Fork Oil Question

[Blapper]

Hi Guys,

Just drained my fork oil and found it was in good condition which leaves me in a quandary. I like supple suspension but don't like dive so was thinking about 15W oil instead of 10W. I am not going to fit upside down forks and am not yet at the stage of fitting emulators.

Does the collective think there is a benefit in going to 15W?

Thanks peeps.

[maviczap]

I used 15w in mine when i had the original front end in, but for my puny 70kg it made it too harsh, and that was with progressive fork springs. The standard springs are the main cause of the dive, so using heavier oil isn't going to help much.

Get some proper linear springs matched to your weight, and fork oil to match. Its the only way to start to improve the crappy standard front end.

[Bibio]

heavier oil will not stop dive. oil is for dampening, springs are for weight and the size of orifice in the damper rod dictates the flow of the oil (dampening effect). simple damper rod forks will always dive unless you fit some sort of device that has a 'popper' valve such as emulators. now having said that the correct springs and oil will go a long way in helping the situation. but the oil viscosity is a trial and error thing to get right.

emulators work by restricting the flow of the oil till a certain velocity (bump) which then opens a sprung valve to allow more flow of oil. the valve should stay shut for 'slow speed' velocity movements such as braking but then open for 'high speed' things such as bumps.

dont confuse high speed and low speed for speed of bike as in MPH, its the speed of the stanchion movement in the fork tube.

EDIT:
heavier oil restricts the speed of the stanchion so you end up with a harsh ride.

suspension is about keeping the tyre in contact with the road while also keeping the chassis for unwanted movement. its a very difficult thing to get right and everyone has a different 'feel' to how they like suspension.

personally i would suggest changing your braking habits, if your front end is diving when your braking then your braking too fierce. its a v-twin learn to use the engine braking. i mostly use my brakes for stopping or scrubbing speed and not for braking into corners or such (unless i go in a bit hot then i'll trail brake).

[Blapper]

Thanks for that Bibio, I didn't know emulators opened up on bumps! I Like that. I do use the engine braking mainly I can assure you but I even find dive on engine braking!

What weight oil do you use/how much do you weigh?

[Blapper]

Cheers maviczap, that's really what I suspected. <sigh> More money....

[carelesschucca]

Bibios settings won't help you, he's got Gixer forks and is about 5 foot tall in his high heels...

I'd need to check what I had in my SV (it was a long Long time ago) I think I used a 50/50 mix of 5w and 10w oil, the big difference was I had WP springs in it, and a Heath Robinson set of washers in the top of the fork to give the spring a bit of pre-load.

[Bibio]

Originally Posted by carelesschucca

Bibios settings won't help you, he's got Gixer forks and is about 5 foot tall in his high heels...

stop telling everyone about my high heels

oil viscosity wont do diddly squat for how heavy you are as thats what the spring rate is for.

unless your 9st then you will need new springs. the correct springs and oil will go long way to help the situation and indeed most people are happy with that but the fact of the matter is you will never stop dive on simple damper rod forks without introducing harshness and in some circumstances tyre to road contact will suffer due to rate of fork movement.

the big problem with not having the correct rate of springs is that you will try to over compensate the dive with heavier oil like most people do. having the correct rate of spring will help dive to an extent.

a lot of people say their bike is superb handling with heavier oil.. well yes that is until you hit a bump/pot hole mid corner then its into a hedge you go.

dont worry too much about front end dive and in some circumstances it can help depending on your riding style, just look at the WSB racing to see how much their forks dive. only difference is that the rate of dive and indeed extension is more controlled to give unwanted 'pop' or 'pogo'.

[Bibio]

down and dirty most cost effective solution for sv forks:

weld up the damper rod rebound holes.
get the correct linier springs for your weight
silkolene 7.5 rsf oil (+bottle of 20wt)

once you have done that then its trial and error with the oil. to set the correct oil viscosity you do the 'bounce test' and see how far or not the rebound overshoot is. if it still overshoots a fair amount then remove 40ml from each fork and replace with the 20wt. reducing the air gap will also help bottoming but at the risk of blowing seals if you go too far.

BTW you cant measure the oil amount in forks you have to measure the oil hight by using a special tool.

[Blapper]

Originally Posted by Bibio

down and dirty most cost effective solution for sv forks:
BTW you cant measure the oil amount in forks you have to measure the oil height by using a special tool.

That would be a ruler?

[Bibio]

ermm sort of but you have to ask the question of how to get oil out if you over fill.