Progressive fork spring experiment

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BigVic64
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Progressive fork spring experiment

Post by BigVic64 » Mon Jul 01, 2019 12:20 pm

It's time to boldly go where, I think, no man has gone before.

I have a 1998 Ural Deco Classic. I hate the front suspension. It bottoms out, has shitty rebound and pisses me off.

I did some research and found Progressive Suspension Fork Springs 11-1109 has the same O.D. and is a half inch longer than the stock spring. I can thread it onto the the hydraulic system and tighten it. Everything fits into the fork tube.

What am I missing? Why wont this work?

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jaybird
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Re: Progressive fork spring experiment

Post by jaybird » Mon Jul 01, 2019 2:44 pm

What's not working?
Does something not fit or are you not getting the results that you had expected?

Happy trails,
Jaybird
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sKiZo
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Re: Progressive fork spring experiment

Post by sKiZo » Mon Jul 01, 2019 5:00 pm

Progressive springs have gone more to "universal" common lengths now. Long as the springs are the right diameter and weight rating, you should be good. Only difference really is the length of the spacers used. When I got mine for the Royal Star, they didn't even include spacers with the springs - just a length and recommended materials. I went with schedule 40 PVC. Just make sure you deburr the ends after cutting.

I wondered about the plastic, but over 10 years time, no noticeable wear ... here's what they looked like after maybe 50k ...

Image

To control excess rebound, change the oil weight. I went from the Royal's recommended 5w to 10w, and eventually settled on a 12.5w blended oil with excellent results.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Evil Kneivel? He got nuttin' on me!
2011 Ural T
Handicap mods include Raceway foot box, tank shifter w/reverse, and DIY rear brake pedal mods.

BigVic64
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Re: Progressive fork spring experiment

Post by BigVic64 » Mon Jul 01, 2019 5:42 pm

sKiZo wrote:
Mon Jul 01, 2019 5:00 pm
Progressive springs have gone more to "universal" common lengths now. Long as the springs are the right diameter and weight rating, you should be good. Only difference really is the length of the spacers used. When I got mine for the Royal Star, they didn't even include spacers with the springs - just a length and recommended materials. I went with schedule 40 PVC. Just make sure you deburr the ends after cutting.

I wondered about the plastic, but over 10 years time, no noticeable wear ... here's what they looked like after maybe 50k ...

Image

To control excess rebound, change the oil weight. I went from the Royal's recommended 5w to 10w, and eventually settled on a 12.5w blended oil with excellent results.
Where did you put the spacers?

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sKiZo
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Re: Progressive fork spring experiment

Post by sKiZo » Mon Jul 01, 2019 5:53 pm

Above the springs ... you'll want to make sure the tubing is cut square and has good flat surfaces to ride against at both ends. Best bet is to go with the largest diameter that will fit inside the forks to minimize any side to side play. You also want them long enough to eliminate any unloading of the springs on full extension. For a good pre-load, mine ended up sticking out of the top of the fork tubes about a half inch with the front end propped up, and I used a socket and long screw driver to get the caps on. Also helps to start the caps about a half turn in the threads without the spacers installed, then back them off till you feel a slight "bump" where the threads engage the cap. Mark that point on both tube and cap, and that makes it a whole lot easier to line things up and get them started again with the spacers in the tubes.

Any bike I ever upgraded benefited, and the improvement in the Royal's ride was pretty impressive. And not to forget, springs are only for compression - the oil is what controls rebound.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Evil Kneivel? He got nuttin' on me!
2011 Ural T
Handicap mods include Raceway foot box, tank shifter w/reverse, and DIY rear brake pedal mods.

BigVic64
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Re: Progressive fork spring experiment

Post by BigVic64 » Mon Jul 01, 2019 7:17 pm

sKiZo wrote:
Mon Jul 01, 2019 5:53 pm
Above the springs ... you'll want to make sure the tubing is cut square and has good flat surfaces to ride against at both ends. Best bet is to go with the largest diameter that will fit inside the forks to minimize any side to side play. You also want them long enough to eliminate any unloading of the springs on full extension. For a good pre-load, mine ended up sticking out of the top of the fork tubes about a half inch with the front end propped up, and I used a socket and long screw driver to get the caps on. Also helps to start the caps about a half turn in the threads without the spacers installed, then back them off till you feel a slight "bump" where the threads engage the cap. Mark that point on both tube and cap, and that makes it a whole lot easier to line things up and get them started again with the spacers in the tubes.

Any bike I ever upgraded benefited, and the improvement in the Royal's ride was pretty impressive. And not to forget, springs are only for compression - the oil is what controls rebound.
Thank you. I appreciate your help.

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sKiZo
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Re: Progressive fork spring experiment

Post by sKiZo » Sun Jul 21, 2019 10:46 pm

Three weeks and you haven't done it yet? I'd demote you from "Comrade", but I guess that's as low as it goes here. <G>

(Any thoughts on the rear springs? Seems to me they're all the same rate OEM, but that just don't sound right ... )
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Evil Kneivel? He got nuttin' on me!
2011 Ural T
Handicap mods include Raceway foot box, tank shifter w/reverse, and DIY rear brake pedal mods.

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Re: Progressive fork spring experiment

Post by Snakeoil » Mon Jul 22, 2019 11:16 am

Progressive springs are not intended to prevent bottoming out or rebound issues. The basic intent is to provide a broader range of compliance. It gives you a softer ride over smooth roads and still provides a stiff spring constant for major bumps so you won't bottom out. Going by your screen name of BIG Vic, I assume you are a big boy. You should have gone with stiffer spring rates than stock when you selected your progressives. If you selected the max spring rate for the progressive such that it is the same as you stock springs' single rate, you'll just have a very mushy spring on smooth roads and will still bottom out on the big bumps. So it is more than just fit, you need to select the correct spring rates for the progressive spring for your weight and the bike application.

When you add spacers, basically, this is setting preload. And based on my limited experienced, they are not really progressive rate springs. They are multi-rate springs. Preload removes some of the lighter sections of a progressive spring because the lower rates give first. So, it is a bit less progressive because you have removed some of the range in that lower rate.
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Rob
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