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.

[Retro Rocket]

I actually know someone here locally that could easily do these but the costs for anything "engineered" here in Australia is ridiculous, thats why i get most stuff made in the US. Thanks for the offer Frank but I have another member here thats already made me some pretty awesome parts and he's getting the work, he's offered me a great price to do all 3 sets eventually. Thanks again for the offer. I will get another frame kit at some stage though {lets get the email addy right this time} 

[sinister902]

If anyone cares, I actually just sat down and spent a couple hours doing the ACTUAL math comparing the GSXR axle to the CB550 axle. If you leave the match basic, the GSXR hollow aluminum axle in a GSXR wheel(hub) would flex 1.8x less than a solid steel 15mm axle IF the load was concentrated at only the centerpoint of the axles. Since this is split over two equal bearings, that distance between the bearings in a cb550 hub vs. a GSXR hub, the 15mm steel solid axle flexes 1/3 as much as the hollow aluminum at the bearings. That said....less flex may not be better....

EDIT:

The cross-sectional area of the solid steel axle is 0.2739, the cross-sectional area of the hollow GSXR axle (accounting for the ID missing) is 0.274

I was blown away how close those numbers are.

The ultimate shear strength of the steel when cross sectional areas are that close is more than double.

ultimate shear yield point is 22Ksi for the aluminum, and 34.8Ksi for the steel. about 33% in favor on steel.

The modulus of elasticity of Aluminum is 10.2E and the steel is 11.5E this is where the calcs got to what I said above. unless the load is concentrated exactly on the middle of the axles, that is the only way the aluminum axle is "stronger"

[GV1390]

I can finally sleep tight now knowing my hodge-podge build may make it around the block.

[sinister902]

I'm gonna look into more....like bearing ratings and stuff. If I find any of it to be worrysome, I'll be re-designing the couple front end swaps I did on my bikes.

[sinister902]

Stock CB front bearing is a 6302-2RS
Dynamic load rating Cr: 11,400 N
Static load rating Cor: 5,400 N
Limiting Speed:
Grease Lubrication: 13,000 RPM

GSXR bearing is a 6205-2RS
Dynamic Load Rating (Cr)   14,000
Static Load Rating (Cor)   7,850
Max Speed (Grease) (X1000 RPM)   13

the load ratings are a touch higher on the GSXR bearings.....but I doubt a cb550 in just about any form is going to be CAPABLE of exerting forces strong enough to see the numbers that separate the bearings.

The only things I think would be a point of failure in GSXR parts vs. CB550 parts with adapters, is the hardware holding the rotor to the wheel. I used stainless hardware on mine for piece of mind, and the stock GSXR bolts from rotor to adapter....I figure they are designed to shear before something else does as a safety feature and don't want to put stainless hardware there that could possibly make something dangerous.

Edit:
if one were to swap wheel bearings to put a GSXR axle into a CB550 hub, you'd need a 6004-2RS bearing
Dynamic Load Rating (Cr)   9,400
Static Load Rating (Cor)   5,050
Max Speed (Grease) (X1000 RPM)   17

so, this is actually less safe than the steel axle on stock size cb550 bearings, as you decrease the load ratings by quite a bit in order to use the GSXR axle.

[calj737]

A problem I see with using an adapter to mount the rotor to the stock hub is the axis of the rotor occurring beyond the line of the bearing. The bearing dissipates force onto the axle, and if the rotor/adapter are outside of that, then all load ratings are off.

And don't underestimate how much load a moving motorcycle with a rider under breaking pressure can create on an axle. A thru bolt mounting a rotor thru and adapter then thru a hub has a very different shear load than a short, equal strength bolt mounting just a rotor. (Since you're calculating material properties...)

[sinister902]

for sake of discussion, what about offset rotors? some factory sportbikes use offset rotors up to 18mm of offset....I did mine a little different than gennaro, instead of using the 550 wheel with through bolts I used a later 750 wheel that was 5-bolt pattern and was already threaded...so I have 25mm long bolts mounting the adapter to the hub, with a 12mm wide adapter and an 8mm offset rotor from a VZ800. similarly on my XS750 yamaha triple I posted earlier in the thread, it's the same setup....short bolts holding the rotor adapter into the factory wheel just as the stock rotors were bolted on and there I used RC51 rotors which are also offset (basically what I do is use a 6-bolt rotor in correct diameter on the xs cause the stock rotor was 6-bolt, and on the cb I used a 5-bolt 750 wheel to use a 5-bolt rotor in the same fashion)

I still think in the case of a cb550, the frame strength is going to cause an issue before these front end mods ever could. the frame would fail first.

[ttr400]

Just to clarify, if you are talking about the GSXR600 around 2011 or so.  this bike does not use an aluminium front axle (i don't know of any superbikes that use aluminium for a wheel axle).
Material: Steel
Part #: 54711-14J0
Weight: 376 g
Size: OD 22mm
ID: 17mm
One end OD 28mm, other with M20 thread.

Kevin

[sinister902]

for that, the calculations are bunk as soon as you realize the modulus of elasticity is the same and the cross sectional area is essentially only different by .0001

[FunJimmy]

That's fine if the axle is only stressed by forces transfering through the hub and bearings but the primary reason for large diameter hollow axles is to ensure parralel flex free alignment of the lower stantions. That's even more important with USD forks as there is no provision for a fork brace.

[calj737]

That's fine if the axle is only stressed by forces transfering through the hub and bearings but the primary reason for large diameter hollow axles is to ensure parralel flex free alignment of the lower stantions. That's even more important with USD forks as there is no provision for a fork brace.

A perfect example of math and calculations will only get you so far. Understanding the application is the delta between knowledge and experience.

[sinister902]

I understand the design for supersport bikes, that see speeds over 180mph and some serious cornering forces in race situations and trackday situations. But What I'm trying to say here is these cb's with those same suspensions on them are not going to see 180mph and the hard cornering a supersports bike is designed/capable of, at least for 99% of the people doing the swap. Supersports bikes are also not the only bikes that use the inverted forks. In 1994, the first sport bike to use them was the GSXR, which at that time had a solid 20mm axle on 20x42x12 bearings. The 97+ suzuki maurader and boulevard use inverted forks, with a 17mm solid steel axle on 17x40x12 bearings. Are these magically not roadworthy either? I agree that a lesser axle design is dangerous, if all of the variables were the same (I.E. high speeds and hard cornering above and beyond the average rider's capabilities)

I also don't agree with saying there's a lack of provision for a fork brace.... while one wouldn't be small or visually simple, it's not impossible to tie the two caliper mounts and/or fender mounts from the lower stantions together over top of the tire. It would just be large and unattractive and aerodynamically unfavorable.