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Fork oil vs. Shock oil. What's the difference?

BmxConvert

Monkey
Aug 6, 2007
715
0
Longview, Washington
I just placed an order for some Silkolene fork oil to rebuild my Boxxer with. As I was cruising around looking for a place that carried the stuff I wanted I came across Maxima selling what they called "Fork Fluid" as well as another roduct they called "Shock Fluid".

From what I can gather the Shock fluid is rated at a minmum of "350+ viscosity index", where as the Fork Fluid is rated closer to 190.

http://www.maximausa.com/products/suspension/shockfluid.asp
http://www.maximausa.com/products/suspension/forkfluid.asp

Can anyone go into a little more detail on the differences between the two products and how they effect performance, especially if used for opposing purposes(ie: shock fluid in fork and Vice Versa)?

-Kevin
 

Hougham

Monkey
Mar 28, 2007
375
1
Some manufacturers add the likes of seal swellers, detergents and the likes in there but basically there all the same thing. Its really just the wights. Most of the additives are not required or can even be detrimental for cycle suspension so its always best to get oils designed for your suspension.
 

davep

Turbo Monkey
Jan 7, 2005
3,276
0
seattle
The general difference (if that mfg differentiates their product lin this way) is that most mfg use full synth for shocks and non or semi-synth for forks...In the case of something like redline, their entire line is full synth with high V.I.

Viscosity index is a measure of how stable the kenematic viscosity (cSt) is as temperature changes. You will find that 'shock' oils have a higher V.I. because generally shocks generally see a larger swing in temp than a fork (for many reasons)...something not need as much in forks (when is the last time you felt your fork get 'hot').

Shocks also in general see longer sevice intervals than a shock due to complexity, so the full synth should/could hold up to this better than a semi or non-synth.
 

Kntr

Turbo Monkey
Jan 25, 2003
7,526
21
Montana
SO WRONG !!!.Try to rebuild your rear shock with FORK fluid and let me know how that go...

Im not sure what the difference is but I know they both behave very differently.
I was refering to REDLINE. The same oil is used for both when you are talking about full synthetic.
 

Udi

RM Chief Ornithologist: “I Brake for Birds”
Mar 14, 2005
4,899
1,168
The same oil is used for both when you are talking about full synthetic.
That's incorrect, you can still have full-synthetic fluids with lower VI's. It's a blanket statement to say that fork and shock fluids are the same because that's the case for one brand.

Silkolene (Pro RSF) and Redline are the only two brands I know of that work like this, their oils are all very high VI (300-400 for most viscosities). Most other brands split their lineups into fork (lower VI) and shock (higher VI) oils.

Motul is probably a good example to explain the difference, their "expert" oil is semi-synthetic, their "factory line" oil is full-synthetic, however they both still have low VI's. You have to get to their specific "shock oil" if you need a high VI.

That's probably a good reason to stick with Silkolene or Redline all round though. :)
 

Kntr

Turbo Monkey
Jan 25, 2003
7,526
21
Montana
That's incorrect, you can still have full-synthetic fluids with lower VI's. It's a blanket statement to say that fork and shock fluids are the same because that's the case for one brand.

Silkolene (Pro RSF) and Redline are the only two brands I know of that work like this, their oils are all very high VI (300-400 for most viscosities). Most other brands split their lineups into fork (lower VI) and shock (higher VI) oils.

Motul is probably a good example to explain the difference, their "expert" oil is semi-synthetic, their "factory line" oil is full-synthetic, however they both still have low VI's. You have to get to their specific "shock oil" if you need a high VI.

That's probably a good reason to stick with Silkolene or Redline all round though. :)
You are right, but most all full syn have a high VI.

Ive only used Redline and absolutely love it. I have a perfect mixture that yeilds me around a 7wt and it works awesome for Zoke forks AND shocks. :)
 

rowlands

Monkey
Nov 26, 2006
159
0
SO WRONG !!!.Try to rebuild your rear shock with FORK fluid and let me know how that go...

Im not sure what the difference is but I know they both behave very differently.
do it all the time on rental bikes... same performance after the re-build :nopity:
 

Pebble

Monkey
Dec 6, 2006
137
0
Nannup
SO WRONG !!!.Try to rebuild your rear shock with FORK fluid and let me know how that go...

Im not sure what the difference is but I know they both behave very differently.
Depends if you're thinking of something like the Fox Foat Fluid? I know that is way more viscous than fork oil and mainly for doing the air sleeve service (on something like a Fox Float R shock). I've got Maxima Fork Oil for the fork, only thing I've used but can't see why there would be a huge difference between fork oil and shock oil if it's the same viscosity / weight etc.
 

BmxConvert

Monkey
Aug 6, 2007
715
0
Longview, Washington
(when is the last time you felt your fork get 'hot').
Shoot, my rear shock has never even gotten hot. I'm slower than hell. I think I got passed by a slug during one of the races at Hood on the sport course last year(actually my poor race standings have more to do with horrible health and inconsistant riding).

My bike is getting pretty clapped out these days. The frame is an '05 the wheels are 2-3ish seasons old and I got the '08 WC in June/July of '07 and so it's got some ride time on it.
I keep up on maintenece with rebuilds every few months. However I just got my Curnutt rebuilt/revalved/resprung(I was riding 100lbs over sprung with an internal tune for a guy 65lbs heavier than I) and I wanted to give the boxxer that final pre-season tune up but really help to freshen up the fork.

I went with:
Slikolene PRO RSF 5wt for my damper assembly.
Maxima Fork Oil 10wt for the Solo Air assembly
Maxima Fork Oil in the lowers if theres not enough enough to do Red Rum. I know I'm low on the Red Rum.
I have an entire bottle of Maxima 7wt shock fluid left from when I still had my dirtbike which got me wondering if there was any practical use for it in the Boxxer.
 
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