Fork oil air gap

[Born again]

I am giving my forks a service, I know the book says an air gap of 104mm, and if you have a smaller air gap it will firm the damping.
Has anyone done a smaller air gap, if so how much of a gap did you use.
I am using 10w oil and standard springs.
Sorry if this has been talked about before, done a search but could not find anything..........

[chazzyb]

I am giving my forks a service, I know the book says an air gap of 104mm, and if you have a smaller air gap it will firm the damping.
Has anyone done a smaller air gap, if so how much of a gap did you use.
I am using 10w oil and standard springs.


It will firm it, however, there will come a point where it's so firm that road shocks won't get absorbed - they'll go straight up into the frame and YOU. Also, at some point, there's the possible question of the fork seals giving up. If you're going to experiment, only add enough oil at a time to change the level by say 5mm a go. A bit of experimentation when the forks are out with a graduated syringe will work out how much to add to achieve 5mm at a time.

Are you sure you don't want to try a heavier oil and perhaps a larger air gap to start with? Reducing the air gap will make compression damping start earlier (less air to compress before oil starts moving) but will not affect rebound damping. A heavier oil will affect rebound damping.

[jambo]

A smaller air gap will not alter the damping, It will increase the effective "air spring", the smaller the air gap, the more the air at the top of the fork is compressed during fork travel, This means that at the end of the travel, the effective spring rate will be higher than it would normally be. Don't go wild, a little change would make quite a difference.

[chazzyb]

A smaller air gap will not alter the damping, It will increase the effective "air spring", the smaller the air gap, the more the air at the top of the fork is compressed during fork travel, This means that at the end of the travel, the effective spring rate will be higher than it would normally be. Don't go wild, a little change would make quite a difference.

Sorry, I should have pointed this out too. The air gap doesn't affect the compression damping, but it does alter when it starts to take effect. The air will get compressed more easily to begin with, rather than pushing oil through damper holes.

[jambo]

Sorry, I should have pointed this out too. The air gap doesn't affect the compression damping, but it does alter when it starts to take effect. The air will get compressed more easily to begin with, rather than pushing oil through damper holes.

If you put oil in the fork without springs and fork caps you can feel the damping by pulling and pushing the fork stanction in and out of the fork lower. The oil is forced through the damper holes by the movement of the fork stanction in the body, not by the air above it.

The air gap affects the spring rate only, effectivly making the final part of travel stiffer like a progressive spring would.

If you were trying to get less dive under braking with adjustable suspension you would probably just up the compression damping rather than messing about with fork oil gap...
</pedant>:smt109

[chazzyb]

If you put oil in the fork without springs and fork caps you can feel the damping by pulling and pushing the fork stanction in and out of the fork lower. The oil is forced through the damper holes by the movement of the fork stanction in the body, not by the air above it.

The air gap affects the spring rate only, effectivly making the final part of travel stiffer like a progressive spring would.

If you were trying to get less dive under braking with adjustable suspension you would probably just up the compression damping rather than messing about with fork oil gap...
</pedant>:smt109

:scratch: Hey, no one likes a smart-**** (I'm kidding), even if you are right :p. Which, thinking about it, you most likely are. My 'knowledge' on the subject is limited, having based it on an old article I found about 'tuning' forks on a racing Laverda Jota.

[Flamin_Squirrel]

If you were trying to get less dive under braking with adjustable suspension you would probably just up the compression damping rather than messing about with fork oil gap...
</pedant>:smt109

You mean oil weight :p

[21QUEST]

What brand of oil are you intending to use.

At the moment, are you using all the suspension travel?


Ben

[jambo]

You mean oil weight :p
No I don't. I'd up the compression damping to slow fork dive rather than increasing the effective spring rate with air gap.

Not that the same principle with air gap doesn't apply to cartridge forks too, it's just that I wouldn't start there...

[johnnyrod]

I'd say use 15W but can't say anything on the air gap. Rebound damping is a bit minimal anyway so the extra from the thicker oil will help there too. If you're on the stock fork springs then damping isn't necessarily your problem...

