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KTM Suspension – PDS versus Linkage
Do I Need To Buy A New Linkage Bike?
Linkage is newer so it must be better, right?
Here is one of those questions that I wish I had a nickel for every time someone asked about it. Which is better? I would now have a pile of nickels, at least enough to buy a gallon of gas. Nevertheless, it is a great question.
I think I have a handle on the issue, but another rider, in different terrain might come up with something different from I do. KTM doesn’t help the matter much, because no matter how much they try to tell people what is best for a certain type of riding, their pro riders are often doing something completely different.
KTM says that linkage is best for motocross and PDS is the choice for off road riding. In general, the SX and XC lines get linkage while the XCW and EXC retain the PDS system. KTM North America does not race XCW or EXC models, but in Europe, they only race those models.
US riders, particularly the GNCC guys, want the lightest, fastest bike they can get. For the most part, it is so they have the most potent package on the starting line, but part of this is also just image, motocross bikes look more badass than ones with headlights. Therefore, nearly every US racer, east or west, is on a linkage bike. As I write this, the race team is playing musical bikes, trying to get the Dungey replica developed for off road competition. So it is a little hard to keep up with just who is on what bike. Mullins has gone back to the “old” twin cam 450sxf for the time being.
The exception to this is the Husaberg. All Husaberg models are PDS, so Lafferty and Fahringer are link less. I talked with Lafferty about the choices some last fall. He said that he had tested the KTM link bikes and did not feel they were the best choice for enduro. You might have noticed that Mike Brown rode a PDS bike in the Endurocross series last year also. His teammate Taddy used the 350SXF with linkage.
I have been lucky enough to ride and race both, so here are some of my impressions.
The new linkage bikes excel at hitting things way too hard. The first time I hit a big road crossing in the desert on the 350xcf, the bike didn’t even move. That was impressive.
Harsher on smaller hits.
Sort of dead feeling, not as much positive feedback,
Very good at absorbing sharp hits, like square edges, on both the track and trail.
The newest PDS shocks have a far plusher ride.
Keeps the rear tire on the ground better, even over roller whoops,
With the tire on the ground getting traction, it drives the bike forward better.
Still suffers some on the bigger hits.
Just last week I rode the 500xcw on the track alongside the 450sxf. This was on a large natural terrain GP style course. For the most part, the two bikes were very similar. Lap times were nearly identical also. The 500 was less tiring to ride, partly due to the motor, but also because it was a much smoother ride.
There was one section of whoops on the track. On the SXF, I would just hit them straight on in third gear, no problem. If I did the same on the XCW, the rear would get out of shape. What I had to do on the 500 was wheelie into the whoops and then double out over the last two. Basically, I had to ride in a manner that let the rear wheel stay on the ground.
This was indicative of what I found on the 350XCF that I raced last year. You never have to think about how to approach an obstacle, just hit it. This is particularly true on the motocross track. For me the real revelation was square edge holes on a jump face, the linkage bike acts as if they are not even there. That is something the PDS bikes still cannot quite match.
Talking with one of the KTM test riders, he tells me he can dial the PDS in to nearly any situation, but it is much more sensitive to changes in conditions. For example, what works in the morning when the track conditions are moist and smooth, does not work in the afternoon when things dry out and get rough. The linkage is far less sensitive to changing conditions.
The PDS has come quite a ways in the last few years. Last fall I raced my 2007 450xc in a desert race and it was clear how far things have come. The RFS is never as planted feeling and the steering is not as accurate because the bike is moving around so much.
When talking about the positive traits of the linkage, I am talking about riding at full race pace. For anything short of race speed, the PDS wins nearly every time. The strong feedback gives the rider a much better understanding of what is going on out back.
So for the most part, KTM is right about the way they portray the two systems. Linkage is best for moto and cross-country racing where high speed hits are common. PDS is better for most other riding for its smooth ride and ability to handle low speed impacts.
The “high/low” speed refers to shock piston speed, not necessarily bike speed. The faster the shock needs to respond, the better the linkage works because it assists the shock. For low speed sensitivity, the PDS is better because it is controlled strictly by the shock dampening without interference from the progressive link.
For maintenance and durability, I think they are about even. The linkage shock is kind of a pain to get out of the bike, the top subframe bolts need to come out. Also, the exhaust mid pipe will not come out until the shock is loose. The PDS is cool because the shock comes out in seconds. The link arrangement seems to be holding up well. It looks vulnerable to damage, but I have not had any issues and that is with a 200lb rider on the smallish 350. When servicing the PDS it is important to understand how to bleed air out of the system, it takes lots of pressure and not every shop is really set up to do it properly.
For me, the PDS is probably the best choice, but it is almost a push. On the 2012 500xcw, it works very well. I still get a few hits that upset the bike, like big road crossings in the desert. However, I am riding it stock with just a heavier spring. I think that with a little valving help and more set up time it could be almost perfect.