Changing Fork Oil Viscosity

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SteveD
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Re: Changing Fork Oil Viscosity

Postby SteveD » Thu Oct 15, 2020 8:53 am

Ah, right. Good idea methinks.

Is it a social domestic pleasure thing only or can you use a wagon (or other vehicle) for commercial work?
Unable to use any red plate vehicle for work, but I do use it occasionally to get to and fro work. But officer, I'm not using it FOR work".:-k :-"

I took it for a local ride around the streets today. It sure feels good, better with ikon progressives and the Spectro 7.5W oil. Just a slow tootle but much more solid under brakes with much less front dive. \:D/
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Re: Changing Fork Oil Viscosity

Postby Mjolinor » Thu Oct 15, 2020 9:46 am

Ah, right. Good idea methinks.

Is it a social domestic pleasure thing only or can you use a wagon (or other vehicle) for commercial work?
Unable to use any red plate vehicle for work, but I do use it occasionally to get to and fro work. But officer, I'm not using it FOR work".:-k :-"

I took it for a local ride around the streets today. It sure feels good, better with ikon progressives and the Spectro 7.5W oil. Just a slow tootle but much more solid under brakes with much less front dive. \:D/
Apologies here for being seriously off topic.

Are those thousands of miles of dirt road away from civilisation classed as roads and covered under the normal Aussie equivalent of the road traffic act?

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Re: Changing Fork Oil Viscosity

Postby Rob Frankhamr » Thu Oct 15, 2020 10:01 am

Did suggest air gap with forks fully compressed, which on most forks will not restrict travel.
That's not what I meant... with no 'air gap' the forks will be hydraulically locked solid and there will be no movement whatsoever. Fork oil, like most fluids, in not compressible. Equally if there is an air gap (and assuming the fork is sealed), you can't close the air gap completely by compressing the suspension unless you get to the point where air ceases to be a gas (an academic point because you would have blown all of the seals long before that point is reached). The air above the fluid in conventional forks acts as a subsidiary spring. The smaller the volume, the greater the springing effect and the less the suspension will compress for any given displacement force.

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Re: Changing Fork Oil Viscosity

Postby CharlieVictor » Sat Oct 17, 2020 3:01 pm

Damn... I was hoping for a yes or no answer... :???:
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Re: Changing Fork Oil Viscosity

Postby andyb » Sat Oct 17, 2020 8:32 pm

Rob,
That is what I said in my post on the front page. Less oil adds more air and softens the forks.
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Re: Changing Fork Oil Viscosity

Postby Rob Frankhamr » Sun Oct 18, 2020 10:17 am

Rob,
That is what I said in my post on the front page. Less oil adds more air and softens the forks.
AndyB
Andy,

Absoultely... My post wasn't targeted at yours, just trying to clarify my earlier post...

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Re: Changing Fork Oil Viscosity

Postby Tincan3 » Sun Oct 18, 2020 10:55 am

This is a situation with multiple variables all influencing the outcome so that it is no wonder there is much discussion and opinion.

We have:
progressive springs
continuous springs
spring rate
oil volume
oil viscosity
suspension travel

Have I left any variables out??!
Normally, with three variables, a three dimensional plot will be quite revealing but I am not sure where you go with five or six variables. :-k

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Re: Changing Fork Oil Viscosity

Postby Mjolinor » Sun Oct 18, 2020 11:34 am

Probably one of the more important factors is temperature.

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Re: Changing Fork Oil Viscosity

Postby barryh » Sun Oct 18, 2020 12:28 pm

The pertinent thing about temperature is that fork oil is marketed with the viscosity at 100 deg C which the oil never reaches. The viscosity at 40 C is better guide and even if the oil should exceed that figure it will still be nearer to reality than 100 C.

In my experience of getting what are relatively crude forks to work well and still have a comfortable ride, the most important factor was increasing rebound damping without increasing compression damping.

