[HAB]

A friend just got a bike that takes a 210x55mm rear shock. He's also got an 8.75"x2.75" RC4 kicking around. Over some post ride beers, I told him I thought I could make a spacer to shorten it into a 210x57.5 for him. We checked tire clearance at bottom out, that's all good. The thing I forgot to account for when I was talking to him is that, if I remember right, the main shaft sealhead closes off the rebound bleed port at topout. It's been a minute since I took an RC4 apart.

Do I recall correctly, and am I right in thinking that that's effectively to make the rebound damping position sensitive, for topout control?

 

[kidwoo]

I took one apart a few years ago with the same thing in mind. Can't do it the way that you're probably thinking.

https://www.ridefox.com/fox17/img/help/page192-YuJav3/shaft_invert-m.jpg

That's the one of the only shocks that does have position sensitive restrictions

 

[HAB]

Dammit!

Thanks. Wonder if there's enough material on the sealhead to tap a couple holes in it, and bolt the spacer back to that so that it moves with the sealhead. Delrin spacer with a reamed bore, floated in on the shaft before bolting up would probably work...

 

[kidwoo]

If it were me (ie: you, a machinist) I'd shorten the shaft and just redo the port.

I might be on crack but I want to say that shaft displacement also dictated how the damping circuits in the piggyback were built too. As in reducing the volume of oil displaced by the shaft shortens the damping range of the boost valve.

You can do this all day long with the poppet/twin tube stuff. That's what's in my megatrail, a shortened dhx2 that used to be a 9.5x3.

That bike doesn't need a special damper to fix stupid though.

 

[HAB]

It'd probably be easier to shorten the other end (and the rebound needle) than it would be to remake the port and get the geometry right. As far as the piggyback goes, the bigger ones have a longer reservoir and presumably a different IFP depth spec, but I could fuck around with IFP depth to get the ramp up to work right.

All of this sounds like way too much work for me to do for my friend's bike though.

 

[Westy]

Uh, just multiply by 25.4

 

[buckoW]

What if you turned down the body for desired i2i length on a lathe and ran a spacer on the shaft to limit travel?

 

[HAB]

Check out the big brain on Brad!

That might work.

 

[buckoW]

I’ve done it in the past. Depending on which shock length there’s usually 6mm of body you could buzz off before bottoming out the piston head bolt. More than 6mm then I would start to reduce travel with a spacer. I like to hoard RC4s as well.

 

[kidwoo]

Now we're talkin makita's language!

 

[buckoW]

Hab should try and get this done with a drill and a grinder. A lathe would be too easy.

 

[Udi]

I've shortened and even slightly lengthened in the past, there's a lot of flexibility and you can usually make the rebound thing work well enough in one way or another.

It's worth keeping in mind there are plenty of shocks which don't even have hydraulic topout control, and then weigh that up with the benefits of installing the RC4.

 

[kidwoo]

I've shortened and even slightly lengthened in the past, there's a lot of flexibility and you can usually make the rebound thing work well enough in one way or another.

I just want to quote this completely out of context and giggle.


What did you shorten, body, shaft, internal spacer etc? The math on a 9.5 x 3.0 shock works perfectly for a 230 x 65 metric so if you figured out a solid way to do it.....

You usually pull the boost valve out of these things too correct? Isn't the 'old' fat shaft true boost valve a position sensitive cone damper or something similar?

 

[buckoW]

I don’t understand the math on that one but thats probably just me. How are you going to make the i2i longer Woo? It might be easier to start with a 10.5in i2i shock to get down to 260mm I2i. It would only need 7mm turned off of the body and then a 29mm spacer to limit travel on the shaft. You might be able to get away with more travel.

The harshness adjuster/boost valve is sub optimal, imo.

 

[kidwoo]

Derp, sorry, typo: 9.5 x 3.0 shock to a 230 x 65

11mm internal spacer

 

[shelteringsky]

Slight thread hijack if anyone can help..

currently got a RS vivid air on my my V10.6 running 26“ #heritagesize wheels. Do mostly park riding (Whistler) but blowing through the travel. Would an RC4 be good? Guess I would lose some liveliness but would like not to worry about pedal strikes so much..

 

[6thElement]

Does the vivid air not allow you to add spacers inside the air can?

If you're blowing through travel on a progressive air shock, won't a linear coil make that worse?

 

[Westy]

Does the vivid air not allow you to add spacers inside the air can?

If you're blowing through travel on a progressive air shock, won't a linear coil make that worse?

If he is wallowing in the travel but not using most of it, a stiffer but more linear spring could help.

 

[kidwoo]

Rc4. Linear. Heh. #damperRamper

What bike?

