Sunday, 29 December 2013

An Uplifting Experience

You want? Can, only RM200,000, and wait one year. Oh, basic truck not included, you have to supply your own. This fabricator is in the outskirts of Bangkok, Thailand.

I am writing this in response to several requests and queries from friends who asked about methods to make their 4X4 vehicles taller. I am neither an engineer nor a mechanic, and can touch only on some theory and my own experiences, good and bad, as a guinea pig. So, be warned, proceed at your own risk. Some of the points and principles that will be touched on would be conveyed best with diagrams and other visual aids but I don't have the skills and tools to create them so words and your imagination will have to suffice.



Think "Big Foot", think "COOL!" So, tall 4X4s look good. The bigger the tyres, the better the truck looks. (Note, the word "truck" is used here as an affectionate term for all 4X4s, not just the 4X4 pick-ups that have become popular in recent years.)
Being tall has real advantages when you go off to play in the rough stuff. Keeping the body high up, away from the mud, is the best way to ensure progress. Being low, it is all too easy to be stranded with your truck's belly sitting on the mud (or sand), with all four wheels spinning futilely. When you are like a beached whale, all traction aids like diff lockers and electronic traction control become useless.
The most effective way to gain stature is to fit bigger tyres. By "bigger", I mean the tyre's diameter. Of course, the bigger tyres tend to be wider as well, and it's the wider or fatter tyres that have come to be associated with what looks good on a 4X4.
The first problem encountered by anyone who has tried to fit tyres substantially bigger than standard is that they are too big. If you're now thinking "duhhh ...",permit me to elaborate.
Larger tyres will hit or foul various parts of the vehicle's bodywork, especially up in front, where the tyres actually have to turn left and right to steer, as well as rotate and move up and down as the suspension flexes.
The problem then will not just be irritating noises, it will eventually lead to parts getting damaged or destroyed.
The typical 4X4 pick-ups come off the showroom floor fitted with tyres that range from 28 to 30 inches in diameter. Don't bother with calculating from the width and aspect ratios, just take a measuring tape or long ruler and measure yours to find out exactly what diameter it is.
Generally speaking, you should be able to upgrade to tyres up to 31" without any major modifications. Depending on which truck you have, there may be minor issues with the rear edge of the bumper or front mud flaps, which may have to be trimmed or removed, respectively.
Lifted (right) and not lifted.
Aside from increased diameter, wider tyres may also cause problems by touching various parts of the suspension, such as springs or radius arms. You could end up with reduced ability to turn the steering. In the jungle, a simple three-point turn could become a 13-point turn.
The problems associated with increased diameter can be fixed with a lift, and with width, by changing to wheels with a more negative offset (i.e. wheels that stick out further from the vehicle.) Both of these "fixes' will give you an instant improvement in looks, but also, possibly, create problems with driveability and durability of your truck.

BODY LIFT

The first way in which you go about fitting bigger tyres is by lifting the body (or cabin) up from the chassis or frame. This is done by undoing the dozen or so nuts that secure the body to the frame, jacking the body up, inserting lift blocks of 3, 3 or 4 inches in height, then securing with longer bolts, and ... Voila! A taller truck!
But it's really not that simple. Some vital components are attached to the chassis (like engine, gearbox and radiator) while others are fixed to the body (electrical and electronic components and wiring harnesses), and some have one end secured to the body and the other to the chassis (like steering and brakes), so adjustments will be necessary.
The scary mods needed include cutting and lengthening the steering shaft, gear shift lever, transfer case lever, and possibly, replacement of brake lines with longer ones. Failure to do these and do them properly, can lead to issues that are irritating at best, and disastrous at worst. Like total brake failure, for example.
My first experience with a body lift went well because the workshop did a professional job. Several years and a new truck later, I went back to the same shop and got the same procedure done, with different results. Perhaps it was a different mechanic who did the job but, whatever the reason, the steering shaft was not done right and I had to endure squeaking whenever turning the steering, and the transfer case lever had to be adjusted several times before it stopped popping out of gear. Suddenly finding yourself in neutral while climbing a steep hill is not a fun experience.
These days, I'd advocate body lifts as a last resort.

