'75 CB550K1 Gulf - Round...3, the fun stuff

Re: '75 CB550 Gulf - round two

My thoughts exactly, eyhonda. It's a 110/90 on a 1.85 or 2.15 width rim. (don't recall exactly and my shop's a little ways away) Funny thing, I was running a 120/90 Dunlop on the XS (same size rim), and the rear was still much closer to the front.

Something else to consider: I can lock up the Avon under hard braking with a single disc on this bike, yet on the XS with dual discs and Dunlops, I could never lock up the front. This seems to speak a little on the grip of both tires...?
 
Re: '75 CB550 Gulf - round two

Hey bud. I searched through your build thread but didnt see one. Do you have a shot of your electronics?
 
Re: '75 CB550 Gulf - round two

Tire squeal and lock up is as much about fork dive and initial bite for the brakes as it is about grip. A light bike with brakes that grip and forks that don't dive will skid the front easily. Heavy bike, softer forks with less compression damping and brakes which come on more gradually allow the front end to pitch down gradually and lad the front end.

Just as a comparison, my son managed to lock the front brake up on our TZ at around 140 and it threw him on the ground. We has set the brakes up with lots of bite and fairly stiff forks and a light bike. brakes applied slightly too fast, forks didn't give and wheel skipped out. And those race tires were not short of grip.
 
Re: '75 CB550 Gulf - round two

Thanks teazer, that settles that then! :)

sxe, I don't believe I do. I can run over to the shop sometime and grab one, but it's pretty tore apart at the moment. I'll be sure to post some up in this thread.
 
Re: '75 CB550 Gulf - round two

hmmm...reading through all of the description, I tend to wonder about suspension tuning as well. i think it would definitely be worth a go after your suspension work before shelling out for new tires. Could overall geometry of the basics like rake and trail be cauing part of that handling issue?
The reason I ask is that on the VTR (though not reknowned for its overly strong forks) I can push pretty hard into a corner, and be using nearly all of the rear tire, with plenty of the front left over. I dropped the forks in the triples a half inch during the build, and immediately notice steering to be more responsive--but with a subsequent lightening feel to the rear end. Now in my case this is what I was trying to accomplish, since the steering was sluggish, and was very rear-bias and heavy. I can't remember, but didn't you raise the rear some with the Hagon's you installed? I wonder if that move doesn't require some suspension work to account for the geometry change.

JAT at any rate...Can't wait to do some work in the composites with you! I'm on the prowl for the clear gel coat now!
 
Re: '75 CB550 Gulf - round two

Sweeeet.

Yes, I raised the rear approximately 1.5". To compensate on the front, I used cb650 fork tubes, which are about 3/4" or so longer, buuuut, the alloy top clamp also allows for the forks to act like they were slipped through the trees, because all three holes are on the same plane at the height of the steering stem hole. Stock 550 clamp has the fork tube holes about a half inch lower than the stem, so I in effect lose a half inch from my fork tubes, giving them only about 1/4" of extra height. It does steer quicker.

I think I need to not jump the gun with the tires, eh? I'll reevaluate after all the bracing, and after the steering damper gets juice. I just don't know enough about suspension to accurately pinpoint the cause when it's likely a combination of things working against me.
 
Re: '75 CB550 Gulf - round two

Just so I understand crrectly, in effect you have raised the whole bike up, and the rear is 1.25" taller in the rear than in stock trim?
I'm not 100% sure, but I think this will tend to give you a forward weight bias, which is compounded when braking (like in good curves), and is taxing the front suspension and thin tire grip on the front to the max. This is going to be especially evident if your compression rates are too weak (I would think more likely than too stiff with stock 650 forks hardware) and the front end in essence bottoms. This will raise (and lighten) the rear uncontrollably and increase the likelihood of a skid.

I am guessing, but I would bet that setting up the front forks properly and installing the forkbrace will do quite a bit more than the rear brace would. My own observations lead me to believe that most bikes are under supsended in the front, and suffer greatly from the effects of working at the supension limits.

just my .02, though. I'm sure there are quite a few here that have a better grasp of suspension tuning than i do!
 
Re: '75 CB550 Gulf - round two

Mmm yeah something like that. The measurements on the front are largely guesstimations, but I've tried to mimic the setup many of the guys on SOHC4 have with their track/race bikes. You've ridden the bike and know that the front end isn't stock feeling at all. It's relatively stiff thanks mostly to the emulators I think, and really doesn't dive much with braking. Anywho, we'll flog it this spring and get a better idea of what's what.
 
Re: '75 CB550 Gulf - round two

I can't remember exactly how it rode, but I seem to remember a fairly taut chassis. It may even be that it is too stiff, in which case the same problem would occur. I do know that the FZ is quite a bit softer than the Gulf (too soft for me), but it does stay well planted in the corners...so who knows.

