Topic: 1973 Honda CB500 Front end fork swap - gsxr 750?

[Madmax92]

Hey guys,

Been seeing a few posts about people swapping out the stock front end for gsxr 750 fronts or yamaha R6 fronts for the disc breaks. This is a build that really interests me and I was curious if anyone had any input? Any suggestions on front ends, what additional parts and labor will I need to complete this swap? I really like the gsxr forks because im going for black/bronze or gold color scheme.

Any input is welcome!

Cheers,
MadMax

[calj737]

It’s easy enough. Parts can be full front ends swapped in with stock GSXR donor parts, including their wheels. If you want vintage styled wheels, then you can buy an adapter hub from CognitoMoto, new spokes from Buchanan’s, and modern sized rims.

For the rear, you can also use a modern Disc adapter hub from CognitoMoto mated to your stock rear and get quality disc brakes front and rear. Add some quality shocks on the back, and you’re all set.

Things to consider is the GSXR triple tree offset will change the steering geometry and rake/trail numbers from stock CB. You can get different offset trees to help restore the factory geometry with this change.

[Madmax92]

@calj737 -

Awesome! yeah I haven't decided if I want to keep the vintage look or not, i'm personally not a huge fan of spoked wheels but i don't hate them enough to not get them. So pretty much I could in theory just adjust a full gsxr front end and fit it on the CB500? Also thank you very much for your help on other posts, this forum community has been more than helpful to me on this project.

[calj737]

All Balls Racing makes conversion bearings to swap the GSXR stem and triple trees into the stock frame neck. Depending upon 750/5x0, the GSXR stem may need to be shorter. The 750 has a longer neck by about .800.

There’s plenty of builds on here in the Project section with GSXR swaps for references. The R6 swap can cost less, but needs some personal “fab” work to make spacers and caliper mounts. The appeal to many who choose the GSXR (Inverted) forks is the abundance of donor bikes and Cognito’s plug-and-play components. Costs more, but builds more easily.

[Madmax92]

@Calj737 -

So lets say I didn't want spoked rims, I could just put a gsxr wheel on the front since it already fits the forks? then with the back end if I wanted to get a rear gsxr wheel to match my front I would just need the cognitomoto disc adapter hub? thinking about going that route if it would be as simple as it sounds.

[calj737]

True for front, incorrect for rear.

To use a GSXR rear wheel, you’d need to adapt the stock axle and swing arm to fit the newer wheel. Might be easier to adapt the GSXR type swing arm from a different year to fit the stock Honda frame. You’re treading into some more involved fabrication now.

If you did use a vintage style spoke wheel front and rear, Cognito makes those to fit the GSXR front end, and an “adapter” rear to use stock cush drive and modern discs for rear. You could lace front and rear to 18” or 17” rims (3.25 front, 4.5” rear) so you could run more modern radial tires.

[Madmax92]

@calj737
So i'm a bit confused (sorry i'm still new) I really don't want to deal with to many alterations because i'm not very mechanically inclined yet. In your opinion whats going to be easier? I'm sure having a gsxr front wheel and a spoked back wheel will look very silly. cost wise whats going to be more expensive? i'm not familiar with spoking wheels either so that would be a process of its own.

[calj737]

Most expensive is the Cognito route. But, it’s the easiest and it’s plug and play especially for someone new to building a bike.

Having your front and rear hub laced with new spokes is easy, and if you order from Cognito, they can lace their hub to a new rim with new spokes then send that to you. I’m not hawking for them, but they do have this conversion down to a few product SKUs as Devin somewhat pioneered this conversion hub.

Cost wise, it’s about $600 per wheel (spokes, hub, rim and labor). Not cheap, but it is easy. And sexy and solid and safe.

