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Author Topic: Modern RSU fork with classic appearance  (Read 469 times)

Offline Henkies

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Modern RSU fork with classic appearance
« on: Jan 09, 2018, 18:10:34 »
Hi,

I'm looking after a modern conventional fork swap that retains the classic look a bit. My 77 CB750k7 has 50mm  offset.

Is there a touring bike that comes close? I found out the 1998-2001 VFR800 has 44mm ofset.

Another plus would be narrow brake calipers and fork tube distance. I know even with a 99 R6 fork it's hard to clear the caliper from the spokes. So the narrow look might be wishfull thinking. But I'd not neccesarily need 43mm tubes. 

Can anyone recommend?

Thanks!

Offline J-Rod10

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Re: Modern RSU fork with classic appearance
« Reply #1 on: Jan 09, 2018, 21:03:19 »
Popular swap on the 750's is the CBR600F2.

Offline Chuck78

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Re: Modern RSU fork with classic appearance
« Reply #2 on: Feb 28, 2018, 21:43:45 »
The last year of the CBR600 F2 is the same as all of the F3 forks iirc, the rest of the F2 forks are not cartridge if I recall. But the last year is definitely the better fork. These are 41mm, and they are several 41mm triples that I have researched over the years that have substantial offset. I don't like the Honda cartridge forks so much aesthetically though because the lower brake caliper mount sticks out much further back off of the fork leg, and my vintage GS forks generally didn't look quite like that.

I do have a real nice set of VTR1000F Super hawk 41mm cartridge forks in Honda PC800 triples here that I wouldn't mind selling, and I have some upgraded calipers for them also, comes with 4 piston and 6 piston calipers to choose from. I was going to angle mill the backs of the calipers for more clearance to the wheel spokes

The Yamaha R6 forks were the lightest modern conventional oriented cartridge forks I've ever felt, but I saw a crashed set, and the tubes are quite thin... also they use a 320mm rotor, I prefer to stick with 310mm as a few Honda floating rotors are that size and have the same bolt pattern as a Suzuki GS hub, and I think that is the same as a lot of the older Honda 6 bolt rotors.

The CBR 600 F4 Fork is 43 mm diameter and fully adjustable compression and rebound, this is a very nice deal here, but has the same type of brake caliper mount.

The 43mm Suzuki Bandit 1200 Forks are quite possibly the best thing out there, as they are as tall as a GS1000 Fork or other similar Japanese Superbikes, and a look completely vintage almost exactly like a 1982 or 1983 GS 1100 GK Fork...
They don't have caliper mounts like a Honda Forks, they have caliper mounts like a vintage Suzuki GS. They also have really great damping stock.

As for triples, Yamaha VMAX 1200 from 1993 and newer takes 43mm Forks, and has 55 mm offset. They use a slightly taller a stem than a Suzuki GS. This may work perfect for the Honda CB750. If you have a CB stem to measure, I have a couple of these triples here.

For a shorter stem like what a Suzuki GS takes, they use the same aluminum Hayabusa and GSXR stem in the V-Strom 1000 triples, which take 43mm forks and have around 44 mm offset. These are modern Adventure bikes with 19 inch front wheels. They have a good bit steeper rake, however. This triple  would work pretty well if it would fit in the CB, with taller rear shocks and an 18 inch front wheel.



I did a huge write up on this on the GS forums. I spent a ton of time one winter scaling pictures of all sorts of different triples for 41 mm and 43 mm forks.

The conclusion that I basically came to is that there are hardly any fork and triple packages which will give you the right offset and a very good performance fork in the proper length; you have to mix and match sport bike forks with adventure bike, cruiser, Etc triples.


