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

[Elipten_imp]

Excellent explanation and thanks for taking the time. More please on the air spring. I hunger for knowledge.


2014 CB1100 DLX
2013 CB1100 Std
1990 BMW K75 RT

[Cormanus]

Thank you spacetiger. I'm not sure how much of that I really understood, but I found it fascinatng.

[curlyjoe_imp]

Very interesting. Thanks for posting spacetiger!

[Paulb_imp]

Very interesting and amazing detail. Just one point I noticed which is confusing, the fork tops both have preload adjustment and Honda ask owners to ensure that exactly the same adjustment is made on each.

[spacetiger_imp]

Very interesting and amazing detail. Just one point I noticed which is confusing, the fork tops both have preload adjustment and Honda ask owners to ensure that exactly the same adjustment is made on each.

Paul,

was a notice for Std riders or both the Std and EX owners? I could see it applying to the std riders since they have the same fork set up on each side. The EX riders have a different set up, so if you added 0.5" to one side, you would add a different amount to the other.

That said, I don't think it makes a significant difference if one was different from the other unless you figured out a way to add 2 extra inches to the preload spacer and you added it to the stiffer side.

Does the EX model have a fork brace of some sorts? It might just be a curved metal plate under the fender. On some Honda bikes, like the ST1100, that utilizes a different damping functionality in each fork leg, you should have something the ties the fork lowers together. It seems with the EX fork internal differences, they would have added a [stonger] brace to keep the forks working in unison.

For the other guys, thanks for the kind words.

Now for the air spring.

Theory
If you could imagine the fork as an enclosed tube with a fixed air volume, then you can start to appreciate the air spring affect. At sea level, the atmospheric pressure is 14.7 lbs/in^2. If you could imagine the tube filled with the damping rod, spring, spacer, and oil taking up all of the volume except the last 6" from the top. Now, if you compress the fork so the air volume is 1/2 of what it was (3" from the top), then the air pressure doubles to 29.4 lbs/in. Now compress the fork another 1.5" (half of 3") and you find the air pressure doubles again from 29.4 to 49.8 lbs/in. Then squeeze it another .75" and the pressure goes to 99.6 lbs/in. squeeze it 0.375" and the pressure doubles again to 199.2 lbs/in^2.You can see at some point the air pressure gets to the point you may not be able to fully compress the fork.

I'll post more info at halftime of the NCAA championship game.

Jerry

[spacetiger_imp]

So I have done a few front suspensions before diving in on the 2014 HD XL1200T. I was looking at stretching the front and rear suspensions, getting the spring rates right for solo riding and lastly getting the damping sorted out. I got the rear sorted out first, then switched my attention to the front.

Pic 1: In testing the front, I found it had really weak springs, a surprise. I also verified the working range of the right fork, 3.63”

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2011%20spring%20analysis_zpslamqhzpv.jpg.html]

Pic 2: Then I got into a good discussion on another web site (caters to sportsters) on spring rates. I wanted to run a higher rate spring. The thing about linear rate RaceTech springs, the stiffer the rate, the shorter the spring. In the pic you see the oem 40 lb/in spring vs the 56 lb/in (I think) spring. I had a RaceTech emulator left over from a GL650 project, so it was going in the 39mm Showa fork too. You can see the parallel magenta lines from the damper rod to the folk lower. These are reference lines to depict how high up in the fork the damper rod sits. That got me to thinking how much over the top of the damper rod the oil level is set. Per factory specs, the oil level is more than 7” above the damper rod. This told me the oil level is not set for damping purposes but to set the overall spring rate. This ment I could play with the oil level to try and get as linear a rate “spring” in the front suspension.

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2014%20spring%20analysis_zpsjquxvdvu.jpg.html]

Pic 3: Here is the result of testing with water. I put all the components in the fork then fill the fork with water. Then, I pour out all the water and measure the water converting the water weight to volume. You can see the max volume in the fork is 16.3 oz. Now, I flll the fork with water to the spec limit, then pour the water out, weigh and convert to volume. Based on my testing, I can see with the factory spring and proper oil level, the oil volume is 70% of the max volume. I collected other fill heights and calculate the fill volume. With the multiple data points, you can build a curve to help figure out how much less oil I can run.

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2012%20spring%20analysis_zpslknl8160.jpg.html]

Pic 4: Back to testing. I assemble the fork with just the spring and check for spring only capability (brown dotted line). Then I add the factory oil (water really) level and test for capacity (green line). You can see adding the oil increases the max capacity from 214 lbs to 270 lbs (66 lb increase!). In fact the green curve tells you the spring is going to behave like a progressive spring (there is no reason to buy a progressive spring when oil makes you linear rate spring act like one). Now, I add to the 76% oil fill (only 1” higher fill over factory levels) and you can see the fork is not going to fully compress (will never compress 3.63”).

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2015%20spring%20analysis_zpsc8cstg3a.jpg.html]

Pic 5. Here is the pic of the fork testing. In pic 1 above, the fork easily compressed with 225 lbs. IN this pic, 385 lbs will not fully compress the fork

[url=http://s93.photobucket.com/user/spacetiger81/media/CB1100/1.%20%2013%20spring%20analysis_zpseplekpsc.jpg.html]

So I learned you CAN use a higher rated spring if you back off the oil a bit. The short spring allows you to run a lower oil level which reduces the air spring affect. This netted a more linear spring rate which helps you dial in the suspension easier and makes the bike easier to ride more aggressive because the suspension is more linear and easy to predict what the bike is going to do.

Clear as mud right?

Jerry

[rboe]

Very interesting. Quite nice to have the weight setup so you can static test the forks. Sweet!