Originally Posted by theDr

It's a limiter, to lower ride height, used as a tuning aid.

Originally Posted by BBSpence

I don't know anyone who uses o-rings inside shocks to lower ride height. That's what spring collars are for.

Originally Posted by sosidge

I don't think anyone has given you an answer yet, too bothered with arguing amongst themselves, so I will.

O-rings on the shaft outside would be a bump-stop, to limit compression travel. It is not something I have ever seen seriously used in RC although they are common in full-size motorsport.

Ideally, you should only use a bumpstop to stop the chassis from bottoming out over the biggest bumps and kerbs. If the car rides on the bumpstop in normal running, you will lose a huge amount of grip because the suspension will effectively run out of travel.

Another reason to run bumpstops is to stop the driveshafts from popping out or similar issues, I know that with my old, old HPI Pro3 I had to run quite a few o-rings on the shaft otherwise the driveshafts would pop out in crashes.

Hope that helps.

Originally Posted by theDr

You really should get out more.
If you're talking about pre-load spacers or spring adjusters, that's at least part of their purpose.

Originally Posted by KHoff7

The only use I can think of is to add droop to a mini cooper. With the o rings.

Originally Posted by Xraycerboy

Using an oring on the shock shaft? its on the xray set up sheet and im not sure what it does or when to use it! im guessing it acts as a limiter so the car doesnt lean as much, any input would be great

Originally Posted by anthony153

What's an O ring?

Originally Posted by Warren Weaver

basicly using a o ring on the shock shaft would limit the amount the shock travels up sort of a bump stop which would work with a very soft spring on high speed corners so the chassis will not scrape the racing surface.