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More modern cartridge fork options - retaining GS wheels & proper/revised geometry

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    #16
    ......... .
    Last edited by Lorenzo; 01-22-2016, 04:07 AM.
    GS1000G '81

    Comment


      #17
      Alrighty well I've done some more sleuthing... I determined that unfortunately for my situation, the RF/Bandit forks have the brake mount bosses further inboard than the Honda's, so at 195mm triple spacing, the Hayabusa 85mm wide 6 pot Tokico calipers *just* rub the GS wheel's wire spokes mounted in the 93-05 VMX12 triples. Funny that the Honda VTR1000F Superhawk forks at 192mm or 193mm width with 85mm wide OEM-VTR1000 Nissin 4 pot calipers give 44.7mm space between the calipers, where as the 195 spaced VMX12/RF900-Bandit combo with 86mm wide Hayabusa Tokico 6 pots gives only 42.5mm between calipers... So the closer spaced VTR forks give 2.2mm more spoke/wheel clearance between calipers, which would allow use of the GSXR1000 01-02 6 pots with a skimming off the back inboard sides of the calipers set up angled in a milling machine, or even some very careful and precise hand filing for clearance.



      The Superhawk triple has a good stem to run in the GS frame, but modern minimal offset requiring 17" wheel or a very short 18" with much taller GS rear shocks.

      The real reason I bring this up is because of the other excellent 43mm cartridge candidate, the CBR600F4/F4i (F4i=fuel iinjection, different wheels/rotor i.d.). they are a bit shorter than the 775mm VTR1000 Superhawks, but are longer than the very cool 745mm 89-90 GSXR1100 43mm fully adjustable cartridge forks.
      I may make it over to the Rice Paddy to measure a $300 set of theirs, but I think I read 772mm top of stachion to bottom of fork, minus 10mm half of axle diameter minus the material below the axle. (CHUCK - EDIT IN ACTUAL AXLE CENTER TO TOP MEASUREMENT HERE)

      The CBR600F4/F4i forks would work awesome with 93-05 VMAX 1200 triples and 01-02 GSXR 6 pots or the even better maybe are the F4i 4 pots (less maintenance on 4 pistons)
      The VMX12/F4-F4i swap I now consider to be the ultimate RSU conventional cartridge fork option for a GS550/650/750/850/1000/1100/1150 upgrade. AND the F4/F4i forks have the same adjustable compression clicker below the brake mounts as the 89-90 gsxr1100k and the ZRX...

      After doing some more reading, it seems that not only the 94-97 VFR750 non-ABS forks, but also the CBR600F2 & CBR600F3 aparently use sliding 2 piston calipers, as I read discussion on 599 Hornet guys saying go the extra mile to swap to 43mm triples so they can run the F4/F4i forks/brakes so they can get 4 pot calipers... The sliding 2 pistons are still a SUBSTANTIAL upgrade over our 1970's technology calipers, and probably even an upgrade over the very popular salty_monk twinpot mod that I and hundreds of others on this forum love.

      Also I have a smokin' $20 deal ebay 41mm Honda PC800 triple clamp set coming in the mail, and I think this stem will work on the GS, has 204mm width, approximately 53-55mm of offset which will get a GS a really good trail number with a tall front tire (110/80-18 on 86 GSXR front wheel or 2.50 aftermarket rim, or stock 19" wheels). This with the VTR1000 Superhawk forks will likely make an AWESOME cartridge fork conversion without altering the geometry much at all from stock. I'd still go 3/4"-1" longer on the rear shocks over stock to get down to as low as 3.75" trail but after careful calculations, but would settle for 3.85"-3.95" trail for a long hauler bike. That's where the ebay Ohlins ride height adjusters or the YSS Shocks' +10mm ride height adjuster (that they ship with every set of shocks) comes in handy. Order shocks a good length to get 3.85"-3.95" trail, when you want a spirited ride in the twisties, add the extra length or crank up the Ohlins adjusters, and get the trail down for that extra quick steering response for the tight twisty backroads!

      I still need to revisit the 84 VF1000F Interceptor triples, and the late model 90's/00's CB750 retro model triples, as both are 41mm and 193-194mm width, so they would work awesome in a GS frame with VTR1000F/CBR600F2-F3/VFR750-94-97-non-abs forks IF the welded in steering stem were adaptable.

