Rear shock preload - Glenn has it figured out

[bchatt]

Originally Posted by 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

Try setting your race (rider) sag 1st. You should aim for a rider sag of 100-110. That should result in a static sag of around 25-30 if the spring is correct for your weight. These are pretty much tried and true figures that should get most modern bikes in the ball park. Don't necessarily worry about how much preload that needs.
I weigh 75kg and get these results with a 4.8 spring, which I replaced the stock 5.2 with.
Remember, if your spring is too soft you will have less static sag than 25-30 for the race sag of 100-110, if your spring is too hard you will have more static sag for the race sag of 100-110.

As a side note my sachs shock blew apart at 50 hrs - I noticed it get all sproingy then within minutes the circlip blew out of the body. It was repaired under warranty with a newly designed seal head and has been brilliant ever since - now about 250 hours.

[Jakobi]

Originally Posted by bchatt

Try setting your race (rider) sag 1st. You should aim for a rider sag of 100-110. That should result in a static sag of around 25-30 if the spring is correct for your weight. These are pretty much tried and true figures that should get most modern bikes in the ball park. Don't necessarily worry about how much preload that needs.
I weigh 75kg and get these results with a 4.8 spring, which I replaced the stock 5.2 with.
Remember, if your spring is too soft you will have less static sag than 25-30 for the race sag of 100-110, if your spring is too hard you will have more static sag for the race sag of 100-110.

As a side note my sachs shock blew apart at 50 hrs - I noticed it get all sproingy then within minutes the circlip blew out of the body. It was repaired under warranty with a newly designed seal head and has been brilliant ever since - now about 250 hours.

I agree with what you say to a certain extent. The range for static sag falls between 20 - 45mm with race sag falling between 95-115mm. The rest is rider preference re geometry. So really 30mm 100-110 puts you right in the middle of the field.

But, what we are discussing here is primarily how less preload provides a more comfortable ride. A bit more static sag will always provide a plusher ride in the initial part of the stroke than a spring that has been screwed down to be stiffer.

The whole thing is a bit of a catch 22. The right spring will give you the right figures. You may be borderline where you can either run with more preload, or go up a rate and run less. In this case I'd go for less preload and a heavier spring.

[wence]

No dramas mate,
If you want to get rid of it let me know.
I don't think they are that expensive anyway.

As for the issue, yes I am in the catch 22 . I will test it how it is as I will be doing logs etc anyway. If it is crap I will get a new spring suited to my weight.

Cheers Mark

Originally Posted by Jakobi

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.

[stainlesscycle]

ok, with 25mm of preload....

30mm sag, 100mm race sag...

i would assume that's about where it should be, but that's a bunch of preload. if i back the preload back to say 15 i would guess the numbers would still be close to where it should be, but then it just feels low in the back to me.

[GMP]

Your spring must be wrong/bad. I just looked at mine, preloaded spring length on the bike is approx 250mm. Free length of a 5.2 I have on the shelf (both Sachs springs, same length) is 260mm, so it works out.

The original point of the thread was to NOT get hung up on the sag numbers, but tune the suspension by FEEL while limiting preload to 10mm. Preload does matter, and affects the feel of the initial travel. I think any tuner will agree that 25mm preload is off the map and something is wrong.

As far as the shock itself, one original issue was the piston band being loose. Les would fix this by using a WP band with a different oring under it, then Sachs updated the part. I have had zero problems with my shock, but it has been to Les for updates, valving and service since new. Not everyone knows the details as well as him. Last time it was just the fluid that needed changing, rebound was creeping up and needed more clicks in. Fine now. I used 195 PSI nitrogen.

[stainlesscycle]

Originally Posted by GMP

The original point of the thread was to NOT get hung up on the sag numbers, but tune the suspension by FEEL while limiting preload to 10mm. Preload does matter, and affects the feel of the initial travel. I think any tuner will agree that 25mm preload is off the map and something is wrong.

yeah, i'm not trying to get hung up on the numbers, but when it feels 'right' or at least close - i end up with tons of preload - which i know is wrong - gonna check my spring length now...

[007neil]

sorry to jump in, but does anyone know the alternative energizer o rings part numbers? i read a post on it a while back before i had a problem with my sachs rear shock. i think they replaced it with a KTM part number?
cheers

[GMP]

Here you go.

http://www.lt-racing.com/html/sachs_upgrades.html

[007neil]

Originally Posted by GMP

Here you go.

http://www.lt-racing.com/html/sachs_upgrades.html

cheers glen, i've been looking everynight for that link!!

[n_green]

Maybe I'm a bit slow, but can someone explain to me exactly what to measure?

Do I measure the preload rings wound all the way up (they are still in contact with the spring at this point and providing minimal preload) and then wind the bottom preload ring down 10mm?

Or do I measure my uncompressed spring which is 261mm and then wind the preload rings down until the spring measures 251mm?

thanks