SCCA Autocross setup thread

At the EcoBoost challenge the Focus ST was usually setting fast time on a fairly tight course.

That was stock cars/tires with no prep but if those results are indicative it will take a very tight course for the Fiesta ST to have an advantage.

I've got to read the rules but I don't think our classification is going to translate to instant domination.

I would like to know if the 225-50r16 BFG Rival fits. It might be better than the Direzza z2 but if it won't fit, the Direzza seems like a good option too.

Rotational weight and acceleration are one thing but light wheels also have the advantage in unsprung weight which makes it easier for the shock to damp wheel motion and that means more grip if you tune for it.

I'm going for light 16's because I want a bit more sidewall. So far the reports on 16" tires I've read say there is very little loss of turn in response so I think that's probably the right direction.

I've heard some people will try 15's so we will have a lot of data to compare pretty soon.

That sounds like the 225-45r16 Direzza ZII is near the sweet spot (at least with 200 tread wear).

Tell us more about the rear bar, what improvement did you see by lowering the rear tire pressure to 31?

Stock tires will start plowing in tight turns if you get them too hot, the brakes seem to get a little cooked toward the end of a long course too.

For me that meant I was faster if I didn't go so deep in to the last two hairpins.

That's course dependent but if you feel it happening you can try to back off toward the end.

Despite our fantastic pads, our brakes are on the small side and the e-diff/torque vectoring doesn't help.

Our tires limit us more but the brakes are not too far behind.

Its a PBR type caliper, there should be pads available from many manufacturers unless the pad thickness is weird.

Ours have extra dust and smell a bit but they stop the car pretty good for the size of our rotors. You might not find anything that works better unless you sacrifice cold stopping, noise, rotor wear or something.

Slowclimb said:

The issue for me is that the tire will contact on top - hitting the fender liner...I am pretty sure they will fit width wise since they are 1/2 an inch narrower than the Dunlop 225 45 16, which we know fits. The 24.7 inch Diameter is what I am curious about.

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This sounds like a bump stop issue.

If you go too far and lower the car, that might leave you with very little bump travel which could make for a bumpy ride on rough pavement.

I'm starting to think the ultimate performance solution that bumps you in to an ST class is Mazda 2 hubs in front and re-drilled rear hubs for 4*100 lug pattern and a set of 949 racing Miata wheels in 15*7.5 or 15*8 with BFG rivals in 225-45r15 (I think) and the biggest brakes that we can fit inside a 15" wheel.

That will be nice and light weight, maybe 10lbs lighter per corner than stock, plenty of room for bump travel and not terribly expensive for tires and wheels.

Radial tire construction is about as far from bicycle tire construction as you can get.

A motorcycle tire might behave similarly, maybe a wrinkle wall slick or sand rail tires too but anything like a road car tire will behave quite differently than a bicycle tire.

What's the verdict on the ZII as a street tire?

I might get a set if they can last more than 15,000 miles on the street.

That photo makes it look like it will fit but reduce ground clearance a bit.

The photos of that sway bar I have seen are on Mazda 2s or a base Fiesta maybe with the twist beam channel facing the rear and the bar tucked right in.

Its good to see an alternative.

Mightymango said:

What pressures were you running in the front? That shot shows how much these cars could use a little more camber. Looks like you were rolling on the sidewall.

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+1,

We need to lower the cg and increase roll stiffness but without making it have too much under steer.

That just unloads the inside front wheel which leads to under steer unless you lower the cg, increase the track or do something else to reduce the rolling moment.

Well look for a base Fiesta front bar, its only a little stiffer than the ST piece.

The alternatives are all too big.

I was a little slow on the reply, I was commenting on adding a large front sway bar, not shocks.

I've never had the chance to tune a car with adjustable shocks or do before and after tests with differently valved shocks.

Since that's not a knob I could adjust I haven't thought about it much.

I have put a big anti-sway bar on an old mustang convertible but it was a mess before and after the change. It traded body roll for chassis twist but at least it felt less boat like.

Luckily modern unit bodies with a roof are stiff enough that suspension adjustments generally do what you think it should.

I need to look at these knuckles. It would be interesting if the difference was just strut mounting holes drilled 15mm lower...

Is that bracket for a sensor or the mass damper?

We probably don't need a mass damper if we go for light wheels and better damping struts.

I'm thinking the Steeda adjustable anti-sway bar end links might be a good tweak to offset the weight of the driver.

Is that legal in the stock class?

I think it might be helpful even on a coil-over car.

Cligedy said:

3.7 ANTI-ROLL (SWAY) BARS A. Substitution, addition, or removal of a single anti-roll bar and supporting hardware (brackets, endlinks, bushings, etc.) is permitted.

There is no rear bar to begin with, so I think you can use whatever mounting hardware you'd like.

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The Steeda end links are for the front anti-sway bar. They just allow you to pre-load it which I'm thinking might help compensate for not quite perfect cross weights.

The back might like pre-load also but I don't think the effect would be as great.

It seems that once you get tires figured out the Eibach rear bar is the thing you want to make the car rotate and if you need to balance it out, you can get a base Fiesta front bar to add a little stiffness at the front. The Steeda end links might be a good tuning aid.

Race wheels, shocks/struts, a big brake kit and weight reduction round out a comprehensive handling upgrade.

How much of that you can do is up to your class rules.

I just wish someone would actually stock the rear bar so we don't have to order and guess about when it will come.