BT Air Bags

Turist I do not know if it is going to be me. Have to talk to BTi and Vehicle Components. Unlike the Firestone Bags added to the F-250 which supplement the leaf springs and shocks, this is an all or nothing and totally reliant on the air bags. If there is a puncture in a line or a bag you are "on the ground floor" driving slowly to the repair facility. I understand these are Firestone truck airbags. Need to do some due diligence before jumping in and giving it a go!! tgintl/jay

I see that Trakmaster use airbag suspension. Is it the same type that BTi will be using. Interesting videos of theirs in operation. Angie

Angie Are the videos on line? URL? Cheers, tgintl/jay

When I looked at the Trackmaster air bag suspension around 18 months ago it was independent but NOT load sharing.
Steve says thiers is load sharing, an important advantage.

Regards
Turist

Hi Will someone please describe the difference between independent and load sharing as applies to the air bags. Thanks. tgintl/jay

Jay, I think it means the weight is spread evenly between axels i.e load sharing. Independant means the wheels move up and down without regard to their oppositite on the other side Regards Macka

Hi Jay, Re the Trackmaster van videos. You have probably seen them by now and they are really only short but this is the site:http://www.trakmaster.com.au/gallery/movies.html Might give you the idea. Angie

Jay, Macka is on the money there. Independent whether air bag, leaf spring, trailing arm/coil spring just means that the wheel travel on the same axle are independent of each other. Single beam axle trailers tend to "bump steer", that is, as a leaf spring compresses on one side from say dropping in a pot hole and coming out (axle goes up in the range it can travel on one side) the length between the axle centre and the leaf spring pivot point (front hanger) becomes greater. This in turn pushes the axle back towards the rear of the trailer on the side that hit the pothole. This takes the wheel back obviously making it track slightly off straight ahead ..... because the axle has a wheel attached at the other side it tracks off centre as well making the trailer steer to the left in the case of hitting a pothole with the left wheel. Independent suspension totally negates this effect. Especially as it is usually trailing arm which pivots off two points stopping the wheel tracking off centre for any reason, with the spring being "slipper" on the trailing arm end. Load sharing is a suspension group (2,3 or possibly more wheels on the same side) which is designed to divide the load carried by the axle group equally between the tyres on the group. The theory is that say a BT with 1500kgs on two tyres on one side and you drive the front tyre onto a brick there is still 750kgs downforce on each tyre. If the axles are not load sharing and you drive onto the brick the front axle will hold weight off the rear axle because the front axle has raised the BT up the brick height (less the slightly more compression in the front spring because more weight is on it) making the front hold, say, 1000kgs and rear 500kgs. This is hard to explain in text ..... See if this helps ....If you drive a BT over a brick slowly, one wheel at a time, the BT chassis will not gain height. If you drive a non load sharing suspended van over a brick the van will rise as the first wheel goes over. It will rise the height of the brick less the amount of extra compression in the suspension because it now has more weight on that axle. The BT load sharing is done by using a single leaf spring to control two trailing arms (one actually faces forward) at the extremity of each end of the spring. If you lift one end of the spring (raise wheel) the other end tries to go down increasing load on the other tyre. So the wheel going over brick instead of increasing load stays at 750kg( the increase is transferred to the other wheel) ...the wheel at the rear instead of lightening has downforce from the spring being lifted at the front so it stays at 750kgs. Thats the theory anyway !! Clear as mud !!! [Smile] Regards Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker

Jay, With regards the air bags they just replace the springs to give a range of movement to the axle albeit adjustable via air pressure. They have no or very little dampening so require shock absorbers to control oscillation. The Simplicity supposedly doesnt need shocks because it is self - dampening. I take this to be done just by sheer friction between the leaves. Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker

Two other observations that need confirmation/clarification. In the Simplicity rig, if one axel goes over a 100mm bump (say at walking pace where no significant spring or tyre deflection comes into play), the upward movement in the van would be, say, 50% or 50mm? I'm assuming the pivot point is half way between the axel sets and therefore travels upward by half the travel of any one set. The weight of the entire van acting on the pivot point also means the load is shared between the two axels, meaning that 100% deflection of one axel doesn't mean that axel bears 100% of the deflecting load, hence "Load Sharing" (probably not half, either, but somewhere in between - need more engineering maths to figure it out - but that's banned on this site, so I'll just have to wonder). If my understanding of "Load Sharing", and how it is achieved, is not completely off the mark, then I am curious about the claim that this new set-up is also 'Load Sharing". It appears to me that there are two independant trailing arm sets that have nothing to do with each other and are therefore not load sharing. As the first set is deflected it will lift the van by the amount of compression that the suspension airbag allows, thus taking a much bigger share of the load than in the previous example as there is no common pivot point. While the first set is compressing, of course, and the van is rising by 100mm less airbag compression, the second set is decompressing as weight is coming off the second set. The opposite occurs as the second axel travels across the obstacle. THis is why load shring is seen as superior to non-load sharing. I think. Have I got this right, or am I mis-interpreting the photos of the set-up? Griffingly Yours

