[Geoff PD]

I can’t afford the expensive upgrade to the front suspension that a RallyRaid kit gives, so I was thinking about simple alternatives.
Without going into the complexity of adjustable systems, is it possible to simply replace the fork oil with a heavier grade?


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[Luma]

I can’t afford the expensive upgrade to the front suspension that a RallyRaid kit gives, so I was thinking about simple alternatives.
Without going into the complexity of adjustable systems, is it possible to simply replace the fork oil with a heavier grade?


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For sure. We would just need to know the oil volume for refill or how high the oil level from fork top edge.

 

[Geoff PD]

For sure. We would just need to know the oil volume for refill or how high the oil level from fork top edge.

I’ve looked through my riders handbook and can’t find any reference to fork oil spec or quantity.
Can anyone shed any light on this?


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[Luma]

I’ve looked through my riders handbook and can’t find any reference to fork oil spec or quantity.
Can anyone shed any light on this?


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Needs to be someone with service manual.

 

[PCV]

Left leg is 480cc, right 395cc (110mm and 120m respectively if you do it that way).

BMW part number for the oil remains the same but, I think in 2019, this changed from 7.5 wt to 11wt. I am not aware of any change to the damping mechanism (across the BMW range) that would justify the change. I'll be putting 7.5 in shortly, not least because 11wt only exists in the BMW branded oil (perhaps the reason for change says this cynical BMW owner) but also because I find my 2018 model forks are fine as is.

 

[hasselman]

As there is no shock absorber in left leg, the oil is only for lubrication. In right leg, where the cartridge is, you can use 10 wt. Bear in mind that different manufacturers specify shock oil differently and you could have considerable difference between brands.
Below is the filling specs for a GS. N.B. Fork oils is specified to "Telescopic fork oil type 3"

 

[Luma]

Thanks, guys, this is a great info. I have been rather thinking to go as low as possible (5 wt maybe), I am a conservative rider and I prefer rather soft suspension.

 

[Geoff PD]

I would like to stiffen mine just a small amount. I do find the front is a little ‘wallowy’ on the road when cornering. Maybe a combination of the high temperatures where I ride, the imperfect road surface and my 90kg weight.


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[hasselman]

I would like to stiffen mine just a small amount. I do find the front is a little ‘wallowy’ on the road when cornering. Maybe a combination of the high temperatures where I ride, the imperfect road surface and my 90kg weight.


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Buy fork oils of different grades, they are mixable. By mixing you can get any thickness from very soft to very stiff. As I wrote earlier, viscosity could vary for same grade between brands, so it's best to stay with same brand.
I personally would not experiment to much with the amount, but I know that also have influence on the stiffness at the end of stroke. To much oil in the leg could cause oil seals to blow when hitting a high bump.

 

[PCV]

To expand on hasselman's point - the way to get consistency between brands is to compare the Centistoke ratings. Look it up, there's no point my doing a lengthy explanation here. You will find comparison tables for some oils on the net as it's a discussion point in mountainbike circles. Of course finding the rating for the BMW oil will probably be impossible - you have to dig just to find the nominal viscosity.

 

[DavidLus]

I would like to stiffen mine just a small amount. I do find the front is a little ‘wallowy’ on the road when cornering. Maybe a combination of the high temperatures where I ride, the imperfect road surface and my 90kg weight.


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You might get the result you are seeking from adjusting tyre pressure and rear spring load. The manufacturer specs are an arbitrary based on who knows what. Do some experiments before trying surgery.

 

[Geoff PD]

My thanks to all who have posted this valuable information. Certainly a few things to digest.
Happy New Year to everyone. Ride safe.


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