Negative preload... help me understand - Honda RC51 Forum : RC51 Motorcycle Forums
 
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post #1 of 6 (permalink) Old 11-18-2012, 11:53 AM Thread Starter
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Negative preload... help me understand

So the stock fork springs have a NEGATIVE 5mm preload from what i gather? Race tech says the springs need to be swapped for this reason. Is this true? Or are spacers made to make up for this typically? I think i remember reading people/tuners use 20MM spacers to correct this. Anyone have a photo or something so know what to look for? i can make my own with ease from Billet if i had dimensions.
Also, can anyone confirm the spring rate on the SP2 forks? 1.0kg/mm?

Current steeds: 2000 RC51 SP1, 2002 KTM 520EXC, 2001 YZ250f
Road bikes I used to own: '03 Bandit 1200s, '02 ZZR1200, '00 Guzzi V11 Sport, '97 H-D 1200c sportster (don't judge me).

"If you don't stand for something, you will fall for anything".
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post #2 of 6 (permalink) Old 11-18-2012, 07:05 PM
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The OEM spring rate is .95 Kg/mm.

And some related info:
http://www.1000rr.net/forums/archive...p/t-88554.html
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post #3 of 6 (permalink) Old 11-20-2012, 10:59 AM Thread Starter
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thanks sub,
that helped some. I have been having to do my fair share of reading and searching to get my head wrapped around the suspension issues on the RC. i See now that the negative preload is caused the top out out springs? the top out on the SP2 is longer than the SP1 so this is more of an issue with SP2?
for the SP1, the way to correct the preload on an SP1 one is to add a 20mm spacer to the fork spring to get a positive preload? Do i have that right?
I just scored a set of 1.0kg springs off of ebay for cheap that came off a sp2 and and i'm trying to figure out what to do when i drop them in. they are shorter too, so will 20MM spacer be enough?
thanks

Current steeds: 2000 RC51 SP1, 2002 KTM 520EXC, 2001 YZ250f
Road bikes I used to own: '03 Bandit 1200s, '02 ZZR1200, '00 Guzzi V11 Sport, '97 H-D 1200c sportster (don't judge me).

"If you don't stand for something, you will fall for anything".
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post #4 of 6 (permalink) Old 11-20-2012, 07:42 PM
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The top out spring on the SP2 forks is about the longest of any bike out there, about 150mm. This really screws up accurate preload adjustments.
I had sent my forks to Kyle Racing and they installed a shorter top out spring (approx. 25-28mm).

The usual range for installed preload on forks is around 15mm, with a range of 10-20mm on average.

If a set of springs are shorted than previous, you can make a spacer to compensate for the difference in length.
Either thin wall steel tubing, or PVC is popular, depending on clearance of I.D. and O.D. of the cartridge you're using.

On some, I could use PVC, and on others I had to use steel tubing (which is harder to come by my area).
You want to sand the cut ends very smooth inside and out to prevent burrs from falling into the fork oil, which can clog up valves.
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post #5 of 6 (permalink) Old 12-03-2012, 12:01 PM Thread Starter
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thanks sub. After doing a little more research here and other places. I get it now. the top out spring is a big issue for the SP2's not so much for the SP1's becauase of the shorter spring. Thankfully mine is a SP1. not as much of a concern, me thinks?
Found this for visual refrence on the super hawk forum. Sp1 spring pictured right. stock SP2 center. Mod sp2 left
Click image for larger version

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http://www.superhawkforum.com/forums...project-17434/

Current steeds: 2000 RC51 SP1, 2002 KTM 520EXC, 2001 YZ250f
Road bikes I used to own: '03 Bandit 1200s, '02 ZZR1200, '00 Guzzi V11 Sport, '97 H-D 1200c sportster (don't judge me).

"If you don't stand for something, you will fall for anything".
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post #6 of 6 (permalink) Old 12-03-2012, 12:18 PM
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That same photo is floating on this site as well from past suspension questions.
Now that we have a Tech Talk area, this should make it easier to search for answers over time.
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