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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 travelling 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
?
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 temporarily remove them for off-roading,
but they must be reconnected when returning to high speed 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 |
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