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Jimski

Beta4Stroke 390 shock spring weight

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I have a new to me 2016 390rr with 42 hours on it. The previous owner installed the 5.8 spring which the chart says should be sufficient for my riding weight of 225lbs. The sag is at 40mm. static and 140 with rider. I can't adjust the pre-load to compensate because the nut is already fully adjusted.  I think a heavier spring is needed but not sure how much heavier or am I doing something wrong when taking the measurements? What are your thoughts?

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Posted (edited)

Sounds like the spring sourced by the po was to short for the application.Should be 260 mm minimum unloaded length.Fwiw.A 260 mm KTM linkage spring will work.

Edited by widebear
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A 5.8 or 6 should work for you. To be that far off there is definitely something wrong with that spring. If you end up purchasing another I'd suggest a 6 to reduce the choppered beta stance and give you more responsive turning.

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Seems like the 5.8 should work for you (though I'd go for the 6.0 at 225). I think widebear is probably right and the spring is too short for the application. That, or it's a cheap, low quality spring with an actual measurement way off from spec. 

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Thank you for the answers, they make sense. Do you have any recommendations for suppliers in Canada?

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I resprung  a 2019 390 RR-S for my weight, 220, using the Beta 5.8 rear spring. The preload was bottomed out with sag at 120mm. No Bueno, the factory spring was too short. I then purchased a Race Tech 5.8 spring which was 5mm (maybe 10mm?) longer and had no trouble setting dynamic sag at 110mm with the preload collar down about 1/3rd. I needed a spring compressor with the Race Tech spring to get the preload rings started on the threads. Go with the 6.0 if you are tall, you sit further back on the seat, or if you will be doing multi day with soft bags. 

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On 8/1/2020 at 9:59 AM, Jimski said:

I have a new to me 2016 390rr with 42 hours on it. The previous owner installed the 5.8 spring which the chart says should be sufficient for my riding weight of 225lbs. The sag is at 40mm. static and 140 with rider. I can't adjust the pre-load to compensate because the nut is already fully adjusted.  I think a heavier spring is needed but not sure how much heavier or am I doing something wrong when taking the measurements? What are your thoughts?

The Race Tech tool is easy to use.  Choose your ride and then once it shows the spring rate, oil type, amount info. Towards the top, there will be a link that says "Click Here For Other types of riding" next to the Standard MX oil level line.  It will allow you to choose the type of riding, your age, skill level, weight, etc. After tat, it will adjust all the suggestions based on your preferences.  

https://racetech.com/ChooseVehicle.aspx

   

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Posted (edited)
On 8/2/2020 at 8:03 AM, Jimski said:

Thank you for the answers, they make sense. Do you have any recommendations for suppliers in Canada?

Riders Edge in Vernon has a good inventory of new and used.I have a 6kg here I could sell you but you might be better off with the 5.8 Remember to not go any wider in dia than the oe spring or you will have rubbing issues on the airboot.

Edited by widebear

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