      As with the 93-05 VMX12 (VMAX 1200) triples, these are slightly too tall on the steerer for the GS, but a very thick and lightweight aluminum Hayabusa or late 90's/2000's GSXR steering stem pressed out of their triples (the ones that are 7.125" bearing surface total height, aluminum, tapered down in the middle, and run the same 30mm i.d. bearing top and bottom) can very easily be turned down in a lathe to swap into the VMX12 triples with converting to a top 15mm fine thread bolt thread vs the original VMAX top nut, shave the top of the stem off and tap the inside for threads, machine down o.d. of bottom press fit and match the o.d. and profile of the VMX12 triple on the top), or swap this modifiable GSX1300R/GSXR aluminum stem into any other aluminum lower triple candidate for that matter.
      I determined that with running taller 775mm or so Bandit 1200 / F4i forks on the VMX12 triples, one could easily get one or two of the thick shims that AllBalls gives with some bearing conversions, and shim the lower bearing up to be maybe 6mm higher (still plenty of machined bearing surface above), and machine or even just hand file the upper bearing's lower bearing surface boundary area a few millimeters lower, and then successfully run the VMX12 triples in a GS frame with no stem swap at all.
      The only down side here is that these 2nd gen VMAX 1200 triples are not as common on ebay. Salvage yards can probably scour their parts locator network and find some. They are a fine looking piece, aluminum uppers and lowers.
      '77 GS750 920cc heavily modded
      '97 Kawasaki KDX220R rugged terrain ripper!
      '99 Kawasaki KDX220R​ rebuild in progress
      '79 GS425stock
      PROJECTS:
      '77 Suzuki PE250 woods racer
      '77 GS550 740cc major mods
      '77 GS400 489cc racer build
      '76 Rickman CR1000 GS1000/1100
      '78 GS1000C/1100

      Comment


        #18
        So if you don't make it through that ranting and rambling, here's conventional RSU cartridge fork breakdown:

        Ultimate swap for slightly lower front, best dampening, fully adjustable rebound&compression, opposed piston 4/6 pots:
        *CBR600F4/F4i 43mm forks 755mm height and modded VMX12 93-05 50mm offset or custom billet triples


        Excellent dampening and stock ride height, 310mm brakes and 4/6 pots, 775mm length:
        *Bandit 1200 43mm forks (no external dampening adjust, need longer shocks and slight drop in front height to get respectable stable trail with 34mm offset GSXR 89-90 triples or other similar triples as discussed by other members - Posplayr etc - see their thread for gen 1 vs gen 2 b12 fork details, different triple width I believe)(custom billet triples will make this a GREAT geometry upgrade/converson)(Suzuki models seem to run the calipers inwards more, need triples spaced 2.5+mm wider than Honda options if brake/spoke clearance issues)


        41mm cartridge fork with external rebound and preload adjustment, near stock ride height, 4/6 pot brakes:
        *Honda VTR1000F SuperHawk (Firestorm non-USA) 775mm tall forks, PERFECT with the scarce GS1100GK triples, may be able to adapt the stem on VTR-width late model 90's/00's CB750 Nighthawk triples, but likely need to lightly clearance (angle mill)calipers inboard side for extra assurance), same possibility on 1984 Honda VF1000F Interceptor triples but they are 190 spacing, must adapt to CBR600F2/F3/VFR750 non-abs calipers - great swap if you go to that length) (dampening could use some mods on these or Racetech gold valve upgrade, same as most of the other forks here really to get dampening perfection) $325-$700 slightly wider custom billet triples will solve all research/modding hassles.
        Honda PC800 triples arrived in the mail, these are very similar to the GS1100GK triples, 55mm offset 204mm width and offset down so you can mill off bar risers & run clipons on top of the triples withour compromising ride height ground clearance in corners. Great trail number with a tall 110/90-18 & minimal rear ride height increase with these 55mm offset pc800's, could be the biggest winner for geometry & cheap availability running the VTR1000F Superhawk forks & 599 Hornet spec rotors (or non-USA CB400SF Super Four, all have greater 23mm offset in 296mm diameter).


        41mm cartridge forks near stock ride height, much easier brake to wheel clearance with sliding 2 piston calipers:
        *CBR600F2 41mm forks
        *CBR600F3 41mm forks
        *VFR750 41mm forks non-ABS '94-'97
        same triple options as the VTR1000F Superhawk although the 1984 VF1000F Interceptor triple, IF the stem can be adapted, would be a great candidate, as well as the newer retro CB750 Nighthawk triples IF stem height can be adapted. $325-$700 custom billet triples will solve all research/modding hassles


        43mm cartridge forks external rebound/preload, A++ factory dampening, shorter than stock @727mm for GS550/650/400-425-450-500/GR650:
        *94-97 RF900R 43mm forks in custom triples, 727mm tall - shortest you can run on a GS without offset triples.


        43mm cartridge forks, fully adjustable rebound/compression/preload, shorter than stock longer than RF's @ 745mm:
        *89-90 GSXR1100K forks and triples, 1"+ taller rear shocks as typical to help reduce rake and trail to an appropriate improved geometry
        (These are a substantial upgrade to any GS, but Racetech says that the dampening is rather crude for a cartridge fork, but they can custom modify their parts to vastly improve the dampening for a reasonable labor charge)



        So far that covers most of the models that I am aware of, with emphasis on RSU (conventional appearance) forks closer to 775mm height as to retain ground clearance.


