XCa Rear Sag - Confused!

[Ragtop]

Hi all,

Little confused about the sag on my '16 XCa. I understand that sag should be around 30% of the total travel. On the XCa I understand that to be 215x0.3 which is around 65mm.

I initially set the shock to the default config of 9 turns CCW from fully closed, and immediately I had 74mm of sag. I had no luggage on (Triumph pannier rack on though), and a much lighter MTC exhaust. I was wearing my riding gear, but I'm only 63kg/140lbs on a heavy day! Essentially, right at the bottom end of load the bike could ever be expected to carry.

I was surprised to have to wind the preload on a further 5 turns to get to the correct sag - which worries me a little about loading the bike up in the future - I've only got 4 turns left in it. The shock is perfectly smooth and pristine condition. The adjustment moves cleanly with no abnormal resistance. Overall the bike is near showroom condition, and only around 6k miles, so it's not a question of wear & tear in my opinion.

To address any concern that I measured wrong - I put the bike on the centre stand and measured (A) from the axle to a known point on the rear of the bike (a bolt on the grab rail). Dropped the bike off the stand, sat on it and bounced up and down a few times, then got the other half to balance the bike with her shoulder, put my feet on the pegs and she took the measurement (B), then took the delta between A and B. I think that's right?

Like I say, I'm not at all heavy, and I'm not the tallest, so I was anticipating (and hoping) I'd be softening things up a little, and lowering the ride height a little - definitely wasn't expecting to dial it up further. I can't believe someone of 100kg or so could jump on the same bike with a touring load and 4 turns would be enough.

It seems strange that the spring rate could be so light - the bike was meticulously serviced before I got it, and there's no paperwork to suggest the spring has been changed.

Any advice?

[tauzero]

I think the static sag should be quite a bit less than 30% of the suspension travel - that's the rider sag, the difference between the height of the unloaded bike on its wheels and the height of the bike with rider and load on. If you look at https://www.maxtonsuspension.co.uk/downloads/manuals/gp10/6.STATIC%20SAG.pdf, they refer to a static sag of 10mm. Setting static sag to 30% means you've lost 30% of your suspension travel before you've even got on the bike.

[Ragtop]

Thanks for the reply - although I think you may have misinterpreted my post?

I didn't measure static sag at any point - the sag I'm talking about is with me on the bike as you suggest (Rider sag).

I'd understood the 30% should be measured from full extension (measured on centre stand) to bike on the ground with me on it (Laden weight) - which is what I did?

[samsgrandad]

Ragtop you are correct in your assumptions, the rear suspension static sag should be 30% of the total suspension travel on the XC that is 65mm.

Measure first with the back wheel OFF the ground and then with you sitting on the bike in full riding gear, the difference in measurements should be 65mm.

You don't lose 30% of the suspension travel, you need the 30% of, effectively 'downward' travel when you hit potholes or other depressions in the roads.

There are several good guides floating around on the net, one I found was from Bikenet by Andy Ibbot, it's quite an old guide but the theory is still good.

[dasf]

Here is the sag values for my 800 XCA -17 25000 km.

Static sag 60 mm =28% of 215 mm (full travel)
Rider sag 110 mm =51% of 215 mm (full travel). Preload 9. My weight 100 kg.

Had some funny sag values earlier and found there were some oil missing in the reservoir. Easy fix in my post https://www.tiger800.co.uk/index.php/topic,24478.msg303099.html#msg303099

[AvgBear]

In an effort to allay some confusion, if your suspension repeatedly "bottoms" you need more ride height, less sag, or a stronger spring.
(if it doesn't repeatedly "bottom"? -- you may need none of the listed remedies?)
Springs lose their energy in-put when manufactured - sag - over time, use/abuse.
Some springs may be better than others? -- a quality issue.

[AvgBear]

Upon further reflection: I prolly shouldn't've used the term "bottom" to describe maximum compression of the suspension unit (shock). Given the nature of progressive, non-linear, linkage controlled suspension, something more like "soft bottom" may've been more appropriate?
The shock may travel exceeding fast near its compressed length limit -- but, never really hard "bottom"?
The question, then, may become: Would some riders prefer less suspension travel of higher quality over "long travel"..? 

[Ragtop]

Thanks for your replies.

I’ve not had issues with the bike bottoming out. I was only really trying to get to ‘correct’ setup as something to do in lockdown! Perhaps I’m just chasing numbers a little too much.

I’ve decided to go back to the stock setup and run with slightly more rider sag than the 30%/65mm - from searching here it seems a lot of people have closer to 70-75mm so I’m just chalking it up to the Tiger being a ‘comfortable’ bike. Come summer when I’m allowed to get it out onto some lumpy stuff I’ll reevaulate!