revtothelimit - motorbike forum

Hello,

Have seen that halfords sell 5w30 fork oil, https://www.halfords.com/motoring/motor ... 24393.html and wondering if anyone had used 5w30 in their forks.

Multi-grade fork oil?

I though it was usually a single grade?

Personally I wouldn't be buying fork oil from Halfords. Check your manual to find your recommended fork oil and buy Fuchs (Silkolene), Motul or Putoline fork oil of the recommended weight online.

Purchase what you need from OpieOils

I certainly used Castrolite multigrade or sometimes a mixture of it with other mineral oils to get the level of damping I preferred on the track. In effect a 5W will be equivalent to viscosity 5 if cold and thin-out less as the temperature rises than non-multigrade so it makes sense. I would also experiment with overfill quantity to get the remaining air gap to influence spring force and dive. Truly shoestring racer!

Modern forks are more difficult to understand because they often only have damping on one leg and perhaps only a spring in the other. Cheapskate idea dressed up as improvement!

I doubt whether the oil in forks gets hot enough for the multigrade effect to take place. Having said that I use 20W/50 in my 1952 ES2 forks as the damping is minimal (and it's what I have on the shelf) - but I'm assuming it's just working as a 20 grade oil.

There will be all sorts of detergent packages and friction modifiers in multigrade oil intended for use in an ICE, you'd hope those would be left out of multigrade fork oil, but I still really can't see the point. Fork oil simply doesn't get hot enough for the supposed multigrade effect to take place, as iansoady says.

I'm told (by people who know about these things) that cst (centistokes) spec at 40 deg C is the important one to check out when comparing oils. The headline number (the one printed on the bottle) is pretty meaningless, as every manufacturer's 5 SAE fork oil is different when you check the Kinematic viscosity (cst) at 40 deg C specification. Showa SS19 5 SAE suspension fluid has a cst of 14.14 at 40 deg C, whereas Castrol 5 SAE synthetic fork oil has a cst of 28 (nearly double) at 40 deg C.

roadster wrote: Wed Jan 03, 2024 9:10 am Modern forks are more difficult to understand because they often only have damping on one leg and perhaps only a spring in the other. Cheapskate idea dressed up as improvement!

Even really high end racing suspension (WSB + MotoGP level) does that sometimes and/or does compression on one side and rebound on the other. Makes a lot of sense, it gives you more room to do both things well. It might be tempting to think that it'd introduce unacceptable asymmetry, but of course the fork is designed to be stiff enough to prevent that sort of thing anyway.

I can see how multigrade would make sense on a road vehicle, and a low performance one more than a high performance one (or perhaps more fairly, one which is only getting light use). Ambient temperature has an enormous effect on oil temp of course. In a racing vehicle you're operating over a narrow environmental temp (because you're only out for an hour or two and you can always change the oil if needed) and a narrow use case (you're always thrashing it!) so the oil only has to work in a very limited range. On a road vehicle which might have the same factory specced oil for -30°C in Sweden and +40°C in the UAE multigrade would make sense.

Decent oil is measured by stroke rate nowadays.
More importantly, what bike is it for?

roadster wrote: Wed Jan 03, 2024 9:10 am I certainly used Castrolite multigrade or sometimes a mixture of it with other mineral oils to get the level of damping I preferred on the track. In effect a 5W will be equivalent to viscosity 5 if cold and thin-out less as the temperature rises than non-multigrade so it makes sense. I would also experiment with overfill quantity to get the remaining air gap to influence spring force and dive. Truly shoestring racer!

Modern forks are more difficult to understand because they often only have damping on one leg and perhaps only a spring in the other. Cheapskate idea dressed up as improvement!

I remember back in the day when some bikes had valves on the forks for air adjustment; I would sometimes let all the air out of just one fork on a mate's bike. Just for t'craic, like. Then see if it hoyed them in the ditch. Just for t'craic, like. It never did FWIW. Maybe it was all bollocks.

MyLittleStudPony wrote: Wed Jan 03, 2024 10:08 pm I remember back in the day when some bikes had valves on the forks for air adjustment; I would sometimes let all the air out of just one fork on a mate's bike. Just for t'craic, like. Then see if it hoyed them in the ditch. Just for t'craic, like. It never did FWIW. Maybe it was all bollocks.

In my experience it was all bollocks. My old VFR had air-assist forks. When it was serviced the tech would dutifully put 6 psi in the forks. By the time I got home it was down to zero.

MyLittleStudPony wrote: Wed Jan 03, 2024 10:08 pm

roadster wrote: Wed Jan 03, 2024 9:10 am I certainly used Castrolite multigrade or sometimes a mixture of it with other mineral oils to get the level of damping I preferred on the track. In effect a 5W will be equivalent to viscosity 5 if cold and thin-out less as the temperature rises than non-multigrade so it makes sense. I would also experiment with overfill quantity to get the remaining air gap to influence spring force and dive. Truly shoestring racer!

Modern forks are more difficult to understand because they often only have damping on one leg and perhaps only a spring in the other. Cheapskate idea dressed up as improvement!

I remember back in the day when some bikes had valves on the forks for air adjustment; I would sometimes let all the air out of just one fork on a mate's bike. Just for t'craic, like. Then see if it hoyed them in the ditch. Just for t'craic, like. It never did FWIW. Maybe it was all bollocks.

Most decent enduro bikes have that. We all do it every ride or the ride is a bit iffy.

KungFooBob wrote: Tue Jan 02, 2024 6:13 pm Multi-grade fork oil?

I though it was usually a single grade?

Yeah, that is what I have known all my life. Saw this and thought I'd ask.

mangocrazy wrote: Tue Jan 02, 2024 8:05 pm Personally I wouldn't be buying fork oil from Halfords. Check your manual to find your recommended fork oil and buy Fuchs (Silkolene), Motul or Putoline fork oil of the recommended weight online.

I'm more of a play fast and loose...with fork oil wieght and amounts.

Demannu wrote: Wed Jan 03, 2024 9:40 pm Decent oil is measured by stroke rate nowadays.
More importantly, what bike is it for?

So is there a list so a comparison is possible?

katana wrote: Sun Jan 07, 2024 5:01 pm

Demannu wrote: Wed Jan 03, 2024 9:40 pm Decent oil is measured by stroke rate nowadays.
More importantly, what bike is it for?

So is there a list so a comparison is possible?

I have a list giving comparisons of various suspension fluids and their viscosities and cSt specifications, but it's in a spreadsheet and it's 2 or 3 pages worth. Not sure if I can post it up here as an attachment or not? And it came off t'Internet so any use you make of it is down to you, no-one (least of all me) assumes any responsibility about anything...

Actually not sure of what fluid goes in the forks as standard but changing 10 year old fluid is a good thing.

Now which supplier as there are no bike shops near me as Burwins (on essex Road, London N1) have now closed.

katana wrote: Sun Jan 07, 2024 5:01 pm

Demannu wrote: Wed Jan 03, 2024 9:40 pm Decent oil is measured by stroke rate nowadays.
More importantly, what bike is it for?

So is there a list so a comparison is possible?

There are several, I did post a link to a website somewhere on here (I think it was the ATF fluid thread). Thing is, the same sae oil differs between different, sometimes the same manufacturers.