        I have also read multiple mentions that the Bandit 1200 and RF900 forks, as well as the CBR600F4/F4i forks are really just about the ultimate RSU fork swap because their stock factory dampening is superior to most counterparts & has a very high level of tunability, and they have 4 pot/6 pot caliper compatibility with mounting configurations used on many highly regarded models for lots of caliper swap options. The Suzuki and Honda run similar calipers in Nissin and Tokico, but the Honda's (vtr1000, f4, etc) run a closer 62mm mount spacing with the lower mount sticking much further out behind the fork legs, Bandit GSF1100 & RF900R run 100mm caliper mounting with both mounts same distance right off the fork lower.
        The RF900R / GSF1200 forks run the calipers more inboard on the forks, where the Honda F4/VTR1000F run the calipers more outboard with the rotors nearly touching the forks. So on the same width triples, the RF900R/GSF1200 forks will put the calipers several millimeters closer to the wheel spokes, where the Honda brake mounts put the calipers further away from the wheel spokes.

        In the RF900R /GSF1200 Bandit fork brake options, the aftermarket $$$ Shindy Nissin 6 pot calipers give 3mm additional brake clearance @ 80mm width vs 86mm on the Tokico OEM Hayabusa 6 pots (& the VTR1000F/CBR600F4/F4i brakes & the 6 pot GSXR1000K2 01-02) calipers.







        I have also read multiple mentions that the Bandit 1200 and RF900 forks, as well as the CBR600F4/F4i forks are really just about the ultimate RSU fork swap because their stock factory dampening is superior to most counterparts, and they have 4 pot/6 pot caliper compatibility with mounting configurations used on many highly regarded models for lots of caliper swap options. The Suzuki and Honda run similar calipers in Nissin and Tokico, but the Honda's run a closer mounting spacing with the lower mount sticking much further out behind the fork leg.

        I was also checking out some ZRX1100 & ZRX1100 RSU forks which were a great height (765mm? Have to look up my notes), have adjustable preload, rebound,&compression, & run the same 6 pot Tokico's as the first 10 years or so of Hayabusa, & for 310mm rotors (98-99 CBR900RR rotors are a shoe-in for bolting to GS hubs!!!). These were VERY NICE RSU fork swap candidates!
        Yamaha R6 RSU forks were the lightest I've had my hands on, 4lbs lighter than the cbr600f4i w/vmax 1200 43mm triples w/steel stem, 6 lbs lighter than the zrx1100 forks with a very long steel stem. R6 had alloy stem like the gsxr/Busa stem I'm using. I've also seen a crashed R6 fork split in two almost it creased so hard, the upper fork tubes are MUCH thinner than my GS750's... The R6 runs an excessive 320mm rotor, no easy bolt ons for a GS 6 bolt 78mm pcd hub. 296mm is plenty, 310mm duals is ALOTTA BRAKE, 320mm probably needs ABS to not tuck the front!
        Last edited by Chuck78; 02-05-2016, 03:28 AM.
        '77 GS750 920cc heavily modded
        '97 Kawasaki KDX220R rugged terrain ripper!
        '99 Kawasaki KDX220R​ rebuild in progress
        '79 GS425stock
        PROJECTS:
        '77 Suzuki PE250 woods racer
        '77 GS550 740cc major mods
        '77 GS400 489cc racer build
        '76 Rickman CR1000 GS1000/1100
        '78 GS1000C/1100

        Comment


          #19
          Originally posted by Lorenzo View Post
          To accomodate for different racing/riding conditions, wider triples holes, could be milled and eccentric bushes slotted in, in order to have two selection of offset/ trail;
          I suppose rake could also be catered for.
          #limeex2
          Same driving averages and road condition over here.
          A few companies make billet triples with adjustable offset through interchangeable stem insert pieces. I have been roughly designing custom triples with a slight step down on top to fit clipons better without the forks dropped too much. When it came to rake and trail, I strapped the CR900 frame from the rafters and adjusted it for tire size choices specifically hand picked (from the 3 brands of very grippy tires I prefer) for fitment on rim & diameters to fit with my elevated rake. Then raised the rear to achieve near the maximum swingarm angle recommended. Measured rake of frame in this 380 mm shock/minimum fork height/ BT45V 110/80-18&140/80-18 simulated ride height. Came up with 25.6 degrees rake and only 4 degrees forward down slope on the seat rails, not bad! Then figured 49mm offset triples for 3.78"/96mm of rake. 95mm is a great quick steering but stable enough figure for racers. 96mm-100mm comes on most modern sport bikes. I figured with the shocks in their full +10mm extended length mode and the shocks mounted on the forward swingarm shock mounts for +8mm ride height, I was pretty good to go. Designed with rear ride height maxed out and the least trail I thought was acceptably stable but quick steering, then I have the ability to increase rake and trail for longer hauls just by moving the shocks to the rear mounts. Brilliant, Rickman 2 position lower shock mounts and YSS Suspension +10mm ride height adjusters on all their nice alloy body models.
          Last edited by Chuck78; 01-25-2016, 09:16 PM.
          '77 GS750 920cc heavily modded
          '97 Kawasaki KDX220R rugged terrain ripper!
          '99 Kawasaki KDX220R​ rebuild in progress
          '79 GS425stock
          PROJECTS:
          '77 Suzuki PE250 woods racer
          '77 GS550 740cc major mods
          '77 GS400 489cc racer build
          '76 Rickman CR1000 GS1000/1100
          '78 GS1000C/1100

