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Gsx TOP shock mounts moved forward


Kraptanaman

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  • 3 weeks later...

Too funny, this is the second reason I joined OSS, to see if anyone had info on moving the shock mounts. 

Current plan for me is based on a picture of (I think) a Yosh bike. looking at it, it seems like they were shooting for a shock angle (to the swinger) of between 40 and 45 degrees. With a 12.5" shock and a 19" swinger, they had to move the shock mount down about 3" from the intersection of the top tubes. This is all rough measurement based on that bike having a 17" wheel. If that wheel isn't 17" then all those measurements are garbage and I don't know what I'm talking about.

It looks to me like sanctuary does about 2.5" and 50 degree shock angles. Anyone have any thoughts on all this? What drives these decisions? I haven't got the first idea of how to set up suspension so my plan was to copy people who knew what they were doing...

Watching this one closely! 

 

Screen-shot-2013-08-13-at-23.36.59.png

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On 2017-11-20 at 5:02 PM, arnout said:

On my Kat I modified the shock mounts on its (GSX750EX) frame. The intention with moving the mounts was to position the shocks flatter to increase the suspension travel. Also the bolt-on mounts allow spacers to be added to adjust the ride height.

skizzokat-details-5.jpg

skizzokat-details-2.jpg

 

What shocks are these? They look like zrx? If so, what is your distance from the pivot point of the swinger to the mounting location? Thanks!!

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21 hours ago, NotStock said:

Current plan for me is based on a picture of (I think) a Yosh bike. looking at it, it seems like they were shooting for a shock angle (to the swinger) of between 40 and 45 degrees. With a 12.5" shock and a 19" swinger, they had to move the shock mount down about 3" from the intersection of the top tubes. This is all rough measurement based on that bike having a 17" wheel. If that wheel isn't 17" then all those measurements are garbage and I don't know what I'm talking about.

It looks to me like sanctuary does about 2.5" and 50 degree shock angles. Anyone have any thoughts on all this? What drives these decisions? I haven't got the first idea of how to set up suspension so my plan was to copy people who knew what they were doing...

Screen-shot-2013-08-13-at-23.36.59.png

Its not 'just' moving the shock top mount. If the shock is the same, then moving it down/forward the suspension will work softer, likewise damping will be less as the rod will move less. Similarly if the shock is more vertical, it will use more of the shock / damper travel so may be harder/stiffer. Both scenarios will / may require shock / spring 're-tuning'. Same when guys change the shock linkages / pick-up points and can't understand why shock is hard when original bike was a lot softer. Even the big OEM's get it wrong as happened with the big K and  the ZXR750 in the 90's!

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23 hours ago, NotStock said:

What shocks are these? They look like zrx? If so, what is your distance from the pivot point of the swinger to the mounting location? Thanks!!

Yup, ZRX shocks. Quite decent stuff for stock twin shocks (adjustable and good travel), but I'm keeping an eye out for something even beterer.

The straight distance from the pivot to the shock mount on the XJR swingarm is about 485mm.

At the time I made a sketch in AutoCAD  to work out the position of the shock that would allow the suspension travel I was aiming for.

swingarm-constraints.jpg

5 hours ago, Gixer1460 said:

Its not 'just' moving the shock top mount. If the shock is the same, then moving it down/forward the suspension will work softer, likewise damping will be less as the rod will move less. Similarly if the shock is more vertical, it will use more of the shock / damper travel so may be harder/stiffer. Both scenarios will / may require shock / spring 're-tuning'. Same when guys change the shock linkages / pick-up points and can't understand why shock is hard when original bike was a lot softer. Even the big OEM's get it wrong as happened with the big K and  the ZXR750 in the 90's!

Exactly. My goal with moving the top mounts was creating more suspension travel because I think that is the biggest downside to using twin shocks compared to monoshock. Some old twin shocked bikes only have 80mm travel (don't know the GSX spec. btw) but newer "retro" bikes are often equipped with longer shocks, at least the ZRX1100/1200 is. The increase from 110 to 125mm in my setup may seem hardly worth the bother, but I am quite pleased with the end result.

Alternatively just using longer shocks (with longer travel) would solve the problem too of course (if you can find the space to fit them on the bike), but for that you might have to convert old motocross shocks or have them custom built.

Why more travel? Apart from increasing the ride comfort, longer travel allows the damping mechanisms to work better (especially with lower quality shocks). (This only works of course if the spring is soft enough to actually use most of the suspension travel during operation.) Laying the shocks flatter will increase the force on the springs and so will compress further.

There is a downside to this setup though. Although the compression/travel starts somewhat lineair, the angle of the shocks however changes during travel making the springs -relatively- softer. So actually the opposite of a progressive suspension.. :/ Oh well.. The shocks haven't bottomed out yet though, but I am not a heavy guy and there are no pillion pegs on the Kat.

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On 12/12/2017 at 2:06 AM, arnout said:

 

 

There is a downside to this setup though. Although the compression/travel starts somewhat lineair, the angle of the shocks however changes during travel making the springs -relatively- softer. So actually the opposite of a progressive suspension.. :/ Oh well.. The shocks haven't bottomed out yet though, but I am not a heavy guy and there are no pillion pegs on the Kat.

not necessarily a downside -- I can "visualise" a good reason for it - up right things yea ok, but picture loading up the rear whilst leaning over on a corner exit - i'd be looking for the softer touch in this condition to help reduce the likelihood of the rear stepping out

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17 hours ago, Gammaboy said:

It's a good modern sportsbike number? Modern stuff is all 120-125mm travel at both ends.

Yup, what Gamma said :tu

I tried an even larger travel (135mm or so) in my sketch but reckoned the shock angle would get too extreme as it would make the mentioned regressive character of the suspension setup even worse. So the 125mm I decided to stick with is a compromise (like all things in life )

 

2 hours ago, nlovien said:

not necessarily a downside -- I can "visualise" a good reason for it - up right things yea ok, but picture loading up the rear whilst leaning over on a corner exit - i'd be looking for the softer touch in this condition to help reduce the likelihood of the rear stepping out

Ah.. not sure whether this scenario would actually happen, but I do like your argumentation. ;)

Oh.. Nearly forgot.. Mind placing the LH top shock mount further outward than the RH one to provide clearence for the chain (if indeed you're planning to use wide modern rubber). Of course it would need to correspond with the mounts on the swingarm you'll be using. (Some swingarmes are asymmetric, some are not) but plan ahead and look at the whole suspension setup before cutting and welding.

(I positioned the symmetric XJR swingarm I used asymmetrically in the frame so the LH shock would have more room. I kept the stock mounts on the swingarm unmodified, but of course you could just move the LH mount instead of the whole swingarm.)

Edited by arnout
forgot a bit
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