If you find the right triple that works for your geometry, but it is around 190 or 195mm width center to center, most modern opposed piston calipersmay give interference with vintage wheel spokes which are wider than modern mags.
Around 204mm (common width) and wider triples the opposed piston modern calipers have a much better chance of fitting, especially with the Honda CBR/VFR forks

Generally I think the best thing to do brake wise would be to abandon the opposed-piston 4-piston (&6 piston) calipers if they will have interference problems with the wider vintage wheel spokes, and then just go with a Suzuki GS500, ninja ex250, ninja 1000, GSX 1100, Concours, Etc 2 piston sliding tokico caliper, as they have a steel mounting bracket which can easily be welded onto with additional metal to make these brakes look as if they were originally intended to go on the forks. These eliminate the inboard clearance problems with wire spokes. I have 8 of these calipers as spares because I like them so much for retrofits.
The F2/F3 calipers are a similar design, one sided 2 piston sliding caliper.
« Last Edit: Mar 01, 2018, 10:36:32 by Chuck78 »

'77 GS750 920cc, 4-1, GS1100E swinger, 18" Sun rims, Fox Factory Shox, twinpot dual disc, CR31, Yosh cams
'74 Rickman VR250MX
'99 Kawasaki KDX220 rugged terrain ripper
PROJECTS:
'77 Suzuki PE250B
"Pure Enduro" trail beast, ported, Wiseco, TüBliss, Fox Factory Shox/RaceTech
'76 Rickman CR GS1000-1120cc roadracer, Yosh cams&4-1, RF900R fork, Works piggybacks
'79 GS425 489cc Formula 500 racer, Tempter cams, GS650 forks, twinpot brakes, DID rims, GS1100E swinger, Fox Factory Shox
'77 GS550's 650-740cc susp&brake mods

Offline Chuck78

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Re: Modern RSU fork with classic appearance
« Reply #3 on: Feb 28, 2018, 22:02:16 »
Here is what I had dug up for Suzuki GS750/1000 swaps when trying to find the best options to retrofit to a vintage bike and adapt the vintage wheels with an 18" rim laced up:

Ultimate swap for slightly lower front, best dampening, fully adjustable, uses opposed piston 4/6 pots:
*CBR600F4/F4i forks and modded VMX12 93-05 or custom billet triples, or V-Strom DL1000 triples


Excellent dampening and close to stock ride height, 310mm brakes, uses  4/6 pot calipers, looks just like 70's forks aside from built in fork brace mounts:
*Bandit 1200 43mm forks (no external dampening adjust)
93+ V Max 1200 triples or V-STROM DL1000

41mm cartridge fork with external rebound and preload adjustment, near stock ride height, uses opposed 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)

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.

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 mx cartridge parts for these 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.

'77 GS750 920cc, 4-1, GS1100E swinger, 18" Sun rims, Fox Factory Shox, twinpot dual disc, CR31, Yosh cams
'74 Rickman VR250MX
'99 Kawasaki KDX220 rugged terrain ripper
PROJECTS:
'77 Suzuki PE250B
"Pure Enduro" trail beast, ported, Wiseco, TüBliss, Fox Factory Shox/RaceTech
'76 Rickman CR GS1000-1120cc roadracer, Yosh cams&4-1, RF900R fork, Works piggybacks
'79 GS425 489cc Formula 500 racer, Tempter cams, GS650 forks, twinpot brakes, DID rims, GS1100E swinger, Fox Factory Shox
'77 GS550's 650-740cc susp&brake mods

Offline Chuck78

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Re: Modern RSU fork with classic appearance
« Reply #4 on: Feb 28, 2018, 22:10:47 »
41mm fork triples info from my GS swap research:



The 1990's (& late 80's/early '00's?) CB750 Nighthawk used the same axle as the VTR1000F, and 41mm forks, and has (from my Photoshop approximations) the exact width of Superhawk triples and around a 45mm offset vs the meager VTR triple (i.e. shallow offset/way too much trail on the VTR's). We may have a winner here! I'm not sure at all on the steering stem height yet, but I'm going to assume it's in the ballparks.

Also the PC800 cruiser/tourer triples run a similar axle in the GS1100GK width that fits Superhawk forks, and has an approximately (i.e. Photoshop scale guesstimation) of 55mm offset, another great candidate, but requiring brakes spaced in further if the steering stem height works out great.

