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Discussion Starter · #1 ·
I weigh 210lb. and just installed a Romic shock on my 08' RFX. Did some research and decided to give a 600lb. coil spring a shot. Sag was a bit high. Did a driveway spin and I could bottom the shock by pulling back on the bars and shifting my weight to the rear. I was @ zero preoad so I cranked it down two then three turns. Did a short trail ride and I decided I probably need a stiffer coil - 50lb ? 100lb ? increase. Does anyone know how much preload affects the spring rate number ? Thanks.
 

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keen said:
Did that from the get go calc's were are all over the place. Romic & Turner agreed on the 600lb. but as mentioned it is too soft.
I'd go 650# first, but I like it active.
 

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I would try 650lb.

How old is the shock does it need servicing or re-working for you and the bike,i hated my romic shock i had on one of my bikes.Exactly for the reason your having.It blew travel even with a harder spring it always lacked compression damping through the stroke.
 

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norcosam said:
I would try 650lb.

How old is the shock does it need servicing or re-working for you and the bike,i hated my romic shock i had on one of my bikes.Exactly for the reason your having.It blew travel even with a harder spring it always lacked compression damping through the stroke.
I was going to mention this too.
 

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keen said:
Does anyone know how much preload affects the spring rate number ? Thanks.
Keen this is a somewhat rough estimate, but pretty close.

Adding 2 turns preload does about the same as adding 10% or 60# more to your 600# spring rate, or like going to a 650# spring with nearly no preload. (On Fox shocks 18 to 20 preload turns = 1 inch. So 2 turns increase is about 2/20 or 10% of 600# resulting in about 60# increase.)

Preload affects sag height more than bottom out resistance, because the spring rate remains the same. A firmer spring compounds that rate increase progressively deeper in travel. However, when adding preload sag is raised, so your weight center is shifted forward, and then there's then less rate of weight on the spring throughout travel to bottom travel. So it feels like adding preload 2 turns raising sag does affect bottom travel about as much as going to a 10% firmer spring without changing sag and weight center.

Adding to the rough estimate is that springs vary as much as 5% or more in accuracy.
 

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Discussion Starter · #8 ·
derby said:
Keen this is a somewhat rough estimate, but pretty close.

Adding 2 turns preload does about the same as adding 10% or 60# more to your 600# spring rate, or like going to a 650# spring with nearly no preload. (On Fox shocks 18 to 20 preload turns = 1 inch. So 2 turns increase is about 2/20 or 10% of 600# resulting in about 60# increase.)

Preload affects sag height more than bottom out resistance, because the spring rate remains the same. A firmer spring compounds that rate increase progressively deeper in travel. However, when adding preload sag is raised, so your weight center is shifted forward, and then there's then less rate of weight on the spring throughout travel to bottom travel. So it feels like adding preload 2 turns raising sag does affect bottom travel about as much as going to a 10% firmer spring without changing sag and weight center.

Adding to the rough estimate is that springs vary as much as 5% or more in accuracy.
It's a new Romic (old stock). I originally wanted a Roco TST but funds are tight - I knew it wouldn't be a 100% performer. The coil is much smoother than the air but dealing w/ getting the right spring will cost more than the shock itself.
 
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