One of the questions I get a lot at MRP is “ Which rear shock should I buy? Ohlins TTX or K-Tech DDS”. While some customers just want someone to tell them which is the best shock, others may be looking for the specific differences so they can decide for themselves. Information about features typically come from many sources. Some spend a lot of time researching online and can’t make light of what their reading or maybe they have been talking to their buddies and are getting conflicting differences, or they have overheard conversations in the paddock and don’t know which opinion to believe. Whatever the reason it is good to have an understanding of what makes each brand/design different over the other. One thing is for sure, all shock brands we sell work great. period. You cannot go wrong with any of them so long as you have it setup correctly for your intended use and riding style. So how do you decide which one you should invest your hard earned money on to propel you to the top of your riding game? I hope to help you answer that questions for two of our most popular brands.
Ohlins TTX GP and K-Tech DDS Pro. Both these companies, Ohlins and K-Tech, produce a twin tube technology shock that is the top-level shock absorber available to street riders, track day enthusiast and racers. While both shocks have a similar build design, I hope to outline the differences on these two models and give you a better understanding of their different features and help you decide which is the right one for you.
While not getting too specific for this article, both these shocks include these common features.
Twin tube technology – The shock body has an inner and outer tube. The shock piston is solid and pushes fluid through valves that are held in the head of the shock. This allows a lower nitrogen pressure to resist inconsistent damping while also allowing for a plusher feel than a standard De Carbon style shock.
External damping adjusters – Both brand shocks have external damping adjusters that restrict the flow of oil. These adjusters slow the movement of the damper shaft from when it compresses and when it extends. The farther you turn the adjuster in, clockwise, the more force it takes to compress the shock or the more you would have to pull on the shock shaft to extend it.
Remote preload adjuster – Both brand shocks have a remote preload adjuster. On some models this remote preload adjuster is mounted at the end of a hose which is typically mounted to the subframe for ease of access. To save a little weight, and crash worthiness, some of these shocks lose the hose mounted on the subframe. The preload is then adjusted using a standard 8mm or 10mm socket and ratchet right on the preload adjuster. This adjustment is located on top of the spring on the shock body. Both designs easily adjust spring preload without breaking your knuckles using a spanner wrench, that always seems to slip off.
Ride height adjustment – Both brand shocks come standard with a ride height adjuster. This adjuster is located on the bottom of the shock. It is usually on the end of shock attached to the linkage and allows a predetermined range of lengthening or shortening the shock from OEM shock length.
Now let’s take a look at what are different between the two awesome shocks and why you might choose one or the other.
Shock Head – Ohlins uses a forged aluminum cylinder head, the topmost part of the shock, that contains the valves (where the damping is created) and where the shock mounts to the frame. I had originally thought these were cast units, until I was corrected in the actual manufacturing process they use. (Suspension technician, not material scientist).
The forged process makes the overall shape of the shocks head. Then critical surfaces are machined, threads, passages, etc. to allow other parts to be bolted in or pressed in. Ie. head bearing, valve bodies, etc. K-tech on the other hand uses a block of billet aluminum and then machines, removing material, to get the entire final shape of the shock head. Which process is better and why manufactures choose between them is debatable. The reason for choosing a forged part over a billet machined part or vise versa are related to manufacture cost, end-user requirements/needs, and selling price.
As a rider, purchasing a shock, all you should care about is which provides better feel, better grip, and better control. So, which one does this? For most of us mere mortals it doesn’t really matter which cylinder head type the shock has. We are never going to be able to tell a difference whether the head is forged or machined from a solid chunk of aluminum. In general, forged parts tend to be stronger than a regular billet part of the same alloy, since the material is forced into shape.
