I hope this helps you when making your spring setup choices.
- Springs are selected according to maximum axle loadings. Axle loadings are 750kg - 39mm Round, 1000kg - 40mm Square, 1350kg - 45mm Round, 1450kg - 45mm Square. (India, China and Australia use different steel, different steel ratings.
- When upgrading springs make sure your axle can handle the extra weight.
- If you are upgrading more than your axle rating then your spring will suffer fatigue because the axle will flex more and cause your spring to wear through excess axle flexing.
- Small springs may have 6mm fishplates so upgrade those to 8mm. Off-Road springs have 10mm fishplates. Care should be taken when tightening U bolts, too much tension on one side may cause spring breakage.
- Make sure your U bolts holding your springs have not rusted and are tight. Loose U Bolts have been known to break your springs. It is very common for springs to rust in between the leaf. If you are dipping your springs in salt water and they are not galvanised then you will get 4 - 5 years life out of your springs.
- To lengthen the life try coating the spring with bitumen paint sealer. (same product is used in waterproofing.)
- Spring loading capacity must be identified when you purchase your springs so have a look at your axle size first. Note: Not all springs are the same, choose a good brand spring.
- If you trailer total weight is say 800kg and you have a 45mm axle, please do not put 6 leaf springs in because it is over kill. Your trailer will bounce all the way down the highway. Try and match your average loads exactly with your spring setup to ensure trouble free trailering. Better to have the right springs on a heavier axle.
- Eye to eye springs are common for campers, tandems, box trailers and some caravans.
- Off-road springs are heavier again and are suited to campers. Why? Because Caravan and Camper springs are 60mm wide as opposed to 45mm for standard spring setup. 60mm wide springs are more durable and can handle extreme loads of tandem trailers when cornering.
- Slipper springs are common on boat and Jet Ski trailers.
- If you are going into some really big spring systems then go for off-road or rocker roller type suspension systems. Rocker Roller spring systems give a better ride than standard tandem suspension system.
Here are a couple of examples of what not to do.
- 39mm Axle (750kg) with 4 left slipper springs (800kg). This system is ok but often it is tempting to put 6 leaf springs (1300kg) on this axle thinking it is also OK. Unfortunately you will break many sets of slippers in 12 months. Why? Because a lot of axle flexing occurs when axles are overloaded. This flex causes rapid detoration of the springs and they are breaking due to fatigue. Upgrade your axle to 40mm Square or 45mm Round Axle which will cost you about $80.
- Another bloke wanted 6 stud Landcrusier hubs on his boat with a 39mm axle. Same problem, broken springs. You need to de-rate axles and springs by 20% when using 6 stud Landcrusier hubs because of the bigger wheel, more weight and more pressure on the axle setup. Again he needs to upgrade his axle.
- Another bloke had a 50mm Round axle with a 4.2mtr boat and wanted 6 leaf springs. Seems OK but the boat was too light for this heavy setup, which would have resulted in it skipping through corners and bouncing down the highway.
- Don't sand blast springs. Measure the width of the spring at the spring centre bolt. If the width has grown either side of the spring centre bolt then your spring has cancer and needs to be replaced.
- Do not put slipper springs on your camper. Under extreme conditions, the slipper springs can dislodge itself from it rear hanger. Campers, especially off-road campers use eye to eye springs. Campers with slippers are restricted to on road use for problem free motoring.
Off-road campers usually take a pounding in comparison to their bitumen only cousins. Off-road brutes need to be built tough from the start. Here's an example:-
Notice the locking nuts on the U bolts?
Off-road outback re-bound springs are a must with 5/8" U Bolts. 1/2" U Bolts are normally installed on all trailers but you need the larger U Bolts when you are trying to kill your suspension in rugged country.
Outback springs are 60mm Wide and cater for a fair whack due to twisting and turning in all sorts of terrain. Normal 45mm wide springs are going to give you trouble soon or later.
Axle width should be no less than 45mm Round or 45mm Square. Brake your trailer with either electric off-road or disc override rotors.
