What options do I have when replacing my fork's elastomers? I'm rebuilding an AntiGravity Fork and converting it to threadless for my 'Blast From the Past' bike (GT Bravado frame, U-Brake, Bullseye hubs and cranks, 21 speed). I really like these forks and I'd like to bring them back to life.

The elastomers are shot. Some are falling apart, others are crushed and don't expand fully, etc. Given that the company is out of business and the chance of locating brand new AntiGravity elastomers is.... not good, I'm looking at what my options are.

AntiGravity Elastomer Fork: Picture

Option A: Wings-Suspension makes killer kits to convert Manitou/RockShox elastomer forks to springs. I emailed them with pictures and details to see if his springs would be compatible, but that's VERY doubtful. This would be my Option A if it worked.

Wings Replacement Springs: Link | Picture

Option B: Round Tubing from McMasters-Carr. I have been trying to just get something to replace them with, at this point. The main suspension uses 4x 1.25" OD 1/4" ID elastomers, and the rebound is controlled by 6x 3/4" OD 3/16" ID elastomers.  McMaster-Carr seems to have close to what I'm looking for, with multiple choices:

Main Elastomers: Neoprene Spring Rubber with 75A Durometer (hard) or Extreme Temperature Silicone Rubber in 60A (medium-hard).

Rebound Elastomers: Only in 1/4" ID (slightly bigger than stock). They have Neoprene Spring Rubber in 75A (hard), Oil Resistant Buna-N Rubber in 75A (hard), and Extreme Temperature Silicone Rubber in 60A (medium-hard).

Option C: ??? (short of buying a new fork)

An answer can either be a link to better replacement material, or which types of the options above are best for a 180-190 lb rider. It would also be really helpful if someone could find a data sheet for this fork showing what the different original durometers were.

In addition, has anyone ever done this before? should I cut them into 4x1.25" and 6x1" pieces, or leave them as one long tube since I'm not swapping them out individually (one of the 'perks' when these were sold)? Does anyone know how to estimate desired durometer / fork force for a given rider weight or desired stiffness? I'd rather be on the stiff side, but I have no idea what 75A or 60A mean in this context - they could be so squishy I bottom them out, or so hard I might as well get a rigid fork.

AntiGravity Fork Internals: Picture

McMasters Carr Round Tubing Link
I had an elastomer suspension a lot of time ago, and did my own maintenance on the elastomer compartment. I would not take a fork like this and put springs inside. Bike suspension elastomers dampen the motion of the suspension in two ways:


They expand laterally and generate friction against the inner walls of the suspension;
They have a natural visco-elastic mechanical behaviour, that doesn't let the suspension "spring back" too fast.


With springs only (and no dedicated way to control the rebound), the suspension would become too "wild", I'd say.

I think you should take any elastomer kit that fits inside your suspension, with enough lateral clearance, and use it, no fear. Micro-cellular urethane (MCU) was the topmost material used in bike suspension elastomer (before becoming almost obsolete).

It is important, too, that you put them inside the fork with lots of grease, and specifically LITHIUM-FREE GREASE, so that they don't chemically react with one other. Most probably, there are specific suspension greases in bike shops.

Hope this helps