CB500X Suspension Overhaul

April 2020 - Present

An ongoing project, the inspiration to tear apart a perfectly good 2017 Honda motorcycle came from equal parts determination to push the limits of a well built machine and quarantine boredom. Below are some snippets from the various project reports I've published thus far.
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In this project, my goal is to improve the off-road capabilities of a 2017 CB500X through changes to the suspension setup. I don’t want to use pre-built kits for the 500X (i.e, no Rally Raid), because I’m a glutton for punishment and I also rather enjoy coming up with my own solutions to problems. So instead, I’ll be stealing components from other motorcycles or kits, and finding ways to fit them to the 500X in such a way as to achieve…

Front end travel increased + 50 mm to 190 mm
- (Stock Travel is 140 mm for 2017)
- RR L2 travel adds +30mm to 170mm
Rear travel increase +60 mm to 180mm
- Stock travel is 120 mm for 2017
- RR L2 adds +50mm to 170mm
Net zero reduction in wheelbase (or increase)
19 or 21 inch front wheel
18 inch rear wheel
Improved ground clearance
Wire Spoke wheels
Switchable Front ABS
Total cost within +/- 10% of RR L2 kit

Already, I’m sure that those familiar with the 500X have rolled their eyes nearly into orbit. Plenty of discussion has been had regarding the limitations of CB500X and why the aftermarket options has chosen the specs they have. I hope you'll trust I'm aware that success in all of these metrics may be impossible to achieve without drastic compromises in the bikes' demeanor . Nevertheless, the goals are set with an eye towards turning the 500X into a genuinely formidable ADV machine, and they will be the metrics by which the success of the project is measured...

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This week’s theory work centered around the rear suspension setup, and man was it a doozy. There’s about 18 pages of flawed, or dead ended math in the notebook on my desk, but in the end, I found a fairly straightforward way to model the suspension geometry of a generic Honda ‘pro-link’ setup via an Octave script. It takes in only a few of various suspension components and determines the spring compression and rear suspension stiffness for various movements in the rear wheel. For now, I’ve populated the model with some really rough estimates for these dimensions and generated the following figures.

In particular, its interesting to note that the pro-link suspension setup is naturally inclined to yield progressive results. It can be seen in the first graph that the stiffness of the setup increases pretty significantly throughout the wheel travel, from something like 60 N/m up to 200 N/m or so before it rockets to the moon. In reality the spike at the end would not be seen, since it’s a product of my dimension estimates, and also because if such a spike did exist with the actual dimensions, the wheel would never travel into that range (the spring would reach full compression first). Note also that my rough estimates for the suspension geometry produce a wheel travel of only ~80 mms in this configuration. This was rougher than I thought, but until I can actually get some reliable measurements of the stock suspension, I don’t see a big reason to change it, especially because I can still model the effects of an extended swingarm. Returning to the first graph, the effects of a 3” swingarm extension can be clearly seen. Specifically, we note that wheel travel for a given swingarm angle is intuitively increased. Less intuitively, we note that the suspension becomes less stiff at every point throughout the wheel’s travel. This means that, to achieve the same effective stiffness as the stock bike, a stiffer spring will be required. It remains to be seen if a greater stiffness will be needed. There is still some work to be done before I can settle that decision.

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I’m fairly satisfied that this design is approaching ‘as good as its gonna get’ levels. Raw materials for both sides of the swingarm would likely run me about USD $120 or so (that’s with 6061 aluminum), which I think is pretty reasonable. One or two of these parts may need to be steel, but I’ll deal with that later. I’m honestly not sure if that’s any cheaper than welding as some of you have suggested. Since I can’t weld for anything, I’d end up paying for that job out of pocket. Maybe it’d be cheaper, maybe not. I’ll certainly check before I pull the trigger on anything.

Now, moving on, I’ve got a need to figure out what all is going on between these extenders. That is, I need to find an 18” rear wheel capable of holding up the 430 pounds of the 500X + gear + mods + myself. The weight consideration would tend to point me towards the ADV segment, but unfortunately there’s a pretty significant lack of 18” rears in that market. The Tenere 700’s got one, but its pricy and damn near impossible to find. The KTM 790r has a few options around USD$600, which is better but doesn’t include kush rubbers, bearings, etc. And for those, the depths of the KTM dealer network must be braved. But there may be a cheaper, albeit more labor intensive option yet. Yes the trusty KLR650 (should I have just bought one of those instead?) comes laced on a 17inch rim, but a few trips to the enemy’s forum revealed that some have had good success relacing the hub with an excel rim meant for the KX500. That 18” rim and the spokes should come in under $300 and the cup of KLR rear wheels under $200 runneth over. To top it off, the KLR rear hub seems to be narrower than the 500X’s unit which should give me plenty of room for adapters and spacers and all that unpleasantness. Also, while I don’t have any qualms about this thing becoming a veritable frankenbike, sticking with KLR parts where I can keeps things simpler.