Forks. Stiffening My Forks.

[Mr.Incredible]

The forks on my Falco are using all their travel in normal road riding and feel as though they dive too much. I've wound the preload and compression up to max and they still do it.

There's a fair amount of fork leg poking through the yokes at present, so I will reduce this to lessen forward weight bias, but that won't be enough to solve the issue. I would rather avoid replacing the fork springs if possible, and am therefore asking what I would do with oil weight and air gap to achieve some of the effect I need.

As standard, they take 475cc of 7.5 oil and have a 110mm air gap.

Comments, suggestions and advice welcome. .

[mick.r]

Err... me thinks Sir should consider going on a diet!

[Barry]

Compression is wound right in you say?

You could try another 10mm of oil in each fork, take the air gap down to 100mm

[porter_jamie]

add compression damping, reduce air gap or increase spring rate.

(stick some more maybe heavier oil in, cut a couple of coils off with an angle grinder)

[daytona63]

Your springs are the problem. Is it cost that stops you wanting to change them?

You could try adding a spacer to the top of the spring maybe.

[chrisexup]

The springs are plenty heavy enough imho, at 1.0 kg/mm.

Although if you are a gert heavy chap, have a look at http://racetech.com/...0 Falco/2001-02 for a suggested spring rate for your weight.

Are the Showas the same as the Milles? i found the RSV didn't have enough rebound damping, so used 15wt oil, with a 120mm air gap. You could start off with this, and add oil until you get the compression you need? iirc i tried 20wt with an air gap <100mm and it felt far too firm.

[porter_jamie]

for road riding racetech (racetech website is for winners) recommends 0.95 springs for an 85kg rider. and stock are 1.0 as stated above. try some oil

[daytona63]

How to disassemble Falco forks guide here.

http://home.comcast.net/~sl_mille/springs2.html

[Mr.Incredible]

Thanks for the comments so far. NB my Falco is very late model and doesn't have the Mille Showa forks mentioned in Daytona63 or chrisexup's comments; it has Marzocchis with odd "internal" preload adjustment:

Yes, it is cost that's putting me off doing the springs, plus fork springs are designed to work with a massive variance in rider weight....having said that, mine have got 30k up now.

What I'd like to know is what weight fork oil to try, what to do with the air gap, and what the effects of doing so are likely to be. Chrisexup, please tell me more - what was the standard air gap in your forks, i.e. by what percentage did you reduce it? Also what was the std weight oil?

Thanks again

[beedub]

Here information about air gaps here. It's about dirt bikes and is off the internet so could be complete bullshit for all I know but it seems to make sense.

http://www.dirt-bike-secrets.com/oil-level.html

[porter_jamie]

racetech recommends 110mm, with the springs in. if you put more oil in you reduce the air capacity above the oil so the spring rate of the air that is left goes up a bit, so the forks feel harder. if you increase the air gap by putting less oil in you make the forks feel softer because the volume of the air increases and the spring rate of the air reduces.

that might seen counter intuitive - less air makes the air spring rate higher, more air makes air spring rate lower?

its the same with a metal spring. you chop a coil spring in half the rate is doubled. (assuming constant wind and wire diameter blah blah)

this is why if you snap a 300mm ruler into 2 150mm bits, a single 150mm bits feel stiffer than the 300mm bit did.

edit for silly typo

[porter_jamie]

No, I am right

[porter_jamie]

http://www.planetspring.com/pages/compression-spring-calculator-coil-calculator.php?id=compression

[porter_jamie]

most of the fork springs i have seen have not been progressively wound. particularly the tz ones were high helix, so no binding. progressive springs then this is obviously not true, but i did say for constant wind and wire diameter etc

i was using an analogy - less air = higher spring rate. less coils = higher spring rate

[porter_jamie]

ok, but my statement about cutting a coil spring in half and doubling it's rate (assuming no silly beehives, or tapered wire, or any of that nonsense) is absolutely, 100%, ten foot of concrete true. no question!

(active coils that is, don't count the ground flat ends)

[Cuzza]

Mr Incredible, you need to buy my Showa forks, that were serviced and re-valved 2 track days ago by Firefox racing, for £200 plus delivery and then sell yours on e-bay. That way you'll get uprated forks for less than £75 ;-)

The Showas came out of my track RSV / Tuono and, despite my considerable salad dodging girth, have never bottomed out on me!

