2014 CB1100EX Front Suspension: It’s different

[spacetiger_imp]

I have to confess, I do not have a CB1100EX – yet and am a lurker on the site. I have 7 motorcycles at the moment and until I get a few things sorted out, I may not get one for a couple of years. But, like all lurkers, we have our favorite things to look and follow. Suspensions, brakes and comfort/convince farkles are my favorite.

So the post that started the question: http://cb1100forum.com/forum/showthread.php?tid=7706

I thought I would add my thoughts explaining how I think the EX front suspension works. The spring design layout is similar to the rear suspension on the PC800. On the PC800, the springs on the SHOWA shocks are different from each other. One spring is a dual rate spring on a shock with no preload adjustment and the other spring is a straight linear rate spring on a shock with preload adjustability. In figuring out how the PC800 set up works, you start with evaluating the springs.

Pic 1: Here I have the PC800 nonadjustable shock in one of my gym equipment so I can load up weights and measure how much the shock (spring really) compresses. I keep adding weights until the shock bottoms out.

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%202%20%20spring%20analysis_zpscjdu35qe.jpg.html]

Pic 2: Here I test out the adjustable shock (the test has no additional preload dialed in.

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%203%20%20spring%20analysis_zps4zstrc2b.jpg.html]

Pic 3: Based on the collected data, I can plot and determine the spring rates of each spring (I use Excel to plot and determine the curve fit). You can see Honda matches the spring rates, so the transition point of the nonadjustable spring aligns with the initial preload setting on the adjustable shock.

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%204%20%20spring%20analysis_zpsvfzczewb.jpg.html]

Pic 4: The 2 springs work together to act as a single spring as depicted by the magenta line.

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%205%20%20spring%20analysis_zps6xsl6der.jpg.html]

Pic 5: And so it is with the CB1100 that we find an interesting spring set up. From the good pic in the referenced post, you can see the 2 springs (I call spring A and Spring B). Besides the obvious length difference, you can see that the spacing between the coils is different; each spring has two zones with different coil spacing’s. This suggests each spring is a dual rate spring. With a total of 4 different rates (it is possible rate 1 and rate 2 are the same lb/in rate but for now, I am showing them as different). The 1 difference in the CB1100EX setup over the PC800 is that the adjustable “side” is that the CB1100 has a dual rate spring; the PC800 is a single rate spring.

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%201%20%20spring%20analysis_zpsiyjiztxp.jpg.html]

So how does the suspension work? Simple, one side is the "fixed setup" using a dual rate spring (A spring) and the other side is the adjustable side also using a dual rate spring (B spring). To the total loads the springs will see, the fixed side only handles part of the load, the adjustable side has the stiffer rate spring and is really the bigger load carier. This is the side you make adjustments to to increase or decrease the preload on the spring. To understand whats going on, I’ll use similar graphs to show what is happening as you load up the front suspension.

Pic 6: In this pic I show 2 dual rate springs. For each spring, the lower rate portion of the spring (spring rate 1 and 2) are relatively short. If you go to pic 5, and add up the spaces between coils on the lower rate portion of the spring, the total length might be between 1-2”. Once all those coils are compressed, the spring transitions t the higher rated portion of the spring. The spec working range is 4.2”, so that defines the max capacity of the spring. So for our hypothetical springs, spring A can hold up 248 lbs and spring B can hold up 299 lbs (with no additional preload added; I am guessing Rate 1 = 40 lbs/in, then proportionalized the other rates to rate 1 to get the hypothetical rates.).

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%206%20%20spring%20analysis_zps2pbkkmhy.jpg.html].

Pic 7: Similar to the PC800, the 2 springs combine to give this combined spring curve (magenta line). When you are setting up your suspension, you will make changes to the B side.

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%207%20%20spring%20analysis_zpsoyqt8seu.jpg.html]

Pic 8: Honda always sets the springs for the USA market too soft for our weights, so it is more likely you will need to add additional preload (you will make that long spacer, spacer B, longer). Adding an additional 0.5” will shift spring B curve down 0.5” as shown by the downward red arrow. The transition point is now at 0.5” (versus 1.0”) and adds 33 lbs of capacity at the top end.

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%208%20%20spring%20analysis_zpsimyjzdlw.jpg.html]

Pic 9: The gains made by adding more preload to spring B translate to the new combined spring shown as the change in magenta lines.

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%209%20%20spring%20analysis_zps6zqxia3t.jpg.html]

So, get a ziptie on the fork to check your bike and rider sag points + check how much of the total suspension you are using. If you find you are bottoming out, and need additional capacity, then you will need to make spacer B longer. I suggest you do this in 0.5” additional lengths; you could also try 1” longer length, but it may be too hard for most to get the end cap on. When you go to make your spacer, many riders use PVC piping. It is cheap and easy to use but I would not recommend it because of the CB1100EX suspension design. Here, the B side requires a really long spacer, so you have to start worrying about volume control.
Pic 10: You can see in this comparison between steel (oem spacer material), PVC, and my choice, copper. You can get copper pipe at Home Depot or Lowes for not a lot, so get copper.

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2010%20spring%20analysis_zps6qvaxhvf.jpg.html]

I’ll write about the effect of the air spring if there is interest, but take my word, the oil level is critical in suspension performance. The reference post cites there are 2 different oil levels for the CB1100EX; that is, each fork has a different oil level. When you look at spring A, you can see it is the longer spring. This means the spring takes up more volume in the fork, so that side has a lower oil level. The side with the shorter spring (spring B) takes up less volume, so it will have the higher fill volume. You can see if you put a longer spacer made of PVC in to increase the preload, you would have to reduce the oil fill by the extra volume of the PVC spacer. You would not have to do this with copper pipe. If you mix up the oil levels between the forks or have too much oil (because you used PVC pipe) in the B side, then the fork will not compress very much (worse case) to not all the way (best worse case).

So now you know, the front CB1100EX spring layout isn't used that much, but is a valid means to get a proper spring setup in the suspension. The positive on going this route is you only have to adjust the preload (to set proper sag) on the B side (fork with the shorter spring). And remember to not confuse the oil fill levels and use copper pipe for spacers.

Jerry