So most know the FL350r as having a very harsh rear suspension due to excessive spring rates. Seems like folks talk about dropping in a 150lb/in spring in place of the factory ~250lb spring.

Has anyone really and successfully done this?

I see a company called HyperCo makes a 12"x1.875(ID)" coil-over spring @ 150lb/inch.

https://www.jegs.com/i/Hyperco/557/1812D0150/10002/-1

Hyperco model number 1812D0150

Anyone? Beuler?

Terry H sis this on his rebuild.

viewtopic.php?f=1&t=18447&hilit=spring

CO - didn't you buy some new springs? I remember you working on this.

I did several write ups on it.
Give me a bit to find them and will post the link.
CO

rmesser posted the best thread on the springs above.
It's long winded but a good one.

Here are two other threads that were related:
viewtopic.php?f=1&t=18465&hilit=spring
viewtopic.php?f=1&t=18233&hilit=spring

There is some good info in those threads. You will note that the stock oddy rear spring is NOT 250 lbs.
Yes I was successful with my spring change -- thanks goes out to adnoh for his work.
When I bought my brothers machine years ago, the previous owner had aftermarket springs on it. They were #135 units. Back then I was still running the stock springs on mine and you could really feel the difference in the two machines.
Last year I ran #145 springs on my machine and it felt a bit soft - but nice. It did bottom out a few times going through washouts and we do ride in some very rough terrain here. So for this year I bought #160 springs but we can't go riding yet because of the snow in the hills. I put the #145's on the death machine and my buddy can drive that one. I did make a spacers out of UHMW and added some more preload to the death machine springs. I weigh #130 so if you're a bit fluffier than I am then take the info and adjust. Can not comment on the #160's yet but if I remember later in the year I will comment and post.
CO

Hypercoil springs are also available in a 175 with the same 12" length and 1.875" ID. Also since its a 12" spring it should pre-load about an extra ~70lb just loading it onto the slightly shorter stock location which would make the 150LB spring likely OK still.

Thoughts? I'm not going to order anything not until this crazy machine is running lol.

At the end of the day you may end up buying two different sets of springs.
I think you may be correct in your thinking here though.
I would take a look at the charts adnoh posted in that thread and then make a call.
I run the 10" Eibach springs and make spacers. That way I got wiggle room to make adjustments. If you run the 12" Hypercoil spring you are stuck with auto preload from the get go.
CO

I had a friend make some bushings so that I can run 10" springs. I bought Eibach 150lb springs and guess what? WAY too stiff still.

I have a set of spare front springs off an FL350. They are dual rate springs. Does anyone know the rates and if they might work in the rear of an FL350r? I may try them :)

That's what I used to run years ago before we bought those Eibach springs.
I found nothing wrong at the time with using the stock front springs on the rear. It made a HUGE difference at the time.
I also find it hard to believe the #150 are WAY to stiff. Adnoh made some great charts in another thread. At that time I purchased some #145 and they seemed soft to me. So I purchased some #160 and I do feel they're a bit stiff.
It could also be that your shocks are still gassed and mine were rebuilds which means the gas was bleed out. That does make a BIG difference because I found that the gassed stock shocks need a softer spring than ones you have rebuilt.
CO

I think I have a thread about it but not sure.
It was one of my closely guarded secrets back then.
CO

Here it is: viewtopic.php?f=4&t=17247&hilit=spring+front
As you can tell I wasn't very specific -- LOL.
CO

So I threw some FL350r front springs onto the rear shocks. They need about a 2.5" spacer. Seems to have loosened up the rear quite a bit. Hopefully this makes for a better trail machine. Of course Works shocks are the best option over stock - its just I had the parts laying around to try it out.

Hey Zero I want to bring this thread back to life.
Are your stock shocks still gassed ?
Or did you rebuild them ?
It makes a difference in the spring poundage.
CO

They appeared to still have plenty of gas in them. Original. In my experience gassed shock shanges initial poundage, like it’ll add maybe 30lb initially, but the lb per inch isn’t that much more. Maybe only 10lb. Once it starts moving it doesn’t rise per inch very much more than initial.

I saw you are running ungassed. You should try adding some shrader valves at some point.

Also I switched out the front springs in the rear for some springs I found from the front of a snowmobile. I think they’re about 125lb springs. It’s a little higher works better than the old front springs. Then I put the 150lb eibach springs on the front which is Farr long travel. It needed heavier springs up there.