Suspension Tuning
From Farkin Wiki
Contents |
[edit] General Suspension
Basics of Suspension - S.
Here is a link to a fantastic article by S. which explains a heap of info about suspension and the basics of how it works. A very interesting read. Thanks S.
The basics of suspension - terms and general info
[edit] All Forks
Initial Set Up for DH
First up is to set the sag. For DH you need about 20-30%. To check your sag place a zip tie on your stanchion and sit on your bike while some one holds it up so that you can put both feet up. Then push the zip tie down to the seal (or get your mate to do it) and then stand up into the 'attack' position. This should move your zip tie up the staunchion. Carefully get off the bike so as not to over compress it past where the zip tie is. Then measure the distance from the top of the seal to the bottom of the zip tie. This is your sag. Then divide your sag by the total amount of travel, then multiply that figure by 100. Eg I measure 50mm sag on a 200mm travel fork. 50÷200=0.25, 0.25x100=25% Here is a very useful video on checking sag from Mojo It is Fox Forx, but the principals are the same for all makes.
Now after measuring your sag you may need to adjust your preload, or if this doesn't offer enough adjustment you will need new springs. It is very crucial to get your spring rate right or your fork will never feel right.
Compression Damping. For DH you really don't want to run any compression damping if you can get away with it. Some forks, like 888's for example, have a tendancy to dive under braking or cornering, and these forks do need some compression damping. Remeber, if your compression damping is too great you will lose all small bump sensitivity.
Rebound damping is a bit trickier. On a fork it is better to, run it on the fast side, so that it doesn't pack down on sucessive hits and send you over the bars. You want to try and get it to a point where if you push down really hard and pull back up again (on the handlebars) in quick succession, you get the wheel to just leave the ground by about an inch. But remeber it is better on the fast side if you can't get it perfect.
Tip: To learn what damping can do for your ride, experiment with the compression adjustments and rebound adjustments ( if your shock model has them ). We suggest you start with compression damping... Turn compression adjuster to full firm ride your bike for awhile and then turn the adjuster to full soft. This will give you an idea what compression damping can do. Like wise do the same with your rebound adjusters..... Feel what fast is ..... Feel what slow is
Tuning Trouble Shooting
Not using full travel, feels harsh, poor traction while making turns Causes: Overly stiff springs or compression damping Solutions: Lower air pressure; reduce compression damping; softer coil springs
Bottoms, soft throughout travel Causes: Spring rate too low throughout travel, or too little compression damping Solutions: More air pressure; increase compression damping; stiffer Coils Springs
Excessive sag, feels soft initially but doesn't bottom Causes: Initial spring rate or preload too low; spring too progressive Solutions: Add air pressure or increase spring preload
Harsh over small bumps but uses full travel Causes:Initial spring rate or preload too high, springing not progressive enough, or too much compression damping Solutions: Lower air pressure or install softer springs; reduce compression damping; reduce spring preload
Takes first bump in a series well but harsh over later bumps, poor traction in washboard corners Causes: Too much rebound damping Solutions: Reduce rebound damping if adjustable - Non adjustable - reduce oil weight
Ride is harsh, but not as bad as too much rebound. As speed increases, so does harshness. Rear end will want to kick when going over medium to large bumps ( shock resist movement even on medium size bumps) Too Much Compression Solutions: Decrease compression until harshness is gone
Wheel chatters over small bumps during braking or downhills Causes: Too much preload (perhaps because of soft springs) causing suspension to top out; possibly too much compression damping Solutions: Reduce preload decrease compression
Front end springs back too quickly after bumps, poor traction in bumpy corners Causes: Not enough rebound damping Solutions: Increase rebound damping if adjustable or increase oil weight.
Fork Oil and Spring Weight Article
Here is a very intersesting article about Fork oil and Springs. You can save your self some money by buying your oil from a moto shop rather than from your LBS.
[edit] All Rear Shocks
Spring Rate Calculator
There is a very good spring rate calculator on [TF Tuned http://www.tftunedshox.com/springcalc.htm] and also on Mojo
[edit] Fox Forx
All Fox Forx
Fox Manuals
Fox Owner's manuals can be found here
Fox 40
Dimensioned Drawing - Cave Dweller
Use this to work out your head angle and such. Shows axle to crown length and other valuable info:
Spring Weights - Cave Dweller
Spring length is 480mm Blue code spring = 40lb Green Code Spring = 45lb Yellow code spring = 50lb
[edit] Manitou Forks
All Manitou Forks
Manuals
Manitou Manuals can be found here:
Dorado
Spring Weights - Cave Dweller
Blue soft = 60 lb red medium = 80 lb yellow firm = 100 lb
Nb. These also apply to the Manitou Xvert Carbon
[edit] Marzocchi Forks
All Marzocchi Forks
The Marzocchi Oil level tables are located here: Marzocchi Oil Tables
And the Manuals are Here: Marzocchi Owner's Manuals
04/05 888R/888RC
Go-Ride Article
There is a very good tuning guide over on Go-Ride.com which goes into some details about setting up and tuning your fork. Go-Ride Article
Spring Weights - Cave Dweller
Ppring length is 300mm Soft = 2.7 kg/cm = 15lbs/in Stock = 3.1 kg/cm = 17lbs/in Stiff = 3.4 kg/cm = 19lbs/in
Mojo Cartridges
Mojo, the makers of the famous Boxxcart have recently released a cartridge and spring kit for the 888. Apparently it has far better speed sensitivity than the standard damper. You can also get a Ti spring to lose some weight from your forks.
