Gsxr Forks to CB Triple opinions- trail, offset

[redwillissuperman]

I'm designing a set of custom triples to adapt the GSXR front end to a CB360, CB350 and CB400F.

The length of the CB fork and GSXR fork is about the same but the offset is only 30mm versus 60mm for the CB.

I was planning to make inserts to allow for customization of the offset- say 30, 45, 60. Cognito has a setup like this but I find the design pretty plain and I need options for handle bar and light mounts- so I'm making my own.

I was looking at 6082 or 7075 Aluminum. I lean towards 7075 but it can be difficult to get a good "squeeze" on the stanchions. Thoughts?

I figured there were many here that had opinions as to the optimum trail figures.

 

[4 stroker]

I think the trail on those bikes should be between 95 and 105 mm, personally I prefer 95 +-2 mm .

 

[redwillissuperman]

The other part of the equation is the gixxer swingarm. I did some measuring (and some thinking) and I don't know if it's the right fit. At least not in the stock frame.
- step one is to mount everything in the frame jig as is and measure

- step two is convert it all to CAD

- step three is design all the options

- step four is machine a set of test parts

Then I can see what is going on.

 

[redwillissuperman]

I think the trail on those bikes should be between 95 and 105 mm, personally I prefer 95 +-2 mm .

Interesting. By the numbers, the CB360 is 92mm and 27.5deg rake.

Looking at adding the gixxer forks and swingarm would have decreased this to 88mm (crude measurement).

 

[irk miller]

There are three different GSX-R fork lengths depending on year and model: 720/726/738mm
and three different offsets: 32/20/28mm

CB360 fork length is 838mm
Offset is 60mm

Not sure how much of these numbers you're using, but I thought they should be put in here.

 

[xb33bsa]

awesome project will
i dont know why you would want those expensive alloys
good old 6061 t6 is cheap ,available and a lot easier to machine and can be welded
as far as offset and the resulting trail stock should be fine but if youare going with the os tire trend then i would look into the effect on the feel and action of tire sizes and maybe you would want to vary from oem speck
i would think if anything more offset to addres wider tire bringing the geometry closer to the unstable end of the spectrum
plenty of beautiful proven designs in mx and road to mimick in the clamping action \
i don't know why anybody would put a gixxer swingarm on tho they are just so so wrong for a 350 and it is nauseatingly common there is just zero imagination or creativity in it it is a very sheep like thing to do bro..why would you use one for twin shocks anyway ?wait are you doing a monoshock ?
swingarms are a pretty simple fab deal and for a machine like the 350 i think fabbing up a nicely designed STEEL arm is the way to go
especially 'cause so few are doing it these days it will set you apart
the only tricky part the precision alignment of the bushing eyes but if you build a very good welding fixture and acurately miter/fishmouth the weldement then all you need is somebody with a sunnen kingpin honing lashup that will work with you then you got it made

 

[xb33bsa]

and if you are looking at wire spoke wheels there is this guy kosman who is back kin business after he got restless i guess
and he is just now introducing his hubs and brake rotors etc for the flat track guys nice stuff real nice,but we would expect that from the ole boy
from what i saw he is sticking with the old school ie like barnes hub ,that is simple hub flanges with hook ended spokes not straight pull ,but thats fine,
anyway he says he is offering some killer pricing now to get the juices flowing.
i found this info in an ad he has posted over on vft
you have heard of sandy kozman eh ?

 

[1fasgsxr]

He was very big in the Drag bike scene for yrs...super nice guy..I follow him on the facebook

 

[redwillissuperman]

I am always looking at vft. I really want a zrx or GPZ swingarm but some guy in Quebec is bogarting all of them. Heading to Winnipeg to see if I can get a ZRX1200R complete to steal the swing arm off.

My other CB360 has Gixxer forks and a braced tubular steel swingarm. I may do a "dresda" or a billet with a 1-inch stretch.

 

[irk miller]

I really want a zrx or GPZ swingarm but some guy in Quebec is bogarting all of them.

I'm running a GPZ750 swingarm on my CB750. It's a perfect fit.

 

[VonYinzer]

"Heading to Winnipeg to see if I can get a ZRX1200R complete to steal the swing arm off."

Unless that ZRX is a wreck, that's a crime.

 

[4 stroker]

Interesting. By the numbers, the CB360 is 92mm and 27.5deg rake.

Looking at adding the gixxer forks and swingarm would have decreased this to 88mm (crude measurement).

Indeed the stock is 92mm but in high speed cornering/cornering non perfect flat road the bike will be a little bit to unstable. How did you calculate this 88mm? Because when the offset of triple clamps is decreased, the trail increases, the smaller front wheel will decrease the trail but not that much to get 88mm trail.
I have a very good rake and trail calculator which I will post next week.

 

[4 stroker]

Why do you want to use usd gsxr forks? In my opinion you just dont need that kind of forks on a little cb. I use a fork of a fzr 600 (38mm) Just a little bit bigger then the original ones and have decent dampening characteristics.
No need to have a stiffer fork then those with such a flexible frame.

 

[J-Rod10]

"Heading to Winnipeg to see if I can get a ZRX1200R complete to steal the swing arm off."

Unless that ZRX is a wreckey, that's a crime.

Agreed. I'd ditch the CB and work on the ZRX.

 

[redwillissuperman]

There are three different GSX-R fork lengths depending on year and model: 720/726/738mm
and three different offsets: 32/20/28mm

CB360 fork length is 838mm
Offset is 60mm

Not sure how much of these numbers you're using, but I thought they should be put in here.

Sorry, getting my gsxr-CB project mixed up with my other CBSM project.

When I put the gsxr front and rear end on the CB I measured 88mm on the surface table. This is with 30mm offset triples. I have a set of adjustable offset triples coming.

I will measure the gsxr front end, stock rear end bike today for comparison.

 

[redwillissuperman]

I measured the gsxr front-stock rear and it was 90mm. This was with the front forks at 715mm ride height. With the higher rear ride height (more praying mantas) I can believe the 88. Both are with 30mm offset.

I should probably go the other way and create 20mm offset inserts.