Due to damping increasing exponentially with input velocity, simple damper rod forks will only ever be comfortable with relatively light compression damping otherwise they will react harshly to high velocity inputs like sharp edges in the road surface. Rebound damping needs to be several times stronger than compression damping to control the forks under extension but thicker oil is not the answer as it increases both compression and rebound. Short of retrofitting expensive cartridge damper valves, the only way to increase one without the other is attention to the tolerances of the damper valve washer which I found leaked more oil than than passed through the rebound orifice itself. Tightening up the tolerance with a custom made washer made the difference I was looking for.

Often the problem with forks is deemed to be excessive dive under braking and sadly the answer is to fit stiffer springs which then needs thicker oil, both of which ruin the ride. A better approach is either to accept the dive, after all what is the point of having X inches of suspension travel if it's never used or alternatively control dive with the oil level by reducing the air space which creates a progressive spring rate without making the forks harsh at normal ride height.

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Re: Changing Fork Oil Viscosity

Postby SteveD » Sun Oct 18, 2020 1:23 pm

Apologies here for being seriously off topic.

Are those thousands of miles of dirt road away from civilisation classed as roads and covered under the normal Aussie equivalent of the road traffic act?
yep, unless private property. Highest speed limit is 110kph generally, though on a few outback bitumen highways they are 130kph. The Nullabor f'instance is 110kph and in WA aerial surveillance isn't unheard of. In the '80's I did it a couple of times on a MG LeMans and sat on 180kph for hours. Great fun, but just not worth it these days.
Last year...4200kms in 6 days.
We got decent fuel economy using a mix of 91, 95, 98 ron. Didn't notice much difference in economy b/w refills and the bike ran well. Most we paid was $OZ 2.10 a litre for 91 ron. Generally sat just above the slight R grip vibe band at 125-130kph.
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Re: Changing Fork Oil Viscosity

Postby Rob Frankhamr » Sun Oct 18, 2020 5:55 pm

The pertinent thing about temperature is that fork oil is marketed with the viscosity at 100 deg C which the oil never reaches. The viscosity at 40 C is better guide and even if the oil should exceed that figure it will still be nearer to reality than 100 C.


The SAE rating normally used for for oil is a 'W' (winter) rating which as at -17.5c not 100c. Not that it makes any real difference to the points you make. It's still a tamperature the forms are unlikely to see.

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Re: Changing Fork Oil Viscosity

Postby CharlieVictor » Sun Oct 18, 2020 6:08 pm

Apologies here for being seriously off topic.

Are those thousands of miles of dirt road away from civilisation classed as roads and covered under the normal Aussie equivalent of the road traffic act?
yep, unless private property. Highest speed limit is 110kph generally, though on a few outback bitumen highways they are 130kph. The Nullabor f'instance is 110kph and in WA aerial surveillance isn't unheard of. In the '80's I did it a couple of times on a MG LeMans and sat on 180kph for hours. Great fun, but just not worth it these days.
Last year...4200kms in 6 days.
We got decent fuel economy using a mix of 91, 95, 98 ron. Didn't notice much difference in economy b/w refills and the bike ran well. Most we paid was $OZ 2.10 a litre for 91 ron. Generally sat just above the slight R grip vibe band at 125-130kph.
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Re: Changing Fork Oil Viscosity

Postby SteveD » Mon Oct 19, 2020 3:55 am

A JPS Australian Special Edition?
Yep, not original though.
Cheers, Steve.
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Re: Changing Fork Oil Viscosity

Postby Mjolinor » Mon Oct 19, 2020 4:08 am

I want to go to Australia. :)

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Re: Changing Fork Oil Viscosity

Postby Roy Gavin » Mon Oct 19, 2020 2:27 pm

Yes, you might, but remember it is populated by Australians-----!

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Re: Changing Fork Oil Viscosity

Postby DEEP DIVER » Mon Oct 19, 2020 3:03 pm

Yes, you might, but remember it is populated by Australians-----!
And snakes, spiders, crocs, #-o
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Re: Changing Fork Oil Viscosity

Postby Mjolinor » Mon Oct 19, 2020 3:07 pm

I nearly went once. I was in Indonesia working and due to some local holiday I had from lunch on Friday until Tuesday morning with nothing to do. Apparently there was a local puddle jumper type aircraft that would have taken me over but I weighed the energy required doing that to the energy required to sleep all weekend and sleep won. I think I regret that decision because no way will I ever go now.

