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post #1 of 5 (permalink) Old 06-07-2019, 12:59 PM Thread Starter
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Which fork oil?

I have a set of used Ohlins FKC 102's on the way and I'm wondering which weight oil and how much I'll need to get it installed. I'd love to use the Ohlins oil, but good golly, that's some pricy oil! I was thinking BelRay instead. What's going to be the difference between using 5W and 10W?

Thanks.
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post #2 of 5 (permalink) Old 06-07-2019, 03:00 PM
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post #3 of 5 (permalink) Old 06-07-2019, 03:54 PM
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Hi WSNuke; do you mean SAE Oil weight= wt? The SAE Motor Oil Grade= w where the letter "w" means winter-grade.

But do not go by the labeled oil weight. For some reason each manufacture use their own propiretary table. I would do some research before choosing a fork oil. As a rule of thumb the forks do not require the same type of oil as the rear shocks or reservoirs. This example is generic but still viable - given an ambient outside temperature of 70F after about 30 mins ride the front suspension will have a temperature of 78F but the rear shocks will be at 105F and a reservoirs in the 110F range.

Modern fluid viscosity ratings are on an ISO VG (visocosity grade) using test standards set down by ASTM D-2422-97 (2002)& ISO 3448:1992 system of: [email protected] / [email protected] / VI. ‘cSt’ stands for CentiStokes, an accurate dynamic measure of viscosity (ISO 3104:1994 & ASTM D445-04).

The Viscosity Index is very important in a suspension oil. «The viscosity index (V.I.) of an oil is a number that indicates the effect of temperature changes on the viscosity of the oil. A low V.I. signifies a relatively large change of viscosity with changes of temperature. In other words, the oil becomes extremely thin at high temperatures and extremely thick at low temperatures. On the other hand, a high V.I. signifies relatively little change in viscosity over a wide temperature range.»

VI for the rear suspension should be over 300 but the front need just over 100 to be functional.

The oil in a bike's fork or shock not only cools and lubricates the system, but is the heart of all the damping control available for the springs. All phases of the damping involve the viscosity of the oil used in the system. Suspension oil is in fact a critical suspension tuning decision so make your choice accordingly.

In my opinion the Bel-Ray Fork Oil (5wt) is the best bet. It is close to the Õhlins fork oil. The Bel-Ray has a 17.10 [email protected] and a VI at 146 wheras the Õhlins has a rating between 16.5 [email protected] and 19 [email protected] but no VI is listed. IMHO

But my buddy mechanic always go for the Red Line oils - they have an impressive range and are made for fine-tuning your suspesnion system.

Cheers
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post #4 of 5 (permalink) Old 06-07-2019, 09:20 PM Thread Starter
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Viking, thank you for that very informative explanation. I have used Bel-Ray in the past and will probably use it again based on yours and other's feedback. If the Ohlins oil isn't twice as good, then I don't see paying twice the cost. I'll look into the Red Line oil. I have someone lined up to install the cartridges in the forks already, but I'll probably give a call to the shop that set them up originally for the first owner to get their take on it. Fortunately for me, the rider I'm buying them from is of a similar weight and riding style as me.

And my question was the difference between using the 5wt fork oil vs. the 10wt fork oil.
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post #5 of 5 (permalink) Old 06-08-2019, 04:41 PM
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Quote:
Originally Posted by WSNuke View Post
Viking, thank you for that very informative explanation. I have used Bel-Ray in the past and will probably use it again based on yours and other's feedback. If the Ohlins oil isn't twice as good, then I don't see paying twice the cost. I'll look into the Red Line oil. I have someone lined up to install the cartridges in the forks already, but I'll probably give a call to the shop that set them up originally for the first owner to get their take on it. Fortunately for me, the rider I'm buying them from is of a similar weight and riding style as me.

And my question was the difference between using the 5wt fork oil vs. the 10wt fork oil.
The lighter the oil will allow the suspension to compress more giving a softer ride but with less stability. .
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