          Comment


            #20
            The PC800 triples & axle are a total winner for the VTR1000F Superhawk forks on a GS750/850/1000/1100!!!!

            ^^^
            A mere 1/16" shorter total bearing height top to bottom versus a gr650 tempter stem that I believe is identical to my GS stem heights... no prob at all, looks like a great fit with only steering stop alterations needed.

            Both triples are offset inward toward each other, which means you could really raise them up even higher to get the 800 mm length of some of the GS katanas that have been compared in other forks swap threads. or you could mill off the handlebar riser mounts and have more than enough room for the tallest of clip ons on top of the triples, then just add rear shocks in 10 mm or 20 mm over stock to decrease your rake and trail.


            this will of course take a 17 inch wheel RF900R/etc speedometer drive, and custom front wheel spacers, or just a collection of super hawk and pc800 spacers cut down to the width needed.
            no other leads yet on 18 inch wheel Cruiser speedometer drives that will work for better accuracy on an 18 or 19 inch gs wheel - custom corrected speedo face vinyl graphics or electric speedometer are options, especially for 19" wheels. 110/80-18 won't be incredibly off like a 19 will. Or look into gutting the speedo drive and swapping parts from a GS? Or just adapt an early 18" wheel GSXR speedo drive to it, or a late model mechanical speedo 20mm axle Suzuki v twin cruiser drive

            PC800 stem uses same lower bearing size @30mm, and 26 mm upper vs 25 mm on the gs and gr stems. No problem getting bearings to fit.

            204mm or so width gives a whopping 57mm clearance between the massively huge and powerful opposed 4-piston and 6 piston calipers. Plenty enough to clear wire spoke wheels and mags alike... more details and geometry estimations later.
            Last edited by Chuck78; 01-28-2016, 11:59 AM.
            '77 GS750 920cc heavily modded
            '97 Kawasaki KDX220R rugged terrain ripper!
            '99 Kawasaki KDX220R​ rebuild in progress
            '79 GS425stock
            PROJECTS:
            '77 Suzuki PE250 woods racer
            '77 GS550 740cc major mods
            '77 GS400 489cc racer build
            '76 Rickman CR1000 GS1000/1100
            '78 GS1000C/1100

            Comment


              #21
              Originally posted by Chuck78 View Post
              So if you don't make it through that ranting and rambling, here's conventional RSU cartridge fork breakdown:

              Ultimate swap for slightly lower front, best dampening, fully adjustable rebound&compression, opposed piston 4/6 pots:
              *CBR600F4/F4i 43mm forks 755mm height and modded VMX12 93-05 50mm offset or custom billet triples


              Excellent dampening and stock ride height, 310mm brakes and 4/6 pots, 775mm length:
              *Bandit 1200 43mm forks (no external dampening adjust, need longer shocks and slight drop in front height to get respectable stable trail with 34mm offset GSXR 89-90 triples or other similar triples as discussed by other members - Posplayr etc - see their thread for gen 1 vs gen 2 b12 fork details, different triple width I believe)(custom billet triples will make this a GREAT geometry upgrade/converson)(Suzuki models seem to run the calipers inwards more, need triples spaced 2.5+mm wider than Honda options if brake/spoke clearance issues)


              41mm cartridge fork with external rebound and preload adjustment, near stock ride height, 4/6 pot brakes:
              *Honda VTR1000F SuperHawk (Firestorm non-USA) 775mm tall forks, PERFECT with the scarce GS1100GK triples, may be able to adapt the stem on VTR-width late model 90's/00's CB750 Nighthawk triples, slightly clearance calipers inboard side for extra assurance), same possibility on 1984 Honda VF1000F Interceptor triples but they are 190 spacing, must adapt to CBR600F2/F3/VFR750 non-abs calipers - great swap if you go to that length) (dampening could use some mods on these or Racetech gold valve upgrade, same as most of the other forks here really to get dampening perfection) $325-$700 custom billet triples will solve all research/modding hassles.
              Honda PC800 triples are in the mail, I think these will be very similar to the GS1100GK triples, 55mm offset 204mm width was my Photoshop guesstimation. Great trail number with a tall 110/90-18 & minimal rear ride height increase, could be the biggest winner for geometry & cheap availability running the VTR1000F Superhawk forks & 599 Hornet spec rotors (or non-USA CB400SF Super Four, all have greater 23mm offset in 296mm diameter).


