make fork adjustments through oil choice

bluechair84

Ok, so the 2005 Boxxers I've picked up are slightly dodgy. I think they will work fine but the adjustable rebound is locked into one position and there's no external preload adjustment, I have to add spacers into the top of the leg. So I'm wondering, without sending it off to be tuned (TF have said they can still tune the fork to a range of rebound speeds), what can I do myself?
The assumptions I'm working too that I'd like confirming;
If I increase the amount of oil in the fork, it will increase bottom our resistance.
Too much oil will limit the maximum travel.
A thicker weight oil will slow down both compression and rebound.
A lighter oil will speed R&C up.
Adding preload spacers will stiffen the fork up and reduce sag.

Are these assumptions correct? Is there anything else I can do?

nicklouse

bluechair84 wrote:

The assumptions I'm working too that I'd like confirming;
If I increase the amount of oil in the fork, it will increase bottom our resistance.
Too much oil will limit the maximum travel.
A thicker weight oil will slow down both compression and rebound.
A lighter oil will speed R&C up.
Adding preload spacers will stiffen the fork up and reduce sag.

Are these assumptions correct? Is there anything else I can do?

first off which Boxxers?
1 nope it will make the air chamber smaller and cause the air spring to ramp up faster. but if you go way to much then yes it could.
2 only if they both use the same oil. but as they use different oils then you can play. again presuming that the compression is actually damped.
3 see above.
4 NO the spring rate will be the same. it will just make it need more force to start moving and you could get coil bind.

bluechair84

nicklouse wrote:

bluechair84 wrote:

The assumptions I'm working too that I'd like confirming;
If I increase the amount of oil in the fork, it will increase bottom our resistance.
Too much oil will limit the maximum travel.
A thicker weight oil will slow down both compression and rebound.
A lighter oil will speed R&C up.
Adding preload spacers will stiffen the fork up and reduce sag.

Are these assumptions correct? Is there anything else I can do?

first off which Boxxers?

2005 Hydarcoil. Spring in both legs, only has rebound adjustment (but as said, it's seized and I've striped the shaft down to it's component parts and it can't be repaired - it's now obsolete so no replacement).
Can you give any recommendations on what I could play with to tailor it any?

nicklouse

bluechair84 wrote:

2005 Hydarcoil.

so the Ride? the Race? the Team? or the World Cup!

and 7" or 8" version?

bluechair84

Opp sorry, pretty noob omission. 2005 Race 8". It's pre U-Turn, no external adjustment other than the rebound.

nicklouse

Ok now the BIG question. How much do you want to spend? Or........ How little?

bluechair84

As the forks only cost me £100 I won't be going mad. When I posted this I was assuming that by changing the oil weight or volume I could make minor adjustments, so costs in the region of £20. A TF tune is £100 but that's far too much, I'd be better selling these and getting a newer adjustable version.
My aim is going to be to get these fitted then mess around with tuning to see if I prefer the Torque with a bigger fork on the front. If I do, then I'll prepare for a much better fork upgrade.

benpinnick

Been a while since I fiddled with 2005 boxxers, and Nicklouse has covered most of it but heres my tuppence:

If I increase the amount of oil in the fork, it will increase bottom our resistance - Not sure, seems unlikely. Theres no airspring so nothing to be affected by oil volume, so no ramp up.
Too much oil will limit the maximum travel. - Absolutely. 190ml springs to mind...
A thicker weight oil will slow down both compression and rebound. The 2005 race was the last year with no MOCO, and so no compression (on the Race anyhow). So your only messing with rebound,
A lighter oil will speed R&C up. Yep (R anyway). Remeber you can also mix oils to get intermediate weights.
Adding preload spacers will stiffen the fork up and reduce sag. No and yes, in that order. Think of it as each bit of extra preload is like you going on a diet, at least in Sag terms.

nicklouse

The air spring is the closed leg.

yes it is not called a spring but as it is a closed chamber it works as one.

benpinnick

Closed leg? I remeber these forks being dual mechanical spring with a dummy damper unit in the non rebound leg, making them essentially the same on both legs, so which is the closed leg - the one with the rebound damper? I guess that since the oil doesnt pee out everywhere they must be sealed to an extent, and so some spring effect will occur. Good point.

nicklouse

benpinnick wrote:

Closed leg? I remeber these forks being dual mechanical spring with a dummy damper unit in the non rebound leg, making them essentially the same on both legs, so which is the closed leg - the one with the rebound damper? I guess that since the oil doesnt pee out everywhere they are sealed to an extent, and so some spring effect will occur mind.

There are very few forks out there tharhave open legs. White brothers being one and some Fox.

They tend to be open bath type IE. take the top cap off and you can poor the oil out. Clse the cap and you have made a closed tube the as you compress the fork you are compressing eveything inside it. Both the spring and the air trapped in it.So yes there is an air spring in there that can be effected by the oil level.

Anyway back to the 2004 Race. You do have some seperate control of the damping internally.

Service manual etc. http://cdn.sram.com/cdn/farfuture/j4IPN ... eGuide.pdf

benpinnick

I dont think the race does - its a neutral shaft only. The WC and Team had an internal compression damper.

bluechair84

Cheers for all the input. So I'll be adjusting the spring rate which should allow me to stiffen up the fork a little, (more towards the end stroke) through oil volume in the rebound leg. And I can adjust rebound speed with oil weight. I've read that small changes make a big difference so I'll be experimenting with small volumes of additional 10 I think.

benpinnick

The air spring will only really impact bottom out. A 1 atmosphere spring will have negligible effect until its almost fully compressed I suspect, as the air spring is progressive, and so assuming it is 100mm long, the change from 100mm to 50mm of air will be easy, offering little or no real resistance, but the change from 20 to 10 will be very hard - hence preventing bottom out.