Author Topic: FED bounce problem.  (Read 2086 times)

Offline Curly1

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FED bounce problem.
« on: June 20, 2020, 07:15:28 AM »
I have a 225 inch FED runs 4.90-5.0X and I am having a problem with it. Data logger is showing some bounce / tire spin down rack. Last race I took the wheelie bar off and weight out of nose to be able to run index in high altitude bad air.  I THINK I know what the problem is but want some input on how to resolve it. Mind you it is not bad but I want this car to get down any track under all conditions as close to perfect as possible.
Last week in final round saw a video that kind of affirms my thoughts. The car took off at the hit and pulled front wheels up about 8 inches and carried them out about 60 foot and then set them down nice and smooth. That is more than normal but no big deal. What I saw that was interesting is a lot of chassis flex in the middle and what I think is happening is with the long car it is flexing and causing bounce down track.  I understand some of that flex helps it hook but I think it is too much here.

I THINK stiffening up the chassis will help it hook better and smoother in the shut down area to. Several tracks we run at is rough in the shut down and it will get my car bouncing. I have also done a lot with tires and tire pressure but this is more than tires now.

My question is how can I test and verify my thinking on stiffening the chassis? Was thinking about tying the chassis with cable under tension to see if it helps and verify it is right direction to go. Something where it attaches in the front and back and goes over middle bar on top to limit downward flex. Then if it works could go in and add more bars to stiffen chassis. I want to do it right but want to verify it is heading in right direction and not making it worse before I do a bunch of major chassis changes.

Offline wideopen231

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Re: FED bounce problem.
« Reply #1 on: June 20, 2020, 08:37:58 AM »
probably off wall idea. Maybe identify where flex is. Either video of chassis.maybe go pro mounted front facing back where you think it is. Maybe something as stupid as piece of good tape around area.If broken you know its flexing. there. Heck use small cable if any real bounce it might show it. Again off the wall ideas

I don't think you will get it all out of a FED. I noticed mine getting good bounce last weekend when entering bleach box. Also noticed I may be doing some rework during extreme heat part of summer,Motor plate seemed to hit with bounce. Might be raising chassis or lowering rear end inch or so. Bigger tires are next option,taller that is. 

After years watching FEDs get real bounce in shut down I have my chute handle setup manual or air for oh shyt moment.Now to get fast enough shot to see how it works.Only 125 so far and was still in throttle thru light. Also applying brakes some while baking off throttle. Man these things do require a driver.Got to love it!
Relecting obama is like shooting right foot because it did not hurt enough when you shot left foot

Offline dusterdave173

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Re: FED bounce problem.
« Reply #2 on: June 21, 2020, 01:42:06 PM »
Our car would bounce if you got on brakes too hard--Ease down GENTLY on the brakes and ours was minimal--I had a 200 in car with torsion bar front--if we ran it out the back door or hit brakes hard and or rough track she would really scare you but we learned if bad get on power start all over again on slowdown and if we did run out of room just ride it out and pray--I had one run my dad was watching and it was a even match so I ran it out the back door to hard then ran out of room and Had to brake hard --it bounced so hard I smacked a place on my helmet--got lucky and did not wreck but taught us a lesson----You can practice like when you run 1/8th on a quarter length track --Brake hard get her to bouncing--get on power --start over--it is a good lesson to learn you car
I have always had a fascination with fast cars at the expense of more normal character development

Offline Curly1

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Re: FED bounce problem.
« Reply #3 on: June 21, 2020, 05:11:00 PM »
It is bouncing some during the RUN under power! And you could see the flex in the chassis when front wheels are in the air. Now the shut down area is a different issue and yes easing into the brakes or throwing parachute out helps.

I can deal with the shut down area but I want it to hook good on any track any time and right now it is not. I suspect it is too much flex in the chassis allowing it to bounce under power. I want this car to be best performing car out there to carry me when driver is not on top of his game. Lol.

Another thing I do not mind adding more bars to stiffen chassis thing is I want to find a way to verify that it will help it before I do it.