Hard to say off guesstimation I guess...sounds like a good excuse for a ride. It will be kind of fun to go out for actual tuning's sake--we gotta get this figured out before next year's builds, eh?
 
Re: '75 CB550 Gulf - round two

In that case, I think I'll hold off on bracing the swinger. I would really like to definitively pin this down, and if I "fix" everything, I might not know exactly which factors were the culprits. Fork brace and an emulator tune will do for now. And as far as the emulators are concerned, I'm only out to remedy the rebound damping. The compression damping feels adequate to me. More to come...
 
Re: '75 CB550 Gulf - round two

Try a lighter oil to lighten compression damping or back off the spring adjustment on the emulators to allow the front to dive a little under braking.

Fork brace can't hurt - as long as it's installed correctly and the tubes are 100% parallel. I forgot what rear shocks you installed, but mushy shocks will adversely effect handling - as will a flexible swingarm.

This is the "D" part of R&D and what separates a great special from the rest.
 
Re: '75 CB550 Gulf - round two

Thanks teazer, I've got Hagons on the rear right now. Talking with JoeyPutt about the RAM shocks, they look promising...

The Hagons are set up for my weight + stock cb550 weight. I ordered them before I realized just how much weight I shaved, and am considering sending them back to Dave Quinn for a slightly softer spring. They're on the lightest preload and very stiff right now.
 
Re: '75 CB550 Gulf - round two

Check and set front and rear sag might be a good next step. You want somewhere around 20-30% of available travel. To be honest, most of our race bikes end up with 0-5mm of sag, but don't tell anyone.

One trick I learned years ago to see if the suspension is balanced: Press down firmly and quickly above the center of gravity ie the rear of the tank. Both ends should dive and return at more or less the same rate. Often one end is more damped in compression or rebound or one end is sprung too hard. If that's the case, one end will drop or return faster than the other end.

It should be firm but pliable - not too stiff and not all mushy and evenly balanced.
 
Re: '75 CB550 Gulf - round two

Ah, sag was one of the things that raised a flag with the rear. Unladen, the front has about 20mm, the rear has less than 5mm. I can't actually push down on the bike to compress the rear, I have to sit on it, it's that stiff. What has me vexed is that as stiff as the rear is, I still use nearly all the travel. The rubber stoppers are about 3/4" from the top of the shock, so I suppose there is a little room to go softer.

All of this tonight has been out of memory, so I'd take it with a grain of salt. I need to get out to the shop and do some actual measuring, because who knows how accurate my memory is. ::) Thanks for the info, teazer. I'll get back with some solid numbers soon.
 
Re: '75 CB550 Gulf - round two

What is it about the rebound damping you didn't like? Was it pulling down on you, and shortening the travel, or was it just non-existent? I'm almost wondering if the compression damping isn't too stiff for as light as the bike is...
 
Re: '75 CB550 Gulf - round two

t71ford said:
What is it about the rebound damping you didn't like?

There is none. I mean literally none. In my latest research on the emulators in a cb550, I came across lots of conflicting info. The manufacturer says to leave open the stock rebound holes in the damper rods. People who've done this have been left with no rebound damping. By welding these holes up, and tuning with oil weight, they've gotten good damping. But Race Tech and the like still insist on keeping them open. So I've had to pick and choose what I believe, and I think I'll follow in the footsteps of the guys who weld them closed. Besides oil weight, which I'll play with this spring, that's the only solution I've been able to find.
 
Re: '75 CB550 Gulf - round two

certainly pioneering, then, eh? ;D i guess that is what makes it fun!
 
Re: '75 CB550 Gulf - round two

Ringo said:
Ah, sag was one of the things that raised a flag with the rear. Unladen, the front has about 20mm, the rear has less than 5mm. I can't actually push down on the bike to compress the rear, I have to sit on it, it's that stiff. What has me vexed is that as stiff as the rear is, I still use nearly all the travel. The rubber stoppers are about 3/4" from the top of the shock, so I suppose there is a little room to go softer.

All of this tonight has been out of memory, so I'd take it with a grain of salt. I need to get out to the shop and do some actual measuring, because who knows how accurate my memory is. ::) Thanks for the info, teazer. I'll get back with some solid numbers soon.

too little sag plus using all the travel usually means the spring rate is too low and pre-load is too high. Try a stiffer shorter spring. last time I had that problem on a set of alloy bodies Konis I had to skim metal off the top and bottom caps and ground down the "nubs" that the adjuster sits on in an effort to reduce preload. That was after trying three different springs.

Rebound is all in the holes. What race-Tech are saying is leave it stock because that should work. It's how the forks were designed to work. Do the forks spring back up hard or is there just not enough damping to slow them up? Thicker oil should change that but it will also change compression damping, so it's a bit of a juggling trick.

On aGT750 we weld up one of the two rebound holes and that seems to work
 
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