Rear suspension sag.

[Ed_Lorca]

Hi everyone.

I bought a 2013 GG txt 300 with the sachs rear shock.  When I stand on it weighing 207lbs, the bike sags 3" and the pegs.  When my 133lb wife stands on the bike the pegs are 2.5" down.  One of my friends who weighs like 155 sags 2" on his bike.  I know sus is supposed to be very soft but it feels way soft to me, the bike will not bunny hop. I am guessing my spring is too soft.  I do not know what spring is on there but according to GG I should be on the +10 spring.  Any thoughts or more accurate ways of measuring what it going on?

Edited April 8, 2018 by Ed_Lorca

[section swept]

Set the ‘sag’ with no weight on bike. You’ll possibly need a second person to help. Hold the bike upright, gently lift the rear of the bike up so as to unload the suspension. Carefully release the bike so that it ‘sags’ back down, look at the way the bike reacts. Now select a good datum point to take measurements from, I would suggest a piece of tape stuck onto the mudguard in line with the rear wheel spindle. Now lift the bike up again a release, but this time measure the full extension and the final resting position measurement. Most manufacturers will have specs for sag but I would look for 20mm. This means that the rear spring is supporting the bike and being compressed by an inch to do so. NOTE this first base line measurment is normally done with any compression and rebound damping fully off. Adjust the spring seat collars to achieve the one inch. There may be a member with more set up experience of the TXT300 that can give you alternative specs. Now the next bit, put on what you would normally ride in including boots and helmet. Have a dump if needed to get closer to racing weight! Get your helper to measure how much further the bike sags when you get on, do this next to a wall and you can balance the bike upright while they measure sag. There is no need to stand up unless you feel compelled. The sag measurement ought now to be somewhere about or 50-60mm. Thats the rear done, now the front. Wipe clean a fork stanchion and put a cable tie around it just tight enough for it to be slide up and down by hand without it moving from where you left it. Slide the cable tie down to sit on the dust seal or cover, push down on the front forks a few times. Now lift the bike at the front by the handlebars so that the forks are unloaded slide the cable tie down to the cover, let the bike settle back down. Lift the front end and measure the distance between the cover and the tie, this is front sag. Aim for about 25-30mm sag. Now still kitted out get back on the bike and measure the front sag. Your added weight will make the cable tie slide further up as the fork compresses. You are looking for approximately 30mm plus the initial sag. Now bounce about on the bike and re-check your measurements, ensure that no rear pivots are sticking or front forks binding. Adjusting the compression and rebound are next and these will be different for the weight of the rider and the type of ground being covered, mostly a compromise setting will be needed. As far as ‘bunny hooping’ that may be down to technique, no disrespect to you, or it may be a combination of tyres and suspension set up. Keith Code, American racing legend has a number of his set up  films that may help further. I have assumed that other contributing factors like damper condition, fork oil levels and oil weights are to spec. Suspension set up is not the dark art some would have you believe, damper internal shims and valves is a bit more complicated. Hope this helps you to get to grips sorting your bike??

[lineaway]

Buy an Ohlins or Rieger as your shock is probably tired. But it still won`t make you bunny hop. Timing,timing and timing, is how it works.

[Ed_Lorca]

Thanks for all the answers.  I would love a reiger but there be no funds for that unless I find a used one then maybe.  As for what I have now, I measured from the rear axle to the exhaust tip.  The bike only sag is 19mm so that is spot on.  Once I get on it, from the bike on ground measurement to having me on it it sags 86mm more.  My 155lb friend was in the vicinity of 60mm.  Just for grins I did a check, if I hop on the bike to compress the rear shock the shock will bottom out.  That cant be normal, I keep thinking I need to go to 1 step up on spring stiffness.  Do you guys agree?  Aside from the spring rate, the shock might just need a rebuild.

 

[Ed_Lorca]

Thanks Oni.  I was wondering if the damper was shot.   I will have to pull it ans check.  I see you are in OC, are you going to El Trial next wknd?

[huski]

Your static sag would be better at 10 mm,which would mean it would sag less with you on it.The standard spring is a bit soft for you and as suggested I'd have the shock off and check the damping,I assume you've tried the damping adjustment screw to see what effect it has?

I never thought the Sachs shock on my previous Gasgas was that special,the Reiger on my present one is hugely better as was The Ohlins on my sons bike.Rather than spend on the Sachs if it's not working properly I'd put the money towards replacing it

[dan williams]

Get a heavier spring for the front and rear. That way you can run minimum preload. The shock has nothing to do with the loaded height of the suspension other than being a holder for the spring. 

OK it has minimal to do with it. You need some space in the shock for the oil volume displaced by the shaft to go. When you compress the shock the gas pressure in the shock goes up because the internal space is less and since the oil can’t compress the gas does. So why pressurize the shock? Because if you don’t the pressure swings cause the gas in the shock to go into solution with the oil. Like CO2 in a bottle of soda. High pressure drives the gas into solution and low pressure allows it to come out of solution. After a few strokes you’ve foamed the oil to the point where its damping properties are unpredictable to say the least. By keeping the gas under pressure the gas that is in solution in the oil stays there so the oil can’t foam.

Edited May 1, 2018 by dan williams