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OK, so I’ve done a bit of research and here's the scoop (for anyone else considering converting any 2003-2007 Marzocchi MX fork to coil):
[b]Firstly, can my 2006 MX Pro TAS/ETA have the rebound leg converted to coil?[/b]
Yes, the exact same rebound piston rod and top cap are used on the 2005 MX Pro Coil, so no issues there.
[b]What length springs do I need?[/b]
For 85mm travel MX forks, you need 165mm springs
For 100/105mm travel MX forks, you need 185mm springs
For 120mm travel MX forks, you need 213mm springs
For the ETA leg on a 100/105mm travel MX you need a 165mm spring
For the ETA leg on a 120mm travel MX you need a 185mm spring
All the springs are a nominal 24mm external diameter.
[b]Wow, that’s simple, what spring rates do I need?[/b]
OK, for an 85mm travel MX, Marzocchi recommend:
For riders of between 120-155lbs a total spring rate of 10-12.4 kg/cm
For riders of between 145-180lbs a total spring rate of 12-13.4 kg/cm
For riders of between 180-240lbs a total spring rate of 13-16.6 kg/cm
For a 100/105mm travel MX, Marzocchi recommend:
For riders of between 120-155lbs a total spring rate of 7 kg/cm
For riders of between 145-180lbs a total spring rate of 8 kg/cm
For riders of between 170-205lbs a total spring rate of 9.4 kg/cm
For riders of between 195-240lbs a total spring rate of 10 kg/cm
For a 120mm travel MX, Marzocchi recommend:
For riders of between 120-155lbs a total spring rate of 5.8 kg/cm
For riders of between 145-180lbs a total spring rate of 6.6 kg/cm
For riders of between 170-205lbs a total spring rate of 7.8 kg/cm
For riders of between 195-240lbs a total spring rate of 8 kg/cm
In all cases, where the rider is about mid way between (for example) a pair of hard springs and a pair of medium springs, they might like to go with one medium and one hard spring.
[b]What spring rates are available?[/b]
165mm: Medium Dual-Rate (5 kg/cm 6.2kg/cm), Hard Dual-Rate (6 kg/cm 6.7 kg/cm), Extra-Hard Dual Rate (6.5 kg/cm 8.3 kg/cm)
185mm: Soft (3.5 kg/cm), Medium (4 kg/cm), Hard (4.7 kg/cm), Extra-Hard (5 kg/cm)
213mm: Soft (2.9 kg/cm), Medium (3.3 kg/cm) Hard (3.9 kg/cm) Extra-Hard (4 kg/cm)
[b]Where can I get the springs?[/b]
CRC sell them new, but sadly only in pairs (a pain for ETA fork owners who need two different length/rate springs)
[b]Useful resources:[/b]
Do a search online for the old (year 2000?) Marzocchi Bomber Technical Details and Tuning Manual (pdf format). Lots of the information contained therein is still applicable to MX forks up to 2007.
Marzocchi springs come in a packet on the back of which is a useful spring rate chart. It’s not a complete resource, but used in conjunction with the sparse info found on the spring rate chart on Windwave’s website it’s OK.
With regards to suspension fluid and oil weights, I used the excellent information available at http://www.pvdwiki.com/index.php?title=Suspension_Fluid, and now use Castrol Synthetic Fork Oil 5w in place of standard oil (both rated at 28 cSt@40C viscosity), and where a 10w oil is specified (like with my heavy springs) I mix 75ml of Castrol Synthetic Fork Oil 5w with 60ml of Castrol Synthetic Fork Oil 10w per leg to achieve a 33 cSt@40C viscosity oil. I buy the 5w off Amazon, and the 10w from Halfords.
Well, that took a while to type; hope that helps someone one day. 😉
Just to add that on my 2006 MX Pro TAS/ETA fork I've gone with a 180mm 4/kg/cm coil in the ETA leg, with a 213mm 4 kg/cm coil in the rebound leg for a total of 8 kg/cm. I weigh about 218lb, and I'm thinking of upping the ETA leg coil to the hard 180mm 4.7 kg/cm coil.
I'm running '5w' (28 cSt@40C) in the ETA leg at from stanchion top level, and '10w' (33 cSt@40C) in the rebound leg again at 55mm from stanchion top level. I have the external rebound damping control about two turns out from slowest rebound (i.e. max damping - fully closed).
These aren't finalised figures, still some testing and fiddling to do.
I had an old pair of mx comp air's converted to springs by windwave, they were plusher but by the time they had added 2 coils they weighed a ton..
Good info, but it all seems like alot of bother and expense for what ?
I have 2004 MXPro's 105mm, 2005 MXPro's 120mm, 2005 AM2's 130mm & 2006 AM2's TAS 130-150. All ETA.
Guess, what, they are all pretty plush.
Why ?
1. Maybe it's because I'm only 11.5 to 12 stone ?
2. No, it's because I service them all anually, strip, clean & change the oil, that's all ?
Ok, the above helps.
But what really makes them run so sweet, is that
3. The oil height in BOTH legs off all the forks has been adjusted to suit my riding & weight. Then you run at pressures around 25-30 psi.
That's all you have to do, it's so easy it's not rocket science, it doesn't cost anything, just your time, as you take oil out.
The trick though is to run with minimum oil in the ETA side, less than specified, but enough to ensure the function still works reliably. If you don't do this it isn't worth tuning up the air side.
Simples. 😆
Good info, but it all seems like alot of bother and expense for what ?
Generally, because coil is way more responsive than air.
But with regards to ETA and my fork, there is no way I could achieve full travel with the 54spi air preload I needed to run to get anywhere near reasonable sag for my 99kg weight. Therefore I needed to run a higher rate spring (or springs). Simples.
Good stuff Tucker, good to see that there are other old bombers still going strong.
I don't suppose you'd have a link to oil heights for each fork would you? There used to be a comprehensive list on Marzocchi website for rider weight but I can't see it any more!! (Marathon S coil 2004 fwiw)
Off the top of my head under 80kg you want 60mm from top of stanchion, over 80kg 55mm from top.
Impressed huh?
Actually I just read it off the [url= http://www.windwave.co.uk/documents/techinfo/oil%20level%20charts.pdf ]Oil Level Chart[/url] at Windwave (Marzocchi importer). 😀