bleedholes in midpiston

if your fussy the bleed shim on the compression side screws with rebound consistency the second shim in the stack bends over the bleed or forces the stack into the voids in the MV body and sometimes seals off suddenly so you get inconsistency in general or a lumpy rebound action.

I use the bleed hole together with a preloaded rebound stack in every set of forks I alter to broaden the operating range of the rebound

in my forks the rebound works differently with a curved limiting plate very small rebound ports and a bleed hole in the mid but it is the same principle of a very soft initial rebound that ramps up very quickly. result is I can ride fast sand tracks, rocky single trail, hardpack MX or 160km/hr beach runs and I don't have to touch the rebound clickers.

Terry hay uses a bleed shim in WPs search his recent posts on Thumpertalk.

benefits are less initial harshness, reduced cavitation, smoother more versatile rebound and longer MV shim life because the closing pressure on the compression shims during rebound movements is reduced.

if using a bleed shim on the face or a bleed hole, the HS rebound needs stiffening.

WP SXS mids are a nicer shape nicer colour and have a 1.2mm bleed hole already. all the jap TCs have 1mm (kx and yz 2 strokes) and 1.2mm (everything else).

IMHO a bleed hole of 1.2 is better than a bleed shim because it results in a more consistent rebound.

you can also move the bleedshim one step away from the piston but then the soft initial rebound is lost so have to use a 0.05mm bleedshim on the rebound side too or just drill a hole

So:

MV
24
12 (bleedshim)
24
24
etc

results in a more consistent rebound because it has no effect on it.

so try a bleed shim and if your happy with the rebound action and consistency then there is perhaps no need for a bleed hole.

from experimenting with both I feel that adjusting a bleed holes diameter provides finer control than adjusting a bleed shim.

there is some info on bleed hole diameter in the penske doc attached to one of my posts in taffys big fork tuning thread.

HTH

the bleed hole works in parallel with the clicker bleed, drilling a 1mm bleed hole needs about 10 clicks in for similar performance.

I guess your wondering why not just use stiff stacks and run the clciker full out ? it might be good enough. one of my freinds has a brand name $1000 revalve job on his bike that won't work unless the rebound clciker is full out..

drilled in the midpiston web near the centre it contributes to initial shimstack lift and two small holes will in theory have less influence at HS than one big one that flows the same at LS.

with rebound I think in theory softer short stroke LS and stiffer HS is better acheived with many small holes rather than one big one. but in practice who knows ? anything is possible. I like predictability and consitency for rebound so I use bleed holes instead of bleed shims but thats just my appraoch. there must be many others that will work great.

what sort of things have you been trying?

would like to see a few guys post their setups, I won't throw poop at them

You guys are something else...... True Suspension nerds !!! I get about 5 pct of this thread.... at max. Very impressing !

Nice to see that knowlege is here should I ever need it !!!

Keep it up

I have no holes in my piston I hope not.... Would just loose compression, so my advise is to you gyus is to weld them up with a 4616 rod, and just go for it !!!

Anders' DK

there is a lot to be gained from making the mid more versatile.

the 11.90mm rod and 28mm cartridge combo make our forks rediculously midvalve biased. I couldnt get a broad enough range out of the forks untill I tried the awesome curved MV backer that smorgasbord came up with. have tried a lot of MV setups with conventional round backers none come close. its a simple thing to make doesn't have to be pretty you could make one with a hand drill and a file.

because the MV has to pass through so much oil it has to cover a very broad operating range so a curved backer with a spring under it to regulate the float is one way of achieveing that range.

the term "blow off" is misleading it should be called a variable float system. ie you like 0.1mm float but then the MV has to be so soft it lasts 20 min or as your finding there are benefits to having a stiff mid. in my experience you can have all the benefits of both if you use a spring to control the MV lift and a curved backer to control progression over a larger range of flow rate. ie it can act sooner so 0.1 - 0.2mm float is possible and still provide stack progression at higher velocities after the conventional has reached its limit.

in a jap TC fork with a pressurised cartridge and 12.5mm rod and smaller cart ID this kind of stuff probably insn't nescessary, they run 0.2mm float with very stiff mids and for the most part they don't have any issues.

even the 09 WP OC fork has reduced cart ID and should be able to be tuned easier. the 07 - 08 OC forks are regarded as a stuff up by many at least here in OZ anyway

solid forged alloy mid with 2 rings and a CR of 17:1 running on high octane ohlins fluid.. sounds good.

the automotive ohlins TTX shock has a solid piston