One way of comparing a vehicle's suspension flexibility with another vehicle is by means of the Ramp Travel Index (RTI). It also gives some indication of how a vehicle will perform under off-road conditions although a lot of other factors come into play here as well. For example a Hummer has a relatively low RTI index of 385 meaning the suspension is very stiff and not very flexible, not very good for off-road work one would assume, yet the Hummer is a formidable off-roader, in no small part due thanks to its diff locks as well as some other traction tricks it has up its sleeve such as tyres which can be inflated/deflated by the driver while on the move. So while the RTI index doesn't tell the whole story it is still a good indicator under normal circumstances for comparing normal production type vehicles.
To determine a vehicle's RTI index it is driven (normally forwards) up a 20 degree ramp with just one front wheel until one of the wheels starts to come of the ground. It is important to stop when one wheel comes of the ground as vehicles with LSD's or locked diffs can drive further up. When this point is reached a measurement is taken along the ramp to a point where an imaginary line perpendicular to the ramp passes through the vehicles front wheel axle. This measurement is how far the vehicle has traveled up the ramp. This measurement is then divided by the vehicles wheelbase and then multiplied by 1000. For example, a Niva has a wheelbase of 2200mm. If it had travelled 1100mm up along a 20 degree ramp its RTI index would be 500. (1100/2200=0.5, 0.5x1000=500) I decided to put my Niva to the test. To this end I constructed a 20 degree ramp in my drive way using some blocks, a couple of car ramps and some planks. This is the result.
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Click on pictures to see it larger

The plank I have placed across the blocks is 1450mm long and at its highest point measures 495mm off the ground. To my suprise the Niva easily drove to the top of this ramp and still had all four wheels on the ground. This gives an RTI index of 659. (1450/2200=0.659, 0.659x1000=659)
I will have to build a longer ramp to see what it is really capable of, but building a ramp out of blocks like this one is not such a good idea. With at least half the vehicle weight on the one front wheel up the ramp it was pretty wobbly and not safe. Below is table downloaded of the internet of some RTI indexes of a variety of vehicles as tested by the american Four Wheeler magazine.

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

As you can see my figure of 659 compares very favourably with the results in the table above with only the older model Range Rovers surpassing this mark. I would be interested in finding out what the RTI index is for a bog stock Niva. As I have now made these suspension modifications to both my Nivas I can no longer find this out myself. If anybody knows the RTI index of a stock Niva or builds their own ramp and finds out could they please let me know. It would be nice to be able to modify the Niva's suspension to a degree where it would be capable of scoring a RTI of 1000 on the ramp. At that point the rear wheel would touch the bottom of the ramp. Some specially modified vehicles are capable of scoring more than 1000. In that case they have to drive the rear wheel alongside the ramp or drive up a steeper ramp and calculate the difference to translate back to a 20 degree ramp.

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