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Discussion Starter #1
It's time to rebuild the front forks on my 916... In the past (with other bikes) I've usually gone one step lighter in fluid weight as I only weigh 135lbs (probably 145 with gear).

So my question is should I go with some 5w fluid or should I stick to 7.5w and get slightly lighter springs? Or should I go 50/50 5w/7.5w and split the difference?
 

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Old Wizard
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I see no reason to change the fork oil weight.

A 916 weighs around 450 lb. wet. The suspension spring rate and damping is selected by Ducati assuming a standard 160 lb. rider. So we’re talking about a reduction of say 20 lb. from an overall 610 lb., about 3%.

The recommended oil weight for the superbike front forks is 7.5 weight. If you decrease the weight, you’re using a lower viscosity. This means that you will decrease the rebound and compression damping at every click setting. Keep in mind that different fluid manufacturers rate their viscosity differently so you can’t compare using labeled oil weight.

Comparative Oil Weights Table

Ducati configures the dampers such that the recommended click settings for a 160 lb. rider falls in the middle between maximum and minimum damping. The only reason to change from the recommended viscosity is if you run out of high (or low) damper settings and you need even more (or less) damping than the maximum (minimum) that the stock 7.5 weight gives.

If you do use a 5 weight, you'll need to compensate for the reduced oil viscosity by increasing your fork low-speed settings to recover your compression and rebound damping rate. However, now you’ll still have less high-speed damping than the fork manufacturer and Ducati engineering intended because high-speed damping is controlled by the flow rate through the internal shim stack and unaffected by the damper low-speed click settings. Low-speed damping basically controls the up-down and dive-squat motion of the entire bike while the high-speed damping controls rapid wheel motion caused by bumps and imperfections in the road surface.

Moving from a 7.5 weight to a 5 weight is a 30% viscosity decrease. This doesn’t translate directly to a 30% high-speed damping reduction but it would appear to be excessive just to address a 3% sprung weight decrease.
 

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The stock Ducati springs are progressive, so going to a straight weight spring will help with full travel of the forks.
 

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Discussion Starter #4
That's why I love you guys :D

Thanks so much for the input. Suspension work is the one thing that I am still fuzzy with (that and shimming crankshafts, or understanding women).

I was always well served with lighter oils in my previous rides, BUT those all had much cruder suspension setups with limited adjustability: preload-only sort of thing.

My manual recommends Shell Advance 7.5 and Showa SS8 - according to the table they have very different cst ratings! Any particular brand/viscosity you recommend Shazaam?
 

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Old Wizard
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Magic 8 ball says ... use the Showa product in Showa forks.

Shell is a Ducati sponsor so they had to include Shell products in their recommendations.
 

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Discussion Starter #6
Hahaha good to know, thanks.
 

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I would say you need lighter springs. On my old 916 forks I had the 10n springs replaced with 9.5n, Ktech valving & 5w oil, they worked very well and I'm significantly heavier than you.
 

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Discussion Starter #8
I'm going to match the SS8 profile with some Ohlins #10 (which I can get locally, the Showa not so much) and install a set of .90 Race Tech springs. Should be good for the type of riding I do (I'm a relaxed rider, I don't push it too hard).
 
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