OEM Suspension on your bike

[SSR Suspension]

In this blog I shall highlight some of the key types of suspension found on OEM Road Bikes. I intend to keep this composed in a simple way so that people can grasp a basic understanding rather than an in depth explanation of how the different systems work.

Lets start with Forks.

Composition of a fork. Forks are made up of essentially 6 main components, these are of an inner tube (stanchion) and an outer tube known to most as the outer fork but its official name is actually a Slide Tube, we also have the internal cartridge (of which there are various designs) the spring, bushes (which provide a bearing surface) and the seals.

Springs are the first part of the equation, damping is the second. If we had just springs, it would be ugly. Every time the wheel hit a bump, it would compress the suspension. The spring temporarily stores up this energy but wants to release it as soon as possible, so it tries to extend—or rebound—pushing the front wheel away from the bike. But it will overshoot, and the suspension will continue in this up-down cycle for a surprisingly long time before settling down. Of course, real roads have more than one bump, so this theoretical, damperless suspension would never settle down and never reach true equilibrium.

Springs come in a variety of rates and three main styles. The first is called a straight-rate spring which is important to us in the bike world. Its coils are equally spaced and it compresses in a linear fashion. Let’s say you have a 1.0kg/mm spring. It takes one kilogram to compress it one millimeter. It takes another kilogram (two total) to compress it the second millimeter (two total). This holds true through the spring’s entire useful travel, so that 50mm of movement requires 50kg. Then there’s the progressive option, this kind of spring is wound with its coils closer together on one end than the other. As the spring compresses, the close-wound coils eventually touch and take themselves out of the equation. The spring rate starts out light and becomes—you guessed it—progressively stiffer.

The springs found on OEM bikes vary hugely, some are progressive, some are linear. Progressive springs are not the best solution for those that want to obtain the best from your bike, no matter what you may read elsewhere.

We have mechanisms that create a very specific kind of resistance to suspension movement, called damping. Typically, these systems use oil—generally very light oil compared to what’s in the engine—forced through some kind of restriction.

A damping-rod fork is a common comodity on so many bikes not only from the late 70's and Early 80's but also modern bikes, in which the damping action comes solely from oil being pushed around inside the fork and through sets of comparatively small holes. The big problem with a damping-rod fork are that they can be soft and underdamped during low-speed movement but suddenly turn harsh over the small stuff. This is because oil forced through a fixed-size hole offers resistance related to its velocity. When the oil is barely moving, there’s little resistance. But try to force it quickly through a small hole and the resistance shoots way up.

A list of some modern bikes fitted with damper rod forks are; Yamaha XSR 700, Honda CBR 500 R, Kawasaki Ninja 650R. These bikes are all less than 6 years old yet use fork technology from the 80's!

Damping rod forks generally do not provide any adjustability, but some models do offer a crude form of rebound damping adjustment.

The technology that has superseded the damping-rod fork in sportbikes and some road bikes is called a cartridge fork. One or both fork legs carry a small cylinder inside the lower section that is, basically, an open-chamber shock absorber. A piston slides through this cartridge, which is submerged in the fork oil. Small, flat metal discs called shims are stacked on top of the piston. As the suspension moves, the piston is forced through the oil, which in turn forces the shim away from the piston face. The thickness and diameter of the shim determines how much force is required to move it out of the way, and therefore how much damping you get. These shims can be fine-tuned to offer resistance even at low suspension speeds—needed to keep the chassis on an even keel—but also “blow off” sufficiently to allow the wheels to move rapidly in response to sharp bumps. The best of both worlds. In theory, anyway.

With the advent of the manufacturers wanting production costs minimised even the cartridge forks fitted to modern bikes are being made substandard. It is not uncommon to now find only 1 damping cartridge in a pair of forks with the 2nd fork only containing a spring. Why? Only half the set of pistons and shims, when your producing tens of thousands of components that is one heck of a financial saving.

So do all forks come with adjustable suspension? No, even when you have a cartridge style fork the design of many suspension components on non sportsbike applications is one of limited adjustability. The reason? Refer to the above statement!

A list of some of the variants found on modern motorcycle forks;

Damper rod fork, no adjustability.
Damper rod fork, adjustable for preload.
Damper rod fork adjustable for preload and rebound damping.

Cartridge fork, adjustable for preload, rebound damping in one leg, compression damping in alternate leg.
Cartridge fork, adjustable for preload in one leg, rebound/compression damping in alternate leg.
Cartridge fork, adjustable for preload, compression and rebound in both legs.
Cartridge fork, adjustable for preload and rebound damping in both legs.
Cartridge fork, adjustable for preload only.
Cartridge fork, non adjustable.

