These numbers 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.
"The ramp" is a Trekmaster-built metal structure with a 20-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. Thus, every vehicle regularly tested by Four
Wheeler since the completion of the ramp has a so-called Ramp Travel Index (RTI)
number listed in the specifications--or should have had, because it's an
important number.
Ramp Travel Index is a slightly cryptic way of telling how far up the 20-degree
ramp a vehicle can go while still keeping all four tires in contact with the
surface underneath. To some extent, the 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. (This way, a Geo Tracker can indeed compete with a GMC
Crew Cab on even ground-even on this uneven ground.) We multiply that number by
1,000 to get kind of a batting average, which we print.
For example, if a 104-inch-wheelbase vehicle goes 39 inches up the ramp, its 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. No stock vehicle has even approached that number,
but a select few trail-prepped machines have indeed reached the perfect score.
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. Trekmaster (no longer in business) built this towable
ramp, which has helped us bring useful information to you, and perhaps a weekend
project with the club could result in your very own "tweak-o-meter." In case you
ever wondered how your customized 4x4 compares to the latest SUVs, a 20-degree
ramp and the numbers in Four Wheeler can tell.
How do you cheat? You can't, but you can be sloppy. Measuring accuracy is
important. We 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.
RAMP TRAVEL INDEX SUMMARY
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
'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
The reigning ramp champ of vehicles tested for Four Wheeler is this '81
Chevrolet Blazer with a Rugged Trail 2.5-inch suspension, topping the list with
a 695 RTI. In the stock class, the '92 Range Rover holds its own with a
not-too-distant 670. Lowest RTI to date was recorded with an unladen '92 Chevy
Crew Cab dually-which wasn't too surprising, considering its big potential
payload.
(
geocities.com/baja/trails) (
geocities.com/baja)