Parabolic Springs?

[detailbarn]

So I have decided to scratch build my own trailer just can't justify the cost of a AT Chaser. It will be of similar design and size of the chaser but will obviously lack the Chaser's great suspension.

I need the suspension to be leafs for ease of fabrication but was wondering if Parabolic Leafs would help the ride quality. Everything I have read says on a vehicle they improve ride quality with out sacrificing load capacity. What do you guys think?

Here is the company's site of the product I was planning on using , originally intended for a jeep yj but should work for a trailer , but not sure if I should the front springs or rear.

http://www.parabolicsuspension.com/jeep/yj.htm


Thanks for the input!

[Martyn]

The Parabolic spring was one of the many options we looked at when we were in the early design stages of our suspension. All the characteristics looked good but from what I remember the practical off road application was bad.

An aftermarket parabolic spring was manufactured for Land Rovers and every report we read about them said that the vehicle became dangerous to handle at speed and off road. I know this is contradictory to what the web site says about their Land rover application, and the fact Santana uses parabolic springs, but the information did seem sound and to be coming from a lot of varied sources.

The problem I see with any leaf spring set up, is you have to calculate the spring rating for the maximum load, so anything below that weight results in a rough ride. The stock reply seems to be I always run my trailer full so that is not an issue. Contrary to this perception we see trailer owners running their trailer both "under loaded" and "overloaded". So there is a huge variation is trailer mass.

An alternative may be a light weight, long spring in combination with an air bag, the trick would be to find the right combination. This combination along with the solid beam axle would price you up into the range of our independent suspension without gaining any of the benefits.

Life is once again a series of compromises.

[jeffryscott]

I had parabolics on my 1967 Series IIa 109 and loved them. The ride was fantastic, and off-road it was great - good articulation. I never felt unsafe with them on either. I'll get parabolics again when I end up with another Series truck.

[Martyn]

Yeah, parabolic springs seem to have differing parties some who love them and some who don't. Apart from manufacturers testimonials on how great they are there is a mixed bag of feedback from owners on how they perform in the field. I've even heard it said that the only vehicle parabolic springs work on are Land Rovers, who knows??

Generally parabolic springs do make a vehicle more tippy and bouncy, but in comparison to the stock Series suspension maybe that's a good thing. But I’m sure there are those that would disagree.

I do like the feature this particular brand has where leaves can be removed or added to change the spring characteristics. It also looks like they use Teflon pads to reduce friction between the leaves, all good stuff.

Looks like they are made in the Netherlands, and no reference to a USA distributor, that could make them very pricey.

It would be a grand experiment to see how they worked out on a trailer, I just wouldn’t want to personally put the money out to get the answer when the variables are so large.

[jeffryscott]

I agree that people either love them or hate them from what I found when I researched it before purchasing.

I think the company you mention is TC Console or something similar to that. I know someone with a set and they like them (he's got them on at least two vehicles). I went with Rocky Mountain Parabolics, formerly from Wise Owl in Vancouver. Wise Owl has since been purchased by Rover Boys or something similar. (Pulling some names out of memory).

While I would put parabolics on another Series truck in a second, personally I would defer to Martyn and the others at AT and trust their research.

[ntsqd]

I don't see how their visually mild difference would result in different ride characteristics from a well sorted "normal" leaf spring.

The way I would approach a low cost adjustable trailer suspension would be to use leaves under rated for the expected max load, with dampers, and then put a single air spring in the center of the axle. That means that the trailer frame has to be designed to have that significant load applier to the center of one of it's cross members. Best to do some engineering there b4 sparks fly.
Could even go so far as to use one of the Cad or Lincoln auto ride leveling switches if a compressed air source is available.

[Martyn]

I don't see how their visually mild difference would result in different ride characteristics from a well sorted "normal" leaf spring.

The parabolic shape for the leaf spring is about the biggest design change for leaf springs since the change from horse to horse power, IMHO. Theoretically it provides for a much more supple suspension that should react to changes in terrain in a more applicable manner than regular springs.

The problem seems to be transferring the theoretical into the practical. Once that has been achieved successfully to decide if you have improved on a design that was faulty in the first place, or come up with something worth it's weight.

This would then return us to the discussion on the merits of leaf springs as a "hanger" on from antiquity, or a product that just needs more work!

Why if leaf springs work so well have we had so many design changes in suspension over the past 40 years? Why are some vehicles still running leaf springs? Does the low cost of leaf spring components enter the equation? May be so if recent postings are correct that major car manufactures are making or losing $1500.00 per vehicle sold in the USA.

[RunninRubicon]

The quick easy kit form has been put together by 4WD.com. Comes with two, Front or Rear CJ-7 4 or 6 leaf springs, the mounts, shackels, U-bolts and mounting brackets. I paid $448.85. I use the 4 leaf pack (rear-they are longer) and added Monroe air-shocks. I added two rubber bump stops that stop the action at 10inches of flex. IMHO they are very smooth and compliant.

