Suspension SETUP, a 'how to' guide...

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Suspension SETUP, a 'how to' guide...
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flag scrippsranchDJ
Posted: Apr 21, 2009 at 12:14 Quote
This thread rules, thanks OP.
flag ctd07
Posted: Apr 21, 2009 at 12:15 Quote
scrippsranchDJ wrote:
This thread rules, thanks OP.
no probs!tup

Salute
flag pbuser102331
Posted: Apr 21, 2009 at 12:24 Quote
have you seen the vivid pocket guide,can anyone translate that for me.
flag joetindale1
O+
Posted: Apr 21, 2009 at 12:37 Quote
ctd07 wrote:
Funkmeister-J wrote:
Great post mate,

Im wondering if anyone can help with my physics cproject ive got to do on suspension desings. I want to explain the different designs and linkages such as DW link, VPP, 4 bar link etc etc, im just really struggling to describe them.

Im getting confused with whats a pivot point and whats not because on a sunday that uses a DW link theres 5 points that are free to move so how many pivot points does it have and which ones are they??

Im just after some advice on how to talk about it i guess, any help appreciated!

Joe
Ok, Single pivot refers to designs where the wheel-path is governed entirely by just one physical pivot, e.g. Orange 224, Kona Stinky, Morewood Makalu e.t.c. This design has the most natural, predictable and compliant form of motion in terms of suspension compression/bump absorption.

Virtual pivot designs are so named as the wheel-path pivots around a 'virtual' [i.e. non-physical] pivot location, this 'virtual' pivot point will remain fairly static throughout the suspensions compression on most deigns where the two frame mounted links rotate in the same direction. The 'virtual' pivot point will move in a slight 'S' shape for designs where the links rotate in opposite ways like with the patented 'VPP' design used by Santa Cruz and Intense...

Virtual pivot designs are conceptually used to try and separate pedalling and braking forces away from the damper by means of the suspensions linkage itself [basically, to work like a 'Brake Therapy' system]. Existing virtual pivot designs can be split into 3 main categories if you like...

- Horst link/Lawwill/ICT/FSR: A pivot is placed quite near the rear axle to re-distribute braking forces off of the damper whilst still mostly maintaining the natural and predictable wheel-path arc of a single pivot design.

- VPP: Characterised by a slightly 'S' shaped wheelpath, its worth noting that... contrary to popular belief and marketing hype, although braking forces are re-distributed by the presence of a link between the lower frame pivot-bearing and rear axle, these re-directed forces aren't then absorbed into the frame/linkage as the upper link will instead move under these re-directed forces, so this design will still suffer a degree of the ever notorious 'brake-jack'.

- Virtual Pivot: e.g. 'DW', 'VF4', 'whatever Canfield's design is called' e.t.c. e.t.c. - This design also effectively separates braking forces from the suspension's compression, variations in design are enormous due to the shear complexity of designing such a linkage, any such design is a well conceived compromise at best.

The latter two 'virtual' pivot linkage types will generally have a very 'propriatory' leverage rate curve and duly benefit from custom tuned shocks to compensate.

That was soo helpful, thanks!!! One more questions and it may sound stupid but i cant get into my head brake jack, how would rear wheel braking would affect suspension??
flag ctd07
Posted: Apr 21, 2009 at 13:09 Quote
Funkmeister-J wrote:
That was soo helpful, thanks!!! One more questions and it may sound stupid but i cant get into my head brake jack, how would rear wheel braking would affect suspension??
Ok, so you ride a Kona with Brake Therapy...

So try grabbing hold of someone else's single pivot bike, then hold onto the saddle and lift the back wheel off the ground, use the cranks to get the back wheel spinning real fast... then jam on the back brake - you will feel a force push up into your hand through the bike - this is basically what brake jack is...

This upwards force is normally transferred into the shock in like-manner to bump inputs from the ground, it is created due the disc brake, when applied, transferring all of your wheel's rotational motion into the lower frame pivot, causing that to rotate instead....

This applies additional pressure on your spring causing it to compress, thus effectively stiffening/adding additional preload your spring and therefore momentarily reducing your suspensions small bump sensitivity....

This may then cause your wheel to 'bounce' over bumps during braking instead of your shock absorbing those bumps as it would without 'brake jack' - this can be mistaken for your brake 'locking up' under braking bumps, as the rear wheel will stop the moment it becomes airborne if the brake is being applied - as there is no force acting pushing it around anymore...

