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 Reworking forks ...

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usedtobefast
Montanarolo
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PostSubject: Reworking forks ...   Fri Oct 12, 2018 10:27 am

Been reading a lot, and riding some Smile , and it seems a general consensus is the GRiSO forks are under sprung and over damped.

Fortunately for me, I'm 155lbs (70kg) so the springs actually seem about right.

I've got the compression all the way out (full open) and this works well on everything except sharp impacts (so a high speed compression type event). Unfortunately the roads in my area are pretty beat up and so this happens a lot on rides.

Seems options are:

1 - revalve (different shim stack)
Pros: inexpensive, might do the trick
Cons: little info, probably end up doing a few revisions/iterations, will it be good enough

2 - piston/shim kit (like Ohlins, Race Tech, Penske)
Pros: still not that expensive, maybe some thought/engineering went into it, might do the trick
Cons: I'm not sure the stock pistons are so horrible, so why toss them away for a different ones, probably still need a few revisions, not super impressed with the kits (like Ohlins, they have one valving stack, so same for a 155lb guy vs a 225lb guy?, Race Tech/Penske have generic stack recommendations, not really well thought out GRiSO ones)

3 - full cartridge kit (like Matris)
Pros: supposedly well engineered/designed, work in one shot(maybe)
Cons: getting pricey at ~$1000 US (kit only price), would include springs that I don't really need, a lot of money to spend for better valving

4 - replace the fork with other (like Ohlins complete fork)
I'm not going this far
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usedtobefast
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PostSubject: Re: Reworking forks ...   Fri Oct 12, 2018 10:33 am

So ... Option 1 ... revalve.

From the awesome Uzidzit post, the stock compression stack is:

17 x .15
17 x .15
10 x .3
10 x .3

Wow. This is a short and odd stack.

Our forks are Showas that are similar to a 06/07 Suzuki GSXR 600/750. But there is no guarantee our pistons are the same or similar to the GSXR ones. For example, Honda also sold bikes with similar Showas on them ... but the Honda & Suzuki pistons are very different ... so you would expect the shim stacks to also be very different.

So not as easy as just finding and replicating a GSXR or Honda shim stack as those pistons might be different.

Anyone ever dug into this? Any suggestions for a different shim stack?

I would be looking for lighter compression (flow more fluid) and lighter high speed compression (better control on those sharp hits).

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usedtobefast
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PostSubject: Re: Reworking forks ...   Fri Oct 12, 2018 10:44 am

Here is an example GSXR shim stack, similar 20mm cartridge Showa fork:

3 x 17mm, 0.1mm
3 x 16mm, 0.1mm
2 x 15mm, 0.1mm
1 x 15mm, 0.15mm
1 x 14mm, 0.15mm
1 x 13mm, 0.15mm
2 x 9mm, 0.2mm

Lots of shims!
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usedtobefast
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PostSubject: Re: Reworking forks ...   Fri Oct 12, 2018 10:51 am

If you really want to go nuts, there is this: [You must be registered and logged in to see this link.]

But lots of debate that the Excel calculations don't match real world hitting bumps. Smile

Also seems more dirt bike oriented.
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usedtobefast
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PostSubject: Re: Reworking forks ...   Fri Oct 12, 2018 11:05 am

Here's a good pic showing different pistons ...

[You must be registered and logged in to see this image.]
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kiwi dave
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PostSubject: Re: Reworking forks ...   Fri Oct 12, 2018 12:34 pm

I too experienced the over dampening in the front forks, and also wound the compression dampening all the way out. Despite being about 24 kG heavier than you (I'm on a diet, honest!), I haven't managed to hit the end of fork travel in either direction, so not contemplating any spring revisions at the moment.

If you're finding the compression still a little harsh, why not experiment with a lighter oil in the forks? A lot cheaper experiment than the other options you've listed.
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usedtobefast
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PostSubject: Re: Reworking forks ...   Fri Oct 12, 2018 2:30 pm

Well, shims are like 0.80 each. Smile

I think I'm going option 1. All the Matris cartridge owners can laugh at me for the next couple of months. I am mentally prepared to pull my forks apart 3-4 times. 5th and 6th time will be like "Oh brother". 7th time? I might be giving up by then, not sure. Smile

Unfortunately it seems most shim stack info on the internet is dirt bike related

If anyone has any shim stack suggestions I'd love to hear them. I'm thinking between the stock one and that GSXR one I posted.

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usedtobefast
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PostSubject: Re: Reworking forks ...   Fri Oct 12, 2018 2:38 pm

As for fork oil change only ... that is way easier than re-shimming for sure.

Here is a decent video of the oil change process: [You must be registered and logged in to see this link.]
And yes that fork isn't the same as ours, but exact same concepts/steps.

But my thinking is ... fork oil weight change is not going to make up for a crappy shim stack. So that will be far far away from a piston/shim kit (Ohlins/RaceTech/Penske) and the full Matris Cartridge.

But a good shim stack in our stock forks (same pistons) I think will be very close to options 2-4. That's my theory.

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Nobleswood
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PostSubject: Re: Reworking forks ...   Fri Oct 12, 2018 3:01 pm

Looking for the emoji that shows watching this with interest & eating popcorn
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beetle
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PostSubject: Re: Reworking forks ...   Fri Oct 12, 2018 3:22 pm

You mean this one?


[You must be registered and logged in to see this image.]



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Nobleswood
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PostSubject: Re: Reworking forks ...   Fri Oct 12, 2018 4:21 pm

Yep !
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usedtobefast
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PostSubject: Re: Reworking forks ...   Fri Oct 12, 2018 9:12 pm

Ok, this pic is from a mountain bike suspension company, but was a very easy to understand diagram.

[You must be registered and logged in to see this image.]


So things to play with ... number of shims, diameter of the shims, thickness of the shims.

As you would expect a shim that is 0.1mm thick is "softer" than a shim that is 0.15mm thick.

But what if you had 2 17mm (diameter) x 0.15mm thick shims vs. 3 17mm x 0.1mm shims? Both of these add up to 0.3mm thick. Seems the 3 0.1mm thick shims would be "softer" than 2 0.15mm thick shims. Just reading and learning here. Smile

One not so intuitive thing ... a 17mm shim is "softer" than a 14mm shim for example.

Most info I'm finding is from dirt bikes (motorcycles) and mountain bikes (bicycles).
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