[detailbarn]

Martyn, I want to thank you for your help, I'm truly amazed at how helpful you have been, you have posted helpful information even though I'm not a customer. The time you've taken to provide useful and helpful information is a rare commodity that is much appreciated. Based upon all the research I've done and information you provided I have come up with a solution to my trailer situation. The Chaser is a great trailer and I would love to own one but it doesn't fit all my needs 100% and i can't afford the cost on top of building the two trucks I'm building.

So I'm picking up a 1/4 ton military trailer and purchasing the AT retro suspension kit. The cost of the suspension is where I feel my money is best spent. I'll be able to modify the trailer to fit my needs by adding a tailgate and removeable rack system, as I don't need a lid.

Martyn , is the suspension kit available at this time, if not what is the ETA?
Thanks again for all you help.

[Martyn]

Martyn, I want to thank you for your help, I'm truly amazed at how helpful you have been, you have posted helpful information even though I'm not a customer. The time you've taken to provide useful and helpful information is a rare commodity that is much appreciated. Based upon all the research I've done and information you provided I have come up with a solution to my trailer situation. The Chaser is a great trailer and I would love to own one but it doesn't fit all my needs 100% and i can't afford the cost on top of building the two trucks I'm building.

So I'm picking up a 1/4 ton military trailer and purchasing the AT retro suspension kit. The cost of the suspension is where I feel my money is best spent. I'll be able to modify the trailer to fit my needs by adding a tailgate and removeable rack system, as I don't need a lid.

Martyn , is the suspension kit available at this time, if not what is the ETA?
Thanks again for all you help.

All the parts are in stock but need to get welded together to form the support cross member. Mario runs production, he's up in Canada right now at the Canadian Off Road Expo but when he gets back we should be able to give you a delivery date.

I fully understand where your coming from in regard to budgetary constraints, we all have to do what we have to do in order to pay the bills and stay afloat.

Both Mario and I don't believe in trying to push a sale. It's much more important that a trailer owner ends up with a trailer that is best suited to their needs, not ours. We often refer sales to other companies when it's obvious to us that our product just doesn't meet a customers requirements.

In the same way disseminating knowledge allows you to make the best choice for you. We have learnt a lot about trailers, sometimes the hard way, so there is no reason you have to learn the same way.

We also know how hard it is to build a trailer and how depressing it is to put weeks of work into a project and end up with a trailer that is a disappointment.

At the same time I'm happy that you choose the route you decided upon. I don't think you will be disappointed the 416 and the AT suspension are a good match.

[oldcj5guy]

Martyn,

I find myself thinking that there may yet be hope for customer service in this world. I thank you for taking the time to share your knowledge with him.

[bigreen505]

Martyn,

I find myself thinking that there may yet be hope for customer service in this world. I thank you for taking the time to share your knowledge with him.
:iagree: I don't need a trailer right now and I'm not in the market, but when I do, AT will be where my money goes.

[detailbarn]

Martyn,

I find myself thinking that there may yet be hope for customer service in this world. I thank you for taking the time to share your knowledge with him.


Indeed if this much effort goes into their customer service I can't imagine how much time effort and passion goes into their product.

Martyn again thanks so much for the time you've spent educating me on the in's and out's of off-road trailers.

[dieselcruiserhead]

It would not be hard to mimic the independent a arm style of the adventure trailers. If it were me this is what I would do. Parabolics can work but I think the adventure trailer design is far superior..

[Martyn]

It would not be hard to mimic the independent a arm style of the adventure trailers. If it were me this is what I would do. Parabolics can work but I think the adventure trailer design is far superior..

Strangely enough the suspension arms are the most difficult thing on the trailer to manufacture. We have a QC rejection rate of 15 - 20 %.

The basic arm design has had a few recent changes with the latest batches. Camber and toe in adjustment features that are now in production. We were also able to find an alloy rod that we had CNC'd into pivot rods for the suspension. The new rods have a much higher shear strength than the rods used in previous models.

We are proto typing a new arm that will take the arm up to a new level. Can't really discuss the details but the arm is going to be really neat.

The new arm will be able to be retro fitted to prior models fitted with the independent suspension.

[ntsqd]

The Devil is Always in the details & reverse engineering is a PITA. :)

[dieselcruiserhead]

Interesting and good to know. I have plenty of projects but have put a lot of time into planning a trailer and love the idea of the adventure trailer suspension after evaluating it on the internet and in person. I had planned for some time to mimic it. Not to take away from your designs but because I have plans to build a trailer from scratch personally. Cheers and good luck with the new designs. Andre


Strangely enough the suspension arms are the most difficult thing on the trailer to manufacture. We have a QC rejection rate of 15 - 20 %.

The basic arm design has had a few recent changes with the latest batches. Camber and toe in adjustment features that are now in production. We were also able to find an alloy rod that we had CNC'd into pivot rods for the suspension. The new rods have a much higher shear strength than the rods used in previous models.