Off-road electrics are the preferred favourite over standard electric brakes. Standard brakes cannot handle the dust and heat associated with off-road warriors but are commonly used by the bitumen dwellers. There is also an issue with magnet rattle, off-road magnets have plastic bushes to help prevent magnet arm failure.
Where do I locate the hanger bracket? Rule of thumb is to measure the box length of your chassis. 1" to 2'' of the length is the distance from the center to the back of the trailer where the center rocker is hung. Boat trailers are heaver in the rear than a camper so the rule varies a little.
The other rule is 10% of your trailer weight should be on your coupling.
IMPORTANT: Some states have different rules when it comes to load sharing and tandem axles so check out your state regulations. Here is a simple explanation of how tandem work.
- Slipper springs put the entire load on one axle in some circumstances so you need each axle to be rated to take the entire load of the trailer. Example: If you wish to have a 2 tonne trailer then you will need 2 x 50mm Round Axle. One 50mm axle is rated at 2000kg
- Tandem spring, eye-to-eye setups are load sharing and allow the load to be shared between two axles. Example: If you wish a 2 tonne trailer then you will need 2 x 40mm Square axles. One 40mm axle is rated at 1000kg.
Here the difference. Go over a gutter and stop.
- Leaf springs will lift one wheel off the ground because it is not sharing the load. All the weight goes to the wheel still on the ground. I use this method to change tyres and check wheel bearings on the boat.
- Eye to eye tandem setups will see one wheel on the top of the kerb and one wheel in the gutter thereby still sharing the load across both axles. The rocker assembly on this tandem setup shifts the weight between axles.
So you can see that when you are selecting your setup, under kill and overkill is not good.
Many times I have heard that Gal Springs are inferior because they are tempered during the galvanising process. How true is this?
Galvanised and most other springs must be rated to carry a specific weight. If springs fail it is because theyy have been poorly designed, poorly constructed or misused.
A galvanised spring rated at 600kg is no less efficient than say a black spring rated at 600kg.
Tempering during the heat process is perhaps an excuse for poor manufacturing and/or poor design. We've seen no spring sagging to breaking due to what has been labeled BADLY TEMPERED SPRINGS. It's a FURPHY.
TIP 1 Boat Trailers
Had an old wise fellow visit me a few years ago for shackle bolts and shackle plates to replace rusted bits on his boat trailer spring assembly. He did not need to replace his springs. I asked him his secret. He said;
Mate I coated the springs 20 years ago with bitumen water proofing paint form the hardware store and the springs are as good as new.
Now this may be an old wives tail but it sounds logical, doesn't it? Waterproof your entire axle assembly including drums, hubs, axle and springs. You certainly will get extended life.
On average you may get 5 years from black springs and 8 years for Galvanised springs. The old wise bloke had black springs.
TIP 2 Boat Trailers
I am a big fan of eye to eye tandem spring setups on boat trailers as opposed to galvanised tandem setups if you give the eye to eye setups a coat of bitumen.
Why? Because no matter what the boffins say, galvanised springs must be weaker than non galvanised springs of the same rating.
All springs are tempered by heat. Galvanising is a hot dipping process where the spring is re-heated and reheating cannot be great for the tempered spring.
There is the added advantage of load sharing with eye to eye springs coupled with smaller axle sizes. For me, load sharing must provide a better ride for your trailer and better tracking behind the tow vehicle. Not too many caravans and campers doing big miles on 45mm slipper springs.
OK, after reading this make yourself a checklist and you are ready to select your spring setups.
Totally confused. Ring our sale team on 07 3348 3822 and I will help you select the best setup, but I will need to know two things.
- How much weight do you want to carry?
- What is the size of your existing axle?
Trailering is so much easier and safer when your setup is correct.
FINALLY YOU DO NOT WANT THIS TO HAPPEN.
Example of boss separation. Two possible reasons
(a) Inferior steel selection.
(b) Too much weight and stress to the hub.
Conclusion: Ask the experts for help. Help is free.
2006 © Steve Wotherspoon