              41mm cartridge forks near stock ride height, much easier brake to wheel clearance with sliding 2 piston calipers:
              *CBR600F2 41mm forks
              *CBR600F3 41mm forks
              *VFR750 41mm forks non-ABS '94-'97
              same triple options as the VTR1000F Superhawk although the 1984 VF1000F Interceptor triple, IF the stem can be adapted, would be a great candidate, as well as the newer retro CB750 Nighthawk triples IF stem height can be adapted. $325-$700 custom billet triples will solve all research/modding hassles


              43mm cartridge forks external rebound/preload, A++ factory dampening, shorter than stock @727mm for GS550/650/400-425-450-500/GR650:
              *94-97 RF900R 43mm forks in custom triples, 727mm tall - shortest you can run on a GS without offset triples.


              43mm cartridge forks, fully adjustable rebound/compression/preload, shorter than stock longer than RF's @ 745mm:
              *89-90 GSXR1100K forks and triples, 1"+ taller rear shocks as typical to help reduce rake and trail to an appropriate improved geometry
              (These are a substantial upgrade to any GS, but Racetech says that the dampening is rather crude for a cartridge fork, but they can custom modify their parts to vastly improve the dampening for a reasonable labor charge)



              So far that covers most of the models that I am aware of, with emphasis on RSU (conventional appearance) forks closer to 775mm height as to retain ground clearance.


              I have also read multiple mentions that the Bandit 1200 and RF900 forks, as well as the CBR600F4/F4i forks are really just about the ultimate RSU fork swap because their stock factory dampening is superior to most counterparts & has a very high level of tunability, and they have 4 pot/6 pot caliper compatibility with mounting configurations used on many highly regarded models for lots of caliper swap options. The Suzuki and Honda run similar calipers in Nissin and Tokico, but the Honda's (vtr1000, f4, etc) run a closer 62mm mount spacing with the lower mount sticking much further out behind the fork legs, Bandit GSF1100 & RF900R run 100mm caliper mounting with both mounts same distance right off the fork lower.
              The RF900R / GSF1200 forks run the calipers more inboard on the forks, where the Honda F4/VTR1000F run the calipers more outboard with the rotors nearly touching the forks. So on the same width triples, the RF900R/GSF1200 forks will put the calipers several millimeters closer to the wheel spokes, where the Honda brake mounts put the calipers further away from the wheel spokes.

              In the RF900R /GSF1200 Bandit fork brake options, the aftermarket $$$ Shindy Nissin 6 pot calipers give 3mm additional brake clearance @ 80mm width vs 86mm on the Tokico OEM Hayabusa 6 pots (& the VTR1000F/CBR600F4/F4i brakes & the 6 pot GSXR1000K2 01-02) calipers.







              I have also read multiple mentions that the Bandit 1200 and RF900 forks, as well as the CBR600F4/F4i forks are really just about the ultimate RSU fork swap because their stock factory dampening is superior to most counterparts, and they have 4 pot/6 pot caliper compatibility with mounting configurations used on many highly regarded models for lots of caliper swap options. The Suzuki and Honda run similar calipers in Nissin and Tokico, but the Honda's run a closer mounting spacing with the lower mount sticking much further out behind the fork leg.

              I was also checking out some ZRX1100 & ZRX1100 RSU forks which were a great height (765mm? Have to look up my notes), have adjustable preload, rebound,&compression, & run the same 6 pot Tokico's as the first 10 years or so of Hayabusa, & for 310mm rotors (98-99 CBR900RR rotors are a shoe-in for bolting to GS hubs!!!). These were VERY NICE RSU fork swap candidates!
              Yamaha R6 RSU forks were the lightest I've had my hands on, 4lbs lighter than the cbr600f4i w/vmax 1200 43mm triples w/steel stem, 6 lbs lighter than the zrx1100 forks with a very long steel stem. R6 had alloy stem like the gsxr/Busa stem I'm using. I've also seen a crashed R6 fork split in two almost it creased so hard, the upper fork tubes are MUCH thinner than my GS750's... The R6 runs an excessive 320mm rotor, no easy bolt ons for a GS 6 bolt 78mm pcd hub. 296mm is plenty, 310mm duals is ALOTTA BRAKE, 320mm probably needs ABS to not tuck the front!
              I confirm that the Bandit 1200 phase 1 forks offer a far better damping than the fully adjustable GSXR 1100 K ( 1989) forks.
              Beware that the disk spacing is slightly different between the GSXR 1100 K and the Bandit 1200!
              On top as the Bandit forks are much longer they will fit on the 1100 Kat's.
              Here with GSXR 1100 triples and clip-ons:

              Last edited by John Kat; 01-28-2016, 04:11 AM.
              sigpicJohn Kat
              My bikes: CB 77, GS 1000 ST Cafe Racer with GSXR 1052 engine, GS 1000 ST, XR 41 Replica with GS 1085 engine,
              GS 1100 SZ Katana with GS 1135 EFF engine, KTM Superduke 1290 R 2020

              Comment


                #22
                Originally posted by John Kat View Post
                I confirm that the Bandit 1200 phase 1 forks offer a far better damping...Bandit forks are much longer they will fit on the 1100 Kat's. Here with GSXR 1100 triples and clip-ons:


                FYI, my good buddies here in Columbus at http://www.RicePaddy.com are blowing the dust and mothballs off of ^^this same model GS1100 Katana (same color even)^^ you have here that has been stored for ages. 500 original miles, owner bought it only to race, 1 owner. Has a Falicon crank supposedly, and other racing goodies - including a silver painted disc over top of the front wheel spokes with racing logos and lettering painted on it. Carbs and brakes in pieces in a box, but they are likely going to resurrect it from it's slumber and get it in in ridable shape and ready to turn over to a new owner as a running project bike, if anyone is looking for one, call them on the phone (closed Wed&Sat) and ask for Grant.
                '77 GS750 920cc heavily modded
                '97 Kawasaki KDX220R rugged terrain ripper!
                '99 Kawasaki KDX220R​ rebuild in progress
                '79 GS425stock
                PROJECTS:
                '77 Suzuki PE250 woods racer
                '77 GS550 740cc major mods
                '77 GS400 489cc racer build
                '76 Rickman CR1000 GS1000/1100
                '78 GS1000C/1100

                Comment


                  #23
                  GS750+ w/VTR1000F forks in PC800 triples - revised geometry

                  Alrighty well I did some rough approximations of geometries based on crude manipulation of the RB Racing online rake and trail calculator (it doesn't allow any input of rear ride height changes and resulting rake and trail changes, only fork length and front tire size changes - I am assuming raising the rear or dropping the front equal amounts will give you the same rake and trail changes, which may not be true from what I've read).

                  So far in my rough estimations, using this as the baseline:
                  *Stock 77-79 GS750 - 58.7" wheelbase 27 degree rake 4.21" trail 4.00H18 26.4" diameter rear tire 3.25H19 26.1" diameter front tire

                  *swapping to modern tire sizes of 110/90-18 (26.1" diam per Avon spec) and 90/90-19 (25.5" diam per Avon spec) on stock 2.15/1.85 rims gets you 26.87 degrees rake and 4.03" trail using the same ride height front end and the almost exact same offset in the 55mm offset PC800 triples and Superhawk VTR1000F forks (a good increase in steering response already! But at 4.03" trail or whatever that gets you, the steering is still a tad bit slow but very stable as we have witnessed in real world GS road testing).

                  *take the above modern tire size swap, 41mm VTR1000F cartridge forks in 55mm offset Honda PC800 triples, and add 20mm to your rear shock length in a nicely sprung/dampened shock upgrade = approximately 26.2 degrees rake and 3.87" trail (A NICE GEOMETRY UPGRADE!)

                  *take the above and make that about 25mm longer than stock rear shocks and 4mm drop in your fork ride height on the triples = approximately 26 degrees rake and 3.81" trail (A VERY NICE SPORT GEOMETRY UPGRADE!)

                  *take the above and make that about 30mm longer than stock rear shocks and 4mm drop in your fork ride height on the triples = approximately 25.75 degrees rake and 3.76" trail (A VERY EXCELLENT SPORT/RACE GEOMETRY UPGRADE!)
                  '77 GS750 920cc heavily modded
                  '97 Kawasaki KDX220R rugged terrain ripper!
                  '99 Kawasaki KDX220R​ rebuild in progress
                  '79 GS425stock
                  PROJECTS:
                  '77 Suzuki PE250 woods racer
                  '77 GS550 740cc major mods
                  '77 GS400 489cc racer build
                  '76 Rickman CR1000 GS1000/1100
                  '78 GS1000C/1100

                  Comment


                    #24
                    Yamaha R6 forks + EBC MD729LD/RD CBR600/900 oversized race rotors 320mm

                    well... now after spotting and looking up the specs of Ducati 748R/998R 6 bolt rotors that I spotted (320mm 15mm offset 6 bolt 80mm pcd, 2mm larger diameter than what we need, could redrill new pattern in between for GS hubs).... I noticed a 78mm PCD 320mm rotor, turns out EBC makes oversized rotors for CBR's at 320mm with 17.5mm offset! They are quite spendy, but this makes the Yamaha RS RSU fork - fully adjustable compression/rebound, lightest fork I have had in my hands at 3.5lbs less than the CBR600F4i, a good possibility for those looking to get the lightest and most ultimate setup out of their bike upgrade... the set I had in hand looked to be 43mm. I did not measure the width of the triples or the width between the brake mounts to see how they'd work in VMAX 1200 triples, but they were somewhere in the 755mm length vicinity, close to the CBR600F4 from memory.



