TC to Fox Air Bump Stop Mathematics

I've lost a lot of sleep doing math over this stuff. Part of that reason partially has to do with the fact that I like to try and see if I can figure all this suspension stuff out mathematically, that way when it comes down to doing it on the truck itself I just set it and forget it and it's ready to run. Anyways, down to business.

If you are looking to do air bumps on your lifted truck. There are some things you should know pertaining to the Fox air bumps mated to a Total Chaos bolt on bump stop can.

First things first. This info I received off of this site:

http://www.billavista.com/Tech/Articles/Air_Bump_Tech/index.html

Highlighted in the basics section you will see this article is analyzing a 3" stroke air bump. Obviously the first thing you should know which is coincidentally not even mentioned in the article, but I specifically know is that the machined lip before the piston measures exactly 1". The stroke itself is 3" (adjust for different stroke lengths), and the striker head on the bumpstop measures 1.125" (1 1/8).

The reason why any of this is important, is that if you go with a 10" stoke shock you will need to make sure the bumpstop is spaced out further from the frame to prevent any bottom out damage to the shock itself.

In my case I am running a Deaver 3 leaf mini pack 1.5 AAL and I kept the overload retained, for a total of 2.25" additional lift to the rear. That leaves me with a 60/40 (60% up travel, 40% down travel) ratio.

Some things you should know is that if you consider going with a TC bolt on air bump can kit for Fox, right off the bat they recommend a 2.5" stroke air bump. After doing the mathematics on that one, I have determined that those particular bumps have a total spacing from the frame of 4.625". Ideal for a shock with a max collapsed height of 13.778" (Fox Piggyback 2.0 Factory Series smooth body shock Part #980-02-372 or shock with similar collapsed height).

A quick determination of how that would work would be by taking the original spacing I noted above of 4.625" then adding the shocks available travel or stroke of 8.416" which = 13.041"

This particular setup (2.5" stroke Fox air bumps mated to a factory series smooth body 2.0 piggyback) leaves you with .737" of shaft travel left after all 2.5" of the air bump is used. Good for that setup, but nowhere near enough spacing for a 10" stroke setup to benefit from.

Enter my simple solution: 3" stroke air bumps made by Fox. With an overall spacing of 5.125 (including stroke), it is PERFECT for a 10" travel or stroke shock with a compressed or collapsed length of 15.19" or similar collapsed height. A quick plug in of the same formula I stated above, 5.125" (air bump travel and spacing) + 10" (shock stroke or travel) = 15.125". Leaves you with a total of .065" of useable shaft left. Which is fine, because even if it begins to approach more shaft then what it should stop at (dynamic specs differ from static) the rubber bump stops at the end of the shock shafts will absorb any additional small slack that may be demanded. Much better utilization of full travel range, especially when you need all of it to run your rig out there in the sand dunes and the desert.

So basically, Overall spacing including travel + Shock stroke or travel should = Close to collapsed or compressed height of shock

This formula can be used for any bump stop spacing setup. Even the King setup.

A small warning, you WILL have to cut into the bed a little, like I have done on mine if you go larger then 2.5" stroke, but you will be able to run proper spacing at this point without having to mess with additional machined spacer inserts under the mounting can, and you get additional cushioning from the extra 1/2" of useable air bump shaft stroke or travel.



Bear in mind, some things changed from this photo. I reset the spacing of the bumps themselves all the way into the cans and cut into the bed more to compensate for that. I also do recommend what's called a relocation U-bolt plate from TC if this is a route you do go, and want to either get, or retain your U-bolt flip mod. It looks like this:



They are 1/4" thick and will further provide proper spacing you need to ensure you get full stroke out of the setup.


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There is another way to obtain proper spacing if you do not want to get as technical as I have done with this:

Determine the up travel remaining for your shock. if a 10" shock and 6" is showing, you have 6" of up travel etc.

Measure the distance from bumpstop mounting location to bumpstop strike plate (any good strike plate should be 1/4" thick or thicker) on the axle. This is the distance your axle can move in an upward direction before slamming into the frame.

Subtract remaining up travel or stroke of the shock (ex above: 6") from distance of frame to axle (ex: 9" or so for a 3" lift) so 9" -6" = 3" and that is the minimum height of compressed bumpstop.

For this to work, the Bump Stop Height should be the bump stop's height under full compression. Example - a 5" bump stop may compress to 3" so you should take into account the 3" measurement, not 5".
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I know this was a long post, but I hope it helps some of you out there!

If you guys want to try and post up your numbers and have us figure them out together, you are more then welcome to! Please make sure you include the type of bumpstop, overall measurement it has, type of shock travel and it's collapsed or compressed length.

Happy wheeling guys.

