Lelandjt said:
I want to get a 500lb and a 550lb spring for my Fastace shock. Does anyone know the inner diameter or what common bike brand springs like Fox or Rockshox fit it? What's the shock's stroke length?
The fast ace is a 10.5" length shock which should have a 3.5" stroke, from trying to measure the stroke on the bike it looks to be 3.5". As you probably discovered you can't easily buy fastace springs so you will have to buy some other brand, which is OK from what I've read and done often in biking.
Without taking the fast ace rear shock out and measuring the fast ace spring, the 10.5" x 3.65" stroke springs by FOX should work. The 10.5" is the shock length and not the spring length, but the springs are called 10.5". For some reason fox only sells 3.65" stroke shocks and not 3.5" stroke, but this is what they sell for their 3.5" stroke shocks.
The fox springs for the 10.5" shocks has a length that is exactly the same as the fast ace, the outer diameter is close, but the fastace spring seems to be about 2mm wider, which doesn't matter. Since the fast ace has a 3.5" stroke, you just need a spring rated for a 3.5" stroke or higher.
I read where spring fitment depends only on the inner diameter of the spring, which the fox spring I measure about 37mm inner diameter. I can't measure the fastace without removing it.
If you want to make sure the fox spring will work you can remove the fastace spring and check to see if an inner diameter of about 35.5 mm will fit on the spring brackets grooves. Or you can measure the inner diameter somehow of the fast ace spring then you will know if the fox spring will work.
I did read that there are a couple of inner diameter springs depending on brand, so if you really want to make sure you will have to remove the fastace spring and check the inner diameter. If you do check it report back on what you find. Everything else matches perfectly with the fox 10.5x3.65 springs.
The only place I know to order 10.5 x 3.65 springs, and I've ordered a few from fox, is calling fox directly on the phone. The prices are reasonable.
https://www.ridefox.com/fox17/contact.php?ref=footer
EDIT: in the picture you can see what you will need to measure. The shock collar measures about 34.5 mm on the fox shocks and the fox springs have 35.5mm inner diameter. If the fast ace has this larger than 35.5mm, you can't use fox springs
I also found this in another forum
There are 3 dirrefent spring ID's for coil shocks:
Smallest is Fox, which is the only one using this size: 1.38" or 35.05mm
Almost every other brand, including Cane Creek, Marz, etc. are all 1.43" or 36.32mm
Then the largest is the Vivid which uses a 1.5" or 38.1mm
As such, Fox specific springs will not fit on any other shock collars (note besides Fox springs RCS also makes Fox specific Ti springs). The 1.43" springs will work on Fox shocks, but they will walk around a bit on the collars, even under preload, when you ride. The Vivid springs really should'nt be used on any of the others as the size difference is enough that the spring will more than just walk around on the collars. They wont sit on there correctly.
so all of this being said, just remove the fast ace shock and measure the shock collar diameter and we can figure out what will work.