“The forging process can produce parts with superb mechanical properties with minimum waste. The basic concept is that the original metal is plastically deformed to the desired geometric shape—giving it higher fatigue resistance and strength.” (https://www.reliance-foundry.com/blog/forging)
The unknown to me is the alloy each company is using, which will factor into the head design strength, along with edge radiuses, gland clearances, etc. If you want to dive deeper into the strengths of materials and which is better, visit your local library or for some extensive, very mind-numbing, detail testing has been done by NASA which is available at https://ntrs.nasa.gov/
Damping adjusters – Both the Ohlins TTX GP and K-tech DDS have external adjusters to change the damping characteristics of their shock absorbers. They are not the same and do not act similar in adjustments. K-tech even gives you one extra adjuster on the DDS that is not supplied, or an optional adjuster, on the Ohlins unit. Just cause the Ohlins unit has one less damping adjuster does not mean it’s lacking in adjustability. In my experienced opinion the Ohlins TTX GP has the best damping adjusters that I have seen. You see, in most practice, those external adjusters are tapered needles 5 to 10 degree that as you screw in, they close off a hole that fluid flows through. The Ohlins TTX GP doesn’t use a regular tapered needle like most shocks. It has what they call a blade needle. While it does regulate flow through a hole like a needle, it is not a needle shape at all. The shape, while very hard to describe in words, is similar to a round rod with two half moon slices taken out of it. There are a couple reasons why Ohlins designed this new needle and the shape is definitely interesting.
The difference between the normal tapered needle and this blade adjuster is that as you screw a tapered needle into its seat, making adjustments closer to the zero position or fully closed, the change in damping force is more than when the needle is further out. A better way to understand this is to think of an adjuster that is at 15 clicks out. You move the adjuster in 3 clicks and are now at 12 clicks out. By changing this setting the shock now takes 40lbs (and arbitrary number for simplicity) more force to compress or extend the shaft. Alternatively, if your adjuster is at 6 clicks out and you move the adjuster the same 3 clicks, to end at 3clicks out, this same 3 click change will cause a different amount of force to compress or extend the shock. If we measured it, it might take 70 lbs of force to compress or extend the shock shaft. Weird huh? It has to do with the percentage of open space the needle consumes in the bore. In general, the closer to zero or fully closed, 1 click has a higher percentage of force change. This phenomenon might not matter to most, but if you are fine tuning a setup for a rider and need finer adjustment, this can make all the difference. The Ohlins blade adjuster does not exhibit this issue. The force adjustment, using arbitrary numbers like above, is the same 35lbs for force change from 1 to 2 clicks out from zero as it is from 15 to 16 clicks out. All those individual clicks are each changing just 35 lbs of force.
Third adjuster- The K-Tech DDS does give you an extra adjuster that they call the bypass adjuster. This adjuster is typically located on the top of the shock head, but sometimes on the side. This adjuster affects very slow speed shaft movements, 0 to 0.5 in/sec. While there are many circumstances where you would want to use this adjuster, it typically works best to adjust for small inconsistencies in pavement and/or geometry and pitch control. This area is typically found in or around the apex of a corner. Most riders will notice a difference in “feel” with the ground or a bike that feels “looser” or “tighter”. While Ohlins does not have this as an external adjuster on their shock, you can make this change internally and it would produce the same effect. The downside is the shock would have to be removed from the bike, disassembled, reassembled, and re installed on the bike. Not a process you want to go through when testing in a 20 min free practice.
We could continue to go on about other subtle differences, inner tube material, oil viscosity used, initial valve spec, and so on. However, these three differences, cylinder head, adjuster design, and bypass are three permanent differences that we cannot change while servicing your shock. Case in point, if you thought the K-Tech oil was better than the Ohins oil (cause a buddy said it lasted longer) we could switch your Ohlins over to the K-Tech oil and change the valving to be “almost” identical to what it was on the Ohlins oil. We cannot machine you a new cylinder head from billet to run on your Ohlins or put an Ohlins adjuster in your K-Tech shock. These changes are not normally feasible. Of course, don’t get me wrong, if someone wants to pay the astronomical price to have a machine shop make an Ohlins cylinder head out of billet, I would be happy to sell you that job, but that’s just not practical. If you think a billet cylinder head is what’s going to make the difference in you winning a race or beating your buddy in a street race, buy a K-Tech shock. If you want a shock with a broad finite range on their compression and rebound adjuster, then buy the Ohlins. Either shock is going to give you the tools you need, it’s just a matter of what’s most important to you. End of story.