Suspension Upgrades

[daves79x]

Dismiss the 1100F swingarm if you wish, but it is about perfect for a modded '79 suspension. About 3/4 in longer axle position, which does not hurt the CBX at all and best part it bolts right on with a custom inner collar made to accept the smaller pivot bolt. No modding to the frame or swingarm at all. But each to his own.

Dave

[EMS]

The reason I didn't consider it, Dave, besides the length, was the cosmetics and the weight. It is made out of steel. And Phil specifically said he wanted an aluminum swingarm.

[Syscrush]

What about rear fender clearance, and the shock eye locations?

I'd like to get that Trac one at that price point, but don't want to effectively reduce the value of the new shocks by messing with the geometry.

BTW - I think that EMS's carb collection is worth more than my motorcycle collection. ;)

[EMS]

The rear fender clearance is no problem. It looks ever so slightly different, but is no issue.
It is smart to consider the shock mount position. I will try to get a measurement of how much further back they sit compared to the stock 80 swingarm.
Theoretically, you would have to use longer shocks to retain the exact same height, but it may also be very little difference. You are planning to use a smaller wheel however, and the combination may be enough to change the rake to have an effect on the front end geometry. Many people do not consider that you indeed do change the rake by raising or lowering the rear axle in relation to the front. As a result, you also change the trail.

But if you consider getting the Trac arm, is their GS product so much cheaper than the CBX part?

[Syscrush]

But if you consider getting the Trac arm, is their GS product so much cheaper than the CBX part?

Still waiting to hear back from them with a quote. They're not replying to email, so I'll probably just give them a call today.

I had a nice long chat with my suspension guy yesterday. He recommends the Ohlins shocks as he has had the best luck with them. He said that the higher-end YSS are built with high-quality components, comparable to Ohlins, but that Ohlins consistently arrive better valved for the intended application. I'm not crazy about the idea of buying a new shock from YSS at about the same price point as the Ohlins and then having to have it rebuilt before it ever goes on the bike.

He also said that swapping fork bottoms across manufacturers is a crapshoot. He's done it, but says he can't know if Showa/GSX-R bottoms will fit onto the WP/KTM forks until getting the parts in hand and trying it. He actually suggested that the Multi forks might be worth considering, and when I told him that they're a very good match for length, he had to go and point out that the S had Ohlins forks... There are a set on ebay right now that I was already kinda lusting after, but they are set up for axial-mount calipers, which is a no-go for me on this project.

He can definitely change the spring rate and change the stop to internally remove travel, but I'm not crazy about how much of the slider would be visible when starting with those long-travel forks.

[Syscrush]

Here is a picture of the Multistrada front end side by side with a modern USD from a ZX-R. From the bottom triple to the axle is not much difference on first sight, but you have to consider that the ZXR forks would need a longer stem, which would move the lower triple down. The Duc stem is almost the same length as the CBX stem, even a tad longer. And there is room to move the tubes down in the trees.

Hmmm... I'm having some trouble figuring this out.

I downloaded profile photos of a Duke 690, SuperDuke 990, and Multistrada, and did measurements using pixel counts. All 3 bikes have 17" wheels, so for each photo I calculated the # of pixels/inch by taking a reference measurement of the front rim, then using that scale I converted the length of the forks in pixels to mm.

Here's what I came up with:

• SuperDuke: 688mm
• Duke 690: 776mm
• Multistrada 1000DS: 730

Of course, these are measurements for the forks with a bit of sag, but with no rider on the sag should be maybe 10mm at most - maybe a bit more on the Multi with its long-travel suspension.

When I checked my CBX forks in person, they measured 830mm - and if your Multi forks are about the same length then I don't understand how my photo measurement is so far off. There will naturally be some error/variance, but what I'm coming up with for the Multi is more than 4" off the CBX.

Do you know which flavor of Multi those came from? Maybe there's another Multi out there with much longer forks than the 1000DS...

[EMS]

Phil: Nobody can accuse you of rushing into things and doing a half-baked job that may or may not yield the right results....

I will make an exact measurement of the CBX and the Ducati fork. How did you measure? From the bottom of the steering neck to the axle?

