1978 750 - GSXR Fork Swap Geometry Compensation

[aceshadow]

Hello all!

Some background (skip for question):
I am new to this forum and bikes in general, and I'm working on my first bike project! I've ridden a couple other bikes in the past but really enjoyed the way the 750sohc rides and sounds so I decided to build one. I have been wanting to do a front end conversion on one of these bikes since the first time I saw one online and that passion has increased even more since I saw one in person! The body lines of the bike become so much more aggressive with the upside down forks and the braking power is increased immensely which is appealing to me. It's not a look for everyone but I love it.

My question:
Having an engineering background comes with it's perks, such as realizing that a front end swap on a motorcycle can drastically affect it's geometry and desynchronize the trail and rake of the wheels, effectively rendering the once-stable platform quite deadly. It's been seen time and time again. Even one of my favorite bike build youtubers CZeroMedia dumped his CB550 after slapping together a GSXR front end conversion without compensating for changes in geometry. Being a new rider, one of the things I fear most is the dreaded death wobble, and thus I am hoping that some of you could help impart some knowledge regarding geometry compensation on a bike with swapped forks. I would really appreciate it. Based on my research thus far, I believe that running a larger front wheel and stiffer rear suspension will drastically improve handling with this setup. Any input and advice would be AMAZING.

Thank you!

 

[aceshadow]

Bump

 

[68grandprix]

First off, I don't know anything about doing an inverted fork conversion besides the fact that it looks cool. I imagine you could measure rake, trail, etc and if you keep it similar to the stock values it should handle similarly stable(with improved damping due to the modern forks). If it's not within generally-considered safe parameters, I believe some people make modified conversion triple trees, but they're expensive. You can sometimes change geometry by moving the fork up or down in the stock trees.

Running any decent newer rear shock is definitely an improvement for sale handling compared to the worn out stockers.

I swapped a '77 GL1000 frontend onto my '75 CB750 with all balls tapered roller bearings. The braking was greatly improved. I'm not sure if the handling was better than stock bc my old forks were rusted through under the headlight ears and had very little oil in them. 20yo me had a serious tank slapper going around a corner at 90mph but luckily I rode it out. Especially lucky because I wasn't wearing a helmet. Young and dumb

 

[Tink]

Hi Ace

Wondering how you're getting on with the GSXR fork swap as I started it myself and am finding all kinds of hurdles after simply getting the All Balls Racing conversion bearings. :/

 

[EMM]

I’m in the same boat, brother. I’ll be keeping an eye on your threads and will share any information I can gather regarding all of this.

 

[loxley007]

I’m about to start my front end swap (GSXR 750 6K) so any advice is appreciated.

I see COGNITO do an offset triple tree but it’s expensive.

Any hints/tips??

 

[hinksy]

They do look good . All you need is an original and do some mesurements . Like trail and rake , fork travel and so forth

 

[loxley007]

They do look good . All you need is an original and do some mesurements . Like trail and rake , fork travel and so forth

Do you then still need to buy a COGNITO offset clamp or machine your own? There is no non physical workaround yes?

 

[loxley007]

They do look good . All you need is an original and do some mesurements . Like trail and rake , fork travel and so forth

Sweet bike by the way.

 

[Mogo]

We built one using 06 ZX10R USD assembly & matching swing-arm rear-end. Bike has no steering issues, but client wanted old school tyres so not exactly mountain racer handling required or expected, but definitely no ill feelings at normal riding speeds.

 

[78cb750k builder]

We built one using 06 ZX10R USD assembly & matching swing-arm rear-end. Bike has no steering issues, but client wanted old school tyres so not exactly mountain racer handling required or expected, but definitely no ill feelings at normal riding speeds.View attachment 14659

Can i get the specs on this complete suspension setup?

 

[Mogo]

The forks are completely original, other than being rebuilt and anodised black, but spring rates etc stock. We expected the front to be a bit soft, but in town riding it wasn't too bad so we left it for the client to make a decision. Rear swing arm had the monoshock sections cut away, and then we fabricated & welded out-board shock points to suit the dampeners. Pretty simple mod.