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2.6 What is RTI (Ramp Travel Index)
If you've been hanging around with the 4x4 crowd, sooner or later someone will brag that their 4x4 has
more flex than someone else's 4x4 or can traverse uneven terrain better than someone else's 4x4.
While that may be true, without going "out there" and testing it, who's 4x4 does actually have more flex? To answer that question, you should know your vehicle's Ramp Travel Index or RTI.
So just what is a "Ramp Travel Index" and how is it measured?
First of all, the ramp. Here's a picture of what one typically looks like (this one was built by a member of TTORA):
"The ramp" is a metal structure with a 20- or 30- degree slope that is used to measure a vehicle's ability to conform to the terrain. Suspension travel and frame 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.
The measurements don't lie. It doesn't matter if it's a live-axle pickup with leaf springs, or a four-coil SUV — they all go just so far up the ramp, in the process generating meaningful numbers for the purpose of comparative testing.
Ramp Travel Index is a slightly cryptic way of telling how far up the 20- or 30- degree ramp a vehicle can go while still keeping all four tires in contact with the surface underneath. 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 frame flex) is divided by its wheelbase. Once the distance up the ramp is determined, you multiply that number by 1,000 to get kind of a batting average.
For example, if a 104-inch-wheelbase vehicle goes 39 inches up the ramp, it's RTI number would be 380 ([39 ÷ 104] 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 tire.
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.
So, how do you cheat? You can't, but you can be sloppy. Measuring accuracy is important. Use a plumb device to measure downward from the hub. Also, differences in tire 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 tires inflated to exact recommended specifications.
A while back, Four Wheeler magazine did an article on RTI. Here's some of the numbers they came up with:
While that may be true, without going "out there" and testing it, who's 4x4 does actually have more flex? To answer that question, you should know your vehicle's Ramp Travel Index or RTI.
So just what is a "Ramp Travel Index" and how is it measured?
First of all, the ramp. Here's a picture of what one typically looks like (this one was built by a member of TTORA):
"The ramp" is a metal structure with a 20- or 30- degree slope that is used to measure a vehicle's ability to conform to the terrain. Suspension travel and frame 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.
The measurements don't lie. It doesn't matter if it's a live-axle pickup with leaf springs, or a four-coil SUV — they all go just so far up the ramp, in the process generating meaningful numbers for the purpose of comparative testing.
Ramp Travel Index is a slightly cryptic way of telling how far up the 20- or 30- degree ramp a vehicle can go while still keeping all four tires in contact with the surface underneath. 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 frame flex) is divided by its wheelbase. Once the distance up the ramp is determined, you multiply that number by 1,000 to get kind of a batting average.
For example, if a 104-inch-wheelbase vehicle goes 39 inches up the ramp, it's RTI number would be 380 ([39 ÷ 104] 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 tire.
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.
So, how do you cheat? You can't, but you can be sloppy. Measuring accuracy is important. Use a plumb device to measure downward from the hub. Also, differences in tire 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 tires inflated to exact recommended specifications.
A while back, Four Wheeler magazine did an article on RTI. Here's some of the numbers they came up with:
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Vehicle / model: RTI '96 Acura SLX: 506 '93 AM General Hummer: 385 '92 Chevrolet S-10 w/Rugged Trail 3.5-inch lift: 351 '81 Chevrolet K-5 Blazer: 653 '81 Chevrolet K-5 Blazer w/Rugged Trail 2.5-inch lift: 695 '92 Chevrolet K-1500 Blazer: 453 '92 Chevrolet K-1500: 421 '92 Chevrolet K-2500HD turbo diesel: 365 '92 Chevrolet K-3500 Crew Cab dually: 303 '94 Chevy S-10 ZR2: 420 '94 Chevy K-2500 Suburban: 401 '95 Chevy ZR2 Extended Cab: 336 '95 Chevy Blazer 2-dr: 405 '96 Chevy K-1500 extended-cab: 376 '96 Chevy Tahoe LS: 433 '92 Dodge Ramcharger: 613 '92 Dodge Dakota Club Cab: 393 '92 Dodge W150: 526 '92 Dodge W250 Cummins: 372 '92 Dodge W250 Cummins w/Natl. Spring 3-inch lift: 406 '94 Dodge Ram 1500: 556 '95 Dodge Ram BR2500 Club Cab: 431 '92 Ford Explorer 4-dr.: 460 '92 Ford Explorer 4-dr. w/Superlift 4-inch lift: 492 '92 Ford Bronco: 516 '93 Ford Ranger SuperCab: 416 '92 Ford F-150 Flareside: 471 '92 Ford F-150: 484 '92 F-350 Crew Cab w/Mac's Spring Shop 2-inch lift: 405 '94 Ford Ranger SuperCab: 406 '94 Ford Explorer Limited 4-dr.: 443 '94 Ford F-250 SuperCab: 383 '95 Ford F-250 SuperCab: 406 '95 Ford Explorer 2-dr.: 391 '95 Ford Explorer 4-dr.: 352 '97 Ford F-150 SuperCab: 441 '92 GMC Sonoma: 354 '93 GMC Sonoma Club Coupe: 334 |
Vehicle / model: RTI '92 GMC K-1500 Suburban: 342 '92 GMC K-3500 Crew Cab: 338 '95 GMC K-1500 Club Coupe: 387 '95 GMC Jimmy 4-dr.: 371 '93 Isuzu Rodeo LS: 435 '92 Isuzu Trooper LS 4-dr.: 497 '93 Isuzu Trooper LS 2-dr.: 508 '93 Isuzu Trooper RS 2-dr.: 529 '94 Isuzu Rodeo LS: 454 '96 Isuzu Rodeo: 464 '75 Jeep DJ-5D: 556 '92 Jeep Cherokee 4-dr.: 399 '92 Jeep Grand Cherokee: 458 '93 Jeep Grand Cherokee: 448 '93 Jeep Grand Cherokee: 439 '96 Jeep Grand Cherokee: 422 '96 Jeep Wrangler: 357 '96 Jeep Wrangler w/Pro-Comp 2.5-inch lift: 532 '97 Jeep Wrangler: 532 '96 Kia Sportage: 471 '94 Land Rover Defender 90: 580 '95 Land Rover Discovery: 588 '94 Mazda B4000 Cab Plus: 409 '92 Mitsubishi Montero 4-dr.: 391 '92 Nissan Pathfinder: 511 '96 Nissan Pathfinder: 466 '92 Oldsmobile Bravada 4-dr.: 411 '92 Range Rover County: 670 '93 Range Rover County LWB: 588 '96 Range Rover 4.0SE: 600 '92 Suzuki Sidekick 4-dr.: 379 '96 Suzuki Sidekick Sport: 440 '96 Suzuki X-90: 441 '93 Toyota 4Runner: 441 '93 Toyota Land Cruiser: 593 '93 Toyota T100: 407 '95 Toyota T100 XtraCab: 369 '96 Toyota Tacoma: 435 |
Frame last updated: January 11, 2009