 

It's a good read but do you (personally) need air bumps on the back with your rear setup? Seems overkill.

 

I have bottomed the HELL out of my rear end before when I was racing through the sand dunes. I used to run polyfoam GM Silverado bumps and they were great, but ultimately did not control heavy bucking like I wanted them to. My rear end was holding back my front end. At this point, I need the additional help of the air bumps in order to keep my rear end under better control during spirited running.

 

Counting ain't my strong suit, so I just stuff the suspension, let the Nitrogen out of the bump and compress it, and hold it in place while I tack welded the cans on. No math required, although I'm sure you're method is more entertaining. I'm running 4" stroke 2.5's. Keep an eye on those TC U-bolt plates. When you run hard they bend. I had to gusset mine to keep it from biting into the spring pack, and with the new axle I did away with them altogether.

 

That rear end

 

That is a pretty sick rear end you got there man!

The whole thing behind it for me is for sure an entertainment factor as well. Not to mention it helps me figure out EXACTLY how much slack I will have to play with at the end of it all.

As far as the plates go, where exactly did you gusset them? I can't see anything really happening to them per se, but if you have or had bent them, I definitely want to know about what can happen to them. Since I run mine pretty hard.

 

Look at the "C" channel the spring rides in. Imagine the force of the U-bolts under tension closing the gap in the "C". I only noticed it after really hammering on the truck, it may be fine for normal use. I gusseted them with a 90* gusset to keep that from happening. Don't think I have pics and I have since scrapped them.

Here is a monkey wrench for your math. Deflection. The frame twists under torsional stress as the bumps absorb energy. A lot more than you would think. You will see evidence of this in the wear marks on the strike plate. Run it for a while and you'll see what I mean.

 

I'm horrible at visualizing what you described, nor can I really think about how they could be gusseted. The only type of gusset I could see being possible is welding a "triangle plate on all four sides of the plating. Its already been done though, so I can't visualize further modification to it.

As far torsional stress I do understand there will be changes as it runs down the terrain dynamically. A lot of that torsional stress rides on the leaf springs as far as I could see in videos of the undercarriage. Regardless, the overall intent of the longer then suggested bump stops are to slow down the suspension sooner during spirited running, which in turn will keep so much down force and torsion at bay sooner in the up travel cycle of the suspension. I have both the dedicated bump stops, as well as the integrated bump stops on the shock shafts themselves to fall back on, just in case the frame does deflect enough to get past the bump stop setup.

Just some thinking out loud here is all.

 

What tear end is that

 

It's a diamond housing with a 9.5" Landcruiser third, full floater 'moly axles, Detroit locker, 4.88 gears and ARP hardware. The brakes are 2004 Tacoma front brakes.

 

Hmmm I wonder how much hp it could handle. I'm in the middle of doin a twin turbo Ls swap an need a good rear end and brakes. How many pennies was it

 

$4700. There are dudes pushing 500HP to them, but if you are running serious HP I would talk to Camburg about their 10" Trophy Truck rear end. http://www.kinetiktrucks.com/trophytruck.html

 

With that kinda money I would buy a ford 9inch way more stout half the price an readily available. Also can handle well over 500

 

The nine inch is more stout than a trophy truck 10"? Or you mean the LC9.5"? It's debatable which one is stronger. Is my axle stronger than a bone stock 9"? Yes. Is it stronger than a strange budget axle? Probably. Is it stronger than a full blown race rear end that costs north of $8K? Probably not.

 

Thats for one serious wheeler right there! What a sexy rear end. I love the Kinetik truck!

 

I'm just saying a 9inch that has some upgrades can handle serious power for a fraction of the price.

 

I think you will have a hard time building any full floater, disk brake, 'moly axled, locked, custom housing axle for less. The parts just cost a lot of money, no matter what axle you go with. Save your receipts when you build yours, and let me know where you honestly end up at. I bet we're pretty close.

 

Would love to have that housing on my FJ40! It is sweet! I'm running a stock housing that has been full floated with Dutchman Axles, non USA fine spline pinion Yota gears, ARB, and mini truck spindles to get rear disc brakes. Has held up well, but that Diamond Housing is simply sick!

 

Thanks man. Being a cruiser guy you'd know better than me, what kind of power will they handle when built well? I know there are quite a few ridiculous power builds in Saudi Arabia and UAE, but don't know of many stateside. (the hennessy performace LC100 is running 500+hp, but it's on a stock 9.5" axle)

http://youtu.be/9Ci0_oa4R-8

(sorry for destroying your thread OP)

 

Haha. This thread went from TC bolt on cans for the rear end and their mating bump stops, to a full blown discussion to rear ends.

Its all good Username.