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Gen 3 Flex-ability

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  • Gen 3 Flex-ability

    I recently conducted some experiments to improve my understanding of the way the Gen 3 suspension works and to measure some baseline performance parameters of the suspension to allow objective comparison if any part of the suspension is modified.

    My investigation focussed on measuring what happens when the suspension is forced to "flex" or articulate in the sense that it would when the vehicle is cross-axled. I believe cross axle flex to be the suspension parameter most relevant to a vehicle's off-road ability.

    My experiments were carried out by lifting an individual wheel (using a trolley jack) until any other wheel just lifted off the ground (this was verified by sliding a sheet of paper under the tyre). The height that the lifted wheel was off the ground was measured at this point and also at several intermediate points. The following pictures show the method:

    Oops, I should have cleaned/tidied the garage up a bit .

    WARNING: Please note that there is an element of danger to this experiment. The car is inherently unstable on the trolley jack when lifting individual wheels, so if you try something similar, please be safe and remember that you are responsible for your own safety and for the safety of anyone that might come close. To minimize the risk of something going wrong and someone getting hurt, chock the wheels that are on the ground, apply the park brake, activate the steering wheel lock and engage 4WD. Don't get any part of your body under the car while it is lifted and don't allow anybody else to do so either.

    The most universally adopted measure of a suspension's "flex" is the Ramp Travel Index (RTI). I think this measure was devised in the USA by Four Wheeler Magazine in the early 90's in order to compare the suspension flex of different vehicles.

    The way RTI is measured is simple. The vehicle is lined up with a ramp and one wheel of the vehicle is driven straight up the ramp until any wheel just starts to lift off the ground. The distance from the base of the ramp to the point where the tyre on the ramp comes in contact with the ramp, directly below the center of the wheel, is now measured and divided by wheelbase. Finally, this figure is multiplied by 1000. It is important to specify the ramp angle as well. The original ramp angle was 20?, but other (steeper) angles have been used to accommodate highly modified vehicles with extreme amounts of suspension flex. If a vehicle with a wheelbase of 2500mm is able to travel 1500mm up a 20? ramp, then the vehicle's RTI is 1500/2500*1000=600. Conventionally, the RTI is measured travelling forward up the ramp as well as in reverse and the two figures are then averaged.

    The RTI figure is simple and easy to measure, but there are several disadvantages to the method. The calculation does not take the track width or tyre pressure into account, for instance. Still, the RTI method is the most common method and most published articulation figures are RTI values measured according to this method. If the height that a wheel is off the ground is known, then the RTI value can be calculated for the vehicle on any ramp angle. I will not bore you with the mathematics (unless you want me to, of course ;D), but this is what I did to compare my car's flex with some published figures for other vehicles (more on that later).

    The front anti-roll bar is very stiff and very restrictive in terms of front axle flex. A rear wheel is lifted long before the front suspension travel is halted by the bump stops:

    Pardon the muddy debris on the lower suspension arm. This shot was taken after some off-road playing before I had time to clean it...

    I could fit my forefinger into the gap between the bumpstop on the lower suspension arm and the stop pad on the chassis.

    At the back, the anti-roll bar is sufficiently flexible to allow the bumpstops on the upper suspension arms to contact the pads on the chassis (the bump stop is at the top of the picture in between the shock and the coil):

    The following picture shows how much the mounting bush of the rear anti-roll bar deforms at maximum flex:

    The average RTI score for my Gen 3 LWB DiD was 482 with the tyres at 2.4 bar and calculated for a ramp angle of 20?. To place that figure into perspective, have a look at the list of RTI values (from this website, but credited to Fourwheeler magazine) below:

    '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
    Let me also be the first to say that it is probably dodgy to compare measurements taken using different, but supposedly equivalent methods . It is interesting to note that the standard Gen 3 does not seem to have less flex than the Gen 2 in the above list ('92 Mitsubishi Montero 4-dr. in the list) and that it seems to hold its own among other vehicles with solid rear axles and even some with solid front and rear axles in terms of flex .

    Whatever the measurement method, as long as one goes about things consistently, it should be valid to make comparisons before and after modifications on the same vehicle, so I then disconnected the rear anti-roll bar and remeasured the RTI.

    Although the rear suspension was reaching the bumpstops with both anti-roll bars attached, disconnecting the rear anti-roll bar improved the RTI rating slightly (about 1%).

    Disconnecting the front anti-roll bar as well, improved the average RTI rating to more than 550 (more than 15% increase).

    As can be seen from the photo below, the front suspension flex is limited by the bumpstops when the anti-roll bar is disconnected.