                    03-04 Yamaha R6, 06-07 R6S Forks is what the pair in this ad fits, $600 fully serviced with Ohlins cartridges added:


                    EBC Race Rotors (May need to have them make you a set with steel floating rivets instead of aluminum if using on the street)
                    MD729LD left MD729RD right 21.1mm offset 78mm pcd 6 bolt:
                    Last edited by Chuck78; 02-05-2016, 03:33 AM.
                    '77 GS750 920cc heavily modded
                    '97 Kawasaki KDX220R rugged terrain ripper!
                    '99 Kawasaki KDX220R​ rebuild in progress
                    '79 GS425stock
                    PROJECTS:
                    '77 Suzuki PE250 woods racer
                    '77 GS550 740cc major mods
                    '77 GS400 489cc racer build
                    '76 Rickman CR1000 GS1000/1100
                    '78 GS1000C/1100

                    Comment


                      #25
                      Originally posted by Chuck78 View Post
                      well... now after spotting nad looking up the specs of Ducati 748R/998R 6 bolt rotors that I spotted (320mm 15mm offset 6 bolt 80mm pcd, 2mm larger diameter than what we need, could redrill new pattern in between for GS hubs).... I noticed a 78mm PCD 320mm rotor, turns out EBC makes oversized rotors for CBR's at 320mm with 17.5mm offset! They are quite spendy, but this makes the Yamaha RS RSU fork - fully adjustable compression/rebound, lightest fork I have had in my hands at 3.5lbs less than the CBR600F4i, a good possibility for those looking to get the lightest and most ultimate setup out of their bike upgrade... the set I had in hand looked to be 43mm. I did not measure the width of the triples or the width between the brake mounts to see how they'd work in VMAX 1200 triples, but they were somewhere in the 755mm length vicinity, close to the CBR600F4 from memory.



                      03-04 Yamaha R6, 06-07 R6S Forks is what the pair in this ad fits, $600 fully serviced with Ohlins cartridges added:


                      EBC Race Rotors (May need to have them make you a set with steel floating rivets instead of aluminum if using on the street)
                      MD729LD left MD729RD right 21.1mm offset 78mm pcd 6 bolt:
                      A quick comparaison of fork lengths can de done by looking at the dimensions of the bare fork tubes.
                      The Tarozzi site provides this kind of information:

                      Among the fork tubes you have mentionned with a 43 mm outside diameter the lengths are:
                      R6 ( 01 to 04) 585 mm
                      GSXR 1100 K ( 1989) 588 mm
                      Bandit 1200 ( up to 2002) 614 mm
                      CBR 600 F1 to F4 587 mm
                      While the GS 1000 in 37 mm OD are 595 mm
                      I'm personally keen to try eitheir the CBR or R6 fork tubes in place of my current GSXR fitting but I wonder if I will be able to adapt them to my GSXR 1100 first or 2nd gen wheels?
                      See page 3: http://www.thegsresources.com/_forum...t-wheels/page3
                      In any case we will have to buy stronger springs to cater for the extra weight of a GS 1000/1100.
                      As a side point I don't understand why you recommend Vmax triples as they won't take 43 tubes?
                      sigpicJohn Kat
                      My bikes: CB 77, GS 1000 ST Cafe Racer with GSXR 1052 engine, GS 1000 ST, XR 41 Replica with GS 1085 engine,
                      GS 1100 SZ Katana with GS 1135 EFF engine, KTM Superduke 1290 R 2020

                      Comment


                        #26
                        Originally posted by John Kat View Post
                        As a side point I don't understand why you recommend Vmax triples as they won't take 43 tubes?
                        93-05 vmax 1200 are 43mm fork tubes, up to 92 are 40mm I believe. I have a set of 93-05 vmx12 triples with rf900r forks mounted in them.

                        Cbr600f2-F3 are 41mm, you quoted tarozzi saying they are 43mm. The last year of the F2 are cartridge forks, all f3+ are cartridge. Early F2 & all F1 are damper rod.
                        Last edited by Chuck78; 02-03-2016, 07:00 PM.
                        '77 GS750 920cc heavily modded
                        '97 Kawasaki KDX220R rugged terrain ripper!
                        '99 Kawasaki KDX220R​ rebuild in progress
                        '79 GS425stock
                        PROJECTS:
                        '77 Suzuki PE250 woods racer
                        '77 GS550 740cc major mods
                        '77 GS400 489cc racer build
                        '76 Rickman CR1000 GS1000/1100
                        '78 GS1000C/1100

                        Comment


                          #27
                          Originally posted by Chuck78 View Post
                          93-05 vmax 1200 are 43mm fork tubes, up to 92 are 40mm I believe. I have a set of 93-05 vmx12 triples with rf900r forks mounted in them.

