Forks

[AJT 11]

I have an NC750XD-E (2015 ). Its done 16,000 miles so it seems like a good idea to change the fork oil. I've read it should be 10W grade and 104mm from the top of the stanchion. Is this information correct or is there a better option? I've read on this forum that thinner oil can give a softer action and a level of 140mm is the correct one to use. I don't ride like I'm on a race track, I'm looking for increased comfort over bumps and pot-holes. What do you all think?

[kayz1 2,928]

****I'm looking for increased comfort over bumps and pot-holes. What do you all think?****

 

X-ADV fits the bill...

You will find a large thread on suspender upgrades...a few people have gone that route i changed bike.

[DaveM59 1,603]

It's a black art, fork tuning!

Thinner oil will allow a more rapid softer action of the forks, but also possibly induce a wallowing and excessive dive under braking, even bouncing onto the stops at times. There is also the need to know if you want less compression or rebound damping or both. Changing the oil alone affects both to a similar degree.

Going a whole grade from medium to light may be too much but the only way to find out is try it. A half grade of a 50:50 mix of fresh whats in now and a lighter grade may be better, but again try it and see.

Now you can see how a simple change in theory can be a lot of work in practice.

Also if you are reasonably happy as it is, and there are no leaks, just because it has 16,000 miles doesn't mean you have to change it at all unless you can tell there is some noticeable deterioration in performance. After all 16,000 miles of relatively smooth motorway miles won't have churned the oil half as much as 16,000 miles of city pot holes so do you have any idea of the bikes history in this respect?

[AJT 11]

According to the Bike's previous owner, its been used mostly in London. I'm planning to fit fork gaiters and since the forks will be out anyway, changing the oil shouldn't be too much extra trouble.

[embee 7,288]

Fork oil is not all the same, even when labelled with a certain grade on the bottle. I use only Fuchs/Silkolene Maintain RSF (previously called PRO RSF, same stuff) fork oil because it has a high "VI" (viscosity index) which means it doesn't change viscosity with temperature as much as oils with a low VI. Have a look at the table of commercially available oils here http://peterverdone.com/wiki/?title=Suspension_Fluid

and compare the viscosity at 40C and the VI. 

FWIW I use RSF 7.5W which if you look at the numbers is actually comparable to most 10W oils (the label is only a guide, somewhere round 35cSt at 40C is about right). I get it from https://www.sportsbikeshop.co.uk/

I usually aim to change fork oil at around 10k miles intervals, which is typically 2yrs of my use.

 

The oil level is specified with the spring and spacer removed, and the fork fully compressed and upright. The air gap affects how much the effective spring rate increases as the forks compress, it doesn't affect the damping as such. I have emulators fitted with stiffer springs and use 130mm in the Integra, 140mm in an X is probably a perfectly reasonable starting point, if you find it using a bit too much compression travel then you can try raising the level a bit more to increase the air spring effect. If you find it under-damped with the 7.5W then go for the 10W (or even a mixture of the two).

 

Depending on how you find the suspension generally, you might consider opening up the damper rod holes a fraction, someone else has done this progressively and reports good effect (need to search for the thread). Mine had holes of 4.5mm dia as std, don't increase them more than 0.5mm dia in one go (it has quite a big effect). You can even consider doing only one hole at a time (there are two in each damper rod). Bear in mind it's a lot more tricky to make the holes smaller again.