I'd like to update the wiki to say something about fork oil.
Trouble is.. after searching around, I cant find much to say!

The two questions I'd like to writeup in the wiki, are:

1. Difference in choosing brands
2. What "weight" to pick.
I've seen reference here and there to, "stock is 10W, but some people put in 15 or 20w". But no explanation as to *why* they might do that, benefits and drawbacks, etc.

If I remember my fluid dynamics correctly, the reason for choosing heavier weight oil is to improve the dampening and slow movement of the forks. The thicker, more viscous the oil, the slower the forks will move up & down. Theoretically, this should lead to the front wheel planting more firmly and tracking better as well as less "fork dive" when applying the front brakes. Likewise, heavier weight oil should help to offset the amount of compression heavier riders will experience just sitting on the bike. Though, if you're changing the fork oil to stiffen the front forks, you might want to consider stiffer/progressive springs as well.

Then again, I may be just proving how little I know about the subject. 

Maybe, if you know zip about fork oil and the like, you should not be writing about it in the wiki 

Better springs prevent the nose dive on a hard brake or turn. Better springs prevent the sag from heavier riders.
Heavier oil will not prevent those - only slow it down a little on a hard brake. Nothing for a couple fatties in the saddle.

Quote from: mister on June 11, 2012, 11:33:07 AM
Maybe, if you know zip about fork oil and the like, you should not be writing about it in the wiki 

Do you know of a better way to make it look like you're a subject expert without actually knowing anything? I mean, other than backhandedly asking a question and regurgitating the responses into the wiki?  Hahaha

Quote from: adidasguy on June 11, 2012, 11:40:11 AM
Better springs prevent the nose dive on a hard brake or turn. Better springs prevent the sag from heavier riders.
Heavier oil will not prevent those - only slow it down a little on a hard brake. Nothing for a couple fatties in the saddle.

Whew! Good thing I qualified my response with liberal use of "theoretically" and "should." I wasn't completely wrong, but at least I wasn't spreading completely false information. 

Quote from: mister on June 11, 2012, 11:33:07 AM
Maybe, if you know zip about fork oil and the like, you should not be writing about it in the wiki 

Maybe, if the people who actually knew about it, bothered to put it in the wiki themselves, I wouldnt have to 

So, meanwhile, can anyone with authoritative knowlege on the subject, please post a good snippet I can put in the wiki?

I'm thinking something like,

"Heavier fork oil slows down the response to fast inputs, whether from a bumpy road, or from a twitchy rider.
Heavier fork oil can thus be good for smoothing out overly fast rider input, but can be bad if you want your forks to quickly absorb and recover from a lot of potholes. Similarly, with heavier oil, a 'dive' from a hard brake, will still happen, but it will reach the bottom of the dive more slowly."

Isn't there another element to differing oil weight in general? .. such as operating temperature.  For instance, heavier weight oil is used in warmer temperatures and lighter weight oil is used in cooler temperatures... thinner weight reduces friction while heavier maintains higher pressures... or something along those lines.  Is that just engine oil? or is it more encompassing than that?

- Bboy

As related to motor oil  in the engine, there is that aspect. But the OP is specifically looking at the use of different oil weights inside the forks and the possible benefit.

I would think the differing viscosity versus ambient temperature effect would be negligible in motorcycle forks, mostly because not many people are going to ride in temperatures cold enough to feel a difference in the forks. Also fork oil is not used for lubrication of the forks, only for the damping/slowing aspect of the liquid.

Lighter viscosity oil is used in engines in cold climates because it provides less resistance to movement when the engine is cold.

I see. Thanks for that clarification... I just didn't know how relevant it was to forks, if any.  It sounds rather negligible if its not much to do with lubrication and so forth. 

- Bboy

While on the question of fork oil, is 15w fork oil any different that 15w motor oil?

Quote from: adidasguy on June 11, 2012, 01:57:45 PM
While on the question of fork oil, is 15w fork oil any different that 15w motor oil?

+1 on that question, I started wondering this myself.

- Bboy

Quote from: adidasguy on June 11, 2012, 01:57:45 PM
While on the question of fork oil, is 15w fork oil any different that 15w motor oil?

i would think that, for comparable grades of oil, fork oil should be cheaper, becuase it does not have to withstand high temperatures.
But, doing some google searches, there is a suggestion that fork oil is meant to withstand "foaming" better.

So, one has advantage against heat, whereas other has advantage against eggbeatering.

They're similar enough you can "get away with" using engine oil in forks, but sounds like you're a bit better off using the right stuff for the job.

Aha. Another informative snippet. stolen from http://uk.answers.yahoo.com/question/index?qid=20120206052713AApAvxA and paraphrased:
viscosity ratings are set around temperature assumptions. "10W" engine oil, is rated "10w" at engine temperatures, not room temperature.
(ie: that "15w engine oil", is going to be more like 17w in your forks, or something)

Best comprehensive answer I've found is here:

http://wiki.answers.com/Q/What_is_the_difference_between_hydraulic_oil_and_engine_oil

Quote from: Phil B on June 11, 2012, 02:11:37 PM

Quote from: adidasguy on June 11, 2012, 01:57:45 PM
While on the question of fork oil, is 15w fork oil any different that 15w motor oil?

i would think that, for comparable grades of oil, fork oil should be cheaper, becuase it does not have to withstand high temperatures.
But, doing some google searches, there is a suggestion that fork oil is meant to withstand "foaming" better.

So, one has advantage against heat, whereas other has advantage against eggbeatering.

They're similar enough you can "get away with" using engine oil in forks, but sounds like you're a bit better off using the right stuff for the job.

Aha. Another informative snippet. stolen from http://uk.answers.yahoo.com/question/index?qid=20120206052713AApAvxA and paraphrased:
viscosity ratings are set around temperature assumptions. "10W" engine oil, is rated "10w" at engine temperatures, not room temperature.
(ie: that "15w engine oil", is going to be more like 17w in your forks, or something)

Best comprehensive answer I've found is here:

http://wiki.answers.com/Q/What_is_the_difference_between_hydraulic_oil_and_engine_oil

Nope. The first number gives the viscosity at ambient temperatures, the 2nd gives it at engine operating temperatures. If you want to learn more about engine oil, visit http://www.bobistheoilguy.com/. Anyways, the oil is there to dampen the spring, and prevent it from "pogo-sticking." An oil that is too light will not fully prevent this, it is over-damped. Too heavy an oil will prevent it, but also absorb too much of the energy and the spring will not use it's full range of motion, this is over-damped. Ideally you want your oil to be right in the middle, damping just enough to prevent the spring from pogo-sticking, this is called critically damped. The proper weight of oil depends on the spring constant and operating temperature of the oil (if I recall correctly, those are the only two things that matter.) And there are differences between motor oil and fork oil, but tbh, I doubt that using motor oil in forks will cause any problems.