Guide to Rear Shocks for Ladder Bar Drag Car (Pro Street)

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72DMag

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Hi guys looking to see if there is a guide available for upgrading and replacing rear shocks on a ladder bar drag car that may possibly see some street use in the future.

The car is a 72 duster and weighs about 3000 lbs with me in it. I'ts all steel. Measuring for the shock height is easy but does anyone have any guides or documentation for the different styles of shocks or that compares them brand to brand. Every car reacts and hooks different so where to start when shopping?? Thanks in advance for any input and assistance.
 
Not sure what power level we are talking but probably a double adjustable for sure so you can adjust street/strip and then talk to the companies your considering about what you expect and they will guide you. I recently got some vikings for my cal track set up and they pointed me to what I needed and helped with set up and 4 races in set a new personal best in 60' and et
 
Think of it in terms of slowing the motion of the rear housing. I am on my fourth set of shocks in back, ending up with Afco BigGun shocks which are able to handle 926 hp, a 11.17 SLR, a 30 inch ladderbar and 10.5x33 Hoosiers plus transbrake.
To see how brutal things can get, hear is the math; engine torque x 2 (converter)1500 x SLR (low gear x rear gear) 11.17= 16,600 ft lbs at the hit trying to swing the rear housing down. With a 30 inch ladderbar (2.5 feet)= about 6500 lbs of torque is what those shocks have to control to slow down the housing at the hit.
 
gregsdart said:
Think of it in terms of slowing the motion of the rear housing. I am on my fourth set of shocks in back, ending up with Afco BigGun shocks which are able to handle 926 hp, a 11.17 SLR, a 30 inch ladderbar and 10.5x33 Hoosiers plus transbrake.
To see how brutal things can get, hear is the math; engine torque x 2 (converter)1500 x SLR (low gear x rear gear) 11.17= 16,600 ft lbs at the hit trying to swing the rear housing down. With a 30 inch ladderbar (2.5 feet)= about 6500 lbs of torque is what those shocks have to control to slow down the housing at the hit.
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Whoa
 
gregsdart said:
Think of it in terms of slowing the motion of the rear housing. I am on my fourth set of shocks in back, ending up with Afco BigGun shocks which are able to handle 926 hp, a 11.17 SLR, a 30 inch ladderbar and 10.5x33 Hoosiers plus transbrake.
To see how brutal things can get, hear is the math; engine torque x 2 (converter)1500 x SLR (low gear x rear gear) 11.17= 16,600 ft lbs at the hit trying to swing the rear housing down. With a 30 inch ladderbar (2.5 feet)= about 6500 lbs of torque is what those shocks have to control to slow down the housing at the hit.
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Exactly. You have to control the motion of the axle. Ladder bars, by their nature are very violent and because you can’t lower the Instant Center (IC) and move it forward you have to have a shock capable of dealing with that violence.

If you don’t get control of it you’ll just beat the tire to death.

As an example, on my best stuff I was at least 200 HP down from Greg’s stuff, and for my gearing, tire size, torque output and curve my IC was 104 inches out and 4 inches off the ground.

If I had a ladder bar I would have been limited to whatever the length of the bar is (usually 32 inches) and whatever the the height of the holes are from the ground.

Clutches and ladder bars HATE each other. BTDT. I’ve seen downloads from stick cars and ladder bars and the shock speeds were so fast that at that time one of the few remedies was to move the shocks to the front of the axle.
 
yellow rose said:
Clutches and ladder bars HATE each other. BTDT. I’ve seen downloads from stick cars and ladder bars and the shock speeds were so fast that at that time one of the few remedies was to move the shocks to the front of the axle.
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Curious about how moving the shocks ahead of the axle improved a ladder bar separation issue? Can't say that I've made that move myself, but I would think moving the shocks closer to the ladder bar's front pivot point would make them less effective.

Grant
 
weedburner said:
Curious about how moving the shocks ahead of the axle improved a ladder bar separation issue? Can't say that I've made that move myself, but I would think moving the shocks closer to the ladder bar's front pivot point would make them less effective.

Grant
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It didn’t change the separation. Moving the shocks to the front of the axle changes the motion ratio and the shock speed slows down. We were trying to get the shock speed under control.
 
I would think moving the shocks ahead of the axle would increase chassis/housing separation speed with ladders. Better shock angle after the move?

