low a rc so the car leans in on the opposite front side, so a bigger spring and bigger sway bar with a thinner rear bar means that itll keep the opposite inside tire on the ground allowing power to be put down?
 
Yes, making the front end stiff helps keep the rear wheels on the ground so that you can actually put power down. The rear end has a very high roll center, so it's like it already has a big sway bar, so you need compensate in the front end with some combination of raising the RC, and adding sway bar. If you look at pics of race cars with similar suspension setups from the 60s thru 80s, you can see that on many of them the front end is so stiff that it will pick up the inside front tire on corner exit. Some cars like the BMW e30 will actually do this on completely stock suspension.
 
mck1117 said:
Yes, making the front end stiff helps keep the rear wheels on the ground so that you can actually put power down. The rear end has a very high roll center, so it's like it already has a big sway bar, so you need compensate in the front end with some combination of raising the RC, and adding sway bar. If you look at pics of race cars with similar suspension setups from the 60s thru 80s, you can see that on many of them the front end is so stiff that it will pick up the inside front tire on corner exit. Some cars like the BMW e30 will actually do this on completely stock suspension.
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So would getting a thinner rear bar actually help? I'm on 23 front, 19 rear. I just think having too thick/stiff front bar would cause for more understeer, unless it's different on our cars compared to others.
 
GeneralBurrito said:
So would getting a thinner rear bar actually help? I'm on 23 front, 19 rear. I just think having too thick/stiff front bar would cause for more understeer, unless it's different on our cars compared to others.
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Going to a thinner bar probably wouldn't "help" as opposed to no bar. But it may be worth clarifying what you're trying to help. The 240 ends up with settings in the front (stiffening) that would of course produce understeer in order to maintain turn exit accel/traction.

I'm without question not as knowledgeable about suspension as some others but we shouldn't forget that we can't simply adjust one setting. We need to adjust to find the BALANCE of the car. In some cases, adding understeer to the equation to aid in traction on exit makes sense. In other cases taking out some understeer at the expense of traction on exit makes sense. The car needs to feel balanced for your style.
 
So if logic follows, currently im running a 25mm front and 23 rear and it feels pretty balanced but definetly tripods still would i make sense to go to a 28mm front bar, and leave the rear as is, or leave the front bar and up the spring stiffness all 4 corners to reduce overall roll

To add to that i have the koni single adjustable all 4 corners and righr bow my rebound damping is cranked to the max, how would adjustinf that help me
 
Also has anyone thought of a modular and adjustable front sway bar, similar to what you can get for most high performance cars.
Ben or anyone try it?
 
dirtbag240 said:
So if logic follows, currently im running a 25mm front and 23 rear and it feels pretty balanced but definetly tripods still would i make sense to go to a 28mm front bar, and leave the rear as is, or leave the front bar and up the spring stiffness all 4 corners to reduce overall roll

To add to that i have the koni single adjustable all 4 corners and righr bow my rebound damping is cranked to the max, how would adjustinf that help me
Click to expand...

I'm running 23 front and 19 rear and the car feels great, I guess it's about balance like said above and driver's preference. Some people like a super stiff track monster that won't do well on normal streets, others want good handling while keeping some form of comfort. A 28 front might help, but like said above, you're only changing one thing.

By the way, editing a post is possible so you don't end up double posting.
 
GeneralBurrito said:
I'm running 23 front and 19 rear and the car feels great, I guess it's about balance like said above and driver's preference. Some people like a super stiff track monster that won't do well on normal streets, others want good handling while keeping some form of comfort. A 28 front might help, but like said above, you're only changing one thing.

By the way, editing a post is possible so you don't end up double posting.
Click to expand...

Noted on the double post thing

And im lucky enough my local roads im driving agressivly are smooth, so im definetly aiming towards more the track monster that i daily, currently ive cornered up to about 1.2g on public roads on semi cold ventus rs-3s, just trying to figure out how to get every ounce of grip i can as well as pure curiosity
 
Like EvilEvo said, from the factory the suspension geometry has a bunch of compromises on these cars (and most cars, as a general rule). With the roll axis so steeply inclined, the handling can't ever be as good as a car that doesn't have that problem. Adding a huge front bar will help put power down on exit, but you'll bulldoze on entry.

The real solution is to not try and bandaid the handling with sway bars, but get the roll centers at more similar heights. The front can only be helped by a few inches, but the rear could be moved down considerably if converted to a Watts link. Also, lowering the car lowers the front roll center much faster than the rear. With stock geometry and the front control arms roughly level, the RC is right around ground level. At stock ride height, it's about 4-5" above ground. The Kaplhenke roll center correcting ball joint mount thingies help move the front RC back up a bit.
 
Okay so in relation to messing with the front roll centre,how could one bring it up higher off the ground past what bens rc correctors (which i have) are already doing, and has anyone done a watts link in the rear,what would be the disadvantages to a watts link vs stock if any?
 
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