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 Good shock for my GRiSO??

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ghezzi
Fra Cristoforo
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PostSubject: Re: Good shock for my GRiSO??   Sat Aug 19, 2017 2:34 pm

Static sag (bike only) is the last thing you measure and is only used to determine if you need a different spring.

Rider (total) sag is you in all your riding gear, ass on bike feet on pegs. Somebody else needs to balance the bike.

General rule of thumb, Sports bikes need 25% of total travel as rider sag. Racing 20% or less. Touring & barge arsed cruisers 30%.
GRiSO spec claim 120mm wheel travel, x 25% = 30mm total sag.

Static sag should be around 25% of total sag. 30 x 25% = 7.5mm
This measurement is quite flexible and its only real purpose is to determine if you need to change your spring rate.

1. If static sag is 0 - 3mm, indicates spring rate is too soft. You added excessive pre-load to keep the rider sag down to 30mm, now the bike can't squat under its own weight.

2. If static sag is 10mm +, indicates spring rate is too hard. You have to wind pre-load right off just to get the bike to move under your own weight.
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Nobleswood
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PostSubject: Re: Good shock for my GRiSO??   Sat Aug 19, 2017 2:37 pm

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klaas123
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PostSubject: Re: Good shock for my GRiSO??   Sat Aug 19, 2017 2:38 pm

Clear as a blue sky to me Ghezzi, thanks Smile
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klaas123
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PostSubject: Re: Good shock for my GRiSO??   Sat Aug 19, 2017 2:40 pm

Nobleswood wrote:
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Same as mine but in a better optical condition, good buy!
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Nobleswood
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PostSubject: Re: Good shock for my GRiSO??   Mon Aug 21, 2017 7:23 pm

Got the shock in today Very Happy

It's an Ohlins AP8271 from an Aprilia 2009 RSV4 1000R.
Measured eye to eye dimension is 317mm
Found a chart of specifications, mind you it's for a 2004 year model, quotes the stroke @ 63.5mm
Type is a 46PRCL

Waterbottle, did you use the longer or shorter clevis ?
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sidrat
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PostSubject: Re: Good shock for my GRiSO??   Mon Aug 21, 2017 11:35 pm

I am going to look forward to the outcome of these Aprilia Shocks, they might be an upgrade to my Stelvio one.
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klaas123
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 2:33 am

Nobleswood wrote:

Found a chart of specifications, mind you it's for a 2004 year model, quotes the stroke @ 63.5mm
Type is a 46PRCL

Nice stroke length Very Happy Sachs is 48mm (without 24mm rubber bump stop).
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ghezzi
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 3:08 am

Nobleswood, 2009 RSV4 (v-four engine) is a completely different bike to the 2004 RSV (twin).

The fact it came to you with a 15+kg/mm spring means either, previous owner was a big fat prick or the rear suspension geometry and rocker ratio is so high (ie. 5:1), it needs a heavy spring which then would correspond to a very short travel shock ................. for 120mm rear wheel travel.

Measure your stroke length with the shock you have in hand.


Last edited by ghezzi on Tue Aug 22, 2017 3:08 pm; edited 1 time in total
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Nobleswood
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 3:58 am

Didn't realise the different years had different engines.

The spring is a 1091 - 31/95 which I'm reading from your chart is a 9.69kg/mm

To measure the stroke length,(of the shock ), I measured from the bottom of the body to where the bumper sits & come up with 63mm.

Reading from the Ohlins spec chart that i found, the measurement reads as 63.5mm
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klaas123
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 4:18 am

Mine came with that stiiff spring Ghezzi.
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sidrat
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 4:23 am

So the spring rate is almost the same as the standard shock?

The Stelvio, by way of comparison is 11kg. I like the harder spring and would suggest at my weight (82kg) it works really well.
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klaas123
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 4:54 am

Just bought a used 95N/mm spring and a short 25mm clevis from the Dutch Ohlins importer for 95 eoro. He had no 100N/mm spring in stock so will try the 95 first.
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Nobleswood
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 5:01 am

Klaas

What's the part no on that clevis mount ?

I've read that getting it on can be difficult. Want to hear what you find.
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klaas123
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 5:12 am

Will have a look when it arrives Nobleswood.
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klaas123
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 5:26 am

sidrat wrote:
So the spring rate is almost the same as the standard shock?

The Stelvio, by way of comparison is 11kg. I like the harder spring and would suggest at my weight (82kg) it works really well.

