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Discussion Starter #1
The shock absorber springs for the Thunder Stroke models are supplied to the OEM by Eibach.
UTV ATV Moto Coilover Race Springs & Accessories | Eibach Springs

Each spring has a series of numbers on it that indicates it's length, inside dimension and spring rate. It looks like a phone number because, for us, the first numbers are 0800, followed by 7 more digits. But 0800 means that the free length (uninstalled) of the spring is 8 inches. It's followed by 225, which means that the ID is 2.25 inches. The last four numbers indicate the spring rate in pounds per inch of compression. I don't have my notebook with me, but as I recall, the air shock models have 0425 springs (425 pounds per inch) and the non-air models have 0450 or 0475 springs. (I'll check those numbers later, when I can access my notes again)

The models with air-adjustable shocks have a softer spring than those with mechanical preload adjustment because it will give a cushier ride and is expected to be accompanied with compressed air in the shock itself, which will increase the effective spring rate above that of the non-air shock models.

Take note: changing the shock or it's spring requires that the shock absorber be removed from the motorcycle. And that takes a few hours.

I have replaced the air shock on my '16 Roadmaster because it insisted on leaking out the air and without any air in the shock, the mufflers are easy to drag in the corners. One of our Indian riding brothers sold me his non-air shock for a song and I've installed it on my 'Master. But with the preload screwed down more than 3/4 of the available threads on the shock, I'm not dragging the mufflers, but it's still a bit too soft for my riding habits and the shock is bottoming out on hard bumps. So I contacted Eibach and ordered a spring rated at 525 pounds per inch of travel. The increased spring rate will require that the preload nuts be backed off toward the end of the shock, allowing more spring travel and a better ride when we hit the bumps.

Now I just have to find the time to remove the shock again and swap the spring to the new one.

Indian shock spring.jpg


indian shock replacement.jpg
 

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Thank you for this info. I have been thinking about upgrading the spring on my rear shock (2016 RM). I'm getting tired of having to air up my suspension every day that I ride, too. The factory spring, according to the handy little air pressure chart, is rated for a 150 pound rider with the trunk on to have 0 psi and I weigh 325, very rarely ride without the trunk, and always carry at least 20 lbs of tools and other cargo, so I would like to reset the scale to where i don't have to add any air just to ride during normal circumstances. I have to think that it would be much cheaper to just replace the spring instead of purchasing a $1000+ rear air suspension system. I think that I would need a spring that offers the extra 205 or so lbs, but I know that the spring rate pounds do not equal cargo pounds. How did you come up with the 525 spring numbers?
 

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I'm getting tired of having to air up my suspension every day that I ride, too.
I used to have that problem too until I moved the Schrader valve to make it easier the air up. Well, in that process I used plumbers thread sealing stuff and I've aired up only that initial time. Not one more. So apparently my real problem was leaking connections that the sealant fixed. I wouldn't have had to waste money to move the darn Schrader valve in the first place. Just disconnect, add sealant and reconnect. Might try that before changing the spring or anything else involving that Schrader valve. Just a thought and suggestion.
 
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Discussion Starter #5
.... I know that the spring rate pounds do not equal cargo pounds. How did you come up with the 525 spring numbers?
I weigh a bit more than 200 pounds and my wife is 100 pounds. The stock Chief spring is too soft. And I tend to ride a bit aggressively in the corners. So I used the SWAG* method to come up with the replacement spring rate.

* Scientific Wild Ass Guess

And the springs are only about $80 from Eibach. The most painful thing that would result if I guessed wrong is the labor that it takes to swap out the spring. :eek:
 

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Discussion Starter #6
I used to have that problem too until I moved the Schrader valve to make it easier the air up. Well, in that process I used plumbers thread sealing stuff and I've aired up only that initial time. Not one more. So apparently my real problem was leaking connections that the sealant fixed. I wouldn't have had to waste money to move the darn Schrader valve in the first place. Just disconnect, add sealant and reconnect. Might try that before changing the spring or anything else involving that Schrader valve. Just a thought and suggestion.
I'm glad that sealing the fittings worked for you, NDC. I tried every trick in the book to find and seal leaks in the system. And being a professional technician with decades of experience building and working on high-pressure AND high-vacuum systems I'm supposed to be an expert on such stuff. But my Roadmaster's rear suspension refused to cooperate. Sometimes it would maintain within a pound of the set pressure for a couple of weeks and other times it leaked down to 0 in a couple of days. No amount of sealants or tests to find the leak(s) worked for long. So I have shelved the air shock and another rider sold me his low mileage Chief shock for a pittance.
 

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Thanks guys. Mucker, I look forward to your review after you get a few hundred miles of ass time with your new spring installed. If you did guess wrong, at least you will be closer to where you want to be and can maybe fine tune it during the following winter's downtime. Great thread, thanks!
 

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