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The original ramp is a metal structure with a 20-degree
slope that is used to measure a vehicle's ability to conform to the
terrain.
Suspension travel and chassis flex are two important qualities needed to
traverse uneven, rutted terrain, and the ramp is a fair, controllable, and
repeatable way to measure them.
There's no room for driver error or luck to influence the outcome; a number
achieved on the ramp is directly comparable between different vehicles, any day,
anywhere in the world.
Ramp Travel Index is an accurate way of telling how far up
the 20-degree ramp a vehicle can go, while still keeping all four tyres in
contact with the surface. To some extent, mathematical manipulations are
necessary; it would be unfair to ask a short-wheelbase vehicle to crawl as far
up the ramp as one with a long wheelbase. Therefore, whatever number of inches a
vehicle can muster before it runs out of suspension travel (and chassis flex) is
divided by its wheelbase. (This way, a 130 can indeed compete with a 90
We multiply that number by 1,000 to get kind of a workable value.
For example, if a 110-inch-wheelbase vehicle goes 52
inches up the ramp, its RTI number would be 472 ([52 ÷ 110] x 1,000).
Obviously, a higher RTI number translates into better conformability to the
terrain. A perfect score would be 1,000, indicating that the vehicle can go as
far up the ramp as its wheelbase is long without lifting a tyre. No standard
vehicle has reached 1000 but Range Rovers come close. A few modified machines have
indeed reached the perfect score and beyond.
Simple as it is, the ramp tells a great deal about a
vehicle's capabilities on the trail. It's also quite useful for evaluating
suspension kits, checking shock lengths, finding interference points and other
things that may only occur at the extremes of wheel travel.
How do you cheat? You can't, but you can be sloppy.
Measuring accuracy is important. Also, differences in tyre pressure will result
in minor gains traveling up the ramp. These can result in slightly different
scores for seemingly identical vehicles. Accuracy can be enhanced by testing
with all four tyres inflated to exact recommended specifications.
So how do you improve your RTI
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Generally, articulation is a function of your
spring rate, shock absorber travel and suspension geometry.
Newer vehicles like Later Range Rovers, Discoveries and Defenders, have various
safety aids fitted such as Anti-Roll bars or Anti-Sway bars.
The basic function of these bars is to male
wheels on the same axle follow each other up or down - if the left wheel goes up
into the wheel arch it will tend to lift the right wheel as well, this in in
contradiction to articulation.
You can temperoraly remove them for off-roading,
but they must be reconnceted when returning to highspeed driving.
Here are some typical values of RTI on a 20 Degree ramp.
| Vehicle |
RTI |
Vehicle |
RTI |
| '96 Jeep
Wrangler: |
357 |
'93 Isuzu Trooper RS
2-dr.: |
529 |
| 95 GMC Jimmy 4-dr. |
371 |
'97 Jeep Wrangler: |
532 |
| '92 Suzuki Vitara
4-dr. |
379 |
'94 Dodge Ram 1500: |
556 |
| '93 AM General
Hummer: |
385 |
'94 Land Rover
Defender 90: |
580 |
| '93 Isuzu Rodeo
LS: |
435 |
'95 Land Rover
Discovery |
588 |
| '93 Jeep Grand
Cherokee: |
439 |
'93 Range Rover
County LWB |
588 |
| '93 Toyota 4Runner: |
441 |
'93 Toyota Land
Cruiser: |
593 |
| '94 Ford Explorer
Limited |
443 |
'96 Range Rover
4.0SE: |
600 |
| '96 Nissan
Pathfinder: |
466 |
'92 Range Rover
Classic: |
670 |
| '96 Kia
Sportage: |
471 |
'80 Range Rover
2dr Classic |
730 |
We have made a pre-calculated table that you can use to calculate your own
RTI.
All you need to do is drive your vehicle up any ramp or obstacle (Provided the 3
other wheels are on level ground) and measure the height of the wheel tread off the
ground.
You can also try hacking up one wheel in your garage, there will be a bit of
error is this since the contact area of the tyre with the would be ground must
be estimated.
This will then be the entry into the left hand column of the table below.
Find the vertical column for your Land Rover, read off the RTI. Click here to
download the file RTI Table.
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