Rear shock preload - Glenn has it figured out

[rgranger]

+100 on GMP and spring numbers. I dropped the KTM two sizes and it is simply fantastic now and still doesn't bottom. I went down one size from speck for my weight and what Les had setup, again another big woods improvement. After looking around, I think most of the numbers are based on MX and jumps. Both my bikes really kicked the back end around in the woods and over roots, softening it up allowed the suspension to do what it is designed to do, absorb shocks! Maybe I am more forward when riding, standing or seated, but it took me from a plodder to keeping up with a B rider...overnight, yeah really!

Play around with that stuff. It moves and is adjustable for a reason

 

[GMP]

The main thing is the preload and the begining of shock/wheel travel, how easy it is for the wheel to respond to small hits, and how fast the wheel is rebounding from those hits. This has the most effect on how the bike sucks up trail trash. If your spring is too light steering may suffer, and jacking the preload to correct it is the whole point of this thread. Keep in mind that the basic shock valving must be sound for your spring/weight/speed/terrain so you don't attempt to over compensate somewhee else. I'm running.44/5.4 combo and I'm 190 lbs. 1mm preload on the fork springs, around 9-9.5mm on the shock. Compression adjusted to as much as possible before harshness. I can soft bottom the bike on some fast whoops, but I don't ride that stuff much. When I do a little more comp F&R takes care of it. We don't have a lot of deep whoops and big rocks in the same area here, its one or the other. The bike eats rocks for lunch, not with a mushy couch type ride at low speeds only, but with a firm controlled feedback and no deflection that allows good speed and stability.

Another thing. Don't soften up the fork in an attempt to get rid of the harsh mid spike in certain conditions. This will pitch the bike foward and make the shock feel worse. Solve the real problem (rebound) discussed in the other thread, and things will start falling into place nicely.

 

[stainlesscycle]

how are you setting preload on the sachs - since it's already preloaded a few mm just to get the spring on? just set approx 10mm preload from fully out?

 

[GMP]

My spring is about zero preload mounted with the rings backed off. I'd work with the actual spring length as a reference.

 

[lankydoug]

how are you setting preload on the sachs - since it's already preloaded a few mm just to get the spring on? just set approx 10mm preload from fully out?

If you use a spring off a Husky Sachs they are a little shorter. I used a GasGas Sachs spring on my Husky and it had a little preload backed off all the way like you mentioned. I started at 10mm and ended up backing it off about 2mm. I just rode the bike and adjusted it little by little until I liked it.

BTW I was using a 5.6 spring.

 

[GMP]

Yes, I have a 5.4 Sachs spring from a Husky WR250. I have to lean on the lower ring to get it on and around the shock shaft, but once on its just about no preload. Lanky basically found the sweet spot by feel which seems to work out less than 10mm. The rear calms down nicely. This a trial and error thing, takes a little time on the same trail/obstacles to dial in.

 

[lankydoug]

Yes, I have a 5.4 Sachs spring from a Husky WR250. I have to lean on the lower ring to get it on and around the shock shaft, but once on its just about no preload. Lanky basically found the sweet spot by feel which seems to work out less than 10mm. The rear calms down nicely. This a trial and error thing, takes a little time on the same trail/obstacles to dial in.

I used two cheapo tie downs with no hook on one end, just a loop strap. Ratchet them down equally on both sides of the spring at the 2nd coil from the end. It's a poor boy spring compressor.

I rode my bike through some hard 3rd gear whoops and set the preload and the clickers so the front and rear balances out with the front slightly nose up so it doesn't dive in whoops but will still dive on the brakes so I can turn. I set the rebound dampening so I don't get kicked in the butt on braking bumps. After I did that the rest kind of fell in to place.

There may be a better way to go about it but this seemed common sense to me and it worked.

 

[wence]

i am going to redo the shock preload on the 12 Glenn.
This should still be similar or is the ohlins a different kettle of fish?
I know that currently my shock is way to compressed( too much preload), and I probably need the next spring rate up.The bike is very jarring and seesaw like to ride which I am putting down to the overcompressed shock spring.
I am going to try the 10-12 mm trick and see what goes.
Cheers Mark

 

[GMP]

I think its a general thing that applies to most bikes. The preload should be < 10mm but there is no substitute for the correct spring(s). Try it and see, did the shock come with the preload all cranked up? I'm hoping I can get away with the stock springs and save a few $$, weighed in at under 180 yesterday.

 

[stainlesscycle]

i think it's time for me to get a spring - 5.4 is just not cutting it - i'm close to 20mm preload to make it sit right.. my weight with gear is 210 - i tried 10mm preload but can't get the sag even close...