Some of the components needed for an IFS lift.

SUSPENSION LIFT

A suspension lift can be a simple matter of spending money to buy longer springs and shock absorbers, or a very messy, complicated affair with many side effects. The easier ones are usually mild lifts of up to 2 inches (50mm or less).
Almost all 4X4 pick-ups today come with independent front suspension (IFS) and rear rigid axle with leaf springs. A notable exception is the pick-up version of the Land Rover Defender, which employs coil springs and rigid axles for both front and rear.
The latest generation of trucks feature IFS that uses a combination coil spring and absorber (or damper) with upper and lower A-arms (also known as wishbone, like the chicken breastbone), while earlier generations mostly used torsion bars with upper and lower wishbones.
There is no such thing as the best type of suspension, each has its own pros and cons, and the final design is the culmination of the engineers' best efforts to reach the best compromise to meet many different criteria of performance, such as handling, comfort and load carrying.
So, do we want to mess with the work of large teams of the best, brightest and most experienced engineers that the resource-rich car makers can find? Of course we do! 'Cos we want our trucks to look cool!
There is usually a cheap and easy way to do things, and then there is the proper way, which is usually not easy, and certainly not cheap.
One subject from the classroom of many years ago that needs to be revisited is geometry. Most suspension systems involve movement of some components relative to some other components that the former are attached to. That means some form of triangulation, and some pivoting around a pivot point. In simple terms, changing the length of one side of a triangle without altering the length or relative angles of other two sides, is impossible.
About this point, I feel like giving up. It's getting complicated. When talking about the front wheels, we need to consider wheel alignment parameters, like caster, camber and toe, all of which can be affected by simply changing the length of the spring.
To bring harmony back to the arrangement, you'd need to change the length of at least one of the A-arms (usually the upper), and change or adjust the steering tie rods. The objective would be to ensure that the new triangles have the same ratios as the original.
Then, for IFS trucks, there is the issue of the front driveshafts. These are articulated in such a way that, in standard form, they can swing up and down comfortably as the suspension and wheel assembly moves up and down with the terrain. By making the suspension taller, the driveshafts will be tilted downwards (a little or a lot, depending on extent of lift), using up part of the downward flex it has. If the lift is taken too far, the shaft will extend downward to its limit, and beyond. If bigger and heavier wheels/tyres are fitted as well, then don't be surprised if the front driveshafts either pop out or break.
One way to address this is to lower the front axle to a similar extent as the suspension lift, so that the driveshafts are as close to horizontal as possible when the suspension is not flexing. This would require some form of lift kit that includes bits for axle relocation.
At the rear, suspension lift kits for leaf springs usually comprise a block (can be made of metal or some form of plastic) that goes between the leaf springs and the axles, longer U-bolts, and longer absorbers. Again, mild lifts should work reasonably well but taken to extreme, they can cause instability. Just think of running around in sneakers, then wearing 2" heels, and then 4" platform shoes, and you should get the idea.
4X4s with rigid front axles and coil springs have to deal with the same forces but they do it in different ways, and so any attempt to achieve a lift will have to be done in different ways ...

RIGID AXLES 

Newer Land Rover with coil springs, i.e., the Defenders, use a suspension design that is slightly different from others. At the rear, the rigid axle is held on the centre line by an A-arm with a ball joint which allows the axle to move up and down but not side-to-side.
Most other 4X4s with coil springs and rigid axles use a Panhard rod, which does a similar job but does allow some side-to-side movement when under extreme articulation, and also when the vehicle is given an extreme lift.
When lifting an axle held in place by a panhard rod, it is necessary to either replace with an adjustable rod, or relocate one of the rod's mounts so that the panhard rod remains more or less horizontal at rest. This applies to a Defender's front suspension as well because it uses a Panhard rod. With the engine at the front, there is no space to use an A-arm similar to that at the rear.
If these modifications or adjustments are not done, the front and rear wheels may not line up properly with each other, and either or both axles may not line up with the chassis.

TO BE CONTINUED