                          Cbr600f2-F3 are 41mm, you quoted tarozzi saying they are 43mm. The last year of the F2 are cartridge forks, all f3+ are cartridge. Early F2 & all F1 are damper rod.
                          Good to know!
                          Tomorrow I'm going to look at an R6 fork that's for sale...
                          sigpicJohn Kat
                          My bikes: CB 77, GS 1000 ST Cafe Racer with GSXR 1052 engine, GS 1000 ST, XR 41 Replica with GS 1085 engine,
                          GS 1100 SZ Katana with GS 1135 EFF engine, KTM Superduke 1290 R 2020

                          Comment


                            #28
                            I believe the R6 conventional right side up fork was 43mm but I didn't put my calipers on it. Very nice fork indeed, but 320mm rotors makes GS wheels require greater lengths to mount. Adapters on the 15mm offset Ducati rotors could be made and could even just re-drill the bolt pattern possibly, it's 80mm circle, shift it between the holes and drill ours 78mm circle. Adapter would just be a top hat spacer to locate it better on the bore than bolt-centric, & spaced out approximately 16.25 mm off hub approximately.

                            I did not measure the distance between the R6 caliper mounts, so I am not sure the clearance to wire spokes. With mag wheels I think you'd be good in vmx12 triples. Youll need to slightly mod steering stem to drop upper bearing surface several millimeters, or machine a gsxr/Busa aluminum stem to dimensions of vmx12 triple, use m14x1.0 top bolt instead of busa/gixxer alloy nut, remove retaining roll pin & press out vmx12 stem press in shorter aluminum busa/gixxer stem turned in lathe to dimensions of vmx12 stem diameters.

                            Of course, if you go your typical route, maybe you'd just get a fancy adapter made to run stock GS calipers? Going to these lengths, I'd definitely look into swapping to the twinpot calipers or just using the R6 and the Ducati rotors or custom ordering those EBC Racelite rotors but with steel floating rivet buttons not aluminum as they come. Don't get too spongy on master cylinder (bore to piston ratios) as you'll end up with immensely powerful brakes that you could lock up too easily in a panic scenario @ 320mm !
                            '77 GS750 920cc heavily modded
                            '97 Kawasaki KDX220R rugged terrain ripper!
                            '99 Kawasaki KDX220R​ rebuild in progress
                            '79 GS425stock
                            PROJECTS:
                            '77 Suzuki PE250 woods racer
                            '77 GS550 740cc major mods
                            '77 GS400 489cc racer build
                            '76 Rickman CR1000 GS1000/1100
                            '78 GS1000C/1100

                            Comment


                              #29
                              By the way the vmx12 stem is slightly too long but can be even hand filed down to allow the bearing to run slightly lower. Swapping the Busa/gixxer aluminum stem will allow you greater ride height as you will now be able to run the upper triple lower, & correspondingly the forks can slide down lower for closer to stock ride height.

                              Matt slikwilli420 on DoTheTon.com is making me custom upper & lower offset triples for my Franken-Rickman/GS project, he could mill a new VMX12 spec upper triple from 2" billet with a 20mm-25mm downward offset on the fork tubes so that you could run the fork tubes even lower up front for near stock ride height. 1" billet is $175/ea, 2" billet would probably drive cost upwards of $225 per triple but allows use of those really nice and light fully adjustable forks with a near stock ride height.

                              Weiss Racing also makes semi-custom billet triples and billet stems for $325, up to 43mm.
                              '77 GS750 920cc heavily modded
                              '97 Kawasaki KDX220R rugged terrain ripper!
                              '99 Kawasaki KDX220R​ rebuild in progress
                              '79 GS425stock
                              PROJECTS:
                              '77 Suzuki PE250 woods racer
                              '77 GS550 740cc major mods
                              '77 GS400 489cc racer build
                              '76 Rickman CR1000 GS1000/1100
                              '78 GS1000C/1100

                              Comment


                                #30
                                *running the 15mm offset Ducati rotors may cause issues with speedo drive, may need to machine an adapter to space it out further if cable connection interferes with rotor/rotor bolts being too close
                                '77 GS750 920cc heavily modded
                                '97 Kawasaki KDX220R rugged terrain ripper!
                                '99 Kawasaki KDX220R​ rebuild in progress
                                '79 GS425stock
                                PROJECTS:
                                '77 Suzuki PE250 woods racer
                                '77 GS550 740cc major mods
                                '77 GS400 489cc racer build
                                '76 Rickman CR1000 GS1000/1100
                                '78 GS1000C/1100

                                Comment

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