To aggressive?? Alignment

j-rho

What type of tires to you run/race on? Square sized or staggered?

2.75 isn't outside the ballpark for a car on R-tires or slicks. For a track car with aero (which adds normal force at speed) it maybe puts it in the ballpark for a good street tire.

What stands out to me is the disparity between front and rear. Your ride frequency split is a good starting point for a FWD race car on street tires :-)

If your front ride frequency was raised to 2.8-3.0 and you had a square wheel/tire setup with sensible bars and alignment, I bet you'd find the car was fairly well balanced - without having changed the rear. But overall those frequencies are a little high for surfaces that aren't pretty smooth.

Every car is different, and what's best depends on the type of racing, level of grip (at each end), and power levels (including where it gets sent), among others.

For a decently balanced and moderately powerful RWD autocross car on good modern street tires, I like starting around 2.5 front and 2.2 rear. The higher the power for the grip level, the bigger the difference I'd probably end up with - a Miata might be 2.5/2.5, but a Corvette I might go 2.7/2.1 - the reasoning being, the more powerful car needs to work the drive tires a little bit less in the corners to make use of its power. Obviously swaybars and their contributions come into play and can influence the resulting frequency splits.

Smoother surfaces and higher grip tires trend those numbers up; rougher surfaces and lower grip tires trend them down.

Good luck, have fun, be safe on the streets!

synolimit

RS-3's right now but later conti slicks. I'm 285/35 square on these RS-3's on 10.5's.

03threefifty did my numbers, how did he figure them out? How do I turn up the front?

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synolimit

Ok I've removed an endlink on the rear. Quick question...why doesn't everyone run a high spring rate and remove the rear bar (for weight reduction) ?

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03threefiftyz

Some of us do. Not so much for weight, though.

synolimit

I thought you told me but what size? True type? What about me being on track and you doing autoX? Won't I want a better rate and rear bar for really long sweepers? Ideally of course.

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03threefiftyz

The principles are the same really....

I am not on a true type, but I might toy with it a bit this rear. I run a lot of spring, though and it will be higher this year since it has real aero.

synolimit

Same here. If Martin is correct and my GTC-250 has a ton more down force than an Aeromotions, then it's a step in the right direction. Now if I can only figure a new tank setup, I want to run the exhaust out the quarters or side skirts. This would allow a real diffursor (took some notes from a 458 ). After that and a flat bottom I should be golden.

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03threefiftyz

The real focus on aero should be up front...

synolimit

Can't do more than that.

Although I was thinking about some edges for the sides of the canards. Like a 90* side there.

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j-rho

Scott you have a lot of good questions but they require conveying a body of knowledge exceeding what makes sense to post. Here's a couple books that make great entry-level to intermediate texts:
http://www.amazon.com/Chassis-Engine...dp/1557880557/ (my favorite)
http://www.amazon.com/How-Make-Your-...our+car+handle

From them, you can gain an understanding of the pros and cons of stiffer vs. softer spring rates and sway bars...

As for how to increase front ride frequency - the easy way is to up spring rate.

03threefiftyz

There is a whole lot more you can do up front, but it is wasted effort unless you can prove it first with sufficient, reliable CFD or in a tunnel. Cost = $texas.

Jason is right, there is a lot to be learned, but there is no reason not to baseline your start point off of what others have proven to work. That said, everyone is not the same in what they look for in a car, so it should be just a starting point. It took me almost 3 years to get a consistent set-up for differing surfaces we run in national autox. Once I got it...I decided to go road racing and had to change everything .

Bottom line, you need to ditch that rear spring. There is no reason to try and cure an oversteery car by adding a ton of rear wing/drag to the butt of the car. It's all about balance, man.

GSS138

Yeah leave aero alone for a while, would agree. This car does not need a ton of aero in the rear to put in good times. If the problem is the springs, don't fix the springs by adding more aero. Like 350 said, it takes a long time to dial in. My car was barely drivable, scared the hell out of me from last august to just this april. It's not gran turismo unfortunately lol, it takes a long long time. If you keep adding problems on top of problems, you will never figure anything out.

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synolimit

Guys I'm just talking, not taking everything seriously. Just having a conversation and seeing what's done. I know there's more to it and know about the springs. Just learning something new everyday and finishing my build 1 thing at a time.

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Rusty

Scott, when are you going to get this thing on the track? That's the only way to know for sure on what your set-up is. Playing around on the street is one thing. The track is a different beast. You should know that.

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synolimit

I know and I've said that. Soon I hope, just a few more things to do. Mid Ohio has a few days coming up.

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