VF750 Magna triples give (??)mm (45? Autocorrect made me lose this figure changing it to 4mm) offset, look really cool (chromed lower, billet looking cast top, some with indicator lamps built in), but are about 215mm width - big rotor spacers needed but zero fuss on these or the pc800 with caliper to wire spoke wheel clearance. Magna axle also looks to be of same Showa style as the VTR axle, and matching width for the Magna triples.
84 vf1000f interceptor triples look to be 190mm (1.5mm less caliper to spoke clearance, may need even the 6 piston gsxr1000 calipers clearanced) but are 41mm tube size  and 48mm or so offset. The nighthawk triples will require 4 piston caliper clearancing (angle milling one edge) or 6 piston gsxr1000 01-02 calipers

'77 GS750 920cc, 4-1, GS1100E swinger, 18" Sun rims, Fox Factory Shox, twinpot dual disc, CR31, Yosh cams
'74 Rickman VR250MX
'99 Kawasaki KDX220 rugged terrain ripper
PROJECTS:
'77 Suzuki PE250B
"Pure Enduro" trail beast, ported, Wiseco, TüBliss, Fox Factory Shox/RaceTech
'76 Rickman CR GS1000-1120cc roadracer, Yosh cams&4-1, RF900R fork, Works piggybacks
'79 GS425 489cc Formula 500 racer, Tempter cams, GS650 forks, twinpot brakes, DID rims, GS1100E swinger, Fox Factory Shox
'77 GS550's 650-740cc susp&brake mods

Offline Chuck78

  • Posts: 291
    • my bike photo album
Re: Modern RSU fork with classic appearance
« Reply #5 on: Feb 28, 2018, 22:20:27 »
DiamondJ's GS1000 with a VTR1000 Superhawk 41mm cartridge fork, CBR600 F2 front wheel, CBR600F3  rear wheel.




The F2 & F3 wheels are basically the only somewhat modern mag wheels which I think I look any bit appropriate on a vintage bike, due to their spoke design. These are probably the only 17 in modern mag wheel I would ever put on a vintage bike. That eliminates the need for substantial offset in the triples, and it eliminates the need for bearing swaps or axle adapters and speedometer Drive swaps or modifications.

The F 2 wheel does not use a floating rotor. The F3 wheel does use the floating rotor with the smaller 6 bolt pattern.


Here is Nate Blackhammer's GS1100E (w/ GS1150 engine!!!! a BEAST!!!!) with the same VTR1000 Superhawk cartridge forks:




If you are interested in a set of these forks, like I said, I have some I'd possibly sell, already mounted in a set of Honda pc800 triples with 55mm offset, and two sets of brake calipers. I'm not sure if I have any plans anymore to use them.

'77 GS750 920cc, 4-1, GS1100E swinger, 18" Sun rims, Fox Factory Shox, twinpot dual disc, CR31, Yosh cams
'74 Rickman VR250MX
'99 Kawasaki KDX220 rugged terrain ripper
PROJECTS:
'77 Suzuki PE250B
"Pure Enduro" trail beast, ported, Wiseco, TüBliss, Fox Factory Shox/RaceTech
'76 Rickman CR GS1000-1120cc roadracer, Yosh cams&4-1, RF900R fork, Works piggybacks
'79 GS425 489cc Formula 500 racer, Tempter cams, GS650 forks, twinpot brakes, DID rims, GS1100E swinger, Fox Factory Shox
'77 GS550's 650-740cc susp&brake mods

Offline teazer

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Re: Modern RSU fork with classic appearance
« Reply #6 on: Mar 01, 2018, 00:30:20 »
If you want a cartridge fork, then you are probably looking at 41mm or 43mm (R6) legs and triples, but what about say 37mm legs which could be bored into your existing triples.  Or move up to say 39mm GL forks.  I don't know if your triples could be bored that far, but there are aftermarket CB750 triple clamps that might be usable.

For brakes, I used SV650 sliding calipers (same as small Ninjas etc) on adapters and CBR 310mm disk rotors and those are on stock GT750 35mm forks.  I have emulators in them, but will swap out the legs soon for a set of 37mm GS1100 forks.