The are some benefits to brake jack though, your suspension will 'squat' under braking forces, lowering your centre of gravity and thus giving you better stability in corners. Your wheel may also (depending on damping settings) rebound slightly faster when its further into its travel due to additional reaction force from the spring, which will help the wheel to 'bite' back into the ground quicker.

......in essence, to ride a single pivot [with 'brake jack'] well, you need to control your braking better and brake before corners so the rear wheel can grip better once your in the corner (you may notice that people who ride single pivot bikes don't 'pump' their bikes as much into corners, as there is no need!) - when done properly, it will teach you to 'pin' corners a lot faster [as your braking distance is longer, so you just have to brake less:P]] and you, as a result, will carry a bit more speed through and out of corners due also to your bike effectively pre-emptively lowering it's CoG for you as you enter corners which allows you to throw the bike down easier into corners and increases your stability too - I think riding a bike with 'brake jack' actually teaches you better riding habits/control and may be beneficial in some instances (less bumpy trails)...
flag ctd07
Posted: Apr 21, 2009 at 13:24 Quote
marquis wrote:
have you seen the vivid pocket guide,can anyone translate that for me.
you mean this? - http://www.sram.com/_media/pdf/rockshox/rearsuspension/vivid/VIVID_PocketGuide.pdf

Basically, the damping reduces the amount of return force your spring pushes back with when your suspension compresses, increased beginning [return] stroke rebound damping allows the suspension to remain more active under heavy impacts - instead of just trying to return to max travel asap. - you would increase this damping if you are riding a slippery/bumpy trail featuring some big impacts along the way.

the same applies for your ending stroke rebound (could be viewed as low speed [impact] rebound) - what they're [Rockshox] are trying to say [but quite badly] is that decreasing the damping will make your shock less susceptible to bump absorption during compression, but will allow your suspension to return to the softer part of its travel quicker for any more bumps just ahead.

They also mention that increasing the end-stroke damping will slow the rebound speed and allow the suspension to 'pack up' a little, which would reduce 'pedal bob' and can be used to give better pedalling efficiency.

hope this helps slightly...Very confused
flag pbuser102331
Posted: Apr 22, 2009 at 3:31 Quote
ctd07 wrote:
marquis wrote:
have you seen the vivid pocket guide,can anyone translate that for me.
you mean this? - http://www.sram.com/_media/pdf/rockshox/rearsuspension/vivid/VIVID_PocketGuide.pdf

Basically, the damping reduces the amount of return force your spring pushes back with when your suspension compresses, increased beginning [return] stroke rebound damping allows the suspension to remain more active under heavy impacts - instead of just trying to return to max travel asap. - you would increase this damping if you are riding a slippery/bumpy trail featuring some big impacts along the way.

the same applies for your ending stroke rebound (could be viewed as low speed [impact] rebound) - what they're [Rockshox] are trying to say [but quite badly] is that decreasing the damping will make your shock less susceptible to bump absorption during compression, but will allow your suspension to return to the softer part of its travel quicker for any more bumps just ahead.

They also mention that increasing the end-stroke damping will slow the rebound speed and allow the suspension to 'pack up' a little, which would reduce 'pedal bob' and can be used to give better pedalling efficiency.

hope this helps slightly...Very confused

yeah that,but i got the which way to turn it mixxed up lol so its all sorted now,i think i should just stick to fettling gears.
flag rstwosix
Posted: Apr 23, 2009 at 6:01 Quote
This is one of the best threads I've read on this site. Thanks ctd07 - your explanations of suspension designs and the DHX shock are very informative.
With regards to the DHX boost valve, I notice you recommend a large volume high pressure setup for fast flowing tracks.
I ride an 07 Kona Coiler with a DHX 5.0 coil shock (& Van 36 RC2 fork)and my current settings are:
1. Propedal 3 clicks in from open
2. Boost valve 150psi (min 120 - max 200)
3. Bottom out resistance 1.5 full turns in from open
4. Rebound 5 clicks in from full slow.
I ride flat out down fire roads with smooth jumps off water bars and also fast flowing singletrack with 2 small rock gardens and plenty of small kicker jumps. There are no big drops on my rides.
I rarely use full travel on the shock and never get past about 120mm on the fork (sag is set correctly on both and the compression adjustors on the fork are set at the factory recommended 1 click in from open).
I'm quite happy with the way my bike rides, but I'm always interested in whether it could be improved. What you think of my setup - do you have other ideas?
flag ctd07
Posted: Apr 23, 2009 at 9:07 Quote
rstwosix wrote:
This is one of the best threads I've read on this site. Thanks ctd07 - your explanations of suspension designs and the DHX shock are very informative.