So as you can see, there is actually a huge variance in the genetic make up of a motorcycle fork and it all comes down to how much money the manufaturer wanted to invest at the time, do not be fooled into thinking that just because you spunked 15K on an all singing all dancing bike that the suspension is going to be top notch, even on a sportsbike!

So thats the front end discussed, what about the rear?

The shock will come in 2 main styles, a monoshock or a reservoir shock. A Monoshock is a single piece bodied shock, it may sometimes be an emulsion shock (typical on cars but not so much so on bikes) or a monoshock with a dividing piston. The difference is that whilst both shocks are charged with a Nitrogen fill, an emulsion shock has no physical division between the shock fluid and the gas. A monoshock with a dividing piston will have a piston which seperates the gas chamber from the fluid, when the fluid is displaced due to the shock being compressed the fluid will push against the piston and force it to move against the gas chamber. It is the gas charge which then reacts and pushes back against the opposite side of the piston and pushes the fluid back, so think of this as a gas spring.

Mono shocks are adjustable for rebound damping only, however even more budget versions of a mono shock exist such as found on certain versions of a Triumph Street Triple have no damping adjustment at all.

The reservoir shock is the 2nd type of shock and predminantly found on higher end bikes/sports bikes. Like the dividing piston monoshock the reservoir contains a piston or a rubber bladder, the piston divides the gas chamber from the oil and works exactly the same as described above. The bladder style shock sits within the reservoir surrounded by the shock fluid and is filled with a fill of Nitrogen, when the fluid is displaced and fills the reservoir it squishes the bladder and the gas fill acts like a spring and pushes back against the fluid, thus forcing the fluid back into the shocks main body. The benefit of a reservoir shock is that they have a compression damping circuit adjuster built into them, this gives them more adjustability and theoretically provide a higher performance due to the increased adjustment.

Reservoir shocks have adjustable damping for both the rebound circuit and the compression circuit.

Again, like forks, it comes down to manufacturer budgets, specs and design brief. Remember the suspension is outsourced to one of the suspension brands that supply OEM Bikes, these predominantly being Showa, KYB, SOQI or Marzocchi. I have deliberatley left out OEM Bikes clad with Ohlins suspension as that is a discussion for another day, all I will say is there are differences between what you find on an OEM bike clad with Ohlins compared to the R&T Spec Ohlins you would purchase aftermarket from myself or an Ohlins dealer.

[Mr Moofo]

Hi SSR suspension
I own a Diavel - which for Ducati, came with awful suspension. The rear was way too soft and bottomed out all the time ( maybe okay for a 60kg Italian bike jockey) and the forks seems to be basically solid ( at the time I was 125kg - and ran them with compression damping dialled to minimum)

They were common issues - some learn to live with them - but I went down the K-Tech internals for the forks and a Nitron rear shock. It has made a huge difference.

One caveat - when the suspension was changed over for me , they didn’t adjust the preload. The bike had rare odd turn in characteristics. In realising what had happened ( after 3 years ) - and then adjusting the static sag - it became a surpringly good handling bike - for one with such a big back tyre.

The point of the post, is that I never fully understand why the standard suspension on many bikes is so awful (cost, I guess) - but how KTM seem to have it well sussed. Surely, they want to sell bikes that work for those who buy them - rather than help fund the aftermarket industry.

Here is the 64k dollar question - should I have taken my Diavel to someone like you, and you could have transformed the OEM suspension with a few tweaks here and there? so I in fact wasted money and was seduced by the aftermarket offerings ( and Diavel bulletin boards)
Or do some bikes just have rubbish suspension out of the box?

[SSR Suspension]

Mr Moofa, I know the Diavel well. I have set many of these up with no real complaints about the stock Marzocchi suspension from my recollection and they actually dialled in quite well for a stock bike, I am actually surprised it came as well specced as it did. They are notoriously undersprung in both the fork and the shock, If I recall the fork spring rate was 6.6N and I do not recall the shock rate. Bearing in mind that for an average 80kg rider the spring rates should be somewhere like 9.5N in the fork and 75N in the rear.

KTM, what makes you think that KTM comes with good Suspension, yes it comes with WP branded Suspension but alot of the WP Suspension requires a lot of work to get to work well. The Xplor forks come on many models in the KTM range and are not a very good fork at all and do not work with the new Xplor shock having been changed and not neccesarily for the better, they ideally need a revalve and bladder conversion along correct springs for riders weight. All KTM bikes come with WP Suspension because WP Performance Systems is wholly owned by Stefan Pierer's Cross Industries, which controls more than 50 percent of KTM.