[Syscrush]

Phil: Nobody can accuse you of rushing into things and doing a half-baked job that may or may not yield the right results....

I will make an exact measurement of the CBX and the Ducati fork. How did you measure? From the bottom of the steering neck to the axle?

I measured from the top of the fork body (so, ignoring the preload adjuster protruding from the top of the Ducati or other modern USD) to the centerline of the axle.

For some further investigation, I just did my photo measurement on a GSX-R750 and came up with 663mm. So my photo approach is telling me that the superbike forks are shorter than the SuperDuke, and that the Duke 690 are longer still. The Multi is between the SD and the 690 - while I expected it to be at least as long as the 690. Incidentally, when I used this method to compare the 3rd generation Duke 690 to the 4th, I came up with identical numbers for the fork length despite the photos being significantly difficult scale - so I am inclined to think that this approach is valid - I just don't know how to relate the results to your real-world measurement and mine.

I did a further experiment, scaling these two images of the 690 and the 1000DS so that the front wheels are the same dia. It looks like the two bikes have similar rake, but the top of the 690's fork is higher than the 1000DS's:



So I'm really interested in your measurement off of the real Multi forks.

[EMS]

Phil: The comparison between forks should be from the seat of the lower neck bearing to the axle considering the same steering stem length for a given frame. This will tell you exactly how much higher or lower the frame will sit.
I will measure tonight!

[Syscrush]

Dismiss the 1100F swingarm if you wish, but it is about perfect for a modded '79 suspension. About 3/4 in longer axle position, which does not hurt the CBX at all and best part it bolts right on with a custom inner collar made to accept the smaller pivot bolt. No modding to the frame or swingarm at all. But each to his own.

Thanks Dave. Sorry I missed this post before - I think that I missed it when one of my replies from the previous page bumped me to a new page.

I would prefer Al, but that box-section steel CB1100F unit does look better than the stock CBX one in my opinion. Given the ease of installation and the low cost, it definitely bears consideration.

What's the story on bearing availability for the CB1100F swinger?

[daves79x]

The bearings for the 1100F swingarm still show as available from Honda. They are the same on both sides. Just to be accurate - is your frame a '79 or '80? Adapting the 1100F arm to a '79 requires either having a new sleeve made to accept the smaller pivot bolt, or drill the frame out 2mm. Otherwise a bolt on with no other mods. For the '80 frame, the pivot bolt is the same size, but you need to remove a bit from the right frame boss so the arm can be centered. No big deal, but not quite bolt-on. I've done both years and they fit and worked well.

Dave

[Syscrush]

The bearings for the 1100F swingarm still show as available from Honda. They are the same on both sides. Just to be accurate - is your frame a '79 or '80? Adapting the 1100F arm to a '79 requires either having a new sleeve made to accept the smaller pivot bolt, or drill the frame out 2mm. Otherwise a bolt on with no other mods. For the '80 frame, the pivot bolt is the same size, but you need to remove a bit from the right frame boss so the arm can be centered. No big deal, but not quite bolt-on. I've done both years and they fit and worked well.

Thanks for the further info.

My bike is a '79. Having that sleeve made up would be a lot more cost-effective than a custom-fabbed swingarm, so this definitely bears serious consideration.

What's the story on the shock eye locations on the CB1100F swinger? Are they closer or farther from the pivot point than the stock CBX ones?

When I asked that about the GS1100 swingarm, EMS rightly pointed out that a big difference there could affect rake, but I'm also concerned about shock geometry changes back there affecting the spring rate.

[Syscrush]

Incidentally, does anyone have ideas about how much the rear can be raised without interfering too much with the chainline and/or anti-squat? I would really like to get the bike sitting a bit higher - I lost some height with the CB1100F wheels, which makes the bike harder to put on the c-stand. Also, I am going to lower the pegs about an inch and so would like a bit of cornering clearance back.

[Syscrush]

I just got off the phone with Trac. They do have the specs for the twin-shock CBX, even though it's not listed in their online catalog. They can do stock length and any desired oversize. Waiting now to hear back with a price.

[daves79x]

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.

Dave