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Fork tube compatibility question

Old 12-23-2012, 06:23 AM
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Fork tube compatibility question

Quick question: Does anyone know if there would be any compatibility isuses in fitting fork tubes from a ST1300 to the (96-97) CBR900RR forks I am using? Both are made by Showa and 45mm diameter. The ST tubes are 42mm longer.....

Thanks in advance
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Old 12-23-2012, 06:48 AM
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not a popular swap.. Don't think you will find a ready database of info..

Are you planning on swapping JUST the stanchion? or the internals as well?

I don't see anyway to do what your looking to do, based on being inside a a few Showa forks.. but, that does not mean it can not be done...

Buy some and lay it all out.....

Last edited by E.Marquez; 12-23-2012 at 10:35 AM.
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Old 12-23-2012, 10:34 AM
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I think you would find they fit. Just because they "fit" doesn't mean they "work" though. More than likely you will need to fabricate some internal spacers to maintain the correct travel. This can prove to be a little complicated but certainly doable.
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Old 12-23-2012, 12:41 PM
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The main reason for looking at the longer tubes would be to get back some of the free length I apparently lost with the 900RR forks. I had read that the 900RR forks used on the Moriwaki race bikes used longer tubes (I would imagine to get them back to "stock" length).

As for the why behind all of this, I found the bike gets a touch nervous when the speeds get up there (like over 100 mph, I very seldom get there as I can't afford to lose my licence, but it happens from time to time that I do a run through the gears). I will try to drop the rear (am currently running a 4.1mm shim on the shock but will either remove it or use a thinner one) to see if that cures it. I thought longer tubes would be a way to get the length back to stock (would have to get a spacer for the spring, 42mm should do the trick as it's the exact length difference from the 900RR to ST tubes).

Incidentally, I recall reading that the linkage essentially multiplies the gain in ride height (compared to shim height) by a factor of 4. Can anyone confirm this?

cheers
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Old 12-23-2012, 02:35 PM
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No, not a factor of four, but yeah it multiplies... The factor varies from model of bike to another, so I can't give you a definitive answer, since I can't measure it out on my bike...

Best guess about 2, perhaps 3, but not as much as 4...
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Old 12-23-2012, 04:39 PM
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Actually, the linkage ratio is 3.88:1. Sorry Tweety! Nothing is as lower than 2:1 that I know of, some models like GSX-R's have the lowest at ~2.25:1.

I think you are right on the track mikster. Often times when folks do front end swaps they go too radical with geometry and it ultimately causes problems. Your shim out back isn't too bad, I suggest a +3mm shock length so you are only a mm or so off. However you manage to do it, get your front back up to where it belongs and I think you would be all set.
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Old 12-25-2012, 02:59 AM
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Originally Posted by JamieDaugherty View Post
Actually, the linkage ratio is 3.88:1. Sorry Tweety! Nothing is as lower than 2:1 that I know of, some models like GSX-R's have the lowest at ~2.25:1.

I think you are right on the track mikster. Often times when folks do front end swaps they go too radical with geometry and it ultimately causes problems. Your shim out back isn't too bad, I suggest a +3mm shock length so you are only a mm or so off. However you manage to do it, get your front back up to where it belongs and I think you would be all set.
Nothing to be sorry about! I knew the 2 definitely was the lower end, and I know for a fact that a lot of bikes are around 3, give or take a little, so if I was to make a more definitive guess, I'd have said 3 for the VTR, as it has a rather "sedate" linkage... I didn't know it was as high as 3.88....
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