Suspension Upgrades

[Syscrush]

Shock mounts on the F swingarm are exactly the same distance from the pivot as the stock arm. If you try to raise the rear with longer shocks, keep in mind that the front with the forks you've considered will never come close to matching the rear rise. I personally wouldn't try to totally reinvent the wheel on this.

Thanks again Dave - that addresses my main concern about the CB1100F swingarm. I'm still leaning towards the Trac one, but nothing's carved in stone at this point.

I just did a quick calc of the amount the bike has been lowered as a result of the swap to CB1100F wheels. My source of data is the recommended tire sizes for both bikes on the Avon website. Based on that, it looks like the front has been lowered 12-13mm and the rear by only 3-5mm.

If that's correct then if I can get the bike ~15mm higher than it sits now, it'll be back to very close to the stock height in front, a bit higher than stock in the back. Given how conservatively I ride on the street, I think I'd have plenty of clearance for 25mm lower pegs.

I could get that 15mm at the front if I stick with the OEM forks and drop them in the triples when I switch to handlebars, since I would no longer need so much fork protruding through the top triple once I don't have clip-ons mounted to them above the triple.

Even so, I'm planning to go visit a shop that has a Duke 690 on the floor now so I can take some measurements of the forks. If they really are within 2" of the length of the stock CBX forks, then a top triple with a drop in the fork clamps might get me there. It would be a lot of money & effort for no meaningful performance increase, but it would be pretty rad if it all works out OK.

One big concern that I had about going to USD forks is mounting the CBX fender in a way that doesn't look horrible. This morning I studied a bunch of pictures of the Ducati Sport Classic front fender mount (the one with the metal mounting bracket), and then my CBX fender, and I realized that the CBX fender actually has steel tabs between the ABS fender and the mounting points on the fork - that should make it easier for a decent welder/fabricator to fashion a workable mount that looks something like the Ducati one:

[EMS]

The KTM 690 forks are 925mm from top to center of axle, according to a buddy of mine who has one. The 990 Super Duke forks are 755mm. The 690s have only one front rotor. This will mean some creative crafting to add a second one.

I just did a quick calc of the amount the bike has been lowered as a result of the swap to CB1100F wheels. My source of data is the recommended tire sizes for both bikes on the Avon website. Based on that, it looks like the front has been lowered 12-13mm and the rear by only 3-5mm.

Phil, I don't know what tires you used for your comparo, but if I use a 110/90 (4.25) x 18 for the CBX and a 130/90 for the F, the rear is actually going to be higher with the F wheels:

The 17" wheel lowers the rear by 12.5mm (½ inch) vs the stock 18". The 110/90 rear tire is 99mm high and the 130/90 is 117mm high. Difference is 18mm. Deduct the 12.5 and you end up with 5.5mm higher.

[EMS]

I am not going to get into any arguments about the quality of CB1100F stuff on CBXes, but the distance from swingarm axle to shock mounts on the 11F swinger I have is 19 inches. The same distance on both my 79 and 1980 CBx is 18 inches,1 inch shorter.

The length of the Multistrada Showa forks from top to axle center is 785mm. The distance from upper edge of top bridge to center of axle on the stock 79 CBX fork is 790mm. Effective difference is 5mm.
The front fender mounts on the caliper mounts and moves with the wheel.

[Syscrush]

The KTM 690 forks are 925mm from top to center of axle, according to a buddy of mine who has one. The 990 Super Duke forks are 755mm. The 690s have only one front rotor. This will mean some creative crafting to add a second one.

That sounds plausible to me. I was almost certain that they'd be longer than the CBX's. They're the longest short-travel forks I've ever seen on any bike. I'm going out to a dealer that has one in stock this Sat anyhow, so it's not a big deal to bring my tape measure to double-check. But if they really are almost 4" longer than the CBX, they wouldn't be usable.

As for the single front rotor, I talked to my suspension guy who said that it may or may not be possible to swap the Showa bottoms from a set of bent GSX-R forks onto the KTM's WP forks - the fact that they're both 43mm doesn't mean that it'll work, but the fact that they're different manufacturers doesn't mean that it won't. The only way to know for sure is to have both parts and try it - which could quickly escalate into a pretty pricey experiment.

Phil, I don't know what tires you used for your comparo, but if I use a 110/90 (4.25) x 18 for the CBX and a 130/90 for the F, the rear is actually going to be higher with the F wheels:

The 17" wheel lowers the rear by 12.5mm (½ inch) vs the stock 18". The 110/90 rear tire is 99mm high and the 130/90 is 117mm high. Difference is 18mm. Deduct the 12.5 and you end up with 5.5mm higher.

The sizes I picked up from Avon's recommendations were:
CBX Front: 100/90-19 (331.3mm radius)
CBX Rear: 120/90-18 (336.6mm radius)
CB1100F Front: 100/90-18 (318.6mm radius = 12.7mm lower)
CB1100F Rear: 130/90-17 (332.9mm radius = 3.7mm lower)

Avon is suggesting a 120 rear, I guess the stock 4.25" was closer to a 110, which would mean that my rear tire shouldn't be shorter than stock - that's good to know.

