The 2021 SR Suntour Auron takes their top-of-the-line mountain bike trail fork and adds their Air EQ system to automatically balance positive and negative air chambers. Combined with their sealed, highly adjustable PCS damping cartridges, they say it gives you a supple, coil spring-like feel with plenty of tuning options.
The tricky part is how they make that work with any length travel within the fork’s 130mm to 160mm range, all without changing the spring curve. Here’s the deep dive on the tech…
How SR Suntour’s EQ air spring works

Beyond the Air EQ air spring, the Auron fork carries over from 2020, so we’ll start by explaining how the EQ works and its benefits.
Using a transfer port on the inside of the air spring, air can slip past the piston when it’s fully extended. So, as you’re pumping up the fork to the desired pressure, it’s filling both chambers simultaneously. Basically, EQ = Equalize.
Technically, that means there’s no need to cycle the fork to pressurize the negative chamber then re-check and re-adjust the positive. Buuut, they still recommend that you do push it down a couple times then re-check just to be sure.
SR Suntour’s This makes set up much quicker and simpler, and helps you get the right air pressure every time. The only reason to adjust it is if you need to add or remove sag.
The Auron can be setup with 130, 140, 150, or 160mm of travel. But, since the position of the air spring’s main piston seal (A) needs to remain constant in relation to the stanchion’s internal check valve, the only way to do that is to change the height of the rod (E).
The other parts in the photo above are the top out bumper (B), main air spring seal (C) to hold all of the air inside the stanchion, and the cap (D) that threads into the bottom of the stanchion to hold it all in.
Here’s where it gets tricky…
No matter which travel length you select, the air volume in both chambers remains exactly the same. So, if you were to only change the height of the piston rod (E), then a long 160mm travel fork would send that piston head (A) almost all the way to the top of the chamber. This would compress the air a lot and create a big ramp on the spring curve.
Auron RC2 PCS damper
Which brings us to price.
- 27.5″ and 29″ wheel sizes
- 44mm and 51mm offsets (44 only for 27.5)
- 130-160mm travel
- eMTB rated
- Integrated fender
- 35mm A7000 stanchions
- 15QLC2TI titanium QR thru axle
- Fits modern trail rim/tire sizes