Topic: original front hub w/ GSX-R front end

[poeperman]

Dear forum members,

my name is Mathias, 27 years old, live in Belgium and this is my first post. This saturday i'm going to Holland to have a look at what is hopefully my first SOHC bike. I'm going to check out a '78 CB550F.

After reading tons of projects, I still wonder why everybody tends to use HD narrow glide or custom wheel a/o hubs.

Isn't it possible to attach some sort of spacer of  ((about an inch thick to match the extra width of the 2 GSXR calipers)) to the original hub holes (I'm not a native English speaker ) where the original disc is normally. Then drill new holes that match the rotor's pattern and go?

I hope you guys understand what I mean. I think that in order to use a HD narrow wheel, the spacers are also a necessity, thus I don't see why it can't be done with original hubs (wheels).

Greets!

[calj737]

The issue of compatibility with the stock hub and the GSXR forks is width and the axle diameter. The gsxr forks use a much larger diameter axle and it will not pass thru the stock hub.

Yes, you can mill spacers to resolve the width and you can mill an adapter to mount the rotors, but a "one way pushed in" axle then has to be turned on a lathe. I know someone who has done exactly this, and I'm sure it would be fine. Send a PM to GV1390 and ask him to show you his axle pictures.

Another option is to use a custom front hub from www.cogntiomoto.com. Devin's hub is bolt on ready to the gsxr, use stock gsxr axles, bearings, rotors, calipers, and allows you to use spokes. It is setup for a 3.5" front rim, but you could use thinner if you preferred.

Hope this helps and that you can understand what's written. Good luck on your bike purchase!

[SOHC4 Cafe Racer Fan]

The issue of compatibility with the stock hub and the GSXR forks is width and the axle diameter. The gsxr forks use a much larger diameter axle and it will not pass thru the stock hub.

Yes, you can mill spacers to resolve the width and you can mill an adapter to mount the rotors, but a "one way pushed in" axle then has to be turned on a lathe. I know someone who has done exactly this, and I'm sure it would be fine. Send a PM to GV1390 and ask him to show you his axle pictures.

Another option is to use a custom front hub from www.cogntiomoto.com. Devin's hub is bolt on ready to the gsxr, use stock gsxr axles, bearings, rotors, calipers, and allows you to use spokes. It is setup for a 3.5" front rim, but you could use thinner if you preferred.

Hope this helps and that you can understand what's written. Good luck on your bike purchase!

Just noticed a small correction to Devin's website: congnitomoto.com

[calj737]

The issue of compatibility with the stock hub and the GSXR forks is width and the axle diameter. The gsxr forks use a much larger diameter axle and it will not pass thru the stock hub.

Yes, you can mill spacers to resolve the width and you can mill an adapter to mount the rotors, but a "one way pushed in" axle then has to be turned on a lathe. I know someone who has done exactly this, and I'm sure it would be fine. Send a PM to GV1390 and ask him to show you his axle pictures.

Another option is to use a custom front hub from www.cognitomoto.com. Devin's hub is bolt on ready to the gsxr, use stock gsxr axles, bearings, rotors, calipers, and allows you to use spokes. It is setup for a 3.5" front rim, but you could use thinner if you preferred.

Hope this helps and that you can understand what's written. Good luck on your bike purchase!

Just noticed a small correction to Devin's website: Cognitomoto.com

Neither of us can spell. Or correct each other. It should be right now though-

[Riceman]

Cognizant moto.....
Good luck with your bike hunting Mathias

[poeperman]

thanks guys! The axle width indeed, didn't really think of that.

I'm gonna ride semi-stock the first few months and maybe put in progressive springs. Who knows I fall in love with the soggy? ride

I come from a 2006 Ducati Monster s2r 800, but I really love the way everyone builds his "own" machine and style.

greets!

[FunJimmy]

Although I choose to use Yamaha R6 forks the issues are simular.
Your suggested approach of spacers is exactly what I did. Works like a charm.
Check out my build thread. The link is at the bottom of this post.
Good luck with the bike.

[calj737]

Another prion that is an "in between" solution is to use cartridge emulators in your stock forks, plus a brace. Less expensive that a gsxr conversion, but creates a very good handling application.

[SOHC4 Cafe Racer Fan]

The issue of compatibility with the stock hub and the GSXR forks is width and the axle diameter. The gsxr forks use a much larger diameter axle and it will not pass thru the stock hub.

Yes, you can mill spacers to resolve the width and you can mill an adapter to mount the rotors, but a "one way pushed in" axle then has to be turned on a lathe. I know someone who has done exactly this, and I'm sure it would be fine. Send a PM to GV1390 and ask him to show you his axle pictures.

Another option is to use a custom front hub from www.cognitomoto.com. Devin's hub is bolt on ready to the gsxr, use stock gsxr axles, bearings, rotors, calipers, and allows you to use spokes. It is setup for a 3.5" front rim, but you could use thinner if you preferred.

Hope this helps and that you can understand what's written. Good luck on your bike purchase!

Just noticed a small correction to Devin's website: Cognitomoto.com

Neither of us can spell. Or correct each other. It should be right now though-

Hahaha. Thanks for catching that Cal.

[sinister902]

GV1390's setup is exactly what you're asking about, he's friends with xnewmanx on here whom machined his hub/rotor adapter and axle. I will say though, that the GSXR triple trees have almost an inch less offset which will play with trail. I've not had a chance personally to measure GSXR vs stock trail on a cb550....but I'm in the middle of doing GSXR forks on my Yamaha xs750 and contending with the same issues...and I am making custom set of triples to correct the offset and bring the trail back to stock.

[poeperman]

Thx again for all info! But then again @Funjimmy,you have used the original hub but not the rim, and no one else seems to use the stock rim. Is it because of width?

