Cross bar pad sub tank!

Hey gang,

Since I'm a hydraulic engineer at heart, I set out on an idea a few days ago to make my own sub tank system. The real kicker was to find a new place to mount the tank. WR's have headlights and a lot of wiring right where the YZ's like to mount their tank(s) (back in behind the number plate). Didn't take too long while I set their in front of the bike with the tank in hand before I found its home.

The usual LH fitting mounted in fork endcap:

The usual RH fitting mounted in fork endcap:

Flow control valve mounted to cross bar pad:

And the best part:

Yes my pad is replaced by a welded tube assembly with the fitting coming out the front side right by the flow control valve.

I added a little (1/4") high density foam to the tube under the cover. Used Polyconn quick connect fittings, and air brake line for all tubing.

Oh and by the way, it works GREAT :)

Nice job TRJ! Now to be perfectly anal (not in a Zigfried and Roy kind of way), figure out how to get rid of the cable ties holding the flow control valve and it will look super clean............:)

Perhaps I'm just ignorant, but what is a sub tank and what is it's purpose?...SC

A sub tank is an extra volume of air for your forks that gives you a plush ride over low speed bumps but stiffens up (that's what the flow control valve is for) over high speed bumps so you won't bottom out. Kind of gives you the best of both worlds.

Check out for a detailed explanation

Anyone ask, tell them its nitrous! :)

Yea, I know. The Ziptie thing is lame looking. They'll do until I can figure out where I want the final home to be for the flow control.

Did you also increase the oil volume in your forks or leave it as is?

Did you find you had to make any changes to your clicker settings after you installed your subtank system?

There's not a lot of room between the bleed hole and clicker tower and a 1/8 NPT fitting doesn't look like it would have enough clearance unless you drilled the hole offset from the beel hole. What size adapter fittings did you use to screw into the fork caps after you drilled / taped them?

Nice work :)

Good questions.

Haven't changed the oil volume or the clicker settings yet. These cold wintery, snowy days make tunning NO FUN. Should know next weekend after I do the "chicken Run" posted about over in the North forum.

As far as the fitting clearance, your right, it was tight to the clicker tower (19mm hex). I had to mill a 1/8" crescent shape out of one flat on the hex to get enough room for fitting and wrench clearance. Having a Bridgeport is a God sent!


By the way, the Zipties are gone. Ended up mounting the flow control right on the LH leg of the billet mount for the trailtech computer. Looks A LOT neater. Thanks for the constructive criticism :)

Joe, that's one of the coolest things I've seen in a long time.. :)

Simply put...THANKS :)

Hey TRJ,

Who makes that flow control valve - it looks like an SMC part. Got a part number?

Couple of questions.

What is the internal volume of the subtank?

Did you consider running the lines into the bottom of the subtank so the oil flows back to the forks?

Is there any oil collecting in the tank?

Does that flow controller have a check valve to let the air back to the forks freely?

If so a part number would be great.

Thanks in advance.

Luke & mjslim,

The flow control is not a Polyconn, good catch, (without running out in the barn...seems like it's an ASO #1301) it just happened to be one we had laying around the shop. I will get the part number posted later today, and yes it is a unidirectional flow control with the check valve in it. If ployconn would have sent the CORRECT fittings I would'nt have had to scrounge. BE CAREFULL if you order flow controls from them, they have had, and still have a problem with their suppliers mixing valves and packaging up. They were labeled right, but were bi-directional controls (no checks).

The tank port is facing forward for now but when I switch to my Jimmy Button Hi-bends the 90° fitting will get rotated down to the bottom for that exact reason. My rod ends are threaded so I can just rotate the tank. Right now I can't move it because the factory 05 bars don't give enough clearance to the bar clamp.

Man I hate Insomnia (it's 4:30AM) :):):p

I start a new job in a couple weeks and get to give notice Monday, so needless to say the anxiety is getting to my sleep patterns :D

Keep those questions coming!


Yeah very neat, the valve is key (and looks great if it works) please provide more info. Also what is the wall thickness of the tank.

It DOES work. I just haven't had the time to put it thru some hard paces and get it dialed in. The wall thickness is .060in impact extruded 6061F tube. It's slightly irrelevant though (overkill). I'm gonna do some pressure traces while I ride, I suspect we're gonna be surprised at how low our pressures run in these forks! We'll see. As a bar pad I'd be more focused on the tubes ability to withstand endloading from bar flex (both in tension and compression), and side loading from our RARE but occasional hitting it with our chests :)

Keep em coming!