[Madmax92]

I just checked out cognitomoto and a full wheel laced and everything runs about $900 per wheel  unfortunately I don’t have that kind of money to throw at this yet. As I research I’m finding more people explaining how the gsxr wheel on the rear rubs against everything if you don’t swap the swing arm and convert to mono shocks? I’m really wanting a modern sport tire look but it’s appearing to be quite complicated and unforgiving. I certainly don’t want to make a mistake after altering my frame and risk permanently damaging something :/

[calj737]

A 500 swing arm will accept a 150 tire, but you might need an offset sprocket to move the chain outboard and avoid the tire. Anything wider, and you’ll need to modify the swing arm itself. You don’t require a monoshock conversion to run a GSXR rear wheel, but you will have to deal with a different diameter rear axle from stock CB.

That’s why some use a donor GSXR swing arm (I think it’s the 1100 model that fits pretty closely and is dual shock) but you might still need to shave the width at the pivot tube.

The moral of the story: you can’t make a 45 year old bike run modern gear without either fab skills or money, or some of each. Sorry to burst your bubble  But there’s plenty of folks on here happy to help guide you through the decision process, and the methods for making it work if you choose a path forward.

[Stev-o]

Hey Max.....if I were you, I would stick with the stock front end.  A little water in it prolly did no long term damage but I would replace the 40 year old springs regardless.

[Madmax92]

maybe i'm getting a little too ahead of myself? im not opposed to taking things one step at a time, would i be able to run the gsxr front wheel with the stock rear? Am i thinking that fitting the spoked wheel to the gsxr front is more labor intensive than it really is? i'm probably going to be buying the gsxr forks with my next paycheck and have a couple hundred left to play with after that. also, any suggestions on shocks for the rear? they probably need to be replaced as well

[Madmax92]

Hey Max.....if I were you, I would stick with the stock front end.  A little water in it prolly did no long term damage but I would replace the 40 year old springs regardless.

@Stev-o
I had thought about just rebuilding the stock forks but I would feel much more comfortable with discs in the front.. plus i really like the look of the gsxr forks and feel it would give my bike more of a custom feeling. I've been using 4into1 for most of my parts that needed replacing and I hadn't seen any fork tube springs, maybe i overlooked them..

[calj737]

Max - you’re a bit all over the place... for clarity’s sake:

If you run a GSXR front end, then the stock CB front hub needs spacers, and a custom axle. The stock axle is smaller in diameter than the GSXR, and you’ll need to make custom brake caliper mounting plates to mate to the stock CB disc(s).

The stock CB rear wheel is a separate issue. You can change that to a stock CB hub that accepts a disc and use CB disc brakes front and rear. You can add a second disc brake and caliper to the stock CB front.

All of this (stock brakes) is accomplished with basically stock parts, a small amount of fabrication and some time. (Read cheapest and easiest)

If you want inverted forks up front, and you’re budget requires patience, then swap in the GSXR front end completely, and bide your time to resolve the rear swing arm to mate up the GSXR rear wheel.

Ikon shocks are the minimum best option, and you can get a great deal on them through member Noblehops (Nils) https://www.restocycle.com/ikon-suspension-products and they will make a marked difference in the handling of your bike.

As for rebuilding the front end of your stock bike, best route is to get a set of single rate springs and cartridge emulators through Racetech with the springs weighted for your weight, setup for you, and then set about tuning your brakes as best you can.

The stock brake disc are heavy, but good. The stock calipers are crappy by modern standards, but work perfectly well if clean, serviced, and functioning properly. You can have the discs thinned and milled to add some slots and holes for improved wet performance and weight savings. You don’t need to turn them into Swiss cheese though...

This route allows you to step through the budget and rebuild process. Purchase and set aside components while you get your bike running really well and accumulate all the goodies to make it your own and go faster, stop better, and look like Max’s bike.

Maybe that helps some?

[Madmax92]

@calj737 -
Sorry for being all over the place, I don’t really know where to begin this swap but I’m pretty determined to make it happen. So just running the gsxr forks I need bearing spacers for the front hub and a new custom axle which I assume cognitomoto has? What about the offset problem with the gsxr forks, I also need the triple tree adjustment right? I’m probably going to take the most cost effective route even if it takes a little more time.. sounds like I’d just have to find some how to’s on the caliper mounting plates and research lacing the wheels?