Grant
 
weedburner said:
I would think moving the shocks ahead of the axle would increase chassis/housing separation speed with ladders. Better shock angle after the move?

Grant
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You change the motion ratio. If the shock is mounted directly in top of the axle the motion ratio is 1:1. If you mount it behind the axle it is higher than 1:1 and I don’t remember exactly how far behind the axle centerline the shock mount was so I’d be guess but it’s easy to measure.

My best guess from 1987 or so is the motion ratio was 1.15:1 with the shock behind the axle and .85:1 in front of the axle. I could be off a bit.

We weren’t trying to limit separation with the shocks. You do that with the IC height as best you can with a ladder bar. We were trying to lower shock speed because we didn’t have enough valving to do it.
 
Not enough valving and killing the tires suggests to me that there was a separation speed issue. Moving the shock forward for the purpose of showing lower shock speed data, while at the same time reducing that shock's ability to control actual separation speed, just having a hard time wrapping my head around how that makes the car quicker.

Here's an example- if you attached a shifter stick to the bench, and attached a shock to the middle of that shifter stick, the closer to the bottom pivot that the shock is attached, the easier it is to move the shifter handle. As the motion ratio of the shock decreases, the shifter handle gets easier to move. Speed data for that shock would show slower due to less distance traveled, even though the handle itself travels the same distance in the same amount of time.

Grant
 
weedburner said:
Not enough valving and killing the tires suggests to me that there was a separation speed issue. Moving the shock forward for the purpose of showing lower shock speed data, while at the same time reducing that shock's ability to control actual separation speed, just having a hard time wrapping my head around how that makes the car quicker.

Here's an example- if you attached a shifter stick to the bench, and attached a shock to the middle of that shifter stick, the closer to the bottom pivot that the shock is attached, the easier it is to move the shifter handle. As the motion ratio of the shock decreases, the shifter handle gets easier to move. Speed data for that shock would show slower due to less distance traveled, even though the handle itself travels the same distance in the same amount of time.

Grant
Click to expand...
I agree. IMHO it is too little available shock control for the job. This became apparent to me when i started examining launch videos frame by frame. At 24 frames per second things were happening so fast my wheeliebars would actually hit and rebound between frames. That is .04 seconds frame to frame. It took several launch vids to see this as then i could see the wheelie bars at different points of travel, and figure it out.
 
@gregsdart Wow that's crazy that your car was doing that. How did you see this? Go Pro under the car?

Well the car is a 72 duster all steel 3000lbs with my big butt in it, small block making right at 500 hp at the flywheel. Its nothing too crazy. I have a 8 3/4 rear axle. I do think the shocks will be mounted on the rear of the axle because the 8 3/4 has a brace and based on mounting locations that looks like they should be there. The other thing is that the car does sit low!! I have 2" drop spindles by pst. I've been reading and still reading/learning Bickell's book regarding the neutral line and the cg and IC points and concepts. Based on his book and my understanding, I think going with a lower ic for a smaller hp car is a good thing because this will keep the tires planted and weight transfer and I do not have the horsepower to shake the tires.

Problem is this car is newly back halfed and never been down the track so no clue where to start for shocks.? :(
 
weedburner said:
Not enough valving and killing the tires suggests to me that there was a separation speed issue. Moving the shock forward for the purpose of showing lower shock speed data, while at the same time reducing that shock's ability to control actual separation speed, just having a hard time wrapping my head around how that makes the car quicker.

Here's an example- if you attached a shifter stick to the bench, and attached a shock to the middle of that shifter stick, the closer to the bottom pivot that the shock is attached, the easier it is to move the shifter handle. As the motion ratio of the shock decreases, the shifter handle gets easier to move. Speed data for that shock would show slower due to less distance traveled, even though the handle itself travels the same distance in the same amount of time.

Grant
Click to expand...


That’s what I’m saying. There wasn’t enough shock that was even close to affordable back then to deal with it.

I had looked at several big block ladder bar stick cars that were measuring shock speed and they were fighting the same thing. Back then, unless you wanted to run Pro Stock level stuff on a bracket car.


The best thing would have been a 4 link. A stick and a ladder bar should NEVER be together. Sadly, most guys fear the 4 link so they screw with stuff like that.
 
72DMag said:
@gregsdart Wow that's crazy that your car was doing that. How did you see this? Go Pro under the car?

