Hey all,
I auto-X a small hatchback car in prepared class and I desperately need rear down force sinc the tail end is so loose it's almost dangerous at speed.
I was thinking of a spoiler but research show them only on sedans, I wonder if it will work on a hatchback? Any inputs? Am I better with a wing? If so, witch one?
thanks!
Go with front spoiler/splitter and rear wings like time attack
Or u could I steal a sprint car wing on the roof lol
what car is it? A more square hatch is easier to rig something than something with a lot of slope
You need this: 
The wing is a good way to go, but in prepared classes, wings aren't usually allowed except for XP. So I would check the rules first, to be sure.
Is there a reason you're jumping straight to aero? I've always been under the impression that it's better to mechanically balance the car first, then add balanced aero on top of that, to avoid the balance changing as the speed changes?
Sway bars? Springs?
rslifkin said:You need this:
That's the hat of a very experienced autocrosser
For autocross, the speeds are not high enough for a stock body to be aero sensitive.
I agree with Codrus on this.
Is your hatch FWD or RWD ? What have you done to the suspension ?
You probably could mount a spoiler on the roof.
The B Spec cars are mostly Hatchback and run at higher speeds on race tracks with no aero support and they have very stiff rear suspension.
something is wrong with your set up.
Does “at speed” mean it’s great on the course but scary on the street? Can you dial out some of the oversteer with strut/swaybar adjustment for street driving and quickly adjust at events?
As someone else mentioned, I *think* non-factory wing would bump you into XP, but I’ve been outta the game for a while.
many FWD cars understeer until they don't, then they go to snap oversteer.
We also need to know what's been done to your car and what class. If you removed a lot of weight, I bet you made the rear a lot lighter than it used to be
It depends on the rear window angle. On a nearly flat hatchback like a CRX, the air will stick to the hatch and you can use a spoiler or wing at the end of the hatch. Nearly vertical windows - as a rule of thumb, within 34 degrees of vertical - have the air separate from them and create a vortex. The spoiler or wing must go at the top of the window. I suspect a spoiler at the bottom of the rear window on a car like this will create lift instead of downforce.
Good way to test which one you've got - hose down the back window and drive on a dusty road. Dust sticking to the window? Separated air flow and have to work with things above the roofline. Rear window clean? You can use a spoiler under the window.
In reply to STM317 :
Yep. I met Brian in college back when his now-built EF sedan was just a $300 DD.
Definitely need more information about the current setup, but let me guess:
The car was under steering so:
Someone told you that you needed a bigger rear sway bar.
Someone else told you that you needed stiffer rear springs.
And a third person said you needed to raise your tire pressures by 10#.
So just to be sure you did all three.
In reply to 81cpcamaro :
You're about right, spoiler -> prepared, wings -> XP...
Now, car was an stf car last year and was doing pretty good, then Scca killed STF and I moved to E prepared..
Car is as follow in 2017
07 Honda Fit, coil over suspension full hard rear about 3/4 from full hard front slight under steer, 10k front 12k rear, rear sway bar, no front, level front a arm so no drastic drop suspension and level front to rear, square tire setup, 205/50r15 RE71r last year, 33 psi front, 28 psi rear, full interior..
what change in 2018:
strip the interior, a bit more power, maybe 10hp, 245/40r15 tires, 35 psi front, 25 psi rear, full soft rear, front still 3/4 full hard, lots of over steer f not cautious at auto x speed..
I pretty much did all I could and think of appart from putting the front bar back in and/or switching springs ....
codrus said:Is there a reason you're jumping straight to aero? I've always been under the impression that it's better to mechanically balance the car first, then add balanced aero on top of that, to avoid the balance changing as the speed changes?
Sway bars? Springs?
You may ght have a point here, didn't think/know about that....
In reply to wheelsmithy :
Hum! Not sure that really help, always tought it's more of a cosmetic thing done like that....
wings like that extend the roof line and add aero effects through a psuedo "kamm tail" effect. It basically fools the air into thinking the car is a LOT longer than it really is. The Volvo 850 wagons used in BTCC made extensive use of it with their long roofs.
rslifkin said:In reply to STM317 :
Yep. I met Brian in college back when his now-built EF sedan was just a $300 DD.
Lol. You can tell this is a car dork's forum. I was talking about the young lady!
mad_machine said:wings like that extend the roof line and add aero effects through a psuedo "kamm tail" effect. It basically fools the air into thinking the car is a LOT longer than it really is. The Volvo 850 wagons used in BTCC made extensive use of it with their long roofs.
So your telling me I should put back on my original spoiler, that it might help? That just extending the roof to the end of he rear bumber (can't go farther by the rules) would be even better?
So I'm not an expert on setting up FWD cars, but I think if you're saying the car is too loose and that it has no front sway bar, then that's the answer to your problem right there...
codrus said:So I'm not an expert on setting up FWD cars, but I think if you're saying the car is too loose and that it has no front sway bar, then that's the answer to your problem right there...
Might have to try that even if it means way to much time to put it back in....
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