Offline wideopen231

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Re: FED bounce problem.
« Reply #4 on: June 22, 2020, 05:08:04 AM »
MAybe some chassis pics would help those who know what they are looking at to see something. By the way I am not one of those folks Roo man or Bruce might see it.

Doe it have diagonals  in front section of frame? Is frame wider style or narrow like older cars? 
Relecting obama is like shooting right foot because it did not hurt enough when you shot left foot

Offline Curly1

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Re: FED bounce problem.
« Reply #5 on: June 22, 2020, 02:47:23 PM »
Frame is wider style with diagonals so it should be relatively stiff chassis. That is part of reason I am reluctant to just start adding more bars.

Offline xlr8

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Re: FED bounce problem.
« Reply #6 on: June 23, 2020, 12:40:02 PM »
I would check the chassis for cracks first. Sounds like a lot of flex.
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Offline BK

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Re: FED bounce problem.
« Reply #7 on: June 23, 2020, 07:27:14 PM »
I just let air out of slicks until it stopped bouncing.

Offline Curly1

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Re: FED bounce problem.
« Reply #8 on: June 24, 2020, 05:21:42 PM »
I have tried 4 different tire combinations at all different air pressure. Will try another tire combination soon but I know the chassis is flexing and I know the tire is bouncing until I drop it down and then it wads up and chatters and all over track at the top end.

My thoughts are tire change will help some at the hit and in the shut down. Parachute will help in the shut down but I THINK the bouncing in the middle of the track is chassis flex and that is what I am trying to eliminate here.

This car is not bad and it is very competitive but it is not perfect yet.

Offline wideopen231

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Re: FED bounce problem.
« Reply #9 on: June 25, 2020, 01:17:10 PM »
 Question and not being smartazz this time.  Are you sure its because of flex? I have had cars act stupid because too rigid or where in bind from chassis work that had been done. If memory serves  you had a bunch of chassis work done. Has cart had this problem  ever since? You stated it rigid chassis now.  Do you have daat recorder on car? If so it would dang sure show any bounce in driveshaft  graph.
Relecting obama is like shooting right foot because it did not hurt enough when you shot left foot

Offline Curly1

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Re: FED bounce problem.
« Reply #10 on: June 25, 2020, 02:35:32 PM »
Data logger driveshaft sensor is showing bounce and tire spin. I also feel it and others have seen it. Could chassis be too Rigid? I guess it is possible but I can see flex and feel it flexing so my thinking is it is probably too much.
When the car pulls a wheelie you can see the flex in the chassis. You can also see evidence of chassis flex on the body panels.  It pulls wheels up nicely and carries them out a way then sets them down pretty soft. But I think after that it is still flexing some and causing the bounce in low gear and after the shift.


Offline gregm784

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Re: FED bounce problem.
« Reply #11 on: July 07, 2020, 11:45:19 AM »
Silly question,  is the car or the track?

mine bounces good on some tracks.  driveshaft speed looks like a sewing machine needle.
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Offline BK

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Re: FED bounce problem.
« Reply #12 on: July 09, 2020, 06:18:26 AM »
I've heard of adjustable cables in rear engine cars.
What are they for and is it anything that might help your problem?

Offline wideopen231

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Re: FED bounce problem.
« Reply #13 on: July 09, 2020, 07:11:20 AM »
normally. Cables in rear engine cars are right in front of drivers compartment. They are adjustable tension wise and allow car to arch more while limiting travel in opposite direction. If car flex is from downward motion and reactions.Then  I guess they could help Curly there.  Now that is my understanding.Not chassis expert like Roo man and Bruce,but I have slept in holiday inn(or what motel in commercial). 
Relecting obama is like shooting right foot because it did not hurt enough when you shot left foot

Offline Curly1

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Re: FED bounce problem.
« Reply #14 on: July 10, 2020, 09:04:18 PM »
I simply do not know just looking for a way to verify it is right direction before I do something more permanent like welding more diagonals.