Well the car is a 72 duster all steel 3000lbs with my big butt in it, small block making right at 500 hp at the flywheel. Its nothing too crazy. I have a 8 3/4 rear axle. I do think the shocks will be mounted on the rear of the axle because the 8 3/4 has a brace and based on mounting locations that looks like they should be there. The other thing is that the car does sit low!! I have 2" drop spindles by pst. I've been reading and still reading/learning Bickell's book regarding the neutral line and the cg and IC points and concepts. Based on his book and my understanding, I think going with a lower ic for a smaller hp car is a good thing because this will keep the tires planted and weight transfer and I do not have the horsepower to shake the tires.

Problem is this car is newly back halfed and never been down the track so no clue where to start for shocks.? :(
Click to expand...


If it’s a 4 link you can get it low enough. If it’s a ladder bar, good luck. You probably won’t get it low or long enough.
 
72DMag said:
@gregsdart Wow that's crazy that your car was doing that. How did you see this? Go Pro under the car?

Well the car is a 72 duster all steel 3000lbs with my big butt in it, small block making right at 500 hp at the flywheel. Its nothing too crazy. I have a 8 3/4 rear axle. I do think the shocks will be mounted on the rear of the axle because the 8 3/4 has a brace and based on mounting locations that looks like they should be there. The other thing is that the car does sit low!! I have 2" drop spindles by pst. I've been reading and still reading/learning Bickell's book regarding the neutral line and the cg and IC points and concepts. Based on his book and my understanding, I think going with a lower ic for a smaller hp car is a good thing because this will keep the tires planted and weight transfer and I do not have the horsepower to shake the tires.

Problem is this car is newly back halfed and never been down the track so no clue where to start for shocks.? :(
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Buy once cry once. Get a shock that can have the valving updated. And look into motion ratios and such.

As I said above...if you have a 32 inch ladder bar, the denominator in any motion ratio equation will always be 32 inches. If the shock is mounted 9 inches behind the axle (thats a WAG because I can’t remember what the shock mount position is any more) that means the simple math is
38/32 which is a ratio of 1.1875.

What that means is the shock has to move 1.1875 inches for every inch the axle moves. Since the two parts (the shock and the axle) are effectively one piece, that means the shock has to move faster over the same distance. That’s the shock speed I’m talking about. If you can’t change the valving to control the shock speed, you can make the shock effectively...non effective.

Now do the math the other way. Put the shock 9 inches in front of the axle (all you are doing is just putting the bracket on the front of the axle and moving the top shock mount to suit).

That means the math would be 23/32 which is a ratio of .71875. That means for every inch the axle housing moves, the shock only moves .71875 inches, and you have effectively slowed the shock speed down.

Now if you do the math for a 4 link you can see that ratios are much smaller, but any IC longer than 32 inches will reduce the ratio compared to a ladder bar. If you have a 54 inch IC (this is what most people start out with...and that number is about 1/2 the wheel base of the Valiant chassis) and the shock is 9 inches behind the rear axle you would have 63/54 for a ratio of 1.116.

So...that says with a 4 link the shock speed will be slower with a 4 link and any IC longer than the standard 32 IC of a ladder bar.

I ran my 4 link at 104 inches out. That math is 113/104 for a ratio of 1.0866 and that I had issues with the Koni shocks I was using, especially when I used a 30 pound flywheel.

That’s what I’m talking about when I say shock speed. The speed that the shaft of the shock travels every time you drop the hammer. You have to be able to control that. If you can’t you fight hook problems every day.
 
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My opinion is that chassis/housing separation speed is what actually matters to the car, not shock speed. Changing the motion ratio between shock and housing means you then need to interpret shock speed data thru an additional calculation to effectively compare separation rates. While moving the shock forward will give slower shock speed data, actual separation speed will increase due to the less effective shock location.

Grant
 
weedburner said:
My opinion is that chassis/housing separation speed is what actually matters to the car, not shock speed. Changing the motion ratio between shock and housing means you then need to interpret shock speed data thru an additional calculation to effectively compare separation rates. While moving the shock forward will give slower shock speed data, actual separation speed will increase due to the less effective shock location.