Setup and sags is something that I will go into at a later point in a seperate thread, but does Rider Sag matter? Yes it does, does static sag matter? Static sag or free sag is a measurement of the motorcycle laden under its own weight only. Rider Sag is far more important initially than static sag but I will not go into that here. Your caveat is relative to the dynamic geometry which is affected due to change in sags/preloads/spring rates.

As for is all stock suspension substandard, is it all worth throwing in the bin? No, but it is far from optimised either and in many cases can be improved hugely over stock but this does require financial investment. Many times alot of people change settings on their bike assuming it will make things better when in fact sometimes it actually makes things worse.

The K-Tech cartridge kit is superior to the stock Diavel internals, but aftermarket kit always will be and yes they do a range of springs and having the appropriate spring for your weight really does matter.

It is always worth having your motorcycle setup, if it has the required adjustability to do so before you spend money on aftermarket kit https://www.ssr-suspension.uk/motorcycl ... sion-setup

I also have to mention that service shedules are vital again another topic worthy of its own thread, but I can put money that most people do not bother with having their shock serviced and do not get their forks serviced properly!

You certainly did not waste your money, the bike is undersprung, your performance you have in that fork would never have been reached in the stock fork. So I guess my answer in truth is that if you have the money then do invest in good internals and at least a basic but branded quality shock, but do know that a simple spring rate change can provide an intermediate solution and should be your priority if your bike is under or over sprung for your weight, the benefits to grip are ten fold.

Lastly yes it is all about costs, manufacturers make a bike for the masses with the sole intention to make money, the cheaper they can build it the more they make.

[Mr Moofo]

The comments about KTM refers to when I was living in the Alps and doing a load of passes on a KTM 950 SM ... which was just brilliant. Maybe I was just lucky. The BMW GS Adv I also had at the time had std suspension on - which over heated all the time - esp two up and high altitude. Fortunately an Ohlins rear shock sorted that. That said , I loved the front suspension feel!.

[mangocrazy]

Hi Mark,

I have a 2017 KTM Duke 690R with the 'uprated' WP suspension compared to the base (non-R) model.What's your opinion of the suspenders on this bike? The forks have compression damping in one leg and rebound in the other. Is this just a cost-saving exercise or does it work well? One thing I do notice is that there is around 30mm of unused travel on the forks, which I find puzzling, especially as the R model has an extra 15mm of travel F & R compared to the base model. Is this just to raise rde height? Also, the forks lack any external preload adjustment, which I also find odd.

The shock is a multi-adjustable item, hi/lo compression, rebound and preload all adjustable. I'm pretty impressed with the shock - it feels like a quality item. My only gripe is that it doesn't seem possible to find a hydraulic preload adjuster to fit the shock.

Interested to hear your thoughts.

Graham

[SSR Suspension]

Hi Graham,

Any suspension requires to be sprung for your weight above all else. The standard Duke 690 has non adjustable forks with the same internals and a monoshock.

The forks being non adjustable for preload is not unusual and like the damping in alternate legs is a cost saving exercise and nothing else (this is common on off road suspension). The stock forks can be quite harsh, as it stands I only know of 2 upgrades for this fork and both are Full blown fully adjustable cartridge kits.

The stock shock is a reservoir shock, it is normal for WP to put a High speed compression circuit adjuster on their shocks because the design is used in other applications so no need to design something new, I have only seen the WP Monoshock on the 690 and have not had my hands on the R spec shock, it certainly would not require replacement.

The 690 Duke has a lower seat (at 835mm, 30mm less than the R) and shorter suspension travel (at 135mm, 15mm shorter than the R), Suspension travel being 15mm longer than the non-R version will mean that the forks and shock are longer contributing to the increased ride height. Why have extra travel? Helps with comfort amongst other things, although for a road bike do need 150mm of travel? Possibly not.

[Skub]

Hi Mark,I've enjoyed reading your very informed opinion regarding suspension,getting a bike the way I want it has always been a top priority of mine.

This year I bought a Kawasaki Z1000R performance edition,it comes with big piston forks,preload on the left,rebound and compression damping on the right. This is something new for me and I remain unconvinced it's a step forward!

What I find so far is difficulty in achieving a compromise setting for the road. I can have the forks set soft and comfortable for our rubbish roads,but for more spirited riding all the travel is used up and an apparent lack of rebound means I'm always fighting the running wide on exit.

If I set the forks up for the faster rides,then they are very harsh for normal riding.

The rear Ohlins while not up there with a proper aftermarket item has settled quite nicely. It was very stiff from new,but around 2k + it has mellowed a little.

The rear will probably do me,but I'd be interested on your thoughts on the forks.

