Fork Oil R80/7

[jackonz]

Right am going to pull the front forks out of the bike and clean them up, while I am at it I will of course drain the fork oil and replace with new, trouble is what oil and grade should go back in, most of the brands listed in the shop manual are either not made any more or not available in NZ, we are a small market you see.
As the grade of oil make a huge difference in damping and I have only ridden the bike about 10klm from where I picked it up to home it was really not long enough ride to assess the damping, NZ roads are quite bumpy and the national speed limit is 100kph (62mph) and here in the south island hilly and twisty, add to the fact am now 70 years young I really don't want to be riding like a racer, had I wanted to do that I would have kept the Ducati Monster.

So if anyone can advise on a good weight of fork oil given the above I would be most grateful, I do know we can get Spectro oil.

Stay Safe all

[jagarra]

A 7.5 weight seems to be a popular choice, I always looked for the available weight rather than a specific brand.

[melville]

Yes, 7.5 wt oil works great. I usually get BelRay, but I'm in the US.

[Rob Frankham]

Buying fork oil by 'weight' isn't really satisfactory. The actual viscosity of fork oil for a given SAE rating (weight) is hugely variable 'normal' temperatures. If you specify manufacturer and SAE rating, you stand a good chance of getting a reliable result. The 'W' in the SAE rating doesn't stans for weight, it stands for winter and shows that the displayed viscosity applies at 0 degrees C (32 degrees f). If there is no 'W', the SAE rating is taken at 100 degrees C (210 degrees F) it makes no comment on the viscosity at any other points in the temperature range. There is a scale of viscosities at various ranges but that's a lot more complicated.

In essence, find an oil you like and stick with it... there is no right answer.

[SteveD]

If you're unable to find some 5W & 10W to mix to get something in the vicinity of 7.5, maybe try some ATF. That should be available almost anywhere.

[gspd]

If you're unable to find some 5W & 10W to mix to get something in the vicinity of 7.5, maybe try some ATF. That should be available almost anywhere.

ATF should perform satisfactorily.
Bonus - It's available anywhere, and at a fraction of the price of dedicated fork oil.

[jackonz]

Buying fork oil by 'weight' isn't really satisfactory. The actual viscosity of fork oil for a given SAE rating (weight) is hugely variable 'normal' temperatures. If you specify manufacturer and SAE rating, you stand a good chance of getting a reliable result. The 'W' in the SAE rating doesn't stans for weight, it stands for winter and shows that the displayed viscosity applies at 0 degrees C (32 degrees f). If there is no 'W', the SAE rating is taken at 100 degrees C (210 degrees F) it makes no comment on the viscosity at any other points in the temperature range. There is a scale of viscosities at various ranges but that's a lot more complicated.

In essence, find an oil you like and stick with it... there is no right answer.

Hi Rob,

I totally agree with what you have written, I was hoping someone would have used Spectro Light and been able to give some feedback on how it performed for them as it seems to be one of the few options available, as for using ATF fluid no am not a fan of using that in forks at all, besides there are so many types of ATF now these days it would be hard to decide on what one to pick, I know as I work on a Polytech here in NZ where we teach Apprentice Mechanics and ATF fluid has become a very specialised product.

Looks like I will use Spectro Fork oil and start with the light grade and see how I get on.

[barryh]

Fork oil designations refer to the nominal viscosity at 100 Deg C which is a bit of nonsense, at least for road bikes as the oil runs much cooler than that. Fork oil manufacturers data sheets will also give you the viscosity at 40 Deg C which is a much better means of comparison between oils. Once you have found a oil that works for you, either keep using it or find another oil with similar viscosity at 40 C. Noting Robs comments on the meaning of W my view is that it is used incorrectly on forks oils and most certainly does not indicate the viscosity at 0 deg C. For example the viscosity of the Castrol Syn 5W is approx. 200 cSt at 0 Deg C

Here's a table of oils I found for sale some years ago ordered in viscosity at 40 C from the thinnest original BMW recommendation upwards. For my forks I a viscosity of 20 cSt at 40 c was about right.

Fork Oil.JPG (48.47 KiB) Viewed 1339 times

[Rob Frankham]

The letter 'W' os not up for interpretation, it is part of the SAE standard and refers to a viscosity measured at 0 degrees c. I doesn't mean anything at 40 degrees c or indeed 100 degrees c... which is the whole point really. It isn't really relevant for fork oils and many manufacturers don't quote it. The numeric definition of the oil is arbitrary and doesn't directly relate to a viscosity at any temperature. There are charts that give various figures that an oil has to comply with to use a number, viscosity is only one of the parameters.

Rob

[barryh]

We don't disagree that W is used inappropriately in most fork oils but most manufacturers do still use it in there designation and even in the few cases where they don't, the outlet selling the product often does.

There is clear correlation that the designated number refers to the approximate oil viscosity at 100 Deg C. I don't believe it's a just an arbitrary number without reference to a unit of measurement. Inappropriate as it is to rate fork oil in this way I believe they simply followed the practice for motor oil.

The bottom line is that the marketing of fork oil is a confusing mess such that the only sensible thing to do is ignore the designation and look at the manufacturers data sheet.