Spring Pre-load - Once and for all understanding - HCS Snowmobile Forums

Rush/Switchback (AXYS Platform) This is a brand-specific forumand a 100% NO BASH Zone. Posts on this forum are assumed to be questions aimed at similar model owners, and are not looking for comments of a sarcastic or "bashing" nature. Please be aware that if you violate this policy you are in danger of losing your posting privileges on this website.The calling out or posting of another members personal information IE phone number or address is prohibited.

Like Tree8Likes
Reply
 
LinkBack Thread Tools
Old 01-27-2018, 05:53 PM   #1 (permalink)
Advanced Member
 
jumpnjehosaphat's Avatar
 
Join Date: Jan 2018
Posts: 46
Current Sled(s): 2017 Switchback Adventure 600
Previous Sled(s): 1983 Excel III,1992 Indy Trail, 1998 Indy Trail Touring
Location: Ontario
Favorite Riding Area: Snow
Riding Since: 1990
Default Spring Pre-load - Once and for all understanding

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.
snowmachine likes this.

Last edited by jumpnjehosaphat; 01-27-2018 at 11:07 PM.
jumpnjehosaphat is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 01-27-2018, 06:25 PM   #2 (permalink)
Super Advanced Member
 
patrioticinnovations's Avatar
 
Join Date: Sep 2005
Posts: 14,605
Current Sled(s): 2015 AXYS Pr-S SB Ann 800, 2019 Indy 850.
Previous Sled(s): 2003 XCR 1100, 2000 XCR 800, 2005 Redline Revolt 800.
Location: SE Lower Michigan
Favorite Riding Area: Cadillac, Gaylord
19-20 Mileage:
18-19 Mileage: 849 so far
17-18 Mileage: 1280
16-17 Mileage: 1115
Riding Since: 1982
Default

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.
patrioticinnovations is offline   Reply With Quote
Old 01-27-2018, 06:33 PM   #3 (permalink)
Super Advanced Member
 
Deephaven's Avatar
 
Join Date: Dec 2006
Posts: 3,906
Current Sled(s): 2017 Assault
Location: Minneapolis
Favorite Riding Area: Closest place with snow
Age: 40
Default

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.
Deephaven is offline   Reply With Quote
 
Old 01-27-2018, 06:46 PM   #4 (permalink)
Advanced Member
 
jumpnjehosaphat's Avatar
 
Join Date: Jan 2018
Posts: 46
Current Sled(s): 2017 Switchback Adventure 600
Previous Sled(s): 1983 Excel III,1992 Indy Trail, 1998 Indy Trail Touring
Location: Ontario
Favorite Riding Area: Snow
Riding Since: 1990
Default

Damn...this is driving me nuts...lol. Back to the drawing board.
jumpnjehosaphat is offline   Reply With Quote
Old 01-27-2018, 07:13 PM   #5 (permalink)
Advanced Member
 
jumpnjehosaphat's Avatar
 
Join Date: Jan 2018
Posts: 46
Current Sled(s): 2017 Switchback Adventure 600
Previous Sled(s): 1983 Excel III,1992 Indy Trail, 1998 Indy Trail Touring
Location: Ontario
Favorite Riding Area: Snow
Riding Since: 1990
Default

Quote:
Originally Posted by Deephaven View Post
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?
jumpnjehosaphat is offline   Reply With Quote
Old 01-27-2018, 07:15 PM   #6 (permalink)
Advanced Member
 
jumpnjehosaphat's Avatar
 
Join Date: Jan 2018
Posts: 46
Current Sled(s): 2017 Switchback Adventure 600
Previous Sled(s): 1983 Excel III,1992 Indy Trail, 1998 Indy Trail Touring
Location: Ontario
Favorite Riding Area: Snow
Riding Since: 1990
Default

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?
jumpnjehosaphat is offline   Reply With Quote
Old 01-27-2018, 07:47 PM   #7 (permalink)
Advanced Member
 
Join Date: Jan 2018
Posts: 51
Current Sled(s): 16 pro s 800 switch , 13 indy 600
Previous Sled(s): fusion 600 edgeX 600 V-max 600 SRV
Location: southern wi
Favorite Riding Area: N WI UP
Age: 50
Riding Since: 1978
Default

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
plowboy800 is offline   Reply With Quote
Old 01-27-2018, 10:53 PM   #8 (permalink)
Super Advanced Member
 
rabbi's Avatar
 
Join Date: Feb 2009
Posts: 3,530
Current Sled(s): 2016 600 Switcback Adventure
Previous Sled(s): Lots of Polaris'
Location: Western Wisconsin
Favorite Riding Area: Wi northwoods
19-20 Mileage:
18-19 Mileage: waiting
Age: 60
Riding Since: 1979
Default

Quote:
Originally Posted by jumpnjehosaphat View Post
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.
__________________
Riding an AXYS, pure adrenalin!
rabbi is offline   Reply With Quote
Old 01-27-2018, 11:06 PM   #9 (permalink)
Advanced Member
 
jumpnjehosaphat's Avatar
 
Join Date: Jan 2018
Posts: 46
Current Sled(s): 2017 Switchback Adventure 600
Previous Sled(s): 1983 Excel III,1992 Indy Trail, 1998 Indy Trail Touring
Location: Ontario
Favorite Riding Area: Snow
Riding Since: 1990
Default

Quote:
Originally Posted by rabbi View Post
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
jumpnjehosaphat is offline   Reply With Quote
Old 01-27-2018, 11:08 PM   #10 (permalink)
Advanced Member
 
jumpnjehosaphat's Avatar
 
Join Date: Jan 2018
Posts: 46
Current Sled(s): 2017 Switchback Adventure 600
Previous Sled(s): 1983 Excel III,1992 Indy Trail, 1998 Indy Trail Touring
Location: Ontario
Favorite Riding Area: Snow
Riding Since: 1990
Default

@rabbi..Oh and by the way...do you change the FTS clicker at all? It came stock at 2.
jumpnjehosaphat is offline   Reply With Quote
Sponsored Links
Advertisement
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -4. The time now is 04:17 AM.



Powered by vBulletin® Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.