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Old March 26th, 2019, 10:27 AM   #1
Cep
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Upgraded front springs, rear shock question

Hello all,

Decided to keep my 250r for another season, and since i'm 210 lbs and my seals were leaking a tad last year, i decided to get the seals replaced and also had .85 racetech springs installed.

my front sag i measured at around 35mm. (not sure what the preload is however)

Now, the rear shock. Racetech calculator shows the stock shock should be just about right for my weight. But i have the preload at setting 5 and my sag is still around 38mm (which i can live with). But as far as i can tell i have 0 static sag (no rider on bike). I am thinking about dropping the preload to 4 and see if i can get even 1 or 2 mm of static sag.

But my question is, how can this be? If the shock is correct for my weight, shouldn't i be able to use less preload and still get a good sag number? Or does it mean my shock is not working correctly? (i bought it used so who knows if its an actual stock shock...)

Anyways the 0 static preload is worrying me after watching countless dave moss videos :P

Any thoughts? Is it not correct that the stock shock should be right for me?
racetech:
recommended: 9.14 kg/mm
stock: 9.3 kg/mm

Also, can anyone tell me the total amount of travel that the stock shock has in mm ?

Thanks!

Last futzed with by Cep; March 26th, 2019 at 12:00 PM.
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Old March 29th, 2019, 05:07 PM   #2
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I think RT's formula may be wrong. This thread has more info. A 160lb guy (though he is a top-notch racer) said it was too soft for him. RT's variation between street and race rates is under 2%, but this was 11% stiffer than RT's suggestion for his weight and he still said it was too soft. With that much difference, I don't think it's just that he's a pro who wants a stiffer suspension than us scrubs.

It's also possible that the NewGen's spring is softer than stated. In my non-scientific experience with that spring/shock on the 500, it doesn't seem to be drastically softer than stated. However, the 500's spring is extremely soft, so it doesn't take much to be an improvement. Based on physical dimensions, the spring seems to match up with the stated rate too.

I would definitely trust your real-world sag numbers over RT's calc, assuming there are no other problems with your suspension causing you to get bad readings. Based on the stated rate and RT's calculator, the stock setup should be quite a bit stiffer than many owners would want. Yet we don't hear a ton about the spring being way off for everyone. I have no trouble accepting that the stock spring is less than you actually need for your weight. But I'm not sure where the error in the calculation is, making it hard to figure out what rate you do actually need.
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Old March 29th, 2019, 05:41 PM   #3
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Thx for the reply InvisiBill.
Do you know if it's normal to have 0 static sag with the preload set to max ?
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Old March 29th, 2019, 05:59 PM   #4
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Stock, the collar is in the middle position. In the firmest position, yes, no sag. You have the tail set way high. I didnt like mine set like that, im heavier than you.
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Old March 29th, 2019, 06:15 PM   #5
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I think Racetech's rear spring calculator is for dual-shock bikes.
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Old March 29th, 2019, 06:40 PM   #6
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Thx again.

May set the preload down to 4 eventually but Maybe I can lose 10 or 20 pounds that would also help things
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Old March 30th, 2019, 07:19 AM   #7
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If you have to set the preload so high to get the proper static (loaded) sag that it leaves you no free (unloaded) sag, that indicates the spring rate is too low for your weight. You're giving it too much preload to compensate for the spring being too soft. A spring of the correct rate will let you set the preload in a way that the static and free sag are both acceptable.

http://web.archive.org/web/201804260...ension_Preload is a good writeup explaining how sag works with the spring rate. In short, sag is just setting the starting point for spring action, so as to optimize the operating range of the spring. A spring of a certain rate will always compress down to a certain length under a given force, regardless of how much or little preload you have on it. That's simple physics.
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Old March 30th, 2019, 07:24 AM   #8
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Do we know what the max travel is for the rear shock?
Is it 130mm?
And 1/3 of that would be 43mm. Wouldn't 43mm be a good sag number?
I keep hearing 30-35 mm but ...

Also, how do I know if the rear shock is bottoming out?

Last futzed with by Cep; March 30th, 2019 at 11:18 AM.
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Old April 3rd, 2019, 07:16 PM   #9
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So I bought an adjustable c spanner for $40 cdn. Lol...
I took off the foot peg bracket and chain guard and... spent an hour of hell trying to get the wrench to the right size and fit on there properly. Crushed 1 fingernail. Was about to give up (I still don't know if this was the correct tool I needed) but I finally did it! Somehow. Down to preload position 4 woot!! Yay me.

I still don't think I have any static sag though. MAYBE 1 mm... MAYBE not.
Took it for a ride, maybe placebo but feels a bit nicer over bumps. I wish I knew what bottoming felt like I can't tell if it's bottoming either..
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Old April 3rd, 2019, 08:08 PM   #10
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race tech is way soft on there calcs. im 185, i run .95 springs, emulators and 15wt oil. the rear is a gsxr with a 1.2 spring. this is on a 300.
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Old April 4th, 2019, 04:49 AM   #11
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Bloody hell :P
Is that for track or street?

I was worried about going to stiff on the front. Well live and learn. I suppose I could just drop new springs in myself if I had to? Rear is another story.. Anyways it should be ok for now.

I've actually been looking at that 2019 zx-6r.
Lots seem to think it's ugly but I don't see it..
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Old April 4th, 2019, 06:03 AM   #12
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Quote:
Originally Posted by Cep View Post
Bloody hell :P
Is that for track or street?

I was worried about going to stiff on the front. Well live and learn. I suppose I could just drop new springs in myself if I had to? Rear is another story.. Anyways it should be ok for now.

I've actually been looking at that 2019 zx-6r.
Lots seem to think it's ugly but I don't see it..
track bike, its miserable on the street, great on the track.
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Old April 4th, 2019, 06:11 PM   #13
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Quote:
Originally Posted by Cep View Post
Do we know what the max travel is for the rear shock?
Is it 130mm?
And 1/3 of that would be 43mm. Wouldn't 43mm be a good sag number?
I keep hearing 30-35 mm but ...

Also, how do I know if the rear shock is bottoming out?
You'll feel a sudden slap on your butt!

Actual shock travel is 64mm, gets multiplied to about 130mm at rear axis due swing of swingarm and leverage of linkage.
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Old April 4th, 2019, 06:15 PM   #14
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Different feel to topping out ?

Quote:
Originally Posted by DannoXYZ View Post
You'll feel a sudden slap on your butt!

Actual shock travel is 64mm, gets multiplied to about 130mm at rear axis due swing of swingarm and leverage.
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Old April 4th, 2019, 06:46 PM   #15
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Quote:
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Different feel to topping out ?
Yes, only force on bike when fully extended is mass of unsprung weight: wheels and 1/2 suspension. Very mild.

On bottoming, entire weight of sprung weight: bike+rider, slams into ground. Might even give you bruised tailbone!

Last futzed with by DannoXYZ; April 6th, 2019 at 12:39 PM.
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Old April 4th, 2019, 06:49 PM   #16
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Lol ok thx
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