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maz20

Dialing in upgraded shock

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maz20

Some retailers for aftermarket FZ-07 shocks offer to "customize" the rear shock based a rider's weight (with gear/luggage) & riding style.

 

However, a while ago I purchased an "uncustomized" default Ohlins FZ-07 rear shock which came with the (default) 115 N/mm spring.

 

I weigh about 210 lbs with full gear, is this the right spring rate? If the default spring is too light, and I replace it with a stiffer spring, can a revalve also be required in order to maintain the desired rebound damping? There is a clicker for rebound damping, but I heard that stuff is for fine adjustments only!

 

*Note: I've actually tried going with a softer spring (replaced it myself) -- the 90 N/mm kind, and it only feels plush no more than 3 clicks from fully closed (max rebound), which is strange since the manual recommends to be only around 14 clicks of rebound.

Edited by maz20

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maz20

(Whoops, I cannot delete this post for some reason 😐  mods feel free to remove it!)

Edited by maz20

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elmo

MAZ,  Making any progress, is the shock new or used?  Do you know your current rider sag number?

You should get your spring figured out before adjusting rebound.

Its easy to verify If the rebound is working correctly, place in vise and remove spring, like photo is max extension.

Start with clicker full  CCW open and compress shock to its max, I used my hammer handle for extra leverage.

With quick release count till full extension occurs, write it down and add 5 clicks CC and repeat until fully closed out.

 

This was my Penske results with best guess counting, this a huge range more than just fine tuning.

Full open  2-sec

+5 clicks  3-sec

+5 clicks  4-sec

+5 clicks  5.5-sec,

+5 clicks  7-sec

+5 clicks  8-sec at 25 clicks total.

 

1327872341_Shockreboundreview.thumb.jpg.2311f908422cf5d8306df1a1982c6fb7.jpg

 

Edited by elmo

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maz20
On 11/7/2018 at 7:47 PM, elmo said:

MAZ,  Making any progress, is the shock new or used?  Do you know your current rider sag number?

Lightly used, 8K miles : ) I'm running the softer 90 N/mm spring at 22 mm rider sag.

On 11/7/2018 at 7:47 PM, elmo said:

You should get your spring figured out before adjusting rebound.

 

Yup : ( that is what I fear, since according to 

I may actually need a spring stiffer than the stock 115 N/mm -- which probably means that putting in the proper spring may necessitate a revalve as well : ( (which is expensive $$$). On the other hand, by going the other direction with a softer spring, I found the resulting shock to be a lot more plush (even if more prone to bottom-outs) -- which oddly enough actually makes sense according to wikipedia:

https://en.wikipedia.org/wiki/Harmonic_oscillator#Damped_harmonic_oscillator

https://en.wikipedia.org/wiki/Damping_ratio

2nd_Order_Damping_Ratios.svg

Basically, the damping ratio (zeta) is inversely proportional to mass & spring rate. So, to keep the same rebound damping "effect" for the heavier riders, you will have to increase the damping. Or, otherwise, compensate for it by actually getting a softer spring, so that whatever rebound damping is built-in there originally could be sufficient given the adjustment range of the clicker. Yes, although, this will make you more prone to bottom-outs : (

 

On 11/7/2018 at 7:47 PM, elmo said:

Its easy to verify If the rebound is working correctly, place in vise and remove spring, like photo is max extension.

Start with clicker full  CCW open and compress shock to its max, I used my hammer handle for extra leverage.

With quick release count till full extension occurs, write it down and add 5 clicks CC and repeat until fully closed out.

 

This was my Penske results with best guess counting, this a huge range more than just fine tuning.

Full open  2-sec

+5 clicks  3-sec

+5 clicks  4-sec

+5 clicks  5.5-sec,

+5 clicks  7-sec

+5 clicks  8-sec at 25 clicks total.

Interesting tip/setup! But, since there's no spring here, doesn't this then only measure the damping against the compressed nitrogen compartment? It might look like a huge range at first, but when you add in the force of the (compressed) spring, those time intervals between full extensions (at different clickers settings) are gonna bunch up a lot more closely together!


I don't believe my rebound damping is necessarily exactly "faulty" -- just that I'm too heavy to make use of it!

Edited by maz20

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twf

Yes he is only measuring nitrogen pressure :)

Without pressure it would not return at all. And that is only low speed damping (your adjuster controls it). Revalve deals with high speed damping.

If your shock comes standard with 115 spring it will work fine couple rates up/down, anything more it will need different valving.

Your 90 is outside of its range. 130 would be closer to your weight and also outside of its range.

 

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elmo

Agree, my rebound comments with no spring method was only to verify the damper clicker is progressively adding rebound. Since bought used, helps verify pressure and everything is working correctly. Are the dyno charts from your shock?

With the light spring  rate at 90N only providing 22mm rider sag is confusing. I have a Penske 8983 and not sure how the spring rates compares to the Ohlins. I am also 210# with gear and just went from 700# spring @ 45mm rider sag to 750# spring and reduced sag to 35mm.

1st twisty test ride yesterday,  had nice planted feel but was firm on bigger bumps but should be just right for my final 2 tracks days coming up. But would probably go back to the 700#  if street riding only.

 

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