[mangocrazy]

Hi Mark,

Thanks for the very quick reply - it certainly confirms my suspicions.

I'd be very interested to hear what upgrades are available for my forks, they are the WP 4357 ROTA Split model. The standard 690 has 4357 forks (according to the manual) but they are non-adjustable and have 15mm less travel, as you know. I'm aware of an Andreani cartridge kit for the base 690, but wonder whether this would fit the 'R' forks.

The rear shock (a WP 4618) has been revalved and re-sprung by Gareth at Reactive Suspension. It came fitted with a 7.5 N/mm spring, but we've gone to the 'soft' option - a 7.0 N/mm spring. I'm now very happy with the shock and need to get the forks similarly improved. From what I can gather it's one of WP's race shocks designed before all the experienced WP guys left.

I'm definitely not a fan of overly firm suspension - give me compliance any day. It's ironic that the R has more suspension travel than the base model but probably uses less of it due to the firmer suspension setup. Spring rate on the R forks is 0.65 N/mm, and on the base model is 0.6 N/MM. I've been toying with the idea of increasing the air gap to see if I can make the forks more compliant, but suspect that full replacement might be the best approach. The manual gives the 'air chamber length' (which I presume is the air gap) as 80mm +/- 20mm, so not sure what that tells me. Gareth was pretty scathing about modern WP fork design when I spoke to him.

Any pointers and options you can offer will be gratefully received.

Graham

[SSR Suspension]

There will be nothing wrong with our shock if Gareth has reworked it-did you bother with a sag setup?

As for increased stroke and a firmer setup. The amount the suspension stroke used is relative to the load placed on it the strength of the spring, how much preload it has alongside how heavy the rider is, how fast he is riding and the topography or where the rider is riding. Again a reason people should consider having their suspension setup for their weight/application.

Real World Example - BSB Rider Yamaha R6 SS600 Class, Fork spring rate 9.5N/mm, 8mm installed preload base setting. Rider bottomed out fork.
Fork Spring rate 9.5N/mm, 12mm installed preload, +4mm was added in the pits mid session, Rider had 12mm stroke left.

So for the rider at the same pace, on the same circuit in the same conditions, the rider required an additional 4mm of support to have a fork with the proportinate amount of support required.

Now move to Sntterton, same rider and same bike. 9.5N/mm 8mm installed preload base setting, rider could not use the last 30mm of stroke even under maximum braking. Swapped to 9.0N/mm with 10mm of preload and we were exactly where we wanted to be with the fastest bike in class.

Your air gap is only going to effect the last 1/3 of the stroke and how progressive that portion of the stroke is, less air gap (more oil) means increased progression and more resistance to bottom out. More air gap (less fluid)means less progression and less resistance to bottom out.

Andreani do not produce the Misano Evo Cartridge kit for the R Spec currently.

ROTA is just an acronym for the fork cap, it means road/race top adjuster. WP have 6 acronyms, which helps to identify their forks.

[weeksy]

Without being too obtuse I hope, we're not talking BSB riders or levels of performance in 98% of requirements though.

Surely even though things can be made better, there's BSB better and there's 1mph quicker round the left hander that leads to the bypass in the A4074.

[Mr Moofo]

Without being too obtuse I hope, we're not talking BSB riders or levels of performance in 98% of requirements though.

Surely even though things can be made better, there's BSB better and there's 1mph quicker round the left hander that leads to the bypass in the A4074.

TBH, I was settling for handling better around the roundabout in the centre of Billingshurst ...

[mangocrazy]

Hi Mark,

Thanks again for a very detailed reply. The points about how suspension setup differs so markedly with the same bike and same rider at two different circuits is very revealing.

Shame about the Andreani kit - I rather thought that might be the case.

Once Covid-19 is less of an issue and better weather is here, I'll be booking in for a sag/suspension setup with you. I didn't take the bike to Gareth, just sent him the shock. He was quite clear that he wasn't interested in trying to fix the forks...

Graham

[SSR Suspension]

Ref the Z1000R, the forks are a Big Piston Fork, however to save money guess what???

Yep they used one fork for the spring and the other for damping, halving their cost of the concventional Big Piston Fork.

A few issues with the Showa Big Piston Fork are that the stock bottom-out mechanism is short and abrupt, the top out spring is long and soft with oversize, yet very restrictive, pistons hence they do not work well especially when pushed hard.

There are currently no upgrades for that bike with that fork, however that is something I can resolve should you wish to invest in a Cartridge kit upgrade, it would mean you have the first K-Tech cartridge kit in world for that bike. I do not think you would want to part with the bike afterwards though!

email me if seriously interested.

[Skub]

Thanks Mark,email sent.