You will need the longer clevis as the Stelvio shock is longer than the Sachs from the GRiSO. 95N/mm is the same as stock GRiSO shock.
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sidrat
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 5:43 am

Klaas the Stelvio shock bolts straight in, no modifications required. I found the standard spring way to soft on the GRiSO. It was one of the reasons to move to the Stelvio shock as it came with a stronger spring as standard.

Given Ghezzi's excellent explanation below, i would stick to the 11kg spring or possibly 10.75kg as being the ideal.

1. If static sag is 0 - 3mm, indicates spring rate is too soft. You added excessive pre-load to keep the rider sag down to 30mm, now the bike can't squat under its own weight.

2. If static sag is 10mm +, indicates spring rate is too hard. You have to wind pre-load right off just to get the bike to move under your own weight.

Really interested in the Aprilia option however has someone measured the open and closed lenghts? or did i miss that

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Nobleswood
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 5:47 am

Sorry ?

Open & closed lengths ?
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klaas123
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 6:38 am

sidrat wrote:
Klaas the Stelvio shock bolts straight in, no modifications required. I found the standard spring way to soft on the GRiSO. It was one of the reasons to move to the Stelvio shock as it came with a stronger spring as standard.

Given Ghezzi's excellent explanation below, i would stick to the 11kg spring or possibly 10.75kg as being the ideal.

1. If static sag is 0 - 3mm, indicates spring rate is too soft. You added excessive pre-load to keep the rider sag down to 30mm, now the bike can't squat under its own weight.

2. If static sag is 10mm +, indicates spring rate is too hard. You have to wind pre-load right off just to get the bike to move under your own weight.

Really interested in the Aprilia option however has someone measured the open and closed lenghts? or did i miss that


Sorry Sidrat, thought you were interested in the Ohlins shock.

I know 95N/mm is on the low side for my weight but it was cheap and in stock so will give it a try.
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sidrat
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 6:56 am

Nobleswood wrote:
Sorry ?

Open & closed lengths ?

What is the length of the shock with the ride height adjuster screwed in (closed length) and the ride height adjuster screwed out (open length) I would guess that the min length of the shock is still longer than original?
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sidrat
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 6:58 am

klaas123 wrote:


I know 95N/mm is on the low side for my weight but it was cheap and in stock so will give it a try.

Far be it for me to comment on peoples weight here!!! Evil or Very Mad
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klaas123
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 7:07 am

Smile Smile Smile
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ghezzi
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 2:27 pm

Gentlemen, springs are a dime a dozen ....................... and if the dimensions are the same, any weight spring can be fitted on your shock.

But, but, but, but, you can't fit any shock on any bike just because it is the same length, (twin shock bikes may be the exception).

With any MONOSHOCK bike, the shock needs to be designed for the specifics of that monoshock system. Not just the rising rate RATIO, but also the rate of rise.

63.5mm shock travel on a GRiSO approximates to 165mm rear wheel travel. That is not well balanced with only 120mm at the front.
1. It is possible the tyre will hit the under seat mudguard.
2. It is possible the drive shaft trunnions will be stressed.

You guys are making me nervous, I see great potential for monumental fuck up!
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klaas123
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 2:56 pm

63,5 is without rubber stop Ghezzi, and when the correct spring is used it would only get to the max under extreme circomstances like a deep hole in the road where the Sachs would bottom out??
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ghezzi
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 3:04 pm

Yeah well, I wasn't game to ask how big a rubber you were using?
sometimes you make me feel insignificant
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sidrat
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PostSubject: Re: Good shock for my GRiSO??   Tue Aug 22, 2017 3:15 pm

ghezzi wrote:
Gentlemen, springs are a dime a dozen ....................... and if the dimensions are the same, any weight spring can be fitted on your shock.

But, but, but, but, you can't fit any shock on any bike just because it is the same length, (twin shock bikes may be the exception).

With any MONOSHOCK bike, the shock needs to be designed for the specifics of that monoshock system. Not just the rising rate RATIO, but also the rate of rise.

63.5mm shock travel on a GRiSO approximates to 165mm rear wheel travel. That is not well balanced with only 120mm at the front.
1. It is possible the tyre will hit the under seat mudguard.
2. It is possible the drive shaft trunnions will be stressed.

You guys are making me nervous, I see great potential for monumental fuck up!

One of the reasons i tried a stevio shock, same engine, swingarm and frame :-)
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