Hello,

I joined the XT660Z owner club by buying a 2008 used bike. Suspension need some work, as I was expecting. So i did my homework and checked available options. Lots of them, and no surprise people are always happy when switching from a standard and tired shock to custom setup brand new aftermarket piece

But something is bothering me: ok it will be better, but how much wheel travel will i get after that? The question occured when i saw wilbers website warns "20 mm less travel, not recommand for off road".
Then the cheaper ohlins shock on the OTR website "35 mm less travel".

Ok so i looked for shock travels, either in spec sheets or by asking manufacturer directly, here is what i got:
Ohlins with external reservoir : 94 mm (different websites)
Ohlins without external reservoir: 83mm (found on only one website). Listed at 35mm "less travel than stock" on OTR
TFX: 80 mm (confirmed by manufacturer)
Nitron: 88 mm ((confirmed by manufacturer)

The XTZ service manual says: "shock absorber assembly travel: 95mm", but also "spring stroke: 0-90mm".

Plus TFX told me they had a stock shock in their hands and measured the stroke at... 85mm

So i'm a bit confused: what is really the stock travel? how does shock travel relates to wheel travel (does not seem to be a 1:2 ratio as the 95 mm/200mm may lead to think.. i guess the linkage makes it non linear, so 1:3 ratio near full compression maybe?)

I would guess that much of the discrepancies in shock travel measurements (including OE) are down to how it is measured. Assembly travel of 95mm means that’s how far the shock will move with no spring fitted. Spring stroke means that is how far the spring (on its own) will travel before its coil-bound. Fit the spring to the shock body with the preload ring in its lowest setting and that all makes for about 85mm of travel.

Bear in mind most shocks require a minimum of 5-10mm preload which effectively robs some of the travel as the spring will become coil-bound earlier in its stroke. Some manufacturers allow that in their calculations, yet others quote the theoretical maximum travel. The more preload you add, the less travel the shock will have too. So the softly sprung OE shock may well have 85mm of theoretical travel, but with 25mm of preload added to maintain the correct sag (which I found it needed to have and I’m by no means heavy), its overall travel will actually only be 60mm. An aftermarket shock, let’s say the Wilbers for argument’s sake, correctly sprung to the rider’s weight should require next to no additional preload, so your “20mm less than stock” is actually irrelevant in real life.

I shouldn’t get too hung up on shock travel. Choosing the correct spring rate is a much more important factor in successful suspension setup. After all, you could have a shock with 100mm of travel, but if it’s fitted with low rate spring and needs 50mm of preload to make it work, all that extra travel is pointless. Just remember… any correctly sprung, properly damped aftermarket shock is going to be better than stock item.

You said it yourself...

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Yeah, i'm sure any shock will be an improvment. I just like to understand what I buy, especially at this price point.

I had figured out that the spring stroke can be the limiting factor... just not realized that adding preload has on effect on it too, just like you said !

So ok spec sheet says 95 mm shock stroke, but the spring can only compress to 90 mm, and has a minimum preload of 5mm.

Good.

But then... why are 20mm shorter shocks listed everywhere as "not suitable for off road". Like the Wilbers for instance.

So far, the 1 way Nitron and 3 ways TFX lead the race. At least they are officially listed as "off road recommended", it buys some peace of mind.

But if OTR is wrong and the ohlins YA 054 is really 83 mm (which it seems to be : http://www.ohlins.com/wp-content/upl...2/MI_YA054.pdf) , then it's also a good option.

Thanks for your answer !

There are also options from Hagon, Yacuga and others...

In the end i chose the Wilbers 641 that was sold around 550� by different german reseller on ebay (630� directly at Wilbers). It's surely psychological but i like having a separate reservoir as the stock shock also have one.

Quick test ride yersterday and everything is good