Suspension Modifications, wheels and tyres
One of the most significant modifications you can do to enhance on- and off-road capability of a vehicle is changing the suspension. However this is no easy task. When you begin mixing up parts without the proper knowledge you will probably get a vehicle less capable and even potentially dangerous. Bear in mind that, if you change any of these components and you happen to have an accident, someone, either police, lawyer or insurance company, will try to prove that you made mistakes and so it was YOUR fault the accident happened.
After this let's go to the subject. Land Rovers use soft coil springs since the development of the Range Rover in the late sixties although it took many years to equip all the line with them. Today we're looking again at another change, this time to air suspension. More on this later.
Basically, for off road performance you need a suspension as flexible as you can get while maintaining good damping and cormering abilities. The suspension must be soft to allow the tires to keep contact with the ground as long as possible - traction is the word of the game. The basic setup is not bad, outperforming many other competitors. But there's still room for upgrades.
RTI is the Ramp Travel Index. It shows how far a car can be driven up a (mostly) 20° ramp with one tire befor any other tire looses contact to the ground.
If you have access to a fork lift, you can determine the RTI: Lift the tire just before the other tires get off the ground. Measure the vertical distance (h) from the bottom of the tire to the ground. Let's say you get h = 25 inches. and that the wheelbase is 92.9 inches (D90). RTI = (h/0.34202)x1000/wheelbase. RTI = (25/0.34202)x1000/92.9 = 787 of course, it's not very accurate, but you can have some idea.
The value gives a good figure on how good the suspension performs in real world. It shows the capability of the vehicle to conserve traction regardless of ground level. Most 4x4's have a RTI under 400, the stock Land Rover 90 with swaybars attached has around 600 which is already quite a lot in real world. Anything around 800 and more is amazing. A couple of years ago 1000 was believed to be the max, but, as you can see, higher values can be achieved- at a price.
|This here is the base they all started from - already a very capable suspension scoring a 600 on the ramp||
|Chris Hinkle's D90 with 35"X12.5" Yokohamas scored an RTI of 1300! Anyone out there who does better? E-mail me|
|A D90 with an OME suspension negotiating the Golden Crack in Moab|
|Bill Ritchie's D90 wearing Goodyear
Wrangler MT 35x12.5x15" on custom 15x8" rims with 5"
|Sean P. Murphy's D90|
|Here's a nice documented photo story on what's involved in adding 13 Inches of travel using the Desert Suspension setup|