 

[GMP]

Wow, that sounds really off. At one time early last year I peaked at 195 lbs. in shorts, so figure I was close to your weight geared up. Same '07 bike too. My 5.4 spring was set to approx 10mm and worked good. My race sag is about 110mm. Maybe your spring is not really testing at 5.4? Is that 20mm preload what it takes to get the bike to steer or to meet a certain sag number?

 

[stainlesscycle]

something is just wonky. it's felt low in the back for a while now, ever since i lost damping - 've rebuilt it twice, and it seems 100% but once it gets hot it sucks. i even switched to just air to try hope when it heats up it would stiffen up. maybe my settings are way off. i have the sachs with the 16mm shaft, but it has 12mm i.d. where the valving sits......... just haven't been happy with it for the last month or 2.

what is your spring length when you get 10mm of preload? i may have a 5.2 on there or something goofy. i'm getting a 5.6 from something else to try it out. i'm 190 in street clothes. it's just felt soft in the back to me. like unbalanced..

 

[Jakobi]

I'm 75kgs in shorts. Around 90-95kgs geared up. Just put a 5.4 Ohlins on the TTX and started at 10mm preload but the static sag came in around 42mm. Added a few more turns by hand to get the static to 35mm. This puts my race sag just over 100 without gear. Haven't measured in gear to confirm yet.

 

[wence]

Stainless, You have not got the dodgy shock problem that occurred with the 07 sachs shock. Mine had the problem and when it got hot the shock just pogo'd all over the place.Once fixed it was great.
Cheers Mark

By the way my ohlins shock has some numbers that I can't see then 10/52 , so I assume mine is a 5.2? It is yellow by the way.
I currently must be in a good paddock(or just need to drink less and exercise more), but I weigh about 90 kilos(200 pounds), in street clothes.
I think I am up for a new spring??

 

[stainlesscycle]

Stainless, You have not got the dodgy shock problem that occurred with the 07 sachs shock. Mine had the problem and when it got hot the shock just pogo'd all over the place.:

that's what mine did - tore into it, changed fluid, etc and it was fixed it seemed. i'll get some sag numbers tomorrow maybe. static is fine, the race sag is way off.

 

[wence]

There was a seal or something that needed to be replaced as a fix for it. Did you do this?

 

[GMP]

Does it measure soft as in way too much sag, or does it feel soft as in a possible compression damping problem? If you lost rebound I would expect it to ride high and kick, not what you describe. Sure you got all the air out? I did mine three times to be sure, first time seemed OK at first but there was trapped air.

 

[stainlesscycle]

it only kicked when it got hot. fluid was bad, reservoir seal was bad (there was a small amount of fluid in res).

i switched to bladder setup.

definitely no air in there. works fine with no spring. when it gets hot it was pogo'ing. doesnt seem so bad now, just seems like it's riding low in the stroke, or maybe i'm just hyper sensitive? it seems like i can throw a leg over it much easier than usual.... what is recommended psi ??

i'll post comparative sag numbers tomorrow

 

[wence]

Just reset my preload on the shock.
It had 16 mm of preload on it and the sag was:
Unloaded on stand:595
Bike resting on ground:557
Me on it no riding gear:465

This gave me a static sag of 38mm and a rider sag of 130???

I adjusted preload on the shock to 10mm.
Unloaded:595
Bike on ground:550
Me on it as above:460

Giving me a static sag of 45mm and a rider sag of 135mm.

Hmmmm

As I said before, I will take it for a blast tomorrow and see what its like, but I reckon I will be up for a new 5.4 or 5.6.
Anyone got one that will fit??
Cheers Mark

 

[Jakobi]

Just reset my preload on the shock.
It had 16 mm of preload on it and the sag was:
Unloaded on stand:595
Bike resting on ground:557
Me on it no riding gear:465

This gave me a static sag of 38mm and a rider sag of 130???

I adjusted preload on the shock to 10mm.
Unloaded:595
Bike on ground:550
Me on it as above:460

Giving me a static sag of 45mm and a rider sag of 135mm.

Hmmmm

As I said before, I will take it for a blast tomorrow and see what its like, but I reckon I will be up for a new 5.4 or 5.6.
Anyone got one that will fit??
Cheers Mark

I've got a 5.4 weight spring on my 888 that I only had one ride on before I bought the TTX. Still planning on running the 888 as a spare. Shame you don't live around the corner or I could have let you borrow that too. I'd offer to post it but might cost more than its worth considering Auspost and the size and weight of the spring.