[FunJimmy]

Thx again for all info! But then again @Funjimmy,you have used the original hub but not the rim, and no one else seems to use the stock rim. Is it because of width?

You would need to remove the hub from the spoked wheel to machine it for the adapters so why rebuild with the steel rim? I switched to an 18" alloy rim for the handling benefits attributed to lower rotating inertia and smaller wheel. That and the fact that my old chrome rims looked like crap. You can read some interesting info regarding the effects of reduced rotating inertia at BST (blackstonetek.com) site. 

[GV1390]

[Retro Rocket]

You using your original Honda speedo drive with that set up...?  What wheel bearings did you use...?

[calj737]

Retro - I know from speak with Gennaro and his pal Cristian who made the spacer and axle for him, that the stock bearings are usable. I also know he's not planning on a speedo, but don't whether the stock speedo drive will fit regardless. And, he's planning on single modern disc only.

The long sleeve above his index finger is movable and gets punched in the right side fork clamp, the axle pushed in from left. The washers and Nylock secure it from the right side.

[sinister902]

Retro - I know from speak with Gennaro and his pal Cristian who made the spacer and axle for him, that the stock bearings are usable. I also know he's not planning on a speedo, but don't whether the stock speedo drive will fit regardless. And, he's planning on single modern disc only.

The long sleeve above his index finger is movable and gets punched in the right side fork clamp, the axle pushed in from left. The washers and Nylock secure it from the right side.

great description. Christian did the same on his own cb550 build....it's on here somewhere (username xnewmanx) He's who told me it's the easiest way to do it, and I did the same on my XS750 I mentioned.









I know most people on here are honda guys, but I did retain stock wheel and speedo drive while getting the GSXR forks on this way. It was about $100 in material to make two rotor adapters and the axle. Helps owning a lathe.

[FunJimmy]

Some of the performance benefits of upgrading the front end are lost with this axle design.
Unlike conventional forks, USD forks are unable to benefit from a fork brace and therefore require a rigid flex free axle to the provide the structural integrity engineers deemed nessesary. GSXR hollow axles are a massive 25mm compared to thin 15mm stock axles Honda used on our bikes. Flex in the axle will cause brake drag and inaccuracies in steering precision. If you're going to go to the effort and expense of upgrading the front end, do the job completely and use the designated axle.

Keep in mind. Fork and brake upgrades will lead to greater confidence and higher speeds. On the straights and in the canyons. Do you want to be burdened with the thought of an under engineered axle keeping it all together?

[calj737]

FJ - I had that discussion with Cristian too. He used 4130 rod, so it's pretty stiff. I'm not sure I would do it this way, but I do see the practicality of it. I suggested a castle nut on the right side and internal threads, but he felt it was not needed after performing the engineering calculations. Can't argue with good math.

I will say this about my limited exposure to Cristian, he is a very talented and knowledgable engineer. He's got an awfully impressive build over on choppercult about a year old (Newmans Turbo Shovelhead). Some awfully impressive engineering and fab skills.

[GV1390]

Not to muff this thread up, but let the work speak for itself:

http://www.chopcult.com/forum/showthread.php?t=26508

[FunJimmy]

That may be true Cal but axles are structural components. What seems adequate today may not be several years and 20,000 miles later. I'd be reluctant openly and publicly recommending any deviations in design of a structural component as important as a front axle with out a disclaimer. Especially in the litigious USA.

[sinister902]

That may be true Cal but axles are structural components. What seems adequate today may not be several years and 20,000 miles later. I'd be reluctant openly and publicly recommending any deviations in design of a structural component as important as a front axle with out a disclaimer. Especially in the litigious USA.

While I see where you're coming from...that GSXR 25mm stock axle is aluminum....and hollow aluminum at that. It deflects/flexes arguably more than a solid steel counterpart would. Additionally, the inverted forks are far above and beyond the limits of these old chassis....and modern sportbikes are designed for heavy abuse and/or track purposes....something I would say only 1% of vintage bike guys are going to be involved in, and at that I don't even think this type of modification is legal. I'd also argue that without adjusting trail (triple trees offset) that the longevity of the axle is pretty low on list of concerns. probably 75% of people putting on inverted forks are doing it for the look rather than performance gains anyways.

Also....the same tech is used now on some cruisers....such as the Suzuki Marauder and Boulevard....which have a 17 or 19mm solid steel axle rather than the 25mm aluminum axle the sportbike variants have. I put boulevard inverted forks on a cb360 and just changed the wheel bearings to fit the axle because it was only 2mm larger.

[Retro Rocket]

So, would it be possible to change the bearings and use the bigger axle..? Is there enough room ? I have a 2006 CB1000 F 41mm front end I am going to use on a build very soon, I'm trying to retain the stock speedo and tacho, to do that I would have to use the stock speedo drive, hence my questions. Making the spacers for discs is the easy part...

[754]

I am going to agree with FunJimmy, I think not using the big axle,  is throwing away performance.
If I were to try a USD fork I would probably only run one disc, then I would need it rigid..

Retro what will you run for trees, I will probably waterjet a set for 41mm, in about 200-215 width for my Rickman replica 41 mm.

[Retro Rocket]

Retro what will you run for trees, I will probably waterjet a set for 41mm, in about 200-215 width for my Rickman replica 41 mm.

I'm planing on having a set made up Frank, I have spoken to someone about having them made, 50mm offset/205mm centers, i'm buying a front axle and bolt next week before confirming those numbers.. I'll eventually need 3 sets of clamps made, 2 x 43mm and the 41mm set. ....

[754]

When I cut them will probably. Cut at least another pair , with fork holes roughed to about 38mm
 Then I could sell a set unmachined. Only flaw in plan, material is spending, i was thinking 1 1/2 or thicker.