K-Tech Spring Rate - Suzuki GSXS1000 Forum
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post #1 of 14 Old 03-24-2019, 11:54 AM Thread Starter
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Question K-Tech Spring Rate

I just received a new K-Tech Razor rear shock and I'm trying to figure out what spring rate it is. I bought from Revzilla and specified 160-190lbs with gear. I'm on the low end of that, but the next step down was 120-150lbs and I'm over the top end of that. The spring on the shock has printed on it 46-180-100. I'm assuming that its the 46-180 series spring and 100N spring rate. Does that seem right?
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post #2 of 14 Old 03-25-2019, 12:14 PM
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Originally Posted by mike d View Post
I just received a new K-Tech Razor rear shock and I'm trying to figure out what spring rate it is. I bought from Revzilla and specified 160-190lbs with gear. I'm on the low end of that, but the next step down was 120-150lbs and I'm over the top end of that. The spring on the shock has printed on it 46-180-100. I'm assuming that its the 46-180 series spring and 100N spring rate. Does that seem right?
Yes, it's a 100N/mm spring, same rate as the standard rear shock spring.

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post #3 of 14 Old 03-25-2019, 05:48 PM Thread Starter
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Originally Posted by Robbieben View Post
Yes, it's a 100N/mm spring, same rate as the standard rear shock spring.
So I'm a little confused, 160-190lbs is way too harsh with the stock shock, so do I need to swap the K-Tech for a lower spring rate or does the same spring rate work better for my weight with the K-Tech?
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post #4 of 14 Old 03-26-2019, 04:31 AM
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It's all to do with the Shock valving.
The KTech has adjustable compression and rebound separately right?
With a bit of tuning I'm sure you will get to a setting which will give you much more control over a wider range of conditions. The standard shock used to tie it's self in knots when the road got a bit rougher and the pace was increased. I don't have any issues since I've upgraded, hopefully you'll be the same
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post #5 of 14 Old 03-26-2019, 09:19 AM
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Same one I bought. I'm under the 160 lb rating by 20 lbs and so far mine works fine, 1000% better than stock. I was leery of going with the one below this one due to my overall weight going up in full race leathers, boots and glove which put me on the upper edge of the spring below the 100 one on the 160 lb + shock.

As mentioned above the valving is where the good stuff is.
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post #6 of 14 Old 03-26-2019, 09:39 AM Thread Starter
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Thanks everyone. I'm sure this one is the right one now, and I have to proceed with the install. I'm still waiting for Paul's full exhaust system, so I'll probably wait till I get that so I can do them at the same time and not have to remove and reinstall the stock exhaust.
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post #7 of 14 Old 03-27-2019, 05:25 AM
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Originally Posted by mike d View Post
So I'm a little confused, 160-190lbs is way too harsh with the stock shock, so do I need to swap the K-Tech for a lower spring rate or does the same spring rate work better for my weight with the K-Tech?
The stock spring rate is a good rate based on bike and average rider weight, unfortunately the stock shock absorber function is poor at best, once you fit the K-Tech you'll notice a massive, night and day difference over the standard rear shock and understand why you invested good money in replacing the $20 standard shock.
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post #8 of 14 Old 03-30-2019, 10:14 PM
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Originally Posted by Slower and Slower View Post
100 NM/mm is the stock Suzuki spring rate from memory.

The K-Tech site show's Mikes spring has a bike + Rider weight range suitability of 90 to 120 NM, which means it will support 90 x 9.8KG = 88KG, to 120 x 9.8KG = 117KG to balance the spring with 0 mm compression.
To set the scene for the bike with a 50/50 weight ration front and back suspension and assuming it weighs 240KG and Mike at 80 KG and with Mikes weight say distributed 60 KG to the back and 20 to the front.
The ratio of the dog bones at the rear shock ratio I found quoted for a 2004 GSX-R1000 is close enough for arguments sake at 2:1 squared. So the back wheel moves 4 times the rate of the shock itself.
So for the bike to have a 40 mm rear sag, the shock would need to be compressed 10 mm.
As far as I can tell the ratio is approximately 2:1 but increases with travel (rising rate), don't know where you get 2:1 squared from?



Also the fact that the shock has a stroke of 65mm and full travel is 130mm would tend to confirm this, which rather mucks up the rest of your figures - Sorry

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Originally Posted by Slower and Slower View Post
So half the bike, 120 KG + 60 KG (Mikes body portion) = 180 KG . That 180 KG divided by 9.8 KG/mm (that's another way of saying 100NM/mm) = 18 mm compression of the shock spring.
So the ideal was 10 mm for sag at the shock end, so there's 8 mm to much; so we crank up the pre load setting to suit. The lowest setting still has the spring compressed somewhat, but I shall just ignore it here.
The step notches for the GSX-S preload adjuster are 2 mm each, so 8 mm dived by 2 mm = 4 ring adjuster notches, the standard Suzuki setting for a Naked, 3 for the F which runs a bit softer for the Girl's amongst us.

The logic being a 90 KG Rider should find the adjuster set OK at the stock setting: a 120KG Rider with 3/4 weight bias towards the rear is 90 KG +120 bike =210 KG.
210 KG on the 9.8KG/mm spring rate = 21.5 mm. Minus the ideal 10 mm sag again = 11.5 mm to have adjusted with the spring's ring adjusted as before.
So 11.5 divided by 2 = 6 in rounded up figures, saying it would be on notch 6 for the 120KG Rider load with a rear preload of 40 mm.

If I have f**cked up the figures and conversions, I'll appreciate your Expert explanation, but don't spoil with with facts, I am too tired to argue.

Rob.
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post #9 of 14 Old 04-01-2019, 05:01 AM
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I've deleted my earlier post No 8 which is displayed in PP reply to it as he deemed it to be incorrect.
I spent 2 - 3 hours researching my post on line and it was in accordance to the Learned Gents who had Degree's with mechanical qualifications who wrote, and applied those argument's to a Bike suspension's.
This included the square of the radius of motion as in the ratio 2:1 which as the same graph I found on google that PP has posted, for a 2004 GSX-R1000 which is closer to 1.75 :1 than 2:1 (that was simplified for easy maths).
I have learned my lesson here; I will never post in that technical detail ever again and mislead you lot, even if it was in my belief, true at the time.

Rob.
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post #10 of 14 Old 04-01-2019, 07:36 AM
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Originally Posted by Slower and Slower View Post
I've deleted my earlier post No 8 which is displayed in PP reply to it as he deemed it to be incorrect.
I spent 2 - 3 hours researching my post on line and it was in accordance to the Learned Gents who had Degree's with mechanical qualifications who wrote, and applied those argument's to a Bike suspension's.
This included the square of the radius of motion as in the ratio 2:1 which as the same graph I found on google that PP has posted, for a 2004 GSX-R1000 which is closer to 1.75 :1 than 2:1 (that was simplified for easy maths).
I have learned my lesson here; I will never post in that technical detail ever again and mislead you lot, even if it was in my belief, true at the time.

Rob.
Rob,

I am sorry you deleted your post, I found it very interesting reading.

I wasn't so much saying it was incorrect, just interested in where you got the squared part from, i was wondering if you theory was correct but 2:1 was the result after squaring already, i.e the mechanical ratio is 1.44:1 but the geometry alters it to 1.44*1:44:1

Please don't let my pedantic OCD nature stop you from posting technical details, even if there are mistakes it gets people thinking and discussing which can never be bad!

Paul
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