Griff, This had me puzzled for some time until I learned (read spoke to VC,albeit quickly) how the airbag loadshares .... it does it (as I understand it) by the airbags having a common airline between the two (or whatever number) on the same side or even all bags maybe ?? As the front bag compresses from going over something the pressure increases as the bag compresses ..this pressure is transferred to the rear bag that is still as normal height ...... I thought this would have made the rear bag increase its height as more pressure is in the bag as it goes over (but maybe this just allows it to hold more weight at the same height), an object ....can it really load share as well as the simplicity ???? I'm going in to look closer at it and see exactly how it loadshares ...... As I have to replace my suspension anyway I need to look at both types as a replacement .... as you probably remember ...from new my BT weighed 2740kg completely empty except for water with a 3000kg limit. I'd love an extra 500kg that everyone gets now !!! Sigh !!! 260kg left is MY food only !! [wink] Regards Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker

Tony, sounds like the principle used on the Morris Mini and 1100 series only air and not hydraulic.

I designed a speedcar suspension using that principle back in the 60's.
Difference was that I had diagonal cross linked hydraulic lines.
Major weight transfer to front outside wheel resulted in more traction on diagonally opposite driving wheel.
Rear outside driving wheel transferred weight to inside front wheel thus improving steering.
Degree of weight shift was programmable by driver while racing.
Unfortunately it was too good for the "Purists" so it was not permitted to be used.

Turist

Bob, I think I remember a suspension as young boy called "Hydrolastic" as was in the Austin Tasman/Kimberley or was it the "Mini" that had a version ?. Is this the same principal ??? Come to think of it ...was the 1100 I remember having it ... Speaking of banning a good thing. I was at the Mt Cotton Hillclimb on Sunday wanting to see about entering a car for a bit of fun. Sorry mate ! The WRX is banned from general competition class and must go into a WRX only class ... so will wait til mate has dedicated WRX race car going ....we will enter the car with two drivers and just try to beat each others time. We're getting too old to go against 20yr olds in WRX's ..... [wink] Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker

Hmmm. Air compressable, liquid not (as a rule). So, unless very short linking air tube between bags on same side, don't really get it. I envisioned a multiple air-line set up (necessary if levelling to be carried out). OK if one line per side, with short, large diameter hose between bags, you MIGHT get sufficient pressure transfer between bags (talking milliseconds here), but, as you can see from the contorted fascial expression (), I'm still suffering from advanced dubiosity. Remaining to Be Convinced Griff

As a result of asking too many questions about protecting the system from projectiles et cetera I no longer will be having the BTI airbags/shocks system installed in our BT. Someone else will be the first in the group to try the system and report to all of us how well it works on the road and when parked and levelling their BT. As part of the shocks and air bags I have installed in the F-250, the system includes a Big Red compressor and a Piranha 20L tank. There is also a connection point in the rear of the F-250 so that I can run a hose to inflate the BT tires. Prehaps one means of cushioning the BT's ride (we do love our BTs and want them to ride softly) is to add air bags and shocks similar to the bags and shocks in the F-250 which work in conjunction with the Simplicity suspension.. I am no engineer - I just ask questions and raise issues - it seems to me that for each bag to operate independently you would need four inflation/deflation points with quick release connections somewhere near the front of the BT (perhaps just in front of the propane tanks) attached to and protected by the drawbar. It would be hard piping to the bags and then a flexible pipe for the final connection. I am going to consult with Vehicle Components (The Airbag Man dealer - also supplying the BT system) about an after purchase addition. Any thoughts from anybody - all are welcome to respond either directly or indirectly through a friendly Bogger. Perhaps this would be a good topic for a BT Newsletter - if someone other than me wishes to make the request. Cheers, tgintl/jay