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Old 08-01-2016, 01:05 PM   #1 (permalink)
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What PSI do you run in your air bumps? *Go Fast People*

Im running 5" of up travel, with 2.0 2.5" length bumps up front, and 2.25" length bumps in the rear.

When running in the dunes over whoops, I get a pogo like effect running at medium speeds. I was going to add more rebound valving to keep the rear held down longer, but then was told this weekend to try lowering my bump pressure, because the bumps are just pushing the suspension back up too fast.

I run 200 psi currently.

I was told to try 75lbs, but that seems a bit low, and he was running a jeep.... Im in a k5 that easily weighs a ton or more than the jeep.

How effective will a bump be at lower pressure like that? Will it just change initial hit? Or decrease the overall stopping force?
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Old 08-01-2016, 01:07 PM   #2 (permalink)
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200.
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Old 08-01-2016, 01:28 PM   #3 (permalink)
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Old 08-01-2016, 01:43 PM   #4 (permalink)
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Mine were at 150 and bumped them up to 250 and it works better for my 5100lb LJ.

I would keep on the shock tuning idea.
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Old 08-01-2016, 02:43 PM   #5 (permalink)
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100 psi. 2" body, 3" stroke with 8" of up travel. 4300 lb rig tuned by Wayne at alltech.
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Old 08-01-2016, 02:45 PM   #6 (permalink)
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Old 08-01-2016, 03:35 PM   #7 (permalink)
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Bump stops usually have a ton of rebound dampening, I really doubt the are pushing.
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Old 08-01-2016, 03:59 PM   #8 (permalink)
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200 in some 2x4 kings. 4" down to 2.5 travel front, full 4" travel rear. 19 rear 18 front travel.
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Old 08-01-2016, 04:24 PM   #9 (permalink)
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Originally Posted by Deuling View Post
Im running 5" of up travel, with 2.0 2.5" length bumps up front, and 2.25" length bumps in the rear.

When running in the dunes over whoops, I get a pogo like effect running at medium speeds. I was going to add more rebound valving to keep the rear held down longer, but then was told this weekend to try lowering my bump pressure, because the bumps are just pushing the suspension back up too fast.

I run 200 psi currently.

I was told to try 75lbs, but that seems a bit low, and he was running a jeep.... Im in a k5 that easily weighs a ton or more than the jeep.

How effective will a bump be at lower pressure like that? Will it just change initial hit? Or decrease the overall stopping force?
First thing to do is make sure your actually bottoming out the suspension and causing the Pogo effect. You might need less compression damping? that can be done by lowering the bumpstop pressure. Put some zipties on your shock shafts and bumpstop shafts and see what your actually using for travel.

If your using the entire shock up and bottoming on the bump you either need to stiffen the front up to hold the nose higher or figure out a way to get the rear stiffer but that's hard to do without causing the Pogo effect to get worse with valving.

We ran no front bumps and 50-100 in the rears on the car. But we had 2.5" 5 tube bypasses with a pretty good bump zone in them to help.
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Old 08-01-2016, 05:50 PM   #10 (permalink)
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I went from 150# to 75# 2" body 2" stroke. That fixed a lot of the buck. 3800# 7"- 8" up travel. Tuned by Chris at Alltech.
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Old 08-01-2016, 10:06 PM   #11 (permalink)
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First thing to do is make sure your actually bottoming out the suspension and causing the Pogo effect. You might need less compression damping? that can be done by lowering the bumpstop pressure. Put some zipties on your shock shafts and bumpstop shafts and see what your actually using for travel.

If your using the entire shock up and bottoming on the bump you either need to stiffen the front up to hold the nose higher or figure out a way to get the rear stiffer but that's hard to do without causing the Pogo effect to get worse with valving.

We ran no front bumps and 50-100 in the rears on the car. But we had 2.5" 5 tube bypasses with a pretty good bump zone in them to help.

I know im into the bump zone of the rear internal bypasses. Not bottomed out, but I set them up to still have a slight amount of shaft left when the bumps were bottomed out at static travel.


Im going up saturday morning and camping over night. I may bring the nitrogen bottle to the campground and play with it. Set it up at 100psi and go play for a bit, I just wont jump it hard.

At least I know at that point that if that works, then I probably just need more rebound valving in the shocks.

When I hit a steep hill with a sharp transition at 50 mph or so, it soaks up the hit great but it unloads and does a slight bounce up the hill.


Quick example of the "pogo"

Doing about 60 when it gets off the ground. What I dont like is that I lose so much control when bouncing like that because the front end is weightless and I have to pretty much set up the steering to react when it lands (and then bounces and do it again etc....

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Old 08-02-2016, 08:36 AM   #12 (permalink)
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bump stops are to prevent 'crashing' when bottoming out. id bet you get more pogo out of your tires then the bumpstop at 200psi. you should focus on the shock tuning first


how much shaft do you have showing at ride height? over all travel of those raptor shocks?
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Old 08-02-2016, 12:16 PM   #13 (permalink)
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bump stops are to prevent 'crashing' when bottoming out. id bet you get more pogo out of your tires then the bumpstop at 200psi. you should focus on the shock tuning first


how much shaft do you have showing at ride height? over all travel of those raptor shocks?
It has been a while. They are 11-7/8" of travel.

I know its very near using all of the compression travel in the shock. Unfortunately I don't have enough spring travel to get the use of the lower rebound zone of the shocks in the rear. I chose one or the other and used the compression zone.

Maybe that is just setting me up for failure though and I should really look at a solution to use all of the shock... But that could be for a different thread.

I was just curious on who is running lower psi in the bumps and what the pros/cons are.
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Old 08-02-2016, 12:28 PM   #14 (permalink)
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a good portion of the ultra4 racers I have tuned are under 100psi as well as my personal vehicle.
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Old 08-02-2016, 01:32 PM   #15 (permalink)
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a good portion of the ultra4 racers I have tuned are under 100psi as well as my personal vehicle.
I think I will try it for this weekend.

Cannot hurt, and if its no good, ill fill them back up.

I plan to tear it down this winter and re-valve. No time right now though.
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