Just as rally cars get firmer suspension to give them less body roll and more traction = road holding, a 4*4 used off road can have its ride improved. Take a Hilux for example, which beats you senseless unless you drive on the Golf Course Greens, why? How does your suspension work and how does the Factory design it? A race truck suspension gets designed by the following Criteria:
How much Suspension travel can we accommodate, 10 Inches of Travel is the minimum nowadays.
Let’s say we jump max. 3 Meter’s in height with a 1000Kg car, this will tell me what force the springs must be able to handle before bottoming the suspension and is the basis of our spring rate in LB/in or Kg/cm. Since we will encounter various types of terrain, one often uses rising rate springs, meaning that under little force the spring moves a lot of distance, giving us a subtle ride. When struck hard it can still absorb the impact without bottoming and transferring the force to the Chassis and driver.
Apart from Jumps, the Tire encounters Dips, where it should fall into without pulling the chassis behind it (droop travel) and spitting it out again (compression). Now you know what happens in your 4*4 Hilux, no wheel travel giving you a pain in various extremities. The Wheel also encounters bumps in the form of mounds and square ledges (such as pavements). These factors all influence spring rate more than Shock absorber characteristics.
Now that we have chosen the spring for the job it is time to see whether the rest of the components are up to the job. On the 2*4 Toyota we boxed the frame to take the shock loads and on the rear the shackles were beefed. While the front received Tubular upper control arms for increased travel and rigidity while the upper Ball joints were redesigned for the travel and punch as well as the strut frame. While the lower control arms and idler arms were gusseted and full floating bushes were fitted all round. Why am I going on about these individual parts on a Heavy Duty 30cm Wheel travel bakkie? Because before you buy a suspension system for your truck, you should know what it has to do and what you have to ask for. The above might be to taai if your Bakkie only sees smooth graded roads, but when you want to race Trans Namib or travel on a zero maintenance road with no time to waste, this is it!
Why am I not going into shocks? Too complicated a territory- let it suffice to say that most Manufacturer sell most of their different shocks with similar valving and just different mounting points and lengths, meaning you get nothing special. You get speed and position sensitive shocks with multi valving (2 or 12 different stages?) and to work properly they have to fit your vehicle like a glove taking weight, speed, springs and a whole lot more into perspective. Brand Names are De Carbon, Doetsch-tech, Bilstein and Rancho. Most others “ Performance Shocks” are made by Gabriel or other Major manufacturers and valved to the “Performance Companies" specs. Double shocking was designed so that the shocks could be valved softer for better heat absorption NOT for correcting some other suspension fault. These “Performance Shocks” are normally better than stock because the manufacturer of the vehicle has other design criteria.
A few years ago we only had a few suspension manufacturers, the rest of the crowd sold Lift kits to give you nosebleed or slammed the truck into the ground to look cool for the Californian babes. Guess who brought in the change to mass-produce a kit to improve handling on a 4*4? From what I gather a few guys working in a popular Californian Dealership grew tired of hearing the hunters and other serious wheelers complain about the ride on their solid axle Hilux. They looked at the Japanese spec sheet and noticed that NHK; the OE spring manufacturer actually had a different version. Due to these having far more droop travel and an increase in up travel (which is only there to give you the same load rating) they were far more comfortable. These guys at the Dealership then discussed Damping with a Friend called Ricky Doetsch, who was well known for equipping most off road racing Trucks with his modified race shocks (using Aircraft Landing shocks) and setting up factory shocks for Factory race teams. He designed a state of the art mass-produced Multiple Velocity shock with 12 stages and patented it. This became such a success that the Toyota guys now own the biggest Toyota accessory parts Manufacturer and Doetsch tech shocks are regarded by many to be the finest affordable shocks. Today all the big names try to get hold of prototype trucks to design suspension systems on, so they can market them on the day these Trucks get their official release.
Lets get to Pumpkins, rears, diffs or whatever else you might call them. The normal diff is open meaning you can jack one wheel up and accelerate, leaving the jacked up wheel spinning helplessly, while the vehicle remains motionless. Limited Slip Diffs sense 1 wheel slipping and then engage a clutch or force a cone or gear to turn the other wheel by a certain percentage (given by the Manufacturer). Best in fast off Road driving conditions and if the slip factor is big enough ideal for tar road driving. Spools have both side shafts locked together permanently used only in Drags and maybe oval track with staggered tires. While lockers can lock the side shafts together and leave them open- forget the type incorporating Lockers and limited Slip in one unit. Some Lockers are under the driver’s control and some are Automatic, the first type is ideal for “Vasbyters” and others who want to be in “Full control”. The second type we found ideal for Farmers, geologists and others who spend the majority of their time of the tarred road. Meaning as long as the axle with the Locker has 1 wheel with traction the vehicle is movable, while around corners the outside wheel freewheels giving little weird handling.
Putting a traction-aiding device in the Front causes weird steering inputs and takes some time getting used to and to me is only necessary in extreme 4 wheeling. The only other thing apart from knowing how strong your Diff is, is your ratio knowledge. You have an Axle input shaft spinning a pinion gear that drives a ring gear at right angles that in turn drives your centre portion (the open, locked whatever diff.). The ratio of few pinion gear teeth to many ring teeth is your ratio, 4 to 1 means your drive shaft spins 4 times to the wheels 1 Revolution. So going numerically higher gives you slower speeds (ideal for Vasbyt) while going to a “Lower” diff means getting a Lower RPM at Cruising. Confused? Well one more, as my teachers used to say.
Gearbox Ratio, No do not throw the Koerant into the Corner as this is the same as Diff ratio. Your Crank turns at so many RPM as your Rev. counter displays, so lets say it turns 5000 RPM and your Ratio in first is 5 (normally we leave out the to 1) it means your output shaft (prop shaft) turns 1000 times per minute. Then your ratios change so you don’t “drop” to many Revs between shifts to 4’th which nearly always is a straight 1 (or 1 to 1) which now lets your prop shaft spin as fast as the motor. And your 5’Th or Overdrive is then .70 (30% Overdrive) meaning at 5000 Engine Rpm your drive shaft is spinning 7142 RPM. Running through your 4.00 diff means the tires are spinning 1785.7 times per minute and since your tire covers 2 meter’s per Revolution, you are covering 3571.4 meter’s per minute and 214.28 Km/h.
This was it on the Technical aspects of Wheeling, next time I will discuss on how to get started in Motor sports.