Suspension - opinions on my sag please?

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Jug_Inspector
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Suspension - opinions on my sag please?

Post by Jug_Inspector » Apr 15th, '17, 17:45

2008 990 SuperDuke.

Max Travel: Front 135 mm, Rear 160 mm.

Static sag: Front 17 mm, Rear 28 mm.
Race Sag: Front 47 mm, Rear 37 mm.

So my front is at 34% of travel and my rear is at 23%.

I've read that I should be aiming for Front 35-45mm and Rear 30/35mm, if that is the case then I'm probably close enough already?

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Re: Suspension - opinions on my sag please?

Post by billinom8s » Apr 17th, '17, 07:08

Wouldn't like to say.
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Re: Suspension - opinions on my sag please?

Post by awkwardbydesign » Apr 17th, '17, 22:05

Are you talking about loaded sag? With you sat on the bike? For road use normally about 33%, for track 25%.
http://racetech.com/articles/SuspensionAndSprings.htm" onclick="window.open(this.href);return false; But of course this assumes the spring is right for your weight. I had my shock made for a 11st rider (me) which is probably lighter than most factory springs.

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Re: Suspension - opinions on my sag please?

Post by Jug_Inspector » Apr 24th, '17, 22:46

Yeh, I was told race sag is what you're called loaded sag.

That article was an interesting read. I had never thought about taking a measurement in both directions to normalise the friction of the seals... I'll have to recheck it again sometime. 8)

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Re: Suspension - opinions on my sag please?

Post by awkwardbydesign » Apr 27th, '17, 13:17

As it happens, I just did a trackday with my son last week (his first), and dug out this guide I wrote many years ago, to email to him. It may be of some use to you. Remember to set loaded sag first, and then check unloaded sag.
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Re: Suspension - opinions on my sag please?

Post by billinom8s » Apr 27th, '17, 19:17

That's a pretty useful gauge.
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Re: Suspension - opinions on my sag please?

Post by Jug_Inspector » Apr 28th, '17, 11:38

Just realised that my measurements are backwards, although I clearly wrote "R" and "F" in my pad my other half choose to ignore that and write them in the wrong columns... She's normally a pretty reliable as helper too... :)):

So the up shot of this is that my Front is at 27% and my rear is 29%, which makes better sense.
Problem is that as the rear travel is longer than the front I need to work out if not dropping equally is desireable.

Suspension drops by,
Front / Rear
28mm / 17mm - Static
37mm / 47mm - Race

So the bike is almost at the same level when I'm on her to compared to her being under her own weight - that's good right?
However the rear is 10mm lower when the suspension is at full length, did KTM intend it to be that way I wonder...

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Re: Suspension - opinions on my sag please?

Post by awkwardbydesign » Apr 28th, '17, 15:04

Both of those unladen figures look a litle high. Which suggests you need to fatten up! Or the springing is too strong. I had that with mine, so changed front springs (Maxton, as they were relatively cheap) and had a rear shock (Nitron) built for me. And I avoid progressive front springs, as they are just for a comfy road ride, but a nightmare to set up for "spirited" riding, IME.

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Re: Suspension - opinions on my sag please?

Post by awkwardbydesign » Apr 28th, '17, 15:12

Right, I just googled the specs of the 990 Super Duke. Front travel - 135mm. Rear travel - 160mm. Use those numbers as your base.

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Re: Suspension - opinions on my sag please?

Post by Jug_Inspector » Apr 28th, '17, 16:14

awkwardbydesign wrote:Right, I just googled the specs of the 990 Super Duke. Front travel - 135mm. Rear travel - 160mm. Use those numbers as your base.
Yup, those figures are in my first post and are what I used to calculate my percentage used figures :)

There is some preload on the rear spring, and I suspect on the forks but I haven't counted the turns yet.
The standard preload for the rear is 5mm but mine is at 11mm so I guess I should put her back to standard front & rear and re-test.
BTW I'm probably 95kgs in full gear so I'm no feather weight... :)):

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Re: Suspension - opinions on my sag please?

Post by Jug_Inspector » Apr 28th, '17, 16:22

awkwardbydesign wrote:Both of those unladen figures look a litle high. Which suggests you need to fatten up! Or the springing is too strong.
BTW - How you working that out?

Your guide suggests Front should be 15-25mm (mine is 28) and Rear 5-12mm (mine is 17mm), so that suggests my rear is too soft surely?

But for laden sag Front 25-33% (mine is 27%), Rear 25-33% (mine is 29%), so is nicely in range?

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Re: Suspension - opinions on my sag please?

Post by awkwardbydesign » Apr 28th, '17, 16:57

Jug_Inspector wrote:
awkwardbydesign wrote:Both of those unladen figures look a litle high. Which suggests you need to fatten up! Or the springing is too strong.
BTW - How you working that out?

Your guide suggests Front should be 15-25mm (mine is 28) and Rear 5-12mm (mine is 17mm), so that suggests my rear is too soft surely?

But for laden sag Front 25-33% (mine is 27%), Rear 25-33% (mine is 29%), so is nicely in range?
If you have set the laden sag first, then if unladen sag is too large, spring is too hard. Look at my guide; I know it is counter intuitive, but it means you have had to wind up the preload less than normal because the spring is too hard, so there is less difference between the two settings. Unless I've gone senile, which is a distinct possibility! :)):
Laden sag is reasonable, depending on how and where you ride. A race track is generally smoother than the road, so you don't need as much upward travel for bumps and hollows, but you do need more downward travel for heavy braking. At least that is the theory. Mine is set for track riding, as I can't be bothered to keep changing it, and I don't try as hard on the road so I get away with it. Hopefully! :-ss

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Re: Suspension - opinions on my sag please?

Post by awkwardbydesign » Apr 28th, '17, 17:29

You know what? The more I think about the details, the more I confuse myself! It's a long time since I wrote that guide, and at the time it made sense, but now I am having trouble getting my head round it again. I'm pretty sure the hard/soft spring reason is correct, but please google it for yourself, I'm losing the will to live here! :-\

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Re: Suspension - opinions on my sag please?

Post by Jug_Inspector » Apr 28th, '17, 17:49

lol

It's seems pretty straightforward to me.

Oh hang on.. I was just typing the response and already I'm question my own logic... and the bottle of Singha I've drunk isn't helping either!
I will ponder this further... ;)

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Re: Suspension - opinions on my sag please?

Post by Jug_Inspector » Apr 28th, '17, 17:59

No.. I think I've got it. Here goes...

If you have the perfect spring both static and laden are where they should be.

If you're too heavy you'll need to crank up the preload to put the laden sag back where it should be. In doing so the static gets loads smaller.

If you're too light you need to back off the preload to make it sag more, but in doing so the static sag will get loads larger, which indicates spring is too hard.

Sound good? 8)

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