[EMS]

[ Avon is suggesting a 120 rear, I guess the stock 4.25" was closer to a 110, which would mean that my rear tire shouldn't be shorter than stock - that's good to know.

I don't think this will be that critical. It is very hard to find a good chart showing conversions from inch to metric. Certain tire sizes in inches haven't been available for a long time and people have replaced them with a range of metric tires without real problems.
In addition the actual dimensions for a certain tire varies from manufacturer to manufacturer. That is an issue with classic BMWs, for example, where the tire width can be a problem when installing/removing rear tires due to the shaft drive obstruction. Same nominal size tire - some brands work some brands do not.

[Syscrush]

Stupid swingarm question:

Where do these bronze bushings go?

If I do get a new swingarm assembly that includes its own bearings, axle, and adjusters, will that also replace the stock plastic/nylon bushings, or would they still be in there someplace causing trouble?

[Syscrush]

Ya DARE me?

[NobleHops]

Ya DARE me?

Only if you want me to. I'm good like that.

That's one blingy swingarm - what is it? Looking at the welds and the size of the box sections etc it looks like aluminum. Are there chain adjusters to match? You're likely going to need to fuss with the brake torque arm. And I hafeta say, I'd want the 16mm pivot if I was putting this stout swinger on. Ahh, the slippery slope! I know it well!

[Syscrush]

That's one blingy swingarm - what is it? Looking at the welds and the size of the box sections etc it looks like aluminum. Are there chain adjusters to match? You're likely going to need to fuss with the brake torque arm. And I hafeta say, I'd want the 16mm pivot if I was putting this stout swinger on. Ahh, the slippery slope! I know it well!

It's aluminum, but it's been chromed. It is supposed to be bolt-in. Yes, it ships with adjusters, axle, and bearings. I have a few measurements to take tomorrow and I'll report back with details then.

[EMS]

That is really nice, no doubt!! I would go for this too, if the price was decent.

The bronze bushings should replace the plastic ones. I wish the vendors would use metric dimensions so you know they are made correctly. That was one of the first modificaations to the rear suspension I made on my 79 about 20 years ago. The palstic ones did not look very good when I took them out.

[daves79x]

To answer your question - the plastic/bronze bushings are only for the stock swingarm. I've never seen any other arm use those. You'll need to adapt whatever pivot mechanism the new one has to the CBX frame. First thing is that I can't imagine using the stock pivot bolt with that arm (14mm). But if you say it's made to 'bolt-on', then maybe.

Dave

[Syscrush]

Thanks, gents. I thought that the bushings might go between the pivot bolt and the frame, and couldn't find anything unambiguous that shows where they go.

I have a '79 with the smaller pivot bolt - how much bigger is the '80 bolt? What do you recommend - swapping in an '80 pivot bolt, or having something bigger made up?

[NobleHops]

Thanks, gents. I thought that the bushings might go between the pivot bolt and the frame, and couldn't find anything unambiguous that shows where they go.

I have a '79 with the smaller pivot bolt - how much bigger is the '80 bolt? What do you recommend - swapping in an '80 pivot bolt, or having something bigger made up?

Well the pivot bolt is obviously going to need to mate up with whatever bearing system this thing uses, and so if it was designed for the 79 bike and has needle bearings or bronze bushings sized for 14mm then the path of least resistance is to just stick with your stocker. It just seems to me that you're going to a lot of trouble and expense to stiffen the paltry stock swingarm with this part and you will probably succeed, and thereby moving the torsional loads to the pivot and the frame. I'm no engineer, but that 14mm pivot looks pretty puny to me and Honda evidently determined that was insufficient, having swapped it for the 16mm pivot used on the '80 and the ProLinks.

That's my $.02 and it's probably worth a lot less.

N.

[Syscrush]

That's my $.02 and it's probably worth a lot less.

Setting aside what it's worth, I agree with you. :) The swingarm uses off the shelf bearings and it should be possible to specify either 14mm or 16mm ID needle bearings. I'm going to confirm.

If I did want/need to upgrade to the 16mm pivot bolt:

1. Is there a good source for them, or do I just start calling every one of the usual CBX parts vendors?

2. Does the frame need to be drilled out to take the 16mm bolt?

3. If so, Is it just a matter of drilling, or does some kind of new plug/sleeve need to be welded into the pivot points?

Thanks,
Phil.

[Syscrush]

Found some 800mm long USD Showa Advantage forks. Shown with axial caliper mounts, but once you're at ~$3k for bare forks, some radial caliper bottoms shouldn't be that big a deal...



LINK.

About $2k too much for me, but might be of interest to others here. EDIT: I forgot to note that they're 39mm.