Today I installed a Hyperpro spring replacement for the shock in the FLXRST. it's the same shock in the FLHC/FLHCS Heritage, and 2022- FXLRS Low Rider S models. This "Tall" 13.1" shock can be bough as a kit for other models part #54000294. It can be fitted to Sport Glide and other models with the swap of the preload adjuster.

I bought the Hyperpro spring part #SP-HD17-SSB010, which on the site is for the FLHCS but we now know it will fit any of the tall shock softails. As you can see in the image, the spring is 5mm shorter than the Stock spring, but is progressive rate. I am a believer in progressive rate springs, even on a rising rate linkage- the progressive springs can design in far more progression in spring rate than a simple linkage.

Prior to disassembly I measured my preferred sag setting which was at "3", I am 100kg and use my bags a lot (always carrying crap). Damping wasn't too bad, but the spring rate was definitely soft. Hence why I decided to try a spring out.

After installation I set the sag to "2" and found I was slightly taller- which demonstrates a 25-30% spring rate increase (initial).

I will follow with a ride review when the temp outside goes below 40c (110F)!!!!

 

This is interesting and I'm looking forward to hearing your results and thoughts on this spring. I'm upgrading to the "tall shock" in the spring and it's on the list of parts to hoard over the winter. I didn't know there was anything being offered as far as spring replacements for the OEM shock. Also jealous of the temps, it's really starting to cool down here in Southern Ontario Canada. Winter will be rearing it's ugly head soon enough and the riding season is over

 

I upgraded my 2018 Heritage FLHCS 114 to Hyperpro progressive springs both front and rear last winter. I have now tested and ridden them for a season and have had good experiences with both. Up front I changed the Hyperpro springs along with Hyperpro oil and additional Burly Brand fork preload adjusters due to the extra weight of my Batwing (for weight/level equalization) and I would do it again! It's much better at the rear than the original spring, as previously, due to my weight of approx. 120 kg plus luggage, the shock absorber would bottom out on extreme bumps or potholes despite the spring preload being at maximum (level 4-5). The Hyperpro rear spring is firmer and no longer bottomed out even on hard potholes and I can now ride with the spring preload set to level 2. All in all, a good investment for me due to the price/performance ratio for not too heavy riders!
However, I wouldn't do it again at the rear, as my Heritage still rocks up on fast, long corners with bumps or when accelerating hard at an leaning angle due to the non-adjustable damping and my next winter project will be to upgrade to the fully adjustable Hyperpro shock with adjustable damping in rebound and compression...and then we'll see!