Grant
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Ok. That means rocker arms don’t work either. Shock speed is EVERYTHING. Since the early 1980’s most dirt bikes have had double adjustable forks and shocks. It’s the same thing. That’s why they were moving the shocks forward and laying them down. Thats why they ALL went to the stupid single shock and linkage arraignment, and not coincidentally, the rising rate of a “modern” bike is about the same as a 1981 490 Maico. That’s what changing the valving on the shock does, doesn’t it? If you reduce rebound damping the shock comes apart easier (and faster). It’s not hard to grasp.

As for separation...like I said I control that with the 4 link. If the car pitch rotates like it should the separation will be minimal anyway.
 
@yellow rose Thank You for all the info!! Unfortunately I am a newer to back half cars so I'm learning this stuff as I go. Again thanks for al the details! :)
 
72DMag said:
@yellow rose Thank You for all the info!! Unfortunately I am a newer to back half cars so I'm learning this stuff as I go. Again thanks for al the details! :)
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If you can find a copy of the Alston Chassis book it’s worth it. It’s very basic and it’s a good starting point. Plus it’s very readable. Once you get through that one Dave Morgan’s Doorslammer’s chassis book. It’s more in depth. I think you said you have the Bickle book. So that’s good.

Read all you can and consider what you are doing. The ideal shock mount would be on top of the axle, but there isn’t really a way to get a full sized shock on the axle and not have it poking out the trunk.

Shocks are critical if you want to go fast and be consistent. Spring rate goes along with it. Most cars I see are terribly over sprung. With today’s shocks you can get the valving you need without going through the hassle of moving the shock.
 
yellow rose said:
Ok. That means rocker arms don’t work either. Shock speed is EVERYTHING. Since the early 1980’s most dirt bikes have had double adjustable forks and shocks. It’s the same thing. That’s why they were moving the shocks forward and laying them down. Thats why they ALL went to the stupid single shock and linkage arraignment, and not coincidentally, the rising rate of a “modern” bike is about the same as a 1981 490 Maico. That’s what changing the valving on the shock does, doesn’t it? If you reduce rebound damping the shock comes apart easier (and faster). It’s not hard to grasp.

As for separation...like I said I control that with the 4 link. If the car pitch rotates like it should the separation will be minimal anyway.
Click to expand...

Thing is typical ladder cars are like the earlier bikes with simple upright shocks. Closer you move their shocks to the front pivot point, the less the shock's ability to dampen motion at the axle. Travel range of the axle increases, but that shock has less ability to dampen reactions.

When you don't have enough shock to begin with, moving that same shock closer to the bar's pivot point makes things worse, not better. Move those same shocks all the way forward to the pivot point, they will have zero ability to dampen axle motion. Degradation of damping ability is pretty linear as an upright shock moves closer to the pivot point, there is no sweet spot or curve where things get better before they start getting worse.

Grant
 
weedburner said:
Thing is typical ladder cars are like the earlier bikes with simple upright shocks. Closer you move their shocks to the front pivot point, the less the shock's ability to dampen motion at the axle. Travel range of the axle increases, but that shock has less ability to dampen reactions.

When you don't have enough shock to begin with, moving that same shock closer to the bar's pivot point makes things worse, not better. Move those same shocks all the way forward to the pivot point, they will have zero ability to dampen axle motion. Degradation of damping ability is pretty linear as an upright shock moves closer to the pivot point, there is no sweet spot or curve where things get better before they start getting worse.

Grant
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I agree. They moved the shocks forward and tipped them forward to do exactly was you say. They wanted to increase the rising rate, and decrease shock shaft movement. Today, they do that with the linkage, which is more complicated.

They want the beginning of shock travel to be very soft and as the rear wheel moves up, the suspension gets progressively stiffer, AKA the rising rate.
 
gregsdart said:
Think of it in terms of slowing the motion of the rear housing. I am on my fourth set of shocks in back, ending up with Afco BigGun shocks which are able to handle 926 hp, a 11.17 SLR, a 30 inch ladderbar and 10.5x33 Hoosiers plus transbrake.
To see how brutal things can get, hear is the math; engine torque x 2 (converter)1500 x SLR (low gear x rear gear) 11.17= 16,600 ft lbs at the hit trying to swing the rear housing down. With a 30 inch ladderbar (2.5 feet)= about 6500 lbs of torque is what those shocks have to control to slow down the housing at the hit.
Click to expand...
Lol I just had my strange axle wheel studs upgraded to 5/8 from 1/2 inch because of that math.
 
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