Thanks for the plug on the shocks, I’ve been looking for a good pair and I like the way those look too! Big ups!

[calj737]

Nope, Cognito won’t sell you that axle. Just use the GSXR wheel and run different front and rear wheels for the time being. Okay, looks a bit dorky, but who cares? It’s a work in progress.

The triple tree offset difference is an argument. You’ll be swapping to a 17” front tire, so you’ll need to swap your rear from the stock 18” else you’ll be all over the place. So you can’t get there in a single step, gotta solve both front and rear or use stock wire spokes on a custom hub and rim to run vintage style with inverted forks.

Ain’t no free lunch I’m afraid....

Regarding the front axle:
The GSXR wheel and forks take a much larger OD axle. To use the CB hub and GSXR forks, you need a wide-thin-wide axle. Problem is the “wide” section won’t pass through the CB hub. So, you need a threaded on adapter on one end that will fit the fork, but install after passing through the hub.

This is a safety issue in the minds of competent people. There’s no way Devin will make such a thing because of liability. Any professionals machinist won’t make it either if they value their butt legally. So you’re down to finding a buddy to make it... And then what happens if it fails?

Some folks have used a Harley hub and modified the discs because the Harley axle is equal to the GSXR. But you’re still onto using rims and wire spokes. Sounds like you prefer the modern GSXR wheels front and rear. So focus on finding and fitting the new swing arm and just plug in the GSXR front end. Screw the offset change.

Rake/Trail:
Swapping GSXR front ends changes the geometry significantly. Many prefer the stock rake of 64* and believe changes from it make the bike unstable. I disagree personally. I ride modern bikes with 24* of rake and 3.8” of trail and they handle brilliantly. They are modern frames with modern suspension though... it’s all what you’re acccustomed to in my book. You can find an online calculator to help you decide tire, shock, offset choices, and make decisions then.

[Madmax92]

So If I just directly port the gsxr front and use the gsxr 17” front wheel I also need a 17” rear wheel to accommodate? What about the sv650 rear wheel, it’s 17” and a 160 which in theory should fit the CB stock swingarm? If not I believe you said the 1100 gsxr swingarm is a close fit? Which would allow the rear gsxr wheel.

- what all is included in swapping out the swingarm?

[RandomOrbit]

I keep thinking about doing something like this, because I feel like upside down forks and modern disk brakes look badass on a CB750, and brake and suspension improvements sound like a good thing to do.

But then when I think about the complexity of doing it so that it actually all fits together and works better than the stock configuration, and the associated cost in real dollars of all that, I have to ask myself what my end goal is:

Is it to make the most badass CB750 ever? Because a thousand other guys have already done that and done it better than I have the money and skill for.

Is it to make my bike handle better? Because I could just buy a used CB600F4, or a GSXR that would be faster and better handling than any CB750 I could build for half the cost of swapping out the front end.

I really admire the custom CB750s I've seen with these kinds of mods, but it's not a cost effective way to get a better bike. Mods like this aren't practical, they are built for entirely unpractical reasons. I admire the people who build them, but I don't have the time or money to spare to build something like that and even if I did, it wouldn't be my only bike.

[calj737]

So If I just directly port the gsxr front and use the gsxr 17” front wheel I also need a 17” rear wheel to accommodate? What about the sv650 rear wheel, it’s 17” and a 160 which in theory should fit the CB stock swingarm? If not I believe you said the 1100 gsxr swingarm is a close fit? Which would allow the rear gsxr wheel.

- what all is included in swapping out the swingarm?

A 160 tire on a 500 isn't a great choice, really. A 130-140 is really good paired with a 110/120 front. Yes, if you use a 17" front a 17" rear is needed.

I don't know the SV wheel for fitment on a CB. I think its the GS1100 arm that is very close to fitting. Might need a tad of shaving off at the pivot tube. I'd stick with the stock rear arm, use a 750F hub that accepts discs, lace to a new 17" rim, and be done with it. Cheap, easy, and will be slick. Kind of like the video you sent me, but with a disc rear.