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Frequently Asked Questions


Q. What is a Parabolic Spring?
A. A parabolic spring is one which has the leaves bent into a parabolic rather than elliptical shape. It also has tapered leaves which flex in a manner which distributes the bending stresses evenly along the length of the spring. Parabolic springs typically have fewer leaves than conventional springs and weigh much less thus reducing the unsprung weight of the axles in a vehicle. In our parabolic springs the leaves are separated along their length to reduce friction. The reduction in unsprung weight and friction gives a spring with improved ride quality. A Land Rover fitted with our springs has a ride similar to a coil sprung truck.


Q. How do Parabolic Springs improve off road performance?
A. The parabolic springs improve off road performance by making the ride much softer and more enjoyable for the passengers, smoothing out corrugations and bumps. The supple nature of the springs keeps all wheels on the ground much better than conventional springs and enables the Land Rover to maintain traction in difficult terrain.


Q. Why do you make a two leaf rear spring?
A. This is not all that unusual. The Land Rover 101 series also has a two leaf rear spring. We make the 73589 spring for owners of '86' and '88' model Land Rovers who generally don't use the full load capacity of their trucks but want to have the best possible combination of smooth ride and great axle articulation. Usually when these springs are installed the owner knows his typical load will be two adults plus a fair amount of camping gear. These springs do not preclude you carrying heavier loads but you have to accept that the rear of the truck will deflect more when such loads are carried.


Q. When is the three leaf rear spring used?
A. The 73590 spring is used on “86” and “88” model Land Rovers which are frequently loaded to maximum capacity. It is also used on "86" and "88" models which have roofracks or which are used for towing trailers. The 73590 is also used on “107” and “109” Land Rovers where the loading on the Land Rover is moderate.


Q. When do you use the four leaf rear spring?
A. The 73591 spring is only used on "107" and "109" Land Rovers with heavier bodies. The typical application is the "109" safari station wagon which can carry up to twelve people. The 73591 is also useful if you have a heavy camper body on a three door "109". These are great springs for expedition Land Rovers which are often loaded to the maximum. The 73591 is not a suitable spring for lighter trucks as it will lift the rear of the truck up to the maximum extension of the shock absorbers.

Q. All your springs have parallel leaves - without an overload leaf - why is that?
A. We have in the past supplied springs with overload leaves but in the opinion of our test team and customers the overload leaf protruding underneath the rear axle was a hazard off road and did little to enhance the performance of the spring so we discontinued it.


Q. I notice you use a larger rubber bushing in your spring eyes. Why is that?
A. Parabolic springs flex more than conventional springs and having an eye 18% larger allows us to use a bushing which can withstand flexure much better than a conventional one. The larger bushing also reduces stresses in the spring eye of the main leaf and insulates the Land Rover better from transmitted road noise.


Q. You put extra clips wrapping the leaves near the end of all your springs. Why is that?
A. Those extra clips perform an important function when the springs are twisted during maximum axle articulation. Without them the second leaf of the spring would slide over the first until it chafes on the sides of the shackle plates. It is details like this that make our products better than other brands. We frequently drive very rough tracks in remote mountainous areas and test under extreme conditions.


Q. Why do you package 'U' bolts with all your springs?
A. We supply high quality 'U' bolts a full ½ inch diameter with rolled threads, washers and nuts. The U bolts are the right length for the springs. Most of the time the old 'U' bolts are rusted, inferior in quality or simply don't fit. You may have to enlarge the holes in your clamp plates very slightly to fit our 'U' bolts but you get much better clamping action. It is very important that a parabolic spring be well clamped or stresses will develop exactly in the middle of the spring where it is drilled for the center bolt.


Q. Can I use my old shock absorbers with your Parabolic springs?
A. Yes if they are in good condition. It pays to replace the rubber shock bushings and we have a kit for that purpose. Using your old shock absorbers will restrict the downward movement of the axles and for off road use using our EXPLORER PRO COMP or OLD MAN EMU shocks will give better axle articulation as they have a longer stroke.


Q. Do I need check straps on my rear axle?
A. Yes. Check straps are important with parabolic springs because the springs are more supple than conventional springs and there is a danger of damaging the shock absorbers by extending them too far. For this reason we always supply you with new check straps when you buy shock absorbers from us.


Q. Will my Land Rover sit higher with your Parabolic Springs?
A. Yes. You will notice the unloaded Land Rover sits a least one to two inchs higher than with factory springs. This amount will vary depending on the truck configuration and accsessories and the condition of the existing springs.
See our data on Parabolic Ride Heights


Q. Can I use extended shackles to increase ride height further?
A. This is not recommended for several reasons. You could make the truck unstable and you could run into problems with drive line geometry. Also you will increase the distance between the axle and the bump stop which could overstress your springs in maximum compression. The only time extended shackles can be used is on Military Land Rovers which have offset rims to improve stability and axle buffers which are fitted lower to prevent the springs becoming overstressed.


Q. Are your springs sold in left hand and right hand sets?
A. No. Our experience with factory springs over the years has been that if you install springs of different camber the truck will always sit tilted. With the parabolic springs of even camber you might notice a slight lean with only one person in the truck or when unevenly loaded, but this is negligible.

Occasionally we hear of a Land Rover which does not sit evenly from side to side with new springs fitted. In some cases of this nature we have found that repairs have been made to the frame which altered the position of the spring hangers.

The trim of the Land Rover can usually be adjusted slightly by making use of the minor differences in leaf sets exchanged from side to side.


Q. Are Parabolic Springs more expensive than conventional springs?
A. It depends what you mean by a conventional spring. There are many cheap shoddy springs sold for Land Rovers and our springs will certainly be more expensive than these. It is safe to say however that our springs cost less that Genuine Land Rover springs and give a much better ride.


Q. Do Parabolic Springs require any maintenance?
A. A little light oil between the leaves will deter corrosion and prevent squeaks. The rubber bushings should be checked occasionally. It is also very important to check that the 'U' bolts are torqued up to 70 ft lb. The 'U' bolt torque should be checked frequently under difficult conditions. You should also check that the shackles are tight by loosening the lock nuts and tightening up the shackle bolts. The condition of the axle buffers and check straps should also be checked occasionally.


Q. Why don't you use plastic pads between the leaves of your springs?
A. Long experience with commercial applications has shown that there is little if any long term benefit to plastic spacers. We like to keep things simple and would not expect such plastic pads to remain in place in serious off road conditions.



If you have any other questions about our Parabolic Suspension packages, please visit contact us.

Address:
Rocky Mountain Products
PO Box 91335, West Vancouver, BC Canada, V7V 3N9

Telephone: (604) 913-7910

Email: rmhighroad@gmail.com