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Discussion Starter #1 (Edited)
Understanding Spring Preload.

Hi there. Newbie forum member...25 year sledding.

First sled was a 97 indy trail touring. Never did anything to it. Just got on and rode. Didn't know about adjustments etc back in the day. Just figured it is what it is. Just bought an Axys switchback adventure..Boy has sledding technology come along way in 20 years. Man oh man..this thing is soft as pillow and handles like a dream. While waiting for snow, I read and studied everything I could about suspension for this beast.

It took a real long time to understand that :

1. Preload does not affect stiffness:

Adjusting preload does NOTHING to the spring rate. in other words compress the spring to a 1/3 of its travel and it will still have the same "resistance" as a spring that isn't preloaded. Yes if you preload to max and the spring is completely compressed it will be infinitely stiff because it can't travel any further. BTW(This does not apply to variable spring rate springs which get stiffer as it gets shorter. A springs resistance is constant throughout its travel until it reaches full compressed in which case it is infinite resistance ;) Each spring has a load rating which should be selected based on the average weight of the load on the sled. Springs can and should be switched based on this weight.

2. Spring preload is ONLY for ride height and weight balance transfer. If the sled springs are preloaded for forward weight transfer the skis will bite. If the preload puts more transfer to the rear it will be "Lite" in polaris speak.

It took me a long time to figure this out. The posts on the forum were so confusing. Some would respond to a question of bottoming or stiffness with a recommendation of adjusting preload...

SO..i decided to test if this was all correct:

1. I pushed down on the rear of my sled with a completely unpreloaded RTS (air pump shock) and felt the effort required to bring it all the way down.

2. I pumped up the air shock with a ruler beside the runners to 25lbs while noticing the ride height increase a half inch or so. Then I pushed back down on the back of the sled and voila...exact same pressure to bring the sled down.

3. Just to make sure this was correct. I pumped the thing right to max..50lbs Ride height increased to about 1 inch total.... Guess what...same resistance to pushing the sled down. So maxing the preload did nothing to the spring rate in this experiment.

4. Then i adjusted the dampner (fox shock 3 settings) as you would expect the energy required to push down was increased significantly with each setting 1 to 3. 1-2 felt like maybe a 20% increase in resistance and three was significant..

So apologize for the long post but this was meant to help a newbie truly understand springs cause it was confusing for me.

Once I understood this..and put on a few hundred miles I adjusted my suspension and this thing floats like a butterfly.

Thanks.
 

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I believe you've become confused.

A spring has a starting tension and an ending tension. This is established based on the amount the spring is compressed.

The "rate" of increase in spring tension per inch of travel is a major factor in determining how much stronger one spring may be versus another.

So is the initial tension versus the final tension.

Several other factors affect this. One is the mechanical leverage used in the suspension geometry to shape the spring tension curve. You can have rising rate or falling rate leverage. Or something in between.

Keep making adjustments until you find the sweet spot for your riding style and other factors.:bc:
 

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Yep, you forgot Hooke's law. Force = Spring Constant * Distance. No way, no how there is a constant rate spring on its own that doesn't follow it.
 

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Discussion Starter #5
Yep, you forgot Hooke's law. Force = Spring Constant * Distance. No way, no how there is a constant rate spring on its own that doesn't follow it.
Okay..I think I understand. The spring rate constant stays the same but the distance travelled changes the multiple to the constant? In otherwords the key consideration is the distance the spring travels changes the amount of force to compress the spring as a multiplier of the spring constant.

in easier terms to understand (for me) adjusting spring preload will change the "stiffness" feel of a spring while also changing ride height?
 

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Discussion Starter #6
But it doesn't explain when I tested pumping my RTS shock to 50lbs that the amount of force to push the back down didn't feel any significantly stiffer?
 

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I would tend to agree that changing springs based on weight and riding style makes sense. After all a XCR suspension gets a lot better reviews on here than the Pro S suspension. I would rather run a little stiffer spring with a small amount of preload than crank up the preload on a lighter spring. Valving would also need to be addressed of course. Just my 2 cents
 

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But it doesn't explain when I tested pumping my RTS shock to 50lbs that the amount of force to push the back down didn't feel any significantly stiffer?
I own a 2016 Switchback Adventure, the same as yours. I'm still learning the nuances of the QS3 air over coil spring RTS. When it comes to ease of making fine adjustments to the RTS on the trail, we have it lucky. But I find myself adjusting clickers more so than air pressure to adapt to changing trail conditions. I weigh 170 before suiting up. I typically run a bare minimum of 5 psi when riding solo, and rarely vary from that.
I find the low setting on the clicker too soft unless the trail conditions are highway smooth. So I'm toggling between middle and high on the clicker as the chop gets worse.
I bought the two up seat and backrest for two up riding with my wife on occasion. The only thing I change is raising the RTS air pressure to compensate for her weight, following the Fox air pressure chart.

