Ractech 919 springs question - Wrist Twisters
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post #1 of 13 Old 06-21-2017, 01:56 PM Thread Starter
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Ractech 919 springs question

Got my springs in the mail and they come with an aluminum spacer and washers. Do I have to cut a new spacer and use their washers or reuse the OEM spacers and washer?
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post #2 of 13 Old 06-21-2017, 03:53 PM
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general rule: length of old spring + old spacer should be = to the length of new spring + new spacer. If race tech is as long as OEM old spring is, you should be fine with old spacer. Don't stress out about a couple of mm +/- difference.

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post #3 of 13 Old 06-21-2017, 04:07 PM Thread Starter
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It comes with a section of pipe to cut for a spacer. Racetechs are slightly longer than OEM. I calculated the distance according to Racetech from the top of the spring to the top of the tube minus the distance between the bottom of the fork cap to the oil ring at 83mm. If I'm correct since it calls for 15mm of installed preload, a 98mm spacer should be perfect. The OEM spacers are just about 98/99mm so I'm assuming I'm good?

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post #4 of 13 Old 06-22-2017, 11:30 AM
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You have a late model front end with ride height adjusters.
Back out the ride height adjusters the whole way so all the rings are showing.
Use the Racetech instructions to determine how long a spacer you need to cut in order to have 15 mm of installed preload.
This is the ONLY way to know how much installed preload you have.
My bike needed a 90 mm spacer for 14 mm of installed preload so you should need 91 mm.
Do not use any spacer washers, they are for non ride height adjuster forks.
When assembled, I suggest you start with 3 rings of your ride height adjusters showing.

Found this in another post. Hope it helps.

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post #5 of 13 Old 06-26-2017, 07:51 AM
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Quote:
Originally Posted by Islandboy View Post
You have a late model front end with ride height adjusters.
Back out the ride height adjusters the whole way so all the rings are showing.
Use the Racetech instructions to determine how long a spacer you need to cut in order to have 15 mm of installed preload.
This is the ONLY way to know how much installed preload you have.
My bike needed a 90 mm spacer for 14 mm of installed preload so you should need 91 mm.
Do not use any spacer washers, they are for non ride height adjuster forks.
When assembled, I suggest you start with 3 rings of your ride height adjusters showing.

Found this in another post. Hope it helps.
those are not ride height adjusters... those are spring preload adjusters... while they may happen to affect dynamic ride height, that is not what they are.
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post #6 of 13 Old 06-26-2017, 11:47 AM
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Quote:
Originally Posted by badmoon692008 View Post
those are not ride height adjusters... those are spring preload adjusters... while they may happen to affect dynamic ride height, that is not what they are.

Sorry, but in the case of a 919 with its very short top out springs, in the normal operational stroke zone, the adjusters change ride height and do not change the compressed length of the spring, nor the stored energy, so can't be "preload" adjusters.
The evidence is the fact that when you turn them in, the bike lifts up upon the springs by the same amount, while the spring remains the same length. So, seeing as the compressed spring length remains the same, the top out spring has not been engaged, the stored energy remains the same, then the only thing that has changed is the ride height, therefore a ride height adjustment was made, not a preload adjustment. So, when one plays with the adjusters, the only thing being changed is front end ride height - the sole exception being the net effective spring rate near and at full extension when the top out spring starts to be engaged.

I see the use of the term Preload Adjusters re the front of the 919 is somewhat akin to at least one manufacturer referring to their low "speed" ("fork stroke velocity") rebound adjuster screw to being a Tension Adjuster, and marking their adjuster with a "T". Hmmmm, low speed rebound adjustment alters the damping force characteristic of the rebound hydraulic circuit when the fork begins to decompress and re-extend due to compressed spring force energy. Where is the "Tension" in that?

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post #7 of 13 Old 06-26-2017, 04:21 PM
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https://www.google.com.au/url?sa=t&s...E4KxSNV__-5UJw

This link has good discussion on the Preload adjuster/Ride height adjuster.

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post #8 of 13 Old 06-29-2017, 07:09 AM
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I'm pretty sure 919 fork design will preload main springs with the adjustment and ultimately affect the ride height. Thanks to short and stiff top out springs, they have very min comp. when adjustments are made. Ride height is a height of the bike with the ride. Compressing the spring with the adjustment, will preload main spring a lot more (make it shorter) while top out springs will comp. slightly.

With long and soft top out springs (RC51, Ohlins). Adjustments will only compress top out spring without practically any preload on main spring. Totally different design concept..... Basically forks will grow if you crank the adjusters and go right back to where they were set originally with the rider on the bike.

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post #9 of 13 Old 06-29-2017, 09:36 AM Thread Starter
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RIP my thread lol

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post #10 of 13 Old 06-29-2017, 09:45 AM
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I'm kinda lost on the point here. The forks have a fixed max length. Inside, the spring and and spacer combine to make up that length. If you cut 2" off of one spacer, put that fork back together, does it drop the max length of that fork?

It might change the length under load, but wouldn't a stiffer/weaker spring do the same?

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post #11 of 13 Old 06-29-2017, 10:02 AM Thread Starter
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I don't think it would change the max length at all. It would change the sag numbers because the suspension has to travel a little further to settle for the same load.

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post #12 of 13 Old 06-29-2017, 05:56 PM
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Quote:
Originally Posted by trollindurty View Post
I don't think it would change the max length at all. It would change the sag numbers because the suspension has to travel a little further to settle for the same load.
Using KarlJay's 2 inch cut as the criteria, the forks would actually collapse some at rest.
Just from the weight of the fork tube, with the fork off the bike so not even seeing any bike weight.
That's because 2 inches is way more than the installed preload would ever be, so at full extension the spring and spacer would be rattling around with many mm's of axial slop.

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post #13 of 13 Old 06-30-2017, 03:50 AM
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Quote:
Originally Posted by mcromo44 View Post
Using KarlJay's 2 inch cut as the criteria, the forks would actually collapse some at rest.
Just from the weight of the fork tube, with the fork off the bike so not even seeing any bike weight.
That's because 2 inches is way more than the installed preload would ever be, so at full extension the spring and spacer would be rattling around with many mm's of axial slop.
I took a guess at the 2" mark, but it was intended to prove a point. So replace the 2 with whatever won't have free play. I think the terms being used on right height adjusting are being misused. The problem here is that we might be giving out mis-information to someone that is reworking their forks.

I think the spacer could act as a cheap way for someone to dial in there settings.

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