Author Topic: chassis mods - length vs suspension?  (Read 330 times)

Offline Dunc the Funk

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chassis mods - length vs suspension?
« on: November 11, 2021, 10:11:50 AM »
Since we removed the coilovers from the rear of our car & made it solid, it launches FAR better. However it is now prone to bouncing in the shutdown area or if the driver has to get off the throttle in a hurry without pulling the chute first.

The wheelbase is 113". I'm thinking there are two ways to go which might improve the situation:

1. Extend the wheelbase to 125" & replace the beam axle with the modern triangulated axle mount system.
2. Keep the wheelbase short but add front suspension (most work I guess).

Any opinions on what would be best?

Offline Calkins

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Re: chassis mods - length vs suspension?
« Reply #1 on: November 11, 2021, 10:45:56 AM »
In my limited experience, a solid suspension car will bounce, period.  Flexie flyier top fuel cars are worse yet (ie, longer wheelbase).  Adding suspension is most likely your only option to correct it.  And, you may never completely fix the issue.  Look at your rear tires.  That big soft sidewall will add suspension, but also make the car bounce.
Justin Calkins - Iowa Falls, Iowa

Offline Finnish Fireball

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Re: chassis mods - length vs suspension?
« Reply #2 on: November 11, 2021, 11:49:14 PM »
Fact above, they bounce. I have had my 150" FED all four up in the air in the shutdown on a bad track. My spine says thank you. Pull the chute first, then "slowly and steady" release the loud pedal helps.
I'm fast. I can make five mistakes while others think.

Offline Dunc the Funk

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Re: chassis mods - length vs suspension?
« Reply #3 on: November 13, 2021, 08:03:18 AM »
Thanks for opinons, I thought that might be the case. We really don't want to go back to rear suspension as the launch was unpredictable. We'll just have to be careful I guess.

Offline Curly1

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Re: chassis mods - length vs suspension?
« Reply #4 on: November 13, 2021, 02:37:28 PM »
I believe a hard tail is going to have a bouncing problem and longer more flexible the chassis the worse it will be. Adding front suspension may help a little but most of the problem is from the rear of the car. They typically have 65% or so of the weight on the rear and the rear tires are much larger which can act like a basketball. I would really want to know why it did not work well suspended. I would make sure it has a good anti-roll bar, take the shocks off and work it through entire range and make sure no binding or slack. Then I would want to put a GoPro camera on the rear suspension and see what it is doing at the hit.  If there is not a good stiff anti roll bar that is first thing I would add. If you have a good one then I would also try the tests for binding and slop with and with out the anti-roll bar.

Rear tire pressure. The higher the pressure the more it will bounce. Too low and it will wallow around and feel mushy down track. On my 225" Front Engine Dragster there is very little between the two. A suspended car has so much more room for error and a shorter stiffer chassis needs the suspension in my opinion. With that said many argue that once you get to a certain ET then a suspended car will not work. I am not sure I believe that. I was told faster than 4.70 in the 1/8 mile you need a hard tail.

Offline THE FRENCHTOWN FLYER

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Re: chassis mods - length vs suspension?
« Reply #5 on: November 13, 2021, 05:05:05 PM »
I believe a hard tail is going to have a bouncing problem and longer more flexible the chassis the worse it will be. Adding front suspension may help a little but most of the problem is from the rear of the car. They typically have 65% or so of the weight on the rear and the rear tires are much larger which can act like a basketball. I would really want to know why it did not work well suspended. I would make sure it has a good anti-roll bar, take the shocks off and work it through entire range and make sure no binding or slack. Then I would want to put a GoPro camera on the rear suspension and see what it is doing at the hit.  If there is not a good stiff anti roll bar that is first thing I would add. If you have a good one then I would also try the tests for binding and slop with and with out the anti-roll bar.

Rear tire pressure. The higher the pressure the more it will bounce. Too low and it will wallow around and feel mushy down track. On my 225" Front Engine Dragster there is very little between the two. A suspended car has so much more room for error and a shorter stiffer chassis needs the suspension in my opinion. With that said many argue that once you get to a certain ET then a suspended car will not work. I am not sure I believe that. I was told faster than 4.70 in the 1/8 mile you need a hard tail.

^^^ X2
Re suspension on faster cars: I don't buy that it won't work. Don't Pro Mods and Pro Stocks and FAST Comp Eliminator altereds have suspensions? Surely then, one can be made to work on a fast altered.

Offline JEFF/21C

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Re: chassis mods - length vs suspension?
« Reply #6 on: November 14, 2021, 12:23:52 PM »
On the 160" fed  we had bad bounce, even ran off the end of an outlaw track with short shut down area,  the remedy for us was to shift into neutral before braking.

Offline Curly1

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Re: chassis mods - length vs suspension?
« Reply #7 on: November 21, 2021, 11:21:59 AM »
On the 160" fed  we had bad bounce, even ran off the end of an outlaw track with short shut down area,  the remedy for us was to shift into neutral before braking.

Using the parachute helps with bouncing in the shut down. Still if you have suspension I would try to make it work.

Offline BK

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Re: chassis mods - length vs suspension?
« Reply #8 on: November 21, 2021, 05:45:54 PM »
How much air pressure in rear tires?
With my FED, once I got under 5#s I could do what ever I wanted with the brakes and it wouldn't bounce.
Once you get rid of the shocks your tires became your suspension.