Jon

[Mr.Incredible]

Cuzza, you make an interesting case. Got a pic of the mudguard and caliper mountings on the lowers?

I can't remember what I tried to set the sag to.

[BudgetBoy]

Go with 10w or 15w oil and reduce air gap to 90-100mm see how that goes.. You can take out 10mm at a time with the fork in situ.Cable tie on the fork leg to see whats happening.

[dansp1]

110mm air gap seems small to me, i would be wary about reducing it further.

You say it has 30k up, when was the fork oil last changed?

[Mr.Incredible]

Not for a while. It's pretty stinky.

Think I'll go with 15wt oil and std air gap for starters. What do we think?

I've had a cable tie on there and it's right near the bottom.

[Cuzza]

Cuzza, you make an interesting case. Got a pic of the mudguard and caliper mountings on the lowers?

I will take a pic for you, but if sir requires a mudguard that will fit and calipers too, then guess what............................I can supply them as I've currently got 3 sets of Brembo calipers in the garage and the mudguard from an 03 Tuono into the bargain ;-)

[peter30]

Set your front and rear sag correctly first, if you can.

Is that wise in a conversation with Mr I? I expect to see his front and rear sag in full 3d at the Excel tomorrow...

[Mr.Incredible]

Heavy dive on the brakes is the main theme, so it's weight transfer that's the problem.

[dansp1]

Do you know what the recommended oil is? most forks these days run a fairly light oil, if you jump from a 5w to a 15w your damping will likely be way out.

Don't under estimate the restorative effect of new (correct grade) oil, but if you do go heavier i would try it in small steps

oops, just re read your post, from 7.5w i would go to 10w, bearing in mind that the rank old 7.5w you are currently using has degraded to a 3w

[lorenzo]

Just to put things in really simple terms, You know when you first get on your brakes, that weight transfer thing you get, the initial slop onto the front, that's air gap. Less air gap, less initial slop. You know when you're already on the brakes and that slop's gone, and you really start to bury the front tyre into the road? That's your damping settings and oil weight.

If you don't know how old your oil is drain it and stick some fresh stuff in. It'll only cost you about £20, it's no biggy really, is it? You might find that initially it feels a bit too firm. I don't know what that is caused by but in an hour or two of riding it'll sort itself out.

[Mrdrink]

I've had a cable tie on there and it's right near the bottom.

Is it on the bottom or near? About 5mm from bottom is perfect.

[dansp1]

Just to put things in really simple terms, You know when you first get on your brakes, that weight transfer thing you get, the initial slop onto the front, that's air gap. Less air gap, less initial slop. You know when you're already on the brakes and that slop's gone, and you really start to bury the front tyre into the road? That's your damping settings and oil weight.

If you don't know how old your oil is drain it and stick some fresh stuff in. It'll only cost you about £20, it's no biggy really, is it? You might find that initially it feels a bit too firm. I don't know what that is caused by but in an hour or two of riding it'll sort itself out.

Now i may have this arse about face, (wouldn't be the first time) but i thought the air gap affected the end of the fork travel, because as the fork compressed the air acts like a secondary spring, smaller air gap stiffens up the end of travel....

[BudgetBoy]

Less air gap = More compression at end of travel.When the fork compresses the volume of air inside decreases,this in turn creates a force in "Addition" to the spring force.So it basically raises the spring rate as the fork compresses.But there is only so far you can go before you really need to replace the spring with a stiffer one.

Thicker oil = slower damping

Eat less= bike faster

Hope that helps

[lorenzo]

Now i may have this arse about face, (wouldn't be the first time) but i thought the air gap affected the end of the fork travel, because as the fork compressed the air acts like a secondary spring, smaller air gap stiffens up the end of travel....

Try it and see. I'm far from a suspension expert, but, by putting a bit more oil in my forks, this is what I found!

[dansp1]

I suspect the result you got was caused by the oil, (weight, condition,) and not the oil level, as mr Boy put it so succinctly it is the compressing of air at the end of the travel that assists the springs