BOS Cartridges
Oliver Bossard’s company BOS has also recently released a pair of cartridges for the 888. These are extremely expensive and are apparently very very good, but so dear.
BOS Engineering Cartridges (Translated from French)
uDi's Low Speed Compression Sleeve
How To
Thought this might interest other 888 owners out there. This mod works for the 04 888R, 05 888RC, and the 05 66RC, which all run an adjustable HSCV cartridge for compression damping.
Now the problem was, the cartridge only offered damping in the last 2-3 inches of travel, leaving very little compression damping in the earlier part of the stroke. Not enough low speed compression damping meant the otherwise excellent fork would dive excessively during hard cornering and hard braking.
The culprit for this was the set of 5 holes on the compression cartridge that allowed oil to escape earlier in the stroke rather than forcing it through the actual damper (the shim stack).
The first two images that I have attached at the bottom of this post are full size pictures of the compression cartridge if you want more of an idea of where these holes are located.
Now those of you who have read the go-ride article on the 888, will know that marzocchi makes an adjuster that allows you to cover combinations of these holes - but after pricing it up it came to about au$80-90. Stuff that!
So I decided to make my own. I started with a 55mm length of 20mm OD PVC piping (actual OD was 19.5mm) and the ID was roughly 15mm. Now the 888 cartridge has an OD of approximately 17mm, so it took some filing to get the inside of the PVC down to the right size - the trick here is to get it so it will slide on fairly tightly and not loose, as that is how it will stay on. I put my round file in an electric drill to get most of it shaved out and then did the rest by hand, checking for fit on the cartridge often. The finished product was 44mm long, but start with 55 so you have more to play with later.
I drilled 3 different sets of holes in the sleeve to give me 3 different settings (better pictures of the sleeve alone are attached at the bottom of the post). I found covering only the small lower holes just made the fork ramp up quicker (ie: not much use), so covering the two large upper holes is the way to go. My advice would be to use that (Setting 1) as a starting point and go from there.
The diagram shows which holes are covered on the compression cartridge for each setting, and the photos below them show the real thing.
Set Up
I ran it in "Setting 1" for about a month, and it was definitely an improvement over stock but not a huge difference. My fork setup then was Motul Factory-Line 7.5wt, 220ml per leg, and the compression knob wound pretty much all the way in. The fork wasnt blowing through it's travel too much but there was still a bit much dive when cornering hard. An important side effect to note when using a compression sleeve is that it will affect the bottom out resistance. I found I was only using 180mm of travel, so the plan was to drop the oil level next time.
I've just changed it to "Setting 3" today, which closes 4 of the 5 holes, and dropped the oil level to 205ml per leg. Just pushing on it on the driveway the difference isn't huge, but once you start moving and cornering at speed you start noticing a big difference. The fork stays higher in its travel and doesn't blow through nearly as many inches. I'm yet to hammer some DH runs with it but this seems to be the ticket. I'm still running the compression knob wound all the way in but if I feel there is too much damping i'll back it off a bit.
I believe treggs is running 10wt in the compression side instead of 7.5wt, and he is running the equivalent of "Setting 2" (2 large holes and 1 small hole covered) - apparently it works quite well. I think 7.5wt is fine for my weight (~60kg) but for a heavier rider the 10wt in the compression side would give you more damping again.
That's it for now. Feel free to PM uDi if anyone wants more details.
A big thanks goes out to treggs on here - he was the first one on here to do the mod to my knowledge, and a bit of inspiration goes a long way.
--Udi
Monster T
Monster T exploded diagram - Cave Dweller
Spring Rates - Cave Dweller
Spring length is 320mm Green = stock springs in 99-02 monsters = progressively wound springs, start at 2.5 kg/cm and ramp up to 3.5 kg/cm (14lbs/inch to 19.6lbs/inch) Yellow = Soft = 2.5 kg/cm (14 lbs/inch) White = Medium = 3 kg/cm (16.8 lbs/inch) Blue = Firm = 3.5 kg/cm (19.6 lbs/inch) Red = heavy = 4 kg/cm (22.4 lbs/inch)
Cave Dweller's Air Sprung Monster Mod
I have been toying with the idea for a while to air spring my monster to shave some weight. There is various ways to do this, drilling in air valves into the cap of each leg is one (like zedros shiver), making some volume reducers like in 888's is another, and the other mod is to completely remove one cartridge of the fork and air spring it. The later is what i have done here.