On your next prototype maybe consider running a stringer through the can to handle the load issues and let the can go back to being simply an air volume??


The can/cylinder has more tensile strength than the rod that was in the bar. I know, I tested them at work. If the cross bar would have been made of steel it would be a different story, but it's not it's a very cheap grade of aluminum. :D

The way the current tube accomodates varrying cross bar lengths is thru the threaded rod ends that attach to the cylinders and also thru eccentric brash bushings where the 6mm allen screw ties the tube to the bar clamps. If I go to a thru bar idea I not only have to seal the bar off from the tank (meaning o-rings) I also have to figure out how to assemble it. Bot the rod ends are larger than the rod (can't get them thru the endcaps). :p

I'm trying to get all the cost out of the current designs out there. My goal is to be able to sell a complete system for under $100. I'm real close to being able to do that. The next one won't even have a welded tube for the tank :)

Keep the ideas coming...I'm all ears :)


Just another thought (can't help myself - do this stuff for a living). Maybe you need to have two versions - one that is a structural and doubles as the cross bar, and one for fat bars that mounts in the same location but is non-structural so the bars can still flex as intended. I already have a vision for the latter. And don't be afraid of O-ring designs - if done right they can be very simple yet reliable. But hey, if you're a hydraulics guy, I should stop babbling.........Good luck with your design! :)

No don't stop babbling...I love this kind of talk! Very few people really like or care about hydraulics, yet they are everywhere in our lives! It seems us oil junkies are a dying breed.

No that I know I can talk "turkey" with ya here goes.

My least expensive design would indeed be a double ended cylinder. with the rod sticking out both ends, let's me eliminate the TIG operations.

One center tube section with twin endcaps crimped on. Pass an already swedged end rod thru one end and out the other, then thread the apposing swedged end fitting on. The design would also include two o-rings for the static tube to endcap crimped seal, and two o-rings for the somewhat static rod seals. Here's the best part, I can get the endcaps (with ports tapped), o-rings, and tubes all from current production stock! and in two different sizes: 1-11/16 ID and 1-1/8 ID.

And you're right with the lands designed properly, O-rings will work just fine. The only real concern I have is that occasionally the cross bar rod would have to be lubricated and moved back and forth a bit to make sure that the O-ring can maintain the seal.

Overall, just a little nervous, I think the pressure traces are gonna show numbers WAY LOWER people think.

Your turn :p:):)

Indeed the pressure traces should be interesting - might be able to get away with an even thinner wall cylinder. Have you considered smaller tubing and fittings? Have you ever seen those instant tube fittings that use a 10-32 thread and a face seal? They are way smaller than 1/8 NPT stuff. Don't know if the ID would be too restrictive, but you might want to experiment with them - could solve some clearance issues.

I'm in the process of geting some risers for my bike that move the bars farther forward - could definitely benefit from your set up, although I want to go to fat bars if I can. Hopefully you'll have it all ironed out soon and I won't have to make my own. Be happy to test a protoype for you :) , just promise to buy me a beer after you make your 1st million......................

You know it's funny you mention the #10-32 port fittings. I have had to replace a couple of those rotten boogers on a test setup. And it's even in a very safe / quiet working environment. Not at all happy with them. They like to shear right at the thread relief for the O-ring groove. I figure they would be nothing but grief in our environment. And yes I looked at them...the air bleed screw is an M5x.08 on our fork caps, so I was looking for a fitting that I could thread right into without having to machine endcaps.

I'm getting ready to switch jobs (YEA I'M GETTING A REAL JOB!!!). The new company I'll be working for uses a high pressure 1/8 OD very flexible line (bend radius is like near zero). I figure those lines will look and work real nice on the setup, they even have some real neat/compact quick connects. Stay tuned. :)



I don't have pressure numbers, but I can tell you that el-cheapo PVC from Home Depot with cheap plastic tubing and flow control valves worked and nothing popped out or exploded. The eye candy factory is pretty bad, but it worked. Shawn_Mc from the TT CRF450 forum also offers sub tanks using high quality tanks, valves and braided lines for people interested in sub tanks and there are people here on TT who are quite happy with the system he has put together for them. I think the cross bar idea is fantastic! There was also a guy here on TT who also used his handlebars as a subtank. He plugged the ends of his bars and drilled / tapped the bars between the clamps for a small fitting that screwed into his flow control valve. He said it worked just great :)

One of the more complex subtank sytems I've seen is manufactured by Racing Suspensions, but they just manufacture it and can't tell you much else about it other than that. It's expensive compared to other products and looks impressive, but I have no idea how well it works compared to other subtank systems.

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