Rear Suspension question

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Rear Suspension question

Post  jones on October 25th 2015, 9:39 pm

I have seen drag cars that squat in the rear and some that raise coming off the line. My 79 f150 with leaf springs seemed to raise off the line. Almost all the factory suspension fox body mustangs squat.

My question:

1. How do you know what is better for you car? (my 79 was running drag radials and never dead hooked, it always spun maybe a rotation but would cut a 1.80 60ft)

2. How do you make a car that normally transfer's weight to a car that get's up on the tire?

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Re: Rear Suspension question

Post  mudranger on October 26th 2015, 3:23 pm

The separation is a product of having leaf spring suspension.
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Re: Rear Suspension question

Post  DILLIGASDAVE on October 26th 2015, 6:09 pm

jones wrote:I have seen drag cars that squat in the rear and some that raise coming off the line.

Don't forget that sometimes what you think looks like the rear suspension it's self squatting at the hit is really just the rear rims physically getting closer to the track surface as they wind-up the slick's sidewalls.
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Re: Rear Suspension question

Post  jones on October 27th 2015, 7:16 am



I use to take picture of cars leaving the line and it's a night and day difference. One the body comes down and causes in some cases the tire to rub the inner fender. The other the body and wheel separate. ( I don't mean a G-body shuffle or a fox body car that twist and pops tail lights out)

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Re: Rear Suspension question

Post  supervel45 on October 27th 2015, 7:42 am

https://www.youtube.com/watch?v=3Wr4yjA1xrU This one squats even spinning. Slapper bar, drag shocks and maybe removing a leaf should help if you don't have them already.

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Re: Rear Suspension question

Post  jones on October 27th 2015, 8:26 am

supervel45 wrote:https://www.youtube.com/watch?v=3Wr4yjA1xrU                                                                                                                                            This one squats even spinning. Slapper bar, drag shocks and maybe removing a leaf should help if you don't have them already.

Me personally: I have thought about caltracs but it's cheaper to just build a set of long bars. The desert racers that are familiar with my body style and suspension say the most of the time the truck center of gravity is around the drivers seat. I'm just trying to wrap my head around suspension systems and how they work and what is the ideal setup.

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Re: Rear Suspension question

Post  DILLIGASDAVE on October 27th 2015, 7:02 pm

jones wrote:........ and what is the ideal setup.

No such animal, most every factory or aftermarket rear suspension type/style out there has it's good & bad points. And traction control/ignition control devices (and similar boxes) have further blurred the lines.Laughing

The thing I have noticed over the years is way too many people focus on just either the suspension linkage/leverage/type it's self, or the associated I/C placement of each type, but forget about what shock valving adjustability & control brings to the table. As an example depending on the quality of the adjustable shock & power numbers you can sometimes make a ladder bar suspension either separate a ton at the hit, or have zero/damn near zero separation, just by adjusting the rear shock extension valving without touching the ladder bar's I/C height.

Also should be mentioned that the launch pics you took, while a helpful learning tool, don't tell the whole story. Video shows a much more complete picture of what's going on in real time during the launch. A picture taken a slit second (or more) after the initial hit actually happened (during the recovery period) that happens to show rear suspension squat doesn't reveal any small/large momentary rear suspension separation that might have happened earlier during the initial hit period. The human eye is often way too slow to pick up everything that is going on at real speed as it happens during the launch. IMO most people that think they saw what happened during "the hit" are actually seeing the recovery period (because it usually lasts longer) and are not really seeing what happened during the actual initial hit it's self because everything is happening so fast at real speed. Because of this it's my opinion that actual real/true suspension squat happening at the initial hit doesn't really happen as often as people think it does. They are actually seeing either the sidewall wind-up and resulting "rim drop", or seeing the recovery period, and mistakenly thinking "suspension squat" happened during "the hit". IMO if a car's rear suspension actually does squat during the initial hit period, (regardless of what it does during the recovery period) it's usually going to spin it's nuts off during the initial hit. Some given amount of separation at the initial hit is what drives the slick into the track surface & helps initial traction.    


Any number of things might be really happening as the launch unfolds that the eye can't keep up with.....

A car might actually separate a decent amount during the hit, then a split second later squat during the recovery period. Or separate some, then stay separated. Or have zero separation at the hit & zero squat during recovery, but it still looks like squat because of the side wall wind-up. Short of having onboard real time shock extension/compression data to tell what's actually really happening during the initial hit & recovery periods of the launch, launch video is the next best tool.




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Re: Rear Suspension question

Post  jones on October 27th 2015, 10:47 pm

That you Dave! I know that it's almost imposable to learn about suspension with out being able to see and feel the changes you make. Atleast that would be the best way for me to learn.




The two trucks that I have ran before both had leaf springs. On both I removed a number of springs and bought aftermarket HD shocks sold for a 1ton. My next project has an added twist, awd! I plan on installing longer radius arms, shorter coil springs, limit straps and the highest quality shock I can find. Rear suspension; remove some leaves, longer shackles, some type of axle bar and quality shocks. My project is going to take some time to figure out. I've been reading up on what the Baja racers adjust on this suspension style in hopes of learning the dynamics a little better.

All I know right know is that for the heavier and more powerful engine the more resistance the shock needs to be able to handle?

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Re: Rear Suspension question

Post  DanH on October 28th 2015, 9:27 am

Jones, you going Baja racing? other type of performance/racing?
trying to use one form of set up on another type will get you noplace in a hurry.

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Re: Rear Suspension question

Post  jones on October 28th 2015, 9:56 am

DanH wrote:Jones, you going Baja racing? other type of performance/racing?  
trying to use one form of set up on another type will get you noplace in a hurry.

Street and No prep racing.

Of course I no better that to think 20" of suspension travel is needed up front with some giant shocks

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