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OVER SPRUNG REAR SHOCK; what to expect?


justplainbill

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I have a low mileage 2006 Hayabusa rear shock to use on the FJ-09. It has the OEM spring (rated 733 pounds/inch).  For my weight, a spring rate of 650 lbs/inch is recommended, but Summit Racing (my vendor of choice) is backordered for that Eibach spring about three weeks.  We're enjoying spring rains now and it's a good time to change the shock but I'd rather wait than have to do it twice.
 
Assuming I can get rider sag set, my question is, what kinds of unpleasant riding effects can I expect using the OEM Hayabusa spring -- rated 80 pounds more than ideal?  (There is plenty of information here on the ill effects of too soft springs, not much on  too hard springs.)
 
Thanks.
 
Bill
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Given the bollocks submitted as replies to my question, I've resorted to finding an authority outside the forum. This is what Paul Thede (Race Tech) has to say: "The quality of the ride will suffer with a spring that is either too soft or too stiff. The spring with a rate that's too soft will dive and bottom easily because the spring doesn't provide enough additional force as it gets deeper into the travel. The spring that has a very stiff rate will feel harsh, like it's hitting a barrier or very stiff spot." http://www.sportrider.com/technicalities-spring-rate-and-preload Thede's article is from 1995 and directly answered my question. But I found another article by Peter Verdone dated 2006 that covers the subject of springs and spring rates even better: http://www.peterverdone.com/archive/springs.htm
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Bollocks, <raises an octave>bollocks? You traduce me, you cad!
 
I'll have you know my reply is serious. It is a tried and tested technique when the rear suspension is oversprung. I used the technique to good effect in my 1970 Ford Capri, my first car after passing my test in 1980, by carrying a bag of cement in the boot.
 
 
This signature is left blank as the poster writes enough pretentious bollocks as it is.
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Bollocks, <raises an octave>bollocks? You traduce me, you cad! 
I'll have you know my reply is serious. It is a tried and tested technique when the rear suspension is oversprung. I used the technique to good effect in my 1970 Ford Capri, my first car after passing my test in 1980, by carrying a bag of cement in the boot.
 

Bollocks. The Capri was undersprung. You carried the cement as ballast to help you drift. Only you didn't call it that then.
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Bollocks, <raises an octave>bollocks? You traduce me, you cad! 
I'll have you know my reply is serious. It is a tried and tested technique when the rear suspension is oversprung. I used the technique to good effect in my 1970 Ford Capri, my first car after passing my test in 1980, by carrying a bag of cement in the boot.
 

Bollocks. The Capri was undersprung. You carried the cement as ballast to help you drift. Only you didn't call it that then.
do you have a permit to stomp your muddy boots over this bank?
This signature is left blank as the poster writes enough pretentious bollocks as it is.
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Bollocks. The Capri was undersprung. You carried the cement as ballast to help you drift. Only you didn't call it that then.
do you have a permit to stomp your muddy boots over this bank?
I don't recall applying
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also, the rebound circuit will likely be overly flow limited to counter the 733 spring vs the 650. So, you'll probably need to have a couple of shims removed. You can try running the rebound needle full open and maybe that will suffice but I wouldn't count on it.
 
Wessie isn't completely full of it. Add 50lbs of weight to the back (secured properly) and that'll get the total weight closer to the "733 is the correct spring" territory. But I'm not sure you want to go about buying 20lb bags of play sand and equipping your bike thusly.
 
It would be interesting to see what kind of static and rider sag you end up with after backing the spring preload way back to say 5mm. Whatever you do, you don't want the spring to have zero preload.
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Thanks folks. The question wasn't how do I get around the problem - it was what effects would the 733 lb. spring have. So the comments were all bollocks. (And I had to look up "bollocks" since I didn't speak Middle English - before.)
 
Wessie, you were not traduced, you were chastised for passing bollocks on as sensible. Fortunately, you had warned us all to be wary of your pretentious bollocks. Though there's not much pretension to sand. In Nevada we are surrounded by it and it's just plain sand.
 
Since my own prime directive is to avoid doing things that cause me pain, and a harsh ride is certain to be painful, I ordered a 650 lb./inch spring and will wait for it to arrive before installing the Hayabusa shock. In the words of Edd China: "problem sorted". (Look mom, I can speak English, not just American.)
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I thought that "the 733lb/in spring would be very stiff and contribute to a jarring ride" was a given and didn't need an exposition.
 
Do yourself a favor and have the shock rebuilt and revalved to match the spring. Not only is it a decade old (shocks should be serviced every 2-3 years), you'll be chasing setting trying to get it to work when you could have it set up properly from the beginning. If a RaceTech service center (or some other trusted suspension outfit) isn't handy send it to @NorWest for his magic touch. Have the spring sent there while you're at it.
 
 
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I thought that "the 733lb/in spring would be very stiff and contribute to a jarring ride" was a given and didn't need an exposition. 
Do yourself a favor and have the shock rebuilt and revalved to match the spring. Not only is it a decade old (shocks should be serviced every 2-3 years), you'll be chasing setting trying to get it to work when you could have it set up properly from the beginning. If a RaceTech service center (or some other trusted suspension outfit) isn't handy send it to @norwest for his magic touch. Have the spring sent there while you're at it.
 
 
 
Nope, it wasn't at all obvious at all since I get a jarring ride over expansion joints and potholes from the FJ's OEM shock with a 560 lb./in spring.  If I had known a stiffer spring gives a jarring ride, my  first thought would be that a 450 lb./inch spring would be a better choice than a 650 lb/in. spring.  But I'm pretty  sure I wouldn't be able to get the sag right with a softer spring so I'm going with the harder spring despite the logical inconsistency.
 
I appreciate the rebuild advice but will wait to see whether the Busa shock provides any improvement before throwing more money at this project.  Sometimes, just the fact you have made a good effort is enough to convince you that you've achieved a good result.  
 
 
 

 
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are you throwing darts at a board? In one post you claim 650lb/in is "right" for your weight, and then observing that the ride from the OE 560 is jarring, you thought going with a 450 would improve matters?
 
harsh ride isn't about spring really, it's about valving. A weaker spring leads to more travel per the same bump so stresses the damping more. on the other extreme a too stiff spring behaves 'rigid' even though the damping is no longer the problem as such.
 
The spring supports the weight/load. Damping controls movement rates. If movement is the problem chasing springs is the wrong answer. Now I realize I'm simplifying a bit since they both work in tandem. 
 
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justplainbill, 
Assuming you got a 8" 2.25" ID Spring you are going to need a collar for each end of the spring to reduce the side to side play to a minimum.
 
 
 
 
 
The stock Hayabusa spring is 7 5/8" x 2.25" ID.  The lower? shock adjusting ring has a collar and the retaining clip at the bottom has a centering bump built in to stabilize the spring.  Is that sufficient?
 
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