Volume Spacers-Can you modify?

[Gardcol]

I have a DPX2 rear shock and after 18 months riding have decided that I want a volume spacer between 0.2 and 0.4 cu inches. Fox however do not make a 0.3.
I weighed (on my non expensive kitchen scales) the 0.2, 0.4 and 0.6 cu inch reducers and they were 3,6 and 9g respectively. This kind of makes sense as 1cu inch of water weighs 16g.
So I sanded down my 0.4 reducer on the writing side until it weighed 4.5g.
Does this mean I will have the equivalent of a 0.3 reducer or does the shape of the reducer affect the progression? Is it purely the volume that affects the progression?

 

[RustyIron]

Sure you can make your own! For over a year I've been running a volume spacer that I made out of a chunk of Delrin. Yesterday I was doing a service on that shock, and decided to cut another 0.050" off the spacer. I've also cut down volume spacers for forks. In my mind, it makes no sense to go out and buy a set of spacers when you can make something that is EXACTLY how you want it.

Bambam is correct in that you'd need to measure water displacement if you wanted to know the exact volume of the spacer. But don't get hung up on the number. You're trying to achieve the best performance, not a specific number.

 

[Gardcol]

Wow Rusty, that is very cool that you make your own. I very much like your suggestion that it's not the number but the performance that counts so I will go ride my sanded down reducer and see how it goes. I had not thought about drilling holes in it as Bam Bam suggests but that is a very quick way to change the volume and much easier.
I have been swapping between 0.2 and 0.4 over the last 18 months and always feel that the 0.2 is using all the travel and the 0.4 leaving too much on the table. I know I could adjust the sag but I like 30% and want to keep it there so hope 0.3ish will be the sweet spot.
Great feedback from you both and many thanks.

 

[Alexbn921]

You can modify the spacers by removing material. Basically anything that changes the volume. You can also add a thick grease behind the top out washer to reduce volume.

 

[steve_sordy]

If you have one spacer at 0.2cuin and one at 0.4cuin, and you want a 0.3cuin, there is no need to measure the volume of the one that you make. Just go off the weight. For example if you start with a spare 0.4cuin, then just remove material until it weighs half way between what the 0.2 and 0.4 spacers weigh.
It won't matter how you remove the material, sanding, machining, drilling holes etc, as long as you reduce the weight proportionately.

 

[Gardcol]

You can modify the spacers by removing material. Basically anything that changes the volume. You can also add a thick grease behind the top out washer to reduce volume.

Thanks Alex. I have installed my sanded down "0.3" reducer and hope to get a ride on Friday.

 

[Gardcol]

If you have one spacer at 0.2cuin and one at 0.4cuin, and you want a 0.3cuin, there is no need to measure the volume of the one that you make. Just go off the weight. For example if you start with a spare 0.4cuin, then just remove material until it weighs half way between what the 0.2 and 0.4 spacers weigh.
It won't matter how you remove the material, sanding, machining, drilling holes etc, as long as you reduce the weight proportionately.

Hi Steve that's exactly what I have done. I wish my kitchen scales were a bit more accurate but I certainly removed a fair bit of material and still looks much larger than the 0.2. Will get a ride on Friday hopefully.

 

[RustyIron]

I had not thought about drilling holes in it as Bam Bam suggests but that is a very quick way to change the volume

I know I could adjust the sag but I like 30% and want to keep it there so hope 0.3ish will be the sweet spot.
Great feedback from you both and many thanks.

Bambam's hole drilling is a pretty good idea. It's easy, most people can drill holes, and figuring out the decreased volume is simply a matter of subtracting cylindrical holes. Weighing the parts is also a good idea, but I got rid of my precision scale when I stopped dealing coke.

It's a common misconception that you can get back the unused travel by increasing sag. The result is greater harshness. Let me explain a little. Let's consider a 160mm fork because the numbers are easier to do in your head.

Suppose we have 25% sag on our 160mm fork. When we're on the bike in a neutral position, we have 120mm remaining travel at our disposal.

Now suppose we're not using all the available travel, and our biggest hits leave 25mm unused. So we increase the sag by 20mm. Now, when in a neutral position on the bike, we only have 100mm travel at our disposal. We're taking the same hits, but absorbing the energy over a substantially shorter distance.

Optimally, we want our suspensions to compress linearly. That's the appeal of coil springs. The more an air spring compresses, the higher the internal pressure. So by its very nature, the more you compress the air spring, the harder it is to compress it further. It's progressive. The more tokens you have in the system, the smaller the volume into which the air can compress, and the ride becomes harsher.

There's more to the equation than just the air spring volume, there's also the dampener to consider. I guess that's why top suspension designers get paid a lot of money.

Now that I've type this out, it seems simplistic. I'm not trying to be pedantic. More than anything, I'm lazy. Rather than retype it, I'm just gonna hit "post reply" and go do something else. Have fun finding the sweet spot for the shock.