    With the anti-roll bars connected, about 70% of the flex comes from the rear suspension and only 30% from the front. When both anti-roll bars are disconnected, the rear axle contributes 57% of the flex and the front 43%.

    Disconnecting the rear anti-roll bar does not affect on-road handling greatly. It would probably make the vehicle slightly more prone to understeer at the limit. Disconnecting both anti-roll bars has a marked effect on the vehicle handling; the roll upon entering corners is increased greatly.

    The vehicle feels more stable off-road in cross-axle situations with the front anti-roll bar disconnected, because the flex is more equally split between the front and rear axles and the body roll angles are less.

    If/when I finally get around to upgrading the suspension, I intend to redo this exercise and determine the effects of the modifications on the flex-ability.
    Last edited by pampaskat; 04-11-07, 01:14 AM. Reason: Fixed images
    2003 Pajero 3.2 DiD LWB A/T (with rear diff lock)
    1999 Patrol 4.5 GRX LWB M/T

  • #2
    Excellent report. Very interesting. Thank you.


    • #3

      '81 Chevrolet K-5 Blazer w/Rugged Trail 2.5-inch lift 695
      '92 Range Rover County 670
      '81 Chevrolet K-5 Blazer 653
      '92 Dodge Ramcharger 613
      '96 Range Rover 4.0SE 600
      '93 Toyota Land Cruiser 593
      '95 Land Rover DIscovery 588
      '93 Range Rover County LWB 588
      '94 Land Rover Defender 90 580
      '94 Dodge Ram 1500 556
      '75 Jeep DJ-5D 556
      '96 Jeep Wrangler w/Pro-Comp 2.5-inch lift 532
      '97 Jeep Wrangler 532
      '93 Isuzu Trooper RS 2-dr. 529
      '92 Dodge W150 526
      '92 Ford Bronco 516
      '92 Nissan Pathfinder 511
      '93 Isuzu Trooper LS 2-dr. 508
      '96 Acura SLX 506
      '92 Isuzu Trooper LS 4-dr. 497
      '92 Ford Explorer 4-dr. w/Superlift 4-inch lift 492
      '92 Ford F-150 484
      '92 Ford F-150 Flareside 471
      '96 Kia Sportage 471
      '96 Nissan Pathfinder 466
      '96 Isuzu Rodeo 464
      '92 Ford Explorer 4-dr. 460
      '92 Jeep Grand Cherokee 458
      '94 Isuzu Rodeo LS 454
      '92 Chevrolet K-1500 Blazer 453
      '93 Jeep Grand Cherokee 448
      '94 Ford Explorer Limited 4-dr. 443
      '97 Ford F-150 SuperCab 441
      '96 Suzuki X-90 441
      '93 Toyota 4Runner 441
      '96 Suzuki Sidekick Sport 440
      '93 Jeep Grand Cherokee 439
      '93 Isuzu Rodeo LS 435
      '96 Toyota Tacoma 435
      '96 Chevy Tahoe LS 433
      '95 Dodge Ram BR2500 Club Cab 431
      '96 Jeep Grand Cherokee 422
      '92 Chevrolet K-1500 421
      '94 Chevy S-10 ZR2 420
      '93 Ford Ranger SuperCab 416
      '92 Oldsmobile Bravada 4-dr. 411
      '94 Mazda B4000 Cab Plus 409
      '93 Toyota T100 407
      '92 Dodge W250 Cummins w/Natl. Spring 3-inch lift 406
      '94 Ford Ranger SuperCab 406
      '95 Ford F-250 SuperCab 406
      '95 Chevy Blazer 2-dr 405
      '92 F-350 Crew Cab w/Mac's Spring Shop 2-inch lift 405
      '94 Chevy K-2500 Suburban 401
      '92 Jeep Cherokee 4-dr. 399
      '92 Dodge Dakota Club Cab 393
      '95 Ford Explorer 2-dr. 391
      '92 Mitsubishi Montero 4-dr. 391
      '95 GMC K-1500 Club Coupe 387
      '93 AM General Hummer 385
      '94 Ford F-250 SuperCab 383
      '92 Suzuki Sidekick 4-dr. 379
      '96 Chevy K-1500 extended-cab 376
      '92 Dodge W250 Cummins 372
      '95 GMC Jimmy 4-dr. 371
      '95 Toyota T100 XtraCab 369
      '92 Chevrolet K-2500HD turbo diesel 365
      '96 Jeep Wrangler 357
      '92 GMC Sonoma 354
      '95 Ford Explorer 4-dr. 352
      '92 Chevrolet S-10 w/Rugged Trail 3.5-inch lift 351
      '92 GMC K-1500 Suburban 342
      '92 GMC K-3500 Crew Cab 338
      '95 Chevy ZR2 Extended Cab 336
      '93 GMC Sonoma Club Coupe 334
      '92 Chevrolet K-3500 Crew Cab dually 303
      NT Platinum. DiD Auto with 265/70R17 ST Maxx, Lift, Lockers, Lockup Mate, Low range reduction, LRA Aux tank, bull bar, winch, lots of touring stuff. Flappy paddles. MMCS is gone!

