My photo
Existentialism-- Just a bloody good excuse to go riding...

Wednesday, July 7, 2010

Modding: RP23 (simple)

Did this awhile back and have since moved on to coil shocks. Nothing new as it's based on a similar mod online while searching for the solution to a wallowy mid stroke and bottoming out easy on my RP23

Apparently the new 2010 RP23 with boost valve is supposed to solve the problem. Unfortunately not all of us gets the latest fancy toy. The mod is simple enough with adding a plastic piece inside the sleeve of the shock. The other alternative that some folks did was to replace with a smaller cannister....but that's not necessary for me after this was done...

After reading the whole post in mtbr I reckon that crux of it all comes down to how much space is displaced by inserting the plastic piece. The 1.2mm sheet seems to thick to me and it was noted that pushing the sleeve back in took a little effort. So if volume is the key, then having a thinner but wider piece would yield similar result.

But first... remove shock and let out all air (even if u are not taking out the internals, its always a good practice to remove all air from shocks or forks before commencing to do anything that requires removing a few parts)
The sleeve is held in place at its end with a C-ring. Lift it off with something sharp. I just happen to have a balisong on the table for the job.

Once out, just pull the sleeve down (pic shows the plastic (white) already inserted as I was taking it apart after the mod rather than before)

Note: there is absolutely no need to pop the seal off the main air chamber unless you are going to do maintenance work with the insides

            I used a soft plastic file. thickness is ~0.6mm according to my not so accurate vernier calipers.

Lengthwise its 140mm (click pic to enlarge). This fit the inner circumference of the sleeve without overlapping.

Therefore the play comes in the form of the width which since the material here was slightly less than half the thickness of what was used in the mtbr artilce, I increased the volume accordingly by doubling the width, plus a little more...Width: 44mm

Fit it inside the air sleeve. Pre bending the plastic helps to form it and makes inserting the whole sleeve back onto the shock easier later

Mine fit almost about 3/4 of the length of the sleeve.
Better to have more now. If the effect is not enough, then it would necessitate cutting a bigger piece. But start bigger and if it is too much, take it out and trim down as needed later on

 Put everything back in reverse order. Don't forget the C-clip and the o-ring indicator if it was slipped out earlier.

Set the air pressure back as desired.

Tip on setting the right air pressure. For air shock, most bikes will have a more or less sweet spot. Check around and see what others say. For the El Guapo, its 30% and it was pretty much spot on after I tried everything from 15-50%. The problem was the wallow, which ultimately led to this mod.

Too little and the rear kicks you square in the butt even when your tire pressure and rebound is supposedly in sync with the front.

A lot of people make the common mistake of asking what pressure to put in the shock.

Truth of the matter is, all bikes are different and the sag should be related to weight of rider and their usual riding position; fore/aft weight bias.

Even factory recommended settings that comes with shock and fork manuals is just a very rough guide. Moreover the reading of the gauge from 1 shock pump to another can differ significantly. I have 4 different shock pumps and all 4 give a slightly different reading at the same measured sag. Therefore I tend to stick to one instead of using them randomly. Because once this gauge to actual measurement is "calibrated" you only need to double check once in a while but not each time u re-pump the shock (same applies to air forks).

The only way therefore is to measure the sag physically. 30% on a 2.5" stroke (63.5mm) is 0.75" or 19.05mm. Ok, 19mm is good enough. For me at 73-75 geared up riding weight, that's 135psi on one particular shock pump. For someone who is 85kg, it would probably means ~145 psi or so.


Testing the mod
All in, the modification should not affect the first part of your stroke and whatever u are already experiencing with small bumps before should feel the same.

But once at speed and you start to hit 4-5 inch high roots, that's where you can feel the difference. Taking small drops at speed also should see a difference in how the rear now react. At the end of the ride, if before, the o-ring has always fell off the stroke (bottom out) then by now it should have stayed on.

Still not up to par...remove and trim the plastic piece till satisfied.

Being a mechanical retard, I love mods where I can't possibly screw up expensive parts but only make things work better.......and this is one of them :)

{update} Just found another thread that started covers more information of the AVA sleeve from FOX. Done on a DHX-Air, so maybe more helpful for those that has one of those.

No comments:

Post a Comment