bigquotesNO PROBS!Beer

- - - snip - - -

If your bike rides fine as is then it's maybe that your local trails just don't require more than the 120mm you're using - getting full travel isn't necessarily a good thing - if you feel you could use more of your travel then...

for both shocks you could try running a little more sag...

for your rear shock, you could try opening the reservoir capacity to maximum [don't adjust this with more than 100PSI in the reservoir], you may then need to re-check your sag, and add a little more pre-load or just inflate the reservoir a bit over 150PSI to compensate - this should make your travel even more linear, on top of this you could even slightly increase your pro-pedal if your trails are smooth and just run less pressure in the reservoir, giving you some plusher travel when its needed but a nice stable pedalling bike the rest of the time.

try also adjusting the high speed damping to fully open on your forks to get all the available travel you can, Fox service centres can even re-tune the in-built internal bottom-out resistance to have less affect if you really wanted [this will affect your final 20%'ish of travel]...

the important thing is to have both your front and rear dampers well matched with each other so they give you a nice predictable and well balanced ridetup
flag Ian-Calgary
O+
Posted: Apr 23, 2009 at 12:44 Quote
thanks this is totally something I have been looking for. Explanations in non-bike tech jargon.
flag rstwosix
Posted: Apr 24, 2009 at 5:52 Quote
'If your bike rides fine as is then it's maybe that your local trails just don't require more than the 120mm you're using - getting full travel isn't necessarily a good thing'
'the important thing is to have both your front and rear dampers well matched with each other so they give you a nice predictable and well balanced ride'tup [/Quote]


I think what you say here is really spot on. I had a feeling that the amount of travel I'm using is appropriate on the smooth trails I'm riding and you've confirmed it. Yes, I also agree that getting full travel isn't necessarily a good thing(contrary to what I've heard from some other 'experts' who say if you haven't used all your travel on a ride, then your suspension is too stiff). When I first fitted my DHX shock I ran it at 135psi and it was using full travel, but it gave me the feeling that I was spending too much time going up and down instead of along. When I increased the boost valve pressure it felt way better and the bike rode faster. My experience also validates your idea that the front and rear should be balanced.
Bottom line - Yes I'm pretty happy with my current setup, but I've opened up the high speed compression on the fork as you suggested and I'll try your other ideas in the coming weeks and report back.
flag ctd07
Posted: Apr 24, 2009 at 7:41 Quote
yep, I abide by the motto - "If it ain't broke, don't fix it!"... but there's no harm in a little tinker here and there!Wink



Let us know how any changes go - would be good to get some real world before/after style feedback on this threadtup


Salute
flag sortex
Posted: May 1, 2009 at 3:11 Quote
hey..i searched before and i couldn't find anything regarding this.... i am 138 lbs and i have a fox dhx 5.0 8.5 x 2.5 and my bike seem like it doesen't use all the rear travel..why is that? (i have a ironhorse sgs dh pro,with rs boxxers,and a dhx 5.0 coil,with 100 psi inside,and a 300 spring) can someone help me? send me a private message or something like that? thanks,i didn't wanted to open another stupid thread for this stuff
flag pbuser102331
Posted: May 1, 2009 at 5:49 Quote
sortex wrote:
hey..i searched before and i couldn't find anything regarding this.... i am 138 lbs and i have a fox dhx 5.0 8.5 x 2.5 and my bike seem like it doesen't use all the rear travel..why is that? (i have a ironhorse sgs dh pro,with rs boxxers,and a dhx 5.0 coil,with 100 psi inside,and a 300 spring) can someone help me? send me a private message or something like that? thanks,i didn't wanted to open another stupid thread for this stuff

find out the rear travel and i will calculate the spring weight for you.

i would aslo check your manual as newer dhx 5.0 are meant to run 125 psi minimum,my 05 dhx 5.0 could run 75.
flag bretski1
Posted: May 1, 2009 at 6:59 Quote
What PSI is a Fox 36 Talas RC2 supposed to run at. I'm having trouble finding the manual online.

 


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