Fork air gap query

[Stormin Ben]

Evening all, long time no post so I figured I'd try and make it a good one

Currently in the process of replacing the oil in the forks
The usual directions for amount of oil are either volume (448cc ±2)
Or distance from fork top with leg compressed and spring removed (130mm)

However I have some different springs in the forks which have a slightly thicker coil
So the measurements above would obviously give a reduced air gap and the possibility of hydraulic locking

Therefore my question is:
Does anyone have any idea what the air gap with the spring IN SITU would be?


Cheers
Ben

[tony.mon]

No idea, and not important, I don't think- I spent a weekend or two setting the forks up and changing the air gap by 5mm at a time- the only good settings I found were 140mm and 145mm, not much difference between the two in terms of feel, but 5mm either side was definitely too hard or too soft.
Dunno if different springs would make a difference, but I wouldn't think so.
Play and let us know.

[Stormin Ben]

Hi Tony,
Cheers for that, interesting you went for MORE air gap than stock, was that with std springs?

Reason for query is if for example you have 140mm gap without springs and you then insert std springs they will obviously displace some oil so the air gap will reduce to sat 120mm
The gauge of the wire in my springs is slightly thicker so in the example above the same 140mm gap would reduce to 110mm.
From your comments this 10mm difference would make a noticeable difference

Out of interest, what symptoms did you encounter when you say 'too hard'?

Ben

[Flatline]

This may be of use buddy

http://www.ablett.jp/bikes/vtr/vtr_sus.htm

[VTRDark]

It's quite an interesting question actually because as little as 5mm air gap can make a significant difference. Which by the way should be 140, not 130, but I guess this is dependant on what weight oil is used. If a 1mm relief hole, can make a difference then we are talking about some tight tolerances here. I suppose there's no harm in experimenting with different weights and gaps as long as you able to end up with the right amount of sag at the end.

So if one uses thicker springs that take up more space inside the cartridge then it's going to displace more fluid which changes the air gap. It's not just thickness of spring but then there is the various lengths between brands, they will also vary in weight. So will all displace more fluid which changes the air gap. Then off course there is the spacer which could vary in length/weight according to how long the springs are to make up the 410mm magic number.

I have never quite understood why fluid levels should be measured with the springs out. It seems more logical to me to do it with the springs in as it would then be irrelevant what springs you have and the gap would be the same no matter what.

(:-})

[tony.mon]

I think on balance the best advice I can give will probably not be followed, but here goes:

Fit new fork bushes and head bearings of needed, then build your forks with a standard setting- say 145mm air gap, 7.5 weight oil, springs out, compressed legs.

Ride it a bit and see how it feels.
Now head for home, and by undoing one fork top at a time, with someone holding the bike over on the side stand so that the front wheel's off the floor, you should have enough of a gap to add enough oil to raise the level to 135mm- someone will be along with a calculation as to how much this will be- 25cc's?
Clue: the internal diameter of the fork tube will be about 35mm....

Refit the fork top, then do the same to the other one.
Ride it again; see which one you preferred.

You can always take some out by loosening the cartridge retaining Allen bolt under the fork leg, but you'll have to take the wheel and axle out first.

keep playing until you find what setting feels best.

Once you have a good air gap, do the same for different oil weights.
It's very laborious, but the only way to get the best set up, not only for your weight, but also riding style- we're all different in that regard.
For example I like to keep my weight as far forward as I can, over the front wheel. This places more weight on the front, and you have to trust your tyre, but reduces wheelies on acceleration.

But set aside a weekend and you'll have it cracked.

[sirch345]

Hi Ben, good to see you back it looks like you have a bit of work on with the forks. Is this on your old Storm

Chris.

[Stormin Ben]

Thanks for all the assistance guys, especially Tony
Your advice WILL actually be taken, but just not this week as I needed to get it sorted before heading abroad at the weekend (nothing like leaving it til the last minute eh )

However in this case I took a view and set the air gap to 145mm with 5wt oil on the basis I can add oil a bit at a time if it was too soft
Previously I had 7.5wt and a 135mm air gap (to reduce the std forks tendency to collapse under hard use)
This caused the front end to feel fine under braking and slow speed compression but go solid for high speed.
I put this down to the thicker weight oil but my interest in the air gap is because that will also affect how the forks behave under heavy use as the air will only compress a certain amount before going solid

After the initial test ride (albeit without fairing so slightly less load) I'm much happier with the forks now as I can actually go over bumps without having to let go of the bars
So now I can add oil a bit at a time if I feel it warrants it but at this point I dont feel the need to

I have never quite understood why fluid levels should be measured with the springs out. It seems more logical to me to do it with the springs in as it would then be irrelevant what springs you have and the gap would be the same no matter what.
(:-})

I think the reason for this is it is MUCH easier to measure sans springs and legs compressed
With the springs in there is no room to measure the level with the legs compressed and measuring from the top of the springs introduces even more variables

This may be of use buddy
http://www.ablett.jp/bikes/vtr/vtr_sus.htm

Ah the old classic VTR suspension bible
Cheers for that buddy

Is this on your old Storm
Chris.

Yep, biggest regret was selling the Blade front end but hey ho, you live and learn and at the time I had no idea I'd still have the Storm 7 years later!!
Lesson learnt