The other interesting thing that happened on that trip was that as we were driving South from the North coast of Java it suddenly went almost dark which baffled me, it then started raining and then piles of ash and what a stink. The hill we were driving round had started erupting, it being an active volcano. I am all like WTF GET ME OUT OF HERE. :eek:

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Re: Changing Fork Oil Viscosity

Postby John Marshall » Mon Oct 19, 2020 3:07 pm

Don’t forget mosquitoes.

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Re: Changing Fork Oil Viscosity

Postby Mike D » Mon Oct 19, 2020 3:49 pm

And a gazillion flies!

You can be driving at speed, then stop the car seemingly nowhere and by the time you are out the flies are around your head. I learned the 'Aussie Wave' very quickly!

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Re: Changing Fork Oil Viscosity

Postby Rob Frankhamr » Tue Oct 20, 2020 9:24 am

And most certainly don't forget the 'Roos... We did 5000k in NSW and Victoria and I'd say that 85% of the Roos we saw were dead at the side of the road. Make you realise why the locals all drive Utes with BIG Roo Bars. Thery can travel at 25 to 30 MPH and have developed no concept of roads or motor vehicles (I guess evolution doesn't work when most of the individuals that meet the problem die!)... They're also quite well camouflaged even when they are moving so they appear out of nowhere. Forget your snakes, mosquitos, spiders and sharks, more people are killed by Roo's in Australia than by any other wild animal.
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Re: Changing Fork Oil Viscosity

Postby Mjolinor » Tue Oct 20, 2020 9:30 am

Camels too. They don't exactly bounce off, neither do cows and they sure have enough of those.

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Re: Changing Fork Oil Viscosity

Postby SteveD » Tue Oct 20, 2020 9:43 am

https://youtu.be/lpcz1qcxYuA

Jeff hit this small version, pulled a branch from the forks that were bent, physically tweaked it to resemble something straight then rode it home 700+kms.

They're just quick and unpredictable. Much worse at dawn or dusk. I've "brushed" one at 140kph :shock: ...both going in the same direction! Kept the speed up and no problems but lucky there was nothing coming the other way as I was forced to meander into the other side of the road. [-o< That was 1983 on a K100.
Two years back out near Broken Hill, at dusk as we were late, 3 'roos jumped onto the road in front and then suddenly scattered at lightening speed in three different directions. Scared the life out of me and we tootled into our destination at 40kph...where we were confronted with 3 donkeys wandering down the road on the outskirts of town. :shock:
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Re: Changing Fork Oil Viscosity

Postby Mjolinor » Tue Oct 20, 2020 10:04 am

Enough roadkill to feed the entire nation for free. Plenty of choice between cow, sheep, goat, kangaroo and camel too. For those with a more eclectic taste there are always snakes and koalas. I have never heard of anyone eating koalas though, I suppose they are too cute.
Last edited by Mjolinor on Tue Oct 20, 2020 10:05 am, edited 1 time in total.

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Re: Changing Fork Oil Viscosity

Postby Rob Frankhamr » Tue Oct 20, 2020 10:04 am

I think the most amusing scanario ea came across was between Barcaldine and Longreach (well I think it was that stretch... somewhere within 1000 k of there anyway.

A smallish herd of cattle on the road driven by Mr Outback Farmer with the help of Mrs Outback Farmer and the dogs with the family Ute following along driven by a lad who can't have been more than 12 years old. He must have been navigating by radar because I can't imagine how he could see over the dashboard. We stopped and kept well out of the way :grin: Ah, Rural life...

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Re: Changing Fork Oil Viscosity

Postby Mjolinor » Tue Oct 20, 2020 10:07 am

You are making me feel so inadequate. The furthest I have ever been on a bike is Burnley to Liverpool then down to Cardiff. I considered that to be an epic back then.


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