      Project: NJ SWB. 285/75R16 ST Maxx, 2" OME suspension, 2" body lift, ARB 110, 120l tank, bullbar, scratches, no major dents. Fully engineered in SA. NW DiD & auto in place - a long way to go....

      Scorpro Explorer Box


      • #4
        nice work pampaskat - so all we need is for someone to design a front anti-roll bar that is easy to disconnect when we take to the dirt!!!!
        NP 3.5L
        16x7 ROH RTX Wheels
        265/75/16 MT FCII's


        • #5
          Well it's already been designed in the land of down under. Just google for "articulator" or visit outerlimits mitsu section.
          1992 GLS Auto, 285/75R16 Yoko MT, ARB bull bar, custom rear bumper, Safari snorkel, AirLift1000, GAST compressor, ARB locker, etc
          2002 GL Auto, 285/75R16 TrXus MT for fun, 275/70R16 Scorpion ATR for life, towbar, Thomas Comrpessor


          • #6
            I've done similar test. Didn't really care about RTI but rather wanted to compare to my Gen 2. They matched at 21" (525 mm) of travel but that winch upfront Gen 2 really helps it to flex front suspension.

            1992 GLS Auto, 285/75R16 Yoko MT, ARB bull bar, custom rear bumper, Safari snorkel, AirLift1000, GAST compressor, ARB locker, etc
            2002 GL Auto, 285/75R16 TrXus MT for fun, 275/70R16 Scorpion ATR for life, towbar, Thomas Comrpessor


            • #7
              Interesting thread, a perspective i havent really thought to much about, good job.


              • #8
                Interesting job

                I would like to know exactly how much high you can lift every wheel from ground to compare with mine NM with OME HD and bilstein.

                Barcelona, Spain
                2002 NM 3.2 Did


                • #9
                  I've got 21" out of front as I mentioned. Didn't try going backwards.
                  1992 GLS Auto, 285/75R16 Yoko MT, ARB bull bar, custom rear bumper, Safari snorkel, AirLift1000, GAST compressor, ARB locker, etc
                  2002 GL Auto, 285/75R16 TrXus MT for fun, 275/70R16 Scorpion ATR for life, towbar, Thomas Comrpessor


                  • #10
                    Enric, I will check my numbers when I am back home and report back. I seem to recall that the maximum height was somewhere near what Monterorider said.
                    2003 Pajero 3.2 DiD LWB A/T (with rear diff lock)
                    1999 Patrol 4.5 GRX LWB M/T


                    • #11
                      Hello again, Enric.

                      Sorry it took me so long to get back with some numbers, but here they are. In my experiment I could lift each of the wheels individually to the height stated before any other wheel lifted off the ground.

                      Here are the figures for the standard suspension with both anti-roll bars connected. Note that my suspension is sagged somewhat on the right hand side:
                      Left hand front wheel: 416 mm
                      Right hand front wheel: 453 mm
                      Left hand rear wheel: 436 mm
                      Right hand rear wheel: 441 mm

                      With both the anti-roll bars disconnected, the picture changes to the following (test only conducted on left hand wheels):
                      Left hand front wheel: 495 mm
                      Left hand rear wheel: 508 mm
                      2003 Pajero 3.2 DiD LWB A/T (with rear diff lock)
                      1999 Patrol 4.5 GRX LWB M/T


                      • #12
                        Thanks a lot,

                        These's usefull information.
                        More than 5cmts it's a lot of diference in disconect the anti-rolls baras.

                        I will think about it.


                        Barcelona, Spain
                        2002 NM 3.2 Did


                        • #13
                          I have done a quick flex test (along the lines described earlier in this thread) subsequent to fitting an Ironman suspension kit to my car. It seems as though the stiffer springs reduce the flex by an average of 8.5%. This was as expected: the lift is achieved through a higher spring rate, while a reduced spring rate is beneficial to flex.

                          Still, if the front anti-roll bar is disconnected, the flex is significantly better than standard.
                          2003 Pajero 3.2 DiD LWB A/T (with rear diff lock)
                          1999 Patrol 4.5 GRX LWB M/T


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