 

[ChrisRobin]

When you talk about trimming down the shock body, isn't there an o-ring to keep oil from leaking between the shock body and the bridge?

 

[HAB]

Yeah. You'd want to take some care to replicate the gland for said o-ring on the shortened end. Pretty easy if you're doing it on a lathe, not so much if Makita is more your style.

 

[shelteringsky]

Does the vivid air not allow you to add spacers inside the air can?

If you're blowing through travel on a progressive air shock, won't a linear coil make that worse?

Yeah, that's a good point re: coil vs. air. Although I also had a X2 air shock on a Glory a few years back and was blowing through travel on that even with the max number of volume spacers installed. Love the weight and supposed adjustability of air shocks but haven't had the best experiences with them.

If he is wallowing in the travel but not using most of it, a stiffer but more linear spring could help.

Yeah, that's a good description of the situation. Maybe a coil shock with a 500lb or 550lb spring would help.

Rc4. Linear. Heh. #damperRamper
What bike?

Santa Cruz V.10.6 (2nd latest gen.). Seemingly the linkage design lends itself to blowing through travel.

 

[kidwoo]

Santa Cruz V.10.6 (2nd latest gen.). Seemingly the linkage design lends itself to blowing through travel.

That's the same bike I have. Just put an RC4 on it, it's better than a dhx2 by a long shot and makes a more consistent midstroke than what you're feeling with the vivid air. Yes the bike tends to blow through the first half of the travel but it's a rare difficult thing to actually get to the last 5%, especially with that vivid. The RC4 has enough damping range and variability that you can get it to work well.

Mine came with a dhx2 and I traded it with a guy who had a year older frame with the rc4. You need to tame down the top end looseness of that frame and the rc shock does it well. Try to get one with the narrower shaft. The piggyback says 'air assist rate' instead of 'boost' something or other.

 

[Flo33]

The blue adjuster end of the piggyback says 'Air Assist Rate' instead of 'boost' something or other.

ftfy

 

[Sandro]

Kidwoo preaching the Udi gospel, lovely to see the world come together in the time of crisis.

 

[shelteringsky]

That's the same bike I have. Just put an RC4 on it, it's better than a dhx2 bike a long shot and makes a more consistent midstroke than what you're feeling with the vivid air. Yes the bike tends to blow through the first half of the travel but it's a rare difficult thing to actually get to the last 5%, especially with that vivid. The RC4 has enough damping range and variability that you can get it to work well.

Mine came with a dhx2 and I traded it with a guy who had a year older frame with the rc4. You need to tame down the top end looseness of that frame and the rc shock does it well. Try to get one with the narrower shaft. The piggyback says 'air assist rate' instead of 'boost' something or other.

Awesome, thanks for the info. The search begins.

 

[Westy]

Kidwoo preaching the Udi gospel, lovely to see the world come together in the time of crisis.

Now we just need Udi to start grinding away his brake mounts.

 

[HAB]

 

[kidwoo]

As I've told you many weekends, you can't just block that hole on the shaft and expect everything to work right.

 

[HAB]

I'm not. The spacer has a tab that's a press fit into the gland for the topout bumper on the seal head, so it'll move with the seal head. It's a good slip fit on the shaft, so the topout rebound control should work as usual.

 

[Westy]

As I've told you many weekends, you can't just block that hole on the shaft and expect everything to work right.

Right before a warm embrace and a kiss on the cheek.

 

[kidwoo]

It's a good slip fit on the shaft

Atta boy.

Call you friday

 

[HAB]

I'm gonna need to see a negative Covid test result first.

Ya know, standard procedure these days.

 

[ChrisRobin]

Do you have any other pics of that spacer before it was installed?

 

[HAB]

No, sorry.

 

[Udi]

I'd really want proper mechanical retention for the spacer into the sealhead rather than just a pressfit into the shallow gland. Then again if the rebound locks and your friend dies, shock remains unharmed + that's another small-shaft Kash RC4 for you.

I approve.

 

[HAB]

Yeah, I thought about that. I was ready to drill and tap a couple holes in the bottom of the gland to bolt the spacer to the sealhead, but once I tried the press fit, I decided I thought that would get the job done. It's pretty solid, and there shouldn't be much load on the spacer to pull it out. Guess we'll find out!

 

[HAB]

Anybody have a good source for shims? I just picked up another small shaft RC4 for myself, but it's valved for a Session and has a fuckton of rebound damping and very little compression, presumably because the average leverage ratio on those was like 14.5:1.

 

[kidwoo]

Anybody have a good source for shims? I just picked up another small shaft RC4 for myself, but it's valved for a Session and has a fuckton of rebound damping and very little compression, presumably because the average leverage ratio on those was like 14.5:1.

Call fox

 

[StiHacka]

Call fox