NOTE:- If you do this i accept no responsibility for your actions, infact, don't do this, it will probably wreck your fork.
First step is to remove the entire cartridge, spring and spacers from one leg. This leaves a hole at the bottom. Get a bolt, stick it in there and put the foot nut back on the bottom. The bottom of the fork leg is now plugged and won't allow oil out.
Next, go to your local tire shop and ask for a tubeless car valve, they cost $5. Stick it into the hole in the valve cap that used to let the cartridge/preload/rebound adjsuters through. Fill the leg with 50-70ml's of oil to allow for lubrication.
NOTE:- there will now be nothing holding this leg together as you have removed the cartridge, it will be held together by the other leg and crowns. So, remeber that you need to release the air pressure from the fork before you undo the tripple clamps otherwise you will end up with a stachion rocket
Open up the other leg and drain the oil out. You will need to put a heavier spring in to compensate as you will only be running one spring, not two. You will also need to put heavier oil in to help slow down the rebound, stock it is 7.5wt, i mixxed up some 12wt oil and put it in, i set the oil level 10-15mm higher the the marzocchi recommendation to help with bottom out resistance. Put it back together and bobs your uncle, air sprung monster
Not sure of the air pressure, i am putting in between 15-20 pumps of my bike pump. Seals are holding the air fine, minimal leakage over the week just gone by.
The fork rides almost the same, slightly more harsh over small bumps due to the air pressure, but it doesn't bottom at all, and the rebound is fine, no nasty top out clunks. Biggest difference is the reduced weight, this has saved around 1.5lbs from the fork making it around 8.5lbs, the fork also feels alot more responsive, probably from the reduction in unpsrung mass.
Shivers
Spring Weights - Cave Dweller
Spring length is 334mm Soft = 2.7 kg/cm (15 lbs/inch) Medium = 3.2 kg/cm (18 lbs/inch) Firm = 3.7 kg/cm (21 lbs/inch)
Exploded Diagram - Cave Dweller
[edit] Rock Shox Forks
All Rock Shox Forks
The Rock Shox Oil height table can be found here
And the Owner's Manuals can be foud here
Boxxers
Known Issues (mostly taken from TF Tuned)
* '04 & '05 Boxxers suffer from a lack of low speed rebound damping in the top 2-3" of the stroke. This can cause the front wheel to wash-out when exiting turns.
* In 05 forks (not sure on 06) the new 8" lower leg assembly has much longer lower bushings which, if not fitted correctly, can cause a high degree of stiction. This leads to what can only be described as a harsh & sticky small bump ride.
* RockShox engineers worked hard to improve the rebound damping on '03 and'04 Boxxer forks. This they did, but unfortunately they created another problem - high-speed compression spiking & inconsistent rebound. Spiking is when you hit a medium to large square-edge bump and the fork cannot compress quickly enough causing the shock to be transmitted to the handlebars. Add to this a very ratchety feel & the fact that the fork is often over sprung (stock springs are suitable for 100kg/15 stone + rider) you can see that there's room for improvement.
Spring Rate Table and Spring Weights- Also from TF Tuned and Cave Dweller
Rider Weight (Kg) Rider Weight (lbs) Spring - Lefthand/Righthand
45 - 55 100 - 120 White/White
55 - 65 120 - 145 White/Silver
65 - 75 145 - 165 Silver/Silver or White/Yellow
75 - 85 165 - 190 Silver/Yellow
85 - 95 190 - 210 Yellow/Yellow (how they come)
95 - 110 210 - 240 Yellow/Red
110 - 120 240 - 265 Red/Red
Spring length is 390mm White = Soft = 10lbs/inch Silver = Medium = 15lbs/inch Yellow = Firm = 20lbs/inch Red = Extra firm = 25lbs/inch (??i think??)
Ti Springs - TF Tuned
You can fit the '05 8" Titanium springs to all models of 7" Boxxers with the aid of a new spacer kit & machining of the compression side spring perch (the 8" springs are 30mm longer & 1-2mm less internal diameter than 7").
Motion Control Damping in pre 06 Boxxers - TF Tuned
You can add Motion Control damping to any Boxxer from '03 & dump all of the plastic! (No more rebound failures) If you have a '03 or '04 Boxxer it will have 7" of travel & '05 keeps 8". If you want 8" on '03/'04 then you need to add new '05 or '06 lower leg assemblies.
Mojo Boxxcart
Mojo has had the Boxxcart for a while now. Most people who have had them love them. They are made from Fox parts (from Vanilla's mostly I think), so they are reliable and very bling looking. These are available from DH Direct in Australia.
For More information on Boxxers please visit the very informative TF tuned Site, which is where I got most of my info for the Boxxer section.
--Top dog 20:40, 16 February 2006 (EST) Article Written By Tom Corbett with the Help of Cave Dweller and S.