[jambo]

Born again, at this point it's probably worth asking the question that's been missed out:

What would you like to change about the fork's characteristics?

Otherwise all the above is just pedantic fluff :p

[Flamin_Squirrel]

No I don't. I'd up the compression damping to slow fork dive rather than increasing the effective spring rate with air gap.

Not that the same principle with air gap doesn't apply to cartridge forks too, it's just that I wouldn't start there...

I mean you don't increase air gap to increase compression damping!

[jambo]

I mean you don't increase air gap to increase compression damping!

Quite right, but air gap can change how the fork travels under braking, if you don't want to change the fork oil as that will affect the rebound damping too, this is one thing you could do. You'd be reducing the air gap to get a stiffer fork spring effect. But you're right it would have no affect on damping, I believe that was my original post, but I sort of got sidetracked....:smt120

Edit: It mostly depends on if you're bottoming out under braking / riding in which case air-gap & springs are the way to go, or the forks are diving too quickley / feel bouncy in corners, in which case it's a damping issue.

I think....
Meh I've started to muddy thie issue by being useless again, I'm off to get lunch. Bornagain, let us know what you want to change and we'll start again from there!

[chazzyb]

The thing I'd add about upping the fork oil weight to 15W is the possible negative effect it has on compression damping. On 'normal' roads, my naked SV is fine. However, encountering some larger surface 'abnormalities' can prove disconcerting, like scary, if you're not expecting it. This is a problem with damper rod forks - damping is not linear.

[Born again]

Born again, at this point it's probably worth asking the question that's been missed out:

What would you like to change about the fork's characteristics?

Otherwise all the above is just pedantic fluff :p

I am using Putoline HPX 10 oil. I would like a little less dive under braking and to try and stop the soggyness on cornering on a bumpy road.
I am not what you could call a fast rider but I am not slow either, I would upgrade the springs but cant find the £80 at the moment.
The oil is being changed as is it well overdue.........Thanks for the advice.....

[Sid Squid]

Changing the air gap, (specifically the volume), won't change the damping characteristics - well, unless you make the air volume so eeeeeenormously large that the resulting volume of oil in the fork is so small as to be insufficient to cover the damper parts themselves, but then the damper wouldn't be working properly, (or at all), anyway, so it's an irrelevant argument.
What it does do is change the spring rate rise curve; higher oil level, (lower air volume), and the overall, (that is: curly bit of metal spring and air spring rates added together), spring rate rises more steeply, and will reach a higher final level. The reverse is also true; lower oil level, (larger air volume), and the overall rate curve will be shallower and will reach a lower final level.

Born Again:

If you lack the money for more suitable springs, change the oil to 15W and, (you having an SY which I think means you lack adjusters on the fork top caps), use spacers to get the spring set about right. That's 80% of what you'll get from a standard SV fork anyway, unless you're rather larger than the average weight yourself and thus require considerably different springs.

[skapegoat]

use 15weight instead of 10w and 104 air gap as per manual.:D

i did this recently and it improves the front end. dont go messing with anything elseunless your racing it.

for race set up on curvy get a spring suited to your weight.
use 17.5w fork oil(by mixing 20 and ten and using maths!)
block the two flow holes with a weld or chemical metal.

This is a basic race guide on a budget always use a cabletie on the fork to check travel after any fork rebuild!!!

[21QUEST]

Personally I'll only use 15W(again depends on what the "15W" actually is...) if I only rode on smooth roads.

You'll have less dive, feels pretty good on the low speed compression but be prepared to have crap high speed compression ie harsh when you hit those square bumps.


Born again, just noticed you are going to be using putoline 10wt. I reckon it may feel a bit harsh on the bumpy bit but in any case you can always try it out. For that oil I'll say start of with an air gap of 110.
Put a cable tie on the fork stanchions and you can always add a little bit(5ml) at a time. How much do you weigh if it's not too personal a question :).

