Hydraulic bump-stops..

[Raptizzle]

I 100% understand your thought process behind the 2.5 vs the 2.0 bump. The 2.5 bump quite possibly is major overkill for this application. Not that it is a bad thing but I would imagine that if ICON is putting out a kit with 2.0's it probably does the job just as well as the 2.5 for this application.

I look at it this way. The 2.0 or 2.5 bumpstop is an emergency item. If your shocks are tuned correctly 99% of the time they are doing 100% of the work. So the difference between the 2.0 and the 2.5 doesn't really matter in this application. Remember while these trucks might weigh the same as a trophy truck what we are doing with this is vastly different.

I'm not saying that using a 2.0 is superior to the 2.5. I just wouldn't discount the 2.0 so quickly. Just because one company is offering a 2.5 bumpstop doesn't mean that 2.0's are inferior to this application.

Let me put it to you this way, I'm not going to use 99% of the time, 100% of the time to make any claims because we all know statistics like that are derived out of peoples asses. It's not hard to watch any of the available bump videos and see that they get used way more than just 1% of the time. In fact they are a critical part of the suspension system working properly, especially out here in the desert southwest.

Let's take the comparison of a Trophy Truck to a Raptor. It's not uncommon for a Raptor to be loaded up in the bed with 500-1000pounds when offroading. The weight of a TT is very balanced with fuel cells, battery's, tires in the rear etc. Here is the difference. Most modern day TT are running 4.5" 5 Tube bypass shocks with a 3.0" coilover, plus a 2.5" bump to control the insanity. And as most of you know, they have at a minimum 15-20" of bump travel to control all of it. Now your Raptor with the same weight over the rear axle and at best a single 3.0" 3 tube bypass and leaf spring is suppose to control 14-20" whoop sections at 80mph with a whopping 4-6" of bump travel. You could actually make the argument a Raptor is in more need of a proper air-bump than is a trophy truck. So I guess the question is what is the right size bump? I'm no expert so I won't throw out statistics for the world to see and possibly get the wrong impression, I will leave that up to the experts. But what I am certain of in the world of offroading is extremes exist, and I'm not sure if the term overkill has anyplace in it. Hence why BFG now makes a 42" race tire, King makes a 4.5" shock etc...

I want to apologize to the guys at Icon if anything I have commented on has derailed their thread. I will recuse myself from any future commentary.

Tizz

 

[bstoner59]

C'mon Tizz....you are on a roll!!

 

[ICONRep]

Let me put it to you this way, I'm not going to use 99% of the time, 100% of the time to make any claims because we all know statistics like that are derived out of peoples asses. It's not hard to watch any of the available bump videos and see that they get used way more than just 1% of the time. In fact they are a critical part of the suspension system working properly, especially out here in the desert southwest.

Let's take the comparison of a Trophy Truck to a Raptor. It's not uncommon for a Raptor to be loaded up in the bed with 500-1000pounds when offroading. The weight of a TT is very balanced with fuel cells, battery's, tires in the rear etc. Here is the difference. Most modern day TT are running 4.5" 5 Tube bypass shocks with a 3.0" coilover, plus a 2.5" bump to control the insanity. And as most of you know, they have at a minimum 15-20" of bump travel to control all of it. Now your Raptor with the same weight over the rear axle and at best a single 3.0" 3 tube bypass and leaf spring is suppose to control 14-20" whoop sections at 80mph with a whopping 4-6" of bump travel. You could actually make the argument a Raptor is in more need of a proper air-bump than is a trophy truck. So I guess the question is what is the right size bump? I'm no expert so I won't throw out statistics for the world to see and possibly get the wrong impression, I will leave that up to the experts. But what I am certain of in the world of offroading is extremes exist, and I'm not sure if the term overkill has anyplace in it. Hence why BFG now makes a 42" race tire, King makes a 4.5" shock etc...

I want to apologize to the guys at Icon if anything I have commented on has derailed their thread. I will recuse myself from any future commentary.

Tizz

Your good brotha, please continue to post as that is the point of these things called public forums.

Dylan asked to reply, so I am going to let him post to your original comment. I was simply asking for knowledge from someone that post often, and just a honest I wonder why he feels that way. You will be happy with the response he gives, and at no point did I want anything other then the answer you gave. I appreciated exactly what you wrote.

 

[BlueSVT]

Get that big 'ol brain of Dylans in here!!!

 

[ICONRep]

Get that big 'ol brain of Dylans in here!!!

He ended up being out most of the day actually dealing with the our Raptor. Master Shift was installing the updated version of the paddle shift system!!! He will jump on tomorrow for all of us to chat with.

 

[DylanICON]

An air bump is hybrid of a shock and an air spring. They can have some very odd characteristics however due to the fact that they are emulsion (gas and oil not separated), they are not connected to the axle, and the current impact partially depends on the previous impact(non linear).

As an air spring its characteristics are based on: shaft dia, stroke, initial pressure and compression ratio. The graph ramps up drastically at the end and how drastically is based on the compression ratio. We set it up for very high compression ratios and sometimes close to infinite or hydraulically locked. Here's the catch.....the shape of the graph is ALWAYS the same if set up this way regardless of size. See attached

The problem with an air spring of this nature is it doesn't really do much till the end of its travel so there isn't really that much energy to be stored. What we do is force it to develop some extra force earlier in its stroke with the valving on the piston. It is also velocity sensitive so the faster it hits the more it ramps the pressure up. This combined with a reasonable initial charge makes it so that first contact is mild and if it's a small hit doesn't upset the attitude or stability of the vehicle or its occupants but when hit hard will create(and dissipate) more energy earlier in the stroke and lift the chassis over the obstacle.

Does size mater? Yes at some point, but not because of heat or performance. It's relative to shaft size more than body size. At some point the pressures get hard to deal with and a larger shaft diameter is called for.

 

[BlueSVT]

There's the big brain!

How do these compare to the fox bumps, like I have currently installed on mine with the Outlaw kit?

 

[DylanICON]

This dyno graph shows some of the characteristics of an air bump.

The blue line is very slow so the hydraulic part is not influencing it very much and the shape is very close to just an air spring

The red line is at 10 inches per second and shows the hydraulic effect add additional force. You can also see that there is a flat spot at the lower left corner. This is because due to the rate of impact as its cycled on the dyno the shaft has not had time to fully extend before the next impact.

The green line is at 30 inches per second and shows how it can develop forces much higher than just those due to nitrogen pressure and shaft diameter. This is being cycled much faster than the random bumps you would encounter in the field yet still returns to 60% of its travel.

The energy that is being absorbed is based on the area under the curve. So you can see that at low speed there is less energy to use the majority travel available and at high speed more energy is absorbed.

Note it is also important to tune the rebound correctly to not kick back but also not overdo it so that it extends to slowly. This is especially bad as it will pack up the bump on the first hit and the second one will slam extremely hard because there is no travel left. This pack up situation can be dangerous and is common when a large air bump is run at low pressure to reduce the initial contact force.

It is not uncommon to see wheel speeds over 100 in/sec

 

[Raptizzle]

Interesting stuff... So if I understand correctly, your assertion with running a 2.5" bump requires less psi so it's comfortable, but the trade off is now a slow rebound which results in packing up? Do I have this right???

 

[BlueSVT]

That's how I interpret it too...