Motorcycle suspension 101.

[Peter_Black]

Today I got into a discussion with a friend over motorcycle suspension. And in the ensuing talk, I figured I might as well put it into proper format and leave it out for anyone to get information. Maybe bring some more traffic to oppo as well.

This started with advice if it is worth getting cartridges for his ninja 400.

Is it worth it really comes down a number of factors.
1: how much money you have floating around. 2: how long do you plan on keeping this bike? And 3: what is the bike going to be used for and more much do you want out of it? For a dude who wants to re-spring his gold wing to carry him, the wife, and luggage and plans on keeping the thing for 20 years, yea, its worth it. For someone who does 2k km a year on a super sports for coffee? Not so much. Now, taking into account my friend, who wants to ride his 400 aggressively take it to the track? I would say that it is worth it. The stock suspension on the bike just isn’t up to the task of road racing, and it should be, it’s a beginner bike!

Now, what are you actually paying for? We have to start with what is suspension. Suspension is a spring to absorb bumps and keep the wheel in touch with the ground, and a damping mechanism to keep it from oscillating constantly. Usually this is done with a fluid (oil or high pressure gas) and some orifices.

So, with that established, what are you actually paying for when you buy aftermarket stuff? Obviously you are paying for different settings (stiffer springs, different valving) but that is hard parts being changed out.

Really you are paying for two things. Rebuild ability and adjustability.

Stuff like high and low speed compression, rebound, preload, ride height, spring rate. These are all settings in a bike (I mention spring rate because of bikes with air suspension, it’s not really a thing anymore). But in a nut shell, more knobs = more better.

I will give you an example of fork emulators and cartridge kits. The emulators will change the setting, but you can NOT adjust them. Once they are in, they are in at that setting. Can’t change it. A lot of the time, this is really all that’s needed, along with a new spring rate for your weight. They are reasonably priced ($190 cad) and solve a lot of issues. Cartridges do the same, but they have the feature of being adjustable. So you don’t have to rebuild the forks to readjust them. They are also way more expensive.

As for the rear shock, not only are you buying adjustability, but you are buying rebuild ability. A lot of OEM rear shocks are not rebuild able. Sure, you can swap springs, but that’s about it. If it blows, it blows, and you are up shit creek without a paddle. Many aftermarket shocks are totally rebuild able and you can change up the valving inside (even with adjustable shocks) to change the range in which it operates.

Now, the reservoirs on rear shocks. Like the forks, the rear shock has a fluid that it uses as a damping agent. As you force it through all of the little passages, it heats up, right? As it heats up, the density and viscosity changes (remember high school thermodynamics?) So we want to take it away from the heat source to cool it down. Hence external reservoirs.

Now, sometimes, you just straight up to not have the space to put in a external res or do not have the performance in mind.(like most budget bikes). So you can have either a remote reservoir or an internal one.

In the above photo we have a WP racing rear shock for my old VFR (high/low speed comp, rebound, ride height and preload adjustable)

The OEM Olhins TTX 36 out of one of my triumphs (compression, rebound, ridge heght and preload adjustable)

and the OEM shock out of my 1992 CBR250rr (preload adjustable only)

You can see just how much more space the reservoir takes up under the bike.

Now, this was meant more as a general break down. different manufacturers will have different tech and patents to sell. Some will be more set for racing, some more for touring, some with off road specialization. For your application, I would suggest going to speak to a suspension specialist.

[Exage03040]

I will also mention that Dave Moss Tuning on YouTube has hundreds of videos on suspension tuning, tires, ergo, controls and all sorts of things track and riding. You have to pay for nitty gritty stuff but the man is doing specific bike set-ups now.

[Rider]

Sometimes your spring compresses fully and high pressure gas is forced out of an orifice. Then it's probably time to upgrade.

[Peter_Black]

@exage03040 oh, yea, his video are very good in individual set ups. this was more of a general: this is how shit works article.

[EssExTee]

My fat ass would bottom out the worn original struts on my Cub when I got it. There aren't really aftermarket struts for it, just OEM replacements so I bought a cheap pair meant for a Harley. Since the Cub's weight + my weight is roughly the same as full size bike, I figured it would be tuned close to correctly. End result is that it rides a bit stiffer than it should but it's still comfortable enough and the suspension travel is what it should be.

[kleebrz]

nice insights!

[nermal]

@peter_black said in Motorcycle suspension 101.:
For your application, I would suggest going to speak to a suspension specialist.

This is the best advice here. Finding a guy that knows wtf he is doing in regards to suspension is invaluable.

As for the rest.... ehhhhhh.... you're missing some bits. A full set of replacement cartridges and shock from somebody like Ohlins or Ktech or Penske have a lot more differences than adjustability and rebuildability relative to stock stuff. You get into things like cavitation (oil gets fuct), stiction (friction that is neither spring nor damper), and heat dissipation. Plus tuning of the valves & shim stack, which is different than turning knobs.

(begin buzzkill)

Realistically, if you're just riding on the road at weenie speeds, the stock stuff is fine. If you're just starting doing track days, the stock stuff is fine. Maybe find a suspension guy there and pay him $40 to adjust your clickers & pre-load. If you've done a few track days and have several thousand $$$ to spend to get faster, keep the stock suspension and go to a legitimate performance riding school (aka YCRS) and learn how to actually ride your motorcycle fast in a controlled environment. Once you've done that, and are actually fast enough to out-ride the stock stuff, then find a suspension guy and upgrade your suspension. Just throwing parts at your bike thinking it will make you faster.... generally won't.

(end buzzkill)

[DaveyD]

@exage03040 Dave Moss is amazing. Came to a local Ducati store in LA a few times to tune people's suspension. Sadly I never made it out there, but getting my Aprilia's suspension tuned was incredible for track/canyon riding.

[orneryduck]

So is he upgrading the Kawasaki?

First things first determine if the springs are right for you, your safety gear, and what you most-often carry. If stock springs are too light, you’ll bottom out forks...

Similar if too firm (rare), the suspension won’t travel the full stroke and your body will have to absorb more forces it could shake off before it got to you. This is all done via some basic math and sag measurements. Set ride height for rider size, hopefully you are 95% of the way there already by picking a bike suitable to your build.

Forks also (in every one I’ve worked on) use an ‘air spring’ In the interior volume, a pocket of compressible air which will dampen the fluid ramp rate. You can fiddle with the amount of air compared to fork oil to adjust initial fork feel. It won’t change spring rates of the coils but can soften or firm up the responsiveness of initial compression/rebound.

Better springs are cheap enough and can be changed at low cost or even DIY, I say it is a worthy investment if your sag numbers are out of wack since rider weight can drastically affect suspension performance if not close to the suspension baseline.

My Triumph Speed Triple was close enough for my weight and had good mid-range components for the period, so I never changed anything, just did maintenance. It served me well over far too many miles, was compliant and handled well for my use case.

In contrast, a close friend is taller, bigger built, but rode a smaller 600cc CBR, he also frequently enjoyed track days. For him, he needed beefier springs to offset the 50lbs delta in his weight and what the bike ‘expects’ as stock, and he wanted better calving/dampening characteristics. The rear was sent off to RaceTech and came back, including a rebuild kit for his front forks and new springs to install while there. It was transformative for him and his ride experience.

[Peter_Black]

@nermal again, this is a very basic break down. 101. thats lessons 102

@orneryduck yea he is upgrading it, he used to have a number of higher end ducatis and what not, just went back to cheap and cheerful. I told him the basics, and go to a proper shop.