We are proto typing a new arm that will take the arm up to a new level. Can't really discuss the details but the arm is going to be really neat.

The new arm will be able to be retro fitted to prior models fitted with the independent suspension.

[Martyn]

Interesting and good to know. I have plenty of projects but have put a lot of time into planning a trailer and love the idea of the adventure trailer suspension after evaluating it on the internet and in person. I had planned for some time to mimic it. Not to take away from your designs but because I have plans to build a trailer from scratch personally. Cheers and good luck with the new designs. Andre

Andre

They say imitation is the most sincere form of flattery, so I take it as a compliment.

Once you get rolling on the trailer let me know. Maybe we can trade knowledge. I'll supply the trailer IQ to you, and you supply the diesel IQ to me ?? Quid Pro Quo

[dieselcruiserhead]

Quid pro quo... :)

[ShearPin]

I have around seven years experience running parabolics on my Series III SWB Land Rover paired with Old Man Emu shocks. Over the years I've done some long distances with heavy loads and the usual light load commutes to work. I've never experienced any of the load carrying difficulties or stability problems often read about on the net. Baja corrugations, pot-holled roads in Guat. - I never loooked back. Granted, even with the overdrive I rarely exceed 60 mph.

Another option my brother used on his 416 trailer we found on Teriann's Expedition site - I noticed she's joined Exped recently. My brother stripped and painted the simple leaf springs and placed the low friction plastic between each leaf. Side by side with my stock 416 spring pack there is a noticeable difference in spring performance. I'll be adding the tape when I get a chance. Teriann is very thorough in her explination and even includes part numbers...

http://www.expeditionlandrover.info/leafSprings.htm

Henry
www.4x4freedom.com

[ntsqd]

Inter-leaf friction in leaf springs causes slow compliance and reduces the damper valving needed due to their own internal friction acting as a damping agent. Hum, sounds like the perfect pavement trailer spring - no dampers required if the internal friction is high enough compared to the spring rate.

By reading TeriAnn's page I now understand what the differences btwn the "parabolic" leaves and std leaves are. The term "parabolic" may or may not be mis-applied. It would be pretty hard to visually see any difference btwn a parabolically arched leaf and a semi-elliptically arched spring. Which was a point of confusion for me.

These "parabolic" features are also found in the late model 65" GM rear springs. These springs feature the leaf tip pads, which is not all that uncommon, but they also feature a shim/spacer btwn each leaf pair at the center pin that creates an air gap btwn the leaves. So the leaves only touch at the tips, considerably reducing the spring's internal friction. I have found that Bilstein's std leaf spring valve stack is not enough with these springs.
I suspect that this lower overall damping value is what leads to complaints of instability etc.

I think it would be an interesting experiment to install such shims in a "normal" spring pack and see what the vehicle's behavior differences are.

[zimm]

ill be slappin a set of tic 4" paras on the fj 40 soon. ill keep yall posted.

[cruiseroutfit]

As noted it is very interesting that parabolic spring experience vary greatly between the vehicles they are installed on. I know several Landcruiser owners that removed them shortly after install... for what they felt was an unstable and scary handling, poor load capacity, etc. Howevery, just about every old Rover guy I have talked to seems to swear by them.

While parabolics reduce the spring to spring friction, its really neither here nor there as long as the friction is accounted for in the design of the spring (for a particular load capacity) and the matching dampner to go with it.

[Martyn]

While parabolics reduce the spring to spring friction, its really neither here nor there as long as the friction is accounted for in the design of the spring (for a particular load capacity) and the matching dampner to go with it.

Kurt, I'm not certain that parabolic springs reduce friction between the leaves. I think the use of the Teflon pads in this case achieves this. It's a little confusing on the web site in that they define a parabolic spring as;

"Basically a HST Parabolic Spring is a spring that consists of two or more leaves. The leaves touch only in the center, where they are fixed to the axle and at the outer ends, where they are fixed to the vehicle. In between those two points the leaves do not touch each other as they do with conventional leaf springs." (if you placed the same Teflon pads between conventional leaf springs you would achieve the same effect!).

Where as the true definition is more like "....the leaf is tapered, from the center (thick) to the outer ends (thin). This tapering is parabolic..."

Have I made this more confusing or less??

[cruiseroutfit]

Kurt, I'm not certain that parabolic springs reduce friction between the leaves. I think the use of the Teflon pads in this case achieves this. It's a little confusing on the web site in that they define a parabolic spring as;...

Yup, all part of the accounting for the friction I was referring too ;)

OME for example uses greasable teflon pads at each spring end. After a few years of use they can start to wear thin, simply replace them with new ones, under $10/springs :D

[ntsqd]

I think that the damping was off or mis-matched in those who complained of instability with the parabolics. Then again, everyone has their own definition of what is 'unstable' so a qualitative analysis is sort of doomed from the start.