high speed top end fish tail

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paint2361
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high speed top end fish tail

#1 Post by paint2361 » Mon Dec 15, 2014 2:14 pm

We just crashed our car. Car got very loose in high gear. In general, what are some common causes of a drag car getting tail loose at high speed? I know there can be lots of reasons. I just wanted to get people to put in there .02 cents...

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Re: high speed top end fish tail

#2 Post by John_Heard » Mon Dec 15, 2014 3:56 pm

I'm sorry to hear about your wreck. There can be of course many reasons, one of the top ones is getting something under the tires, ie transmission fluid, water, oil etc. This can be hard to catch at times, sometime video can help.

Getting out of the groove is certainly another situation. Cars won't got straight with one tire in the marbles and the other in the glue - of course the driver's typically involved in that one knowing when to lift. Oh, and my personal favorite, once the car gets out of shape, lifting then stabbing it again.

There could be problems with the car itself, such as broken heim end, screwed up front end geometry, the list goes on and on.

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Re: high speed top end fish tail

#3 Post by paint2361 » Mon Dec 15, 2014 4:12 pm

I lifted when I started to feel it get loose but it got worse and worse. Here is a link to a youtube video of our crash. Looks very bad but I walked away.
https://www.youtube.com/watch?v=9v1eC7O ... G-6XLwLHnA

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Re: high speed top end fish tail

#4 Post by John_Heard » Mon Dec 15, 2014 5:12 pm

The place that got you was when it went left, then you pulled it back "maybe" a little to hard. I certainly ain't trying to Monday morning quarterback you here, but that is where the problem started at about 10 sec mark / 330' in your video. It made a move left, you brought it back right, then the whipping got worse. Again take this as constructive cristism, but when it made that first move at the 330 to the left, lifting then let it move some left on it's own vs fighting it back right might have worked better.

Those kinds of situations are hard to get out of - of course in hindsight lifting earlier would have been a good idea. Sometimes you have to let the car go where it wants to when you lift instead of trying to force it. For example, you were far out enough in front of the other guy you could have let it move over into the other lane in front of him instead of trying to yank it back that might have worked. Of course it helps to have a very good idea where the other guy is when you pull a stunt like that.

I've also seen a friend run into similar situation, car was whipping back and forth violently and we all thought it was goner - but once it was pointed straight and he locked up all 4 brakes HARD and it broke the whipping cycle and saved it.

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Re: high speed top end fish tail

#5 Post by paint2361 » Mon Dec 15, 2014 5:24 pm

This was my thought too. Its good to hear someone thinking the same.

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Re: high speed top end fish tail

#6 Post by John_Heard » Mon Dec 15, 2014 5:45 pm

Good luck on getting her put back together. It sucks stuffing one in the wall, been there done that, got the T-Shirt.

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Re: high speed top end fish tail

#7 Post by paint2361 » Mon Dec 15, 2014 6:14 pm

it was a brand new build, the crash was its 5 run. We prob. ran it too hard too fast. The rear suspension is a traditional 4 link. but the front is a mustang 2 a-arm set up. We have coil overs all around but that front suspension never really looked good to me. It took a 650lb spring to hold up the car and has very little travel. Its fixable but need to rethink the front end. Could be why I had so much trouble controlling it.

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Re: high speed top end fish tail

#8 Post by John_Heard » Mon Dec 15, 2014 11:06 pm

How quick was it? I assume slicks but couldn't really tell. Were you running them pretty low on pressure? That'll certainly make some of them really sloppy feeling.

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Re: high speed top end fish tail

#9 Post by paint2361 » Tue Dec 16, 2014 12:18 am

yes we are running 13.5" slicks. 16 psi.
runs were in the upper 6's 1/8 mile. The last run I
crossed the finshed sideways at 7.22
So not super fast but fast enough to get into trouble.

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Re: high speed top end fish tail

#10 Post by John_Heard » Tue Dec 16, 2014 6:55 am

16 psi isn't low, in fact that's more than most run.

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Re: high speed top end fish tail

#11 Post by bracketchev1221 » Tue Dec 16, 2014 8:25 am

The travel didn't look too bad on the front end when it left. I assume its a rack and pinion steering setup, so steering box ratio Shouldn't be a big issue here? Just wondering also what the 4 wheel corner weights on the car are. Is it possible that with the height of the rear of the body that there is a lot of weight over the back end and once it gets moving sideways its hard to stop it?

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Re: high speed top end fish tail

#12 Post by apacheracing » Sun Dec 21, 2014 10:35 pm

Big slicks will feel like the car is getting loose until you get used to them. Lots of sidewall flex makes it feel like the car is moving more than it really is.
Nothing wrong with the air pressure at 16 psi if the chassis set up is sound. Lower air pressure will mask a chassis setup that is not quite right.
Once you get a 4 link car out of shape its very hard to catch back up with it because the way the car wants to pitch under the side load on the tires when sideways.
Sorry about the crash,
Nice looking car.

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Re: high speed top end fish tail

#13 Post by Craig W. » Tue Dec 23, 2014 10:13 pm

Could it be a mismatch of spring rates, front to rear? 650 lb front springs is quite stiff and I'm sure the rear isn't close to that.
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Re: high speed top end fish tail

#14 Post by paint2361 » Wed Dec 24, 2014 3:23 pm

Yes, We had to go with 650lb in front to keep it up.
The rears are a lot less. I think around 350 or 450....

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Re: high speed top end fish tail

#15 Post by Craig W. » Wed Dec 24, 2014 6:22 pm

I think you're on the right track to rethink the front suspension. Try to get some travel up front so you can get some weight transfer. I'd also look at the rear setup and try some more anti-squat possibly to help stick the tires. Looks like it was hazing them and that's what got it out of shape to start with.
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