Topic: Opinions needed: 77 CB550 Frame "Rake/Stance"

[paulschell]

Hey guys,

Just wanted to run an option by you for my first build. I'm pretty far into it, subframe is cut up and I'm about to get a new rim/spokes for the rear wheel. I put a brand new wheel on the front (see picture, 17"), and I have a brand new 150/70-17 tire lined up for the back.

1) My question is, since I want a slightly more aggressive rake/stance towards the bike, do you think it would be beneficial to run an 18" back there, or would sticking with the 17" be conducive, and weld the subframe accordingly to obtain the correct rake (have Cognito led hoop with upsweep). I know it's a bit hard to picture without picture of the frame, I'll try and attach one as soon as I can.

2) Secondly, I made a mistake in ordering a 36 hole hub for the front, and then realizing the rear hub is 40 hole, the mix-match of spokes won't be an eyesore/noticeable will it?

Any/all opinions welcome,

Thanks guys!

[BomberMann650]

No one is gonna be able to count spokes when they're spinnin 

There are some risks to budging the rake/trail of the front around.  Are you using a stock fork?  Fender/no fender?  Brace?  Somewhere in the archives there is a guide on how to plum bob and straight edge your front end to measure the degree of your fork rake and axle posit (trail)

But just for reference, modern sport bikes are raked around 22-25 deg which is more dramatic than a 550's "commuter friendly" geometry, which is somewhere between sport and cruiser angles.

Just going to the smaller front wheel is going to make your bike turn in quicker.  Shorter shocks (with the proper rear wheel clearance) will alleviate the dramatic effect of said turn in.  And give you that low slung bonneville salt flat aesthetic.

You probably already know the general rule of thumb of making the tank and seat line parallel with the ground.  Part of that cafe racer thang. 

One thing i would NOT do is make the rear wheel bigger than the front.  Its a bad idea on four wheeler atvs and even worse on motorcycles. 
36spoke front and 40 spoke rear is technically sound.  You'll end up with a marginally lighter front wheel (good) and a robust rear drive wheel (also good)

[paulschell]

Thanks for the words of wisdom @BomberMann650!

Forgot to mention a small fact in that the build has 05 GSXR-600 forks (I know, it's all the craze right now, but I thought I'd try something new haha). Very correct on not being able to tell when they're spinnin! I just want the bike to have a few degrees of stance (back end higher than the front), was just unsure as to how to accomplish this.

Plumb bob sounds like a pretty good idea, to make sure everything's in alignment. Only other modification to the frame is going to be a monoshock conversion, so with this information, would you still stick with the 17 in the back?

Appreciate your time!

Paul

[BomberMann650]

That "back end higher" is a visual illusion. 
Us sohcheads had a discussion about that when I posted a pick of the new naked ducati 900. 
You can fab a seat cowl to give you the "look" without making the suspension geometry downright dangerous.  Either way, with the gsxr forks, your overall stance is gonna be lower than stock.
Like the pegasus 550 in the pic.
I hope I can talk you out of jacking up the rear end.  I did it to my bike...kinda by accident when ordering a pair of rfy shocks.  They were 14mm longer than stock, and it made quite a difference with stock forks.  Yeah my handling was quicker, but I noticed some oddities after putting them on.  I've since done what I could to shorten the shock and soften the preload to get me back down.  Worked good when I had a 125# passenger on pillion, but once the passenger was gone I was back to wtf-ville.

Try to get your fork rake around 25 deg or greater, for safety's sake.  And try not to crush the header pipes 

[calj737]

The greatest change you are making with the GSXR swap is offset in the triple tree, which changes the steering. Using 17" tires frnt and rear allows a greater variety of tire brands and compounds.

Some argue the reduction in trail by the offset change makes the bike twitchy. Others, and many who ride these bikes after this modification, don't feel that way. If you do feel the front end has become "too fast" after some riding time, you can always go back to Cognito and get an adjustable triple tree with variable offset. Simple as that.

You can also run an 18" front wheel to help restore a bit of trail, but it's a very slight increase at best. Devin's first 550 is almost exactly what you're running (17-17 stock GSXR offset) and it rides perfectly well and stable to me. The riding position with rear sets "seems" to negate the steering effect making the bike "predictable" to my experience with it.

Some times with custom stuff, you really won't know until you've add the changes whether they work out for you or not. I'd be more curious about your monoshock conversion and who/how you to plan to execute that?

[bwaller]

I'll not play the old poop here, build what you please & ride how you choose. I'm sure most ride these 40 yr. olds accordingly because they have something newer parked in the garage. But frame geometry is not "alternative facts"  too little trail can be dangerous. Here's what can happen.....

I'm one who ignored a lack of trail, raced for two seasons with minimal trail of 89mm. It handled perfectly...until it didn't.    Eventually some combination of conditions aligned and I experienced the worst tank slapper. This is how "too little trail" manifests itself. Beat me up badly & nearly destroyed the motorcycle.

Will it happen to everyone? Likely not, partly because most will not ride these bikes aggressively anymore. Just be forewarned, it can happen in an instant.

Old poop out! 

[OldSchool_IsCool]

"Alternative" Old Poop in.

Less trail is actually ideal... If your plan is to trike or hack the thing.

Other Old Poop out

[calj737]

See if this diagram gets you close, Paul

[rotortiller]

Some bikes came that way factory stock. It depends on the fork length a person installs and how they position those in the trees. I agree not a good idea on an otherwise stock bike. Pulling the fork tubes up too much in the trees does a similar thing.. A Frankenstein often looks the part but handling is often reduced, a good enough tradeoff overall in a "poser".

One thing i would NOT do is make the rear wheel bigger than the front.  Its a bad idea on four wheeler atvs and even worse on motorcycles.