That being said, in answer to your comment about rear air pressure,I disagree. When at 0 psi, the rear end compresses somwhat easily. Maxing out at 50 psi, and the rear end is quite stiff.
 

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Discussion Starter #9
I own a 2016 Switchback Adventure, the same as yours. I'm still learning the nuances of the QS3 air over coil spring RTS. When it comes to ease of making fine adjustments to the RTS on the trail, we have it lucky. But I find myself adjusting clickers more so than air pressure to adapt to changing trail conditions. I weigh 170 before suiting up. I typically run a bare minimum of 5 psi when riding solo, and rarely vary from that.
I find the low setting way to soft unless the trail conditions are highway smooth. So I'm toggling between middle and high on the clicker as the chop gets worse.
I bought the two up seat and backrest for two up riding with my wife on occasion. The only thing I change is raising the RTS air pressure to compensate for her weight, following the Fox air pressure chart.

That being said, in answer to your comment about rear air pressure,
I disagree. When at 0 psi, the rear end compresses somwhat easily. Maxing out at 50 psi, and the rear end is quite stiff.
Yes similar riding situations. I have the two up seat as well (great convenient unit) and use the air pump to adjust rider height.

I have to try the experiment again. I swear pumping that thing to 50 did not change the perceived force of pushing the back end down. Maybe it changes perceived stiffness at speed? (aka doing it forcefully like hitting a bump).

I'll keep working at understanding this whole suspension thing. In any event..its riding really nice..I just want to understand why lol
 

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Yup. FTS on low setting is too soft for my liking. Last season I ran it on med on a bag trip. When I went to experiment with clicker settings it was a frozen ball of ice so I didn't get to experiment much with that.
BTW, I'm running Hygear twisted dual rate springs on the IFS. The Pro series has a threaded collar between the soft spring and the stiff spring. So not only can you adjust ride height as always, you can adjust the actual crossover point of when your soft spring compresses and you get into the firm spring. Adjusting the crossover collar is quite noticeable in actual trail conditions.
 

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I have to try the experiment again. I swear pumping that thing to 50 did not change the perceived force of pushing the back end down.
I get where you're coming from and its true to an extent. Changing air pressure will not change force needed to initially compress the suspension, but... it will change how far you can compress it.
 

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Rabbi, Out of curiosity, what rate springs did you get for your dual spring setup? I have been considering trying dual springs for my IFS springs. I'm running 100 lb springs now and like them better that the stock 80 lb.
 

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It was always explained to me that the springs get the ride height correct so your shock valving is being used correctly. I.e. if your springs are too soft your shocks compress more than they should and will be farther into their travel where the valving is stiffer making a stiffer ride and not using the softer initial valving that it normally would if the springs were set correct.
 

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That guy is correct and the pre-load on the Front suspension adjust ride height.

I think what's confusion is the entire 'technical' discussion on preload and effect on force required. Yes you compress the shock more it will require more force (ie Hooke law) to move, however, in the case of the Axys and an attempt to simply,,,,

- preload adjust on FTS will adjust the balance point of the sled which can impact ski pressure (some will also say weight transfer because essentially that's the fulcrum of the sled).
- preload adjust on RTS plays a critical role in Weight transfer but also will impact ski pressure.

General rule of thumb,,,, set everything to standard and start adjusting one by one. Need more ski pressure, then the easiest is to adjust the RTS. After you riding you feel the ski pressure is good but you feel the weight transfer back isn't as pronounced, then move RTS back to Std setting and adjust the FTS. Then ride and if ski pressure need try a little less RTS.

I'm sure you have more question so fire away.

NOTE: On the front end ride height,,,, not really sure about what needs to be done there, since 90% of the time people talk about adjusting RTS and FTS. I guess if you want the sled with a lower stance then put on more preload (yes I know that seems backwards but putting more preload will short the distance between the shock ends thus lowering ride height and I suppose that could impact ski pressure,,,, but not so sure you want to play with that much.
 

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Discussion Starter #17
Thanks Fellas...I didn't expect suspension setting to be so complicated but the physics behind all this is fascinating. I'm am however starting to understand it better and its fun learning and experimenting to get things dialled just right.

I'm going to ride this weekend and keep trying things. Appreciate the help.
 

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The springs job in the IFS is to control ride height. The valving controls the way the shock moves through its travel as it is impacted. So if you are bottoming out then you need to adjust your valving and not your spring rate. Chances are you will still bottom out no matter the spring rate. Use the RTS and FTS to set ski pressure.
 
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