I've currently got Putoline 7.5wt in my forks. Last year I tried the Putoline 15wt or 10wt (can't remember) with the vicosity measured in centistokes compared to the Suzuki fork oil, I decided to go with the 7.5 as a known base and work from there.

The Putoline 7.5 has a slightly higher Viscosity compared to the Suzuki fork oil (L10 or something like that). it could possible do with a bit more low speed compression and rebound but as already said the high speed can only get worse. For now untill I have time to experiment more it's a good compromise IMO.

As an aside, if you use Putoline 15WT, you would have effectively doubled the oil viscosity ;).
Debateable I guess, if that is a good thing or not. I wouldn't want to ride that on bumpy back roads and such myself.


Ben

PS: ...and as SS said try and get your SAG as close as you can with the acceptable range for both Bike and rider. I think I've got spacers(aluminium) somewhere. I just have to remember where they are. PM me if you want them and I'll search for them and let you know.

[Born again]

I weigh about eleven stone without riding gear, I have stripped and rebuilt the forks given them a good clean, filled them with the putolin 10w and leaving them to stand to make sure the air bubbles are gone so I can get the air gap even.
I will do a search on setting the static sag. I did notice on one leg the dust cap wasn't to good and let some water in, that could explain a lot anyway.

[21QUEST]

Did you fully compress and extend(slowly) the stanchions to help with removing any air bubbles ie bleeding. Hope I'm not teaching you"how to suck eggs" here. :) .I just do it slowly until I can see any bubbles rising to the top before leaving them to stand.

What air gap have you settled on? Putoline 10wt is about 50% higher viscosity compared to the Suzuki oil.


Ben

[Born again]

Yes I did pump them, leaving them overnight to settle I will measure the gap again, I think I might go with 104mm and see how it handles with the new oil.

[21QUEST]

It's easier to add oil than to remove ;) .
Looking forward to your feedback though as it's the same Brand I use. Might provide some useful information for me.


Ben

[Born again]

Thanks for the advice everyone, should get it all back together tomorrow (work gets in the way sometimes) I will give feedback as to how the bike feels when I get out on a decent ride..........

[Born again]

Just an update.....I used Putoline 10w, 102mm air gap, standard springs, took it out for a good run today. A mix of 'A' roads and lots of twisties, it felt a lot firmer with the new oil & oil seals. I think the limiting factor now is me.
I dare say come the end of the summer I will be picking holes in the suspention again, once I have more riding time in and my skills improve..
Thanks for the advice given.......

[Big Chris]

This is an oldish thread but it has the information I'm looing for in it. I've scanned through and see reference to "Suzuki oil". Don't seem to be able to see the weight of it, Can I assume from reading this that it is around 7.5wt oil?
I'm going to be trying a 15wt oil for a test as I find the front end to be extremely soggy to say the least.

[Big Chris]

Well, I have to say after a run out on the bike, the 15wt oil done the job! Still need to sort out the sag on the front but, it now feels like it's working it's tyres and you don't have a feeling of disapearing over the bars every time you shut off the gas, it also feels a lot more stable when cranked over a ways. Well happy :D

[skapegoat]

use 15weight instead of 10w and 104 air gap as per manual.:D

i did this recently and it improves the front end. dont go messing with anything elseunless your racing it.

for race set up on curvy get a spring suited to your weight.
use 17.5w fork oil(by mixing 20 and ten and using maths!)
block the two flow holes with a weld or chemical metal.

This is a basic race guide on a budget always use a cabletie on the fork to check travel after any fork rebuild!!!


Told you 15w on the road was best.
Did you put in progressive springs?

[Big Chris]

No not yet, think they may well be on the list of purchases. The front was flopping round like a beached Herring, it had no grip problems but, every time you brake or shut off the gas you were looking at the front tyre with the dive! It's infinitely better and much more confidence inspiring. Stop it sagging like ya granny's tights and it's a sure fire winner this bike, just needs a motor like my XJR to give it some go and I might just take it off it's owner :D :D