1977 GS750B - my long awaited first bike!

[Chuck78]

Thanks for posting updates, you've done a great job on the bike, very well thought out mods.

I found some VTR-1000 (02 superhawk) forks and calipers I can get pretty cheap, no discs though..im thinking about picking them up now after reading your enthusiasm for them instead of using the GK 41s I've currently got..

if you are running GS wheels, refer to my somewhat comprehensive listing of all rotor donor bikes to get the 296mm rotors needed in the 78 mm PCD bolt pattern for our bikes. I believe I posted it on page 7 or 9 of the "twinpot mod for 78 skunk" thread that is the go to page for information on the ninja caliper and CBR rotor swap.

[Chuck78]

The 599/Hornet rotors for 2 years or so were the best candidate, as they had nearly everything dead on, including the 22.5 mm offset, greater than most of them. You will definitely need that and then maybe some more spacing still with the Superhawk forks which I would imagine are slightly wider. Have not gotten my hands on a set yet to see what it would take to fit a GS wheel in them, but certainly doable.

[blackhammer]

So I grabbed the forks and calipers/mc before I saw your posts here Chuck, the deal was just too good and I figured I could move them on if I couldn't make them work.

I will read your posts on discs as I need to find a set to use. I suspect I may need disc spacers and new axle spacers to get my spoke hubs to work. But I won't be able to get an idea till I get the forks next week.

I thought I might just use the GK 41mm triples I already have. But I'll have a look and see how the VTR triples work in my gsx frame.

Thanks for your thoughts on these forks, I never would've thought to look for them if I hadn't read your posts.

[blackhammer]

Chuck, in case you're interested the VTR triples are about 15mm narrower than the GK ones, even with the 23mm ofset discs i will still need some substantial spacers. Caliper clearance may be a concern also.

[Chuck78]

We can probably get by with spacing the calipers in slightly as well, but I'd rather take most of it up with spacers behind the rotors. More in the calipers and a fork brace would be a good idea to help stabilize the lowers from twisting forces on the axle.

Custom bullet triples could be made but then the vtr superhawk fork braces wouldn't fit, and we'd need a custom center fork brace piece made. Still, these are some very awesome advanced forks for our bikes, and are fully supported by racetech on cartridge upgrades. So at about 190 triple spacing I'm guessing we'll need 5-10mm on each rotor/hub? Easy spacer to machine up.

[blackhammer]

Some pics in my build thread. Im using the GK bottom triple and having a custom billet top triple made currently. The fork brace dilemma is occupying some significant brain power currently.

Ive got CB 600 discs with the 23.5mm offset in the post. Going to use standard GK 15mm axel instead of the VTR 20mm (too short using GK triples). Disc spacers will be in the region of 20mm, leaving caliper mounts for maximum spoke clearance.

[Chuck78]

Oh wow didn't realize you were using the GK triple on the vtr forks, you are going to have massive spacers.

Did you look into an SV650 triple, or gsxr??? Around 190mm or so, would solve some problems if you got one with the steering stem a good length that was useable. I compared some at the junkyard and thought they'd work, no precise measuring though.

[Chuck78]

Why couldn't you use the vtr triples?? I know of two GS1000's running them with AllBalls bearings.

[blackhammer]

Although i dont have bearings i still mocked it up with the VTR triples, the problem was the clearance of the calipers.
Spacing out the calipers is not an option as the discs in the standard mounting position is very close to the fork.
i think the VTR standard wheel must have very thin spokes
i could probably use the narrower VTR triples with a standard snowflake front wheel... but i worry about clearance using wire spoke wheels.

[T8erbug]

Although i dont have bearings i still mocked it up with the VTR triples, the problem was the clearance of the calipers.
Spacing out the calipers is not an option as the discs in the standard mounting position is very close to the fork.
i think the VTR standard wheel must have very thin spokes
i could probably use the narrower VTR triples with a standard snowflake front wheel... but i worry about clearance using wire spoke wheels.

I think you'll be ok with wire wheels. It will be close but I'm pretty sure you'll clear. I did a similar swap on my GS750 and made brake adapters with a 2001 GSXR600 fork and the spokes cleared the brakes. I ended up going a different route with the front end on it but I did complete the swap and everything cleared without modification. It looks very close to the VTR setup that you have pictured.

[Chuck78]

I can't get a picture from the same angle head on like you have (due to the rims and tires being installed), but I have nearly the same clearance to the plane of the hub flange from the backside of the caliper as your picture shows, & I have more than enough clearance to the spokes. The spokes angle inwards quite a bit toward the center of the rims even on these substantially wider aftermarket rims that I am running. this gives you more than adequate clearance. I would switch back to using the VTR triple for sure.

[Chuck78]

GS front hub flanges are about 2" (about 50mm) wide center to center, and I have 2-3/8" (60.3mm) clearance between the inner most points on the Ninja/Tokico brake calipers. I have 7/16" (11.2mm) clearance on each side at the closest point between the calipers and the spokes. I think you would be perfectly fine with the VTR setup.

My brakes' innermost point in the photo is a slight bit over 4mm more outboard than the CENTER of each hub flange. comparing that to your photo, it looks like you are nearly the same place.

I have read of other people using the Superhawk VTR1000C fork as an upgrade swap and using the Honda rc51 factory race bike calipers instead of the Super hawk calipers. Maybe they are a smaller casting and lighter weight, hence more clearance?

[Chuck78]

maybe some of these aftermarket calipers would give you even more clearance?

Then bought some Discaciatti racing calipers (4 pot) from the factory to go with a Brembo RCS18 master cylinder.
These are much the same as Brembo's best racing calipers at less than half the price.

[blackhammer]

I really need to have the wheels built before making a final decision on what triples to use. Cant really think about spacers until then.

I'm leaning towards the GK triples though as i've had a top triple milled to integrate an electronic dash into it. But if the VTR triples allow the use of smaller spacers that would be preferable.

The standard VTR calipers are interesting, they've not got good feedback on the superhawk forums, lots of owners definitely do the RC51 upgrade and there are other options to fit the standard mounts. Those Discaciatti calipers are good looking things, but at almost 500 Euro each not something i think i need.

Although my GSX has an 1150efe with 33 smoothbores it will still be more a street cruiser/bruiser than a track bike, so i think the standard VTR calipers will be enough.

[Chuck78]

Well I just snatched up a set of VTR1000F forks lower triple and calipers for $130, too good of a deal to pass up. I'll probably be using these on the 894cc 11:1 GS750 powered '76 Rickman CR900 frame that I just acquired. the bike is going to be a nightmare of axle and brake spacing, converting from 11/16 inch rear axle required on the original Rickman CR900 swingarm to a 20 millimeter axle GS rear hub bearing setup with a custom machined sleeve, fork bearing conversion from standard to metric, front and rear axle spacing completely custom, and it looks like I will need some more custom hub rotor spacers to make the Superhawk brakes work. I will be getting some 04 cb600 rotors as well. I think I will be just fine with the Superhawk calipers even though I ride fairly aggressively, but I may look into other options before I put any money into these if they need pads or a rebuild kit.