Installed Honda F4 BACK SHOCK

[chiz]

Hey all
Have not had a ride this year as was concentrating on my FJ, I just rolled it out of the shed with new wheels, rubbe,r calipers, pod filters, and back shock. Can anyone tell me out there what sort of feeling I should feel when I push down hard and fast on the tail section in terms of shock feel?
  Right now what I am getting is a few inches of relatively easy downward motion with an immediate return to rest position, is this acceptable?
Chiz

[Pat Conlon]

"Immediate return"....That's alarming....it sounds like a pogo stick.

What spring are you using? (Should be at least 900-1,000 lb)

Has the shock been valved for the spring?

Does the Honda shock have provisions for rebound adjustment?

I sure hope so....

[racerrad8]

(Should be at least 900-1,000 lb)

Why...?

Randy - RPM

[Pat Conlon]

(Should be at least 900-1,000 lb)

Why...?

Randy - RPM

Shim stack shock vs IAT valve shock....apples to oranges...you're not sucking me in young fella .....nice try.

[racerrad8]

(Should be at least 900-1,000 lb)

Why...?

Randy - RPM

Shim stack shock vs IAT valve shock....apples to oranges...you're not sucking me in young fella .....nice try.

Are you sure the Honda shock is a shim stack or a controlled/adjustable orifice?(that is what those adjusting screws are for)

I know the RPM shock has both the shim stack & IAT valving along with the proper spring rate specifically for the FJ.

But, to answer Chiz's question, if the rebound of the shock is too high then it will "pop" right back after compression.

Randy - RPM

[Pat Conlon]

Good question Randy, I don't know.

After I asked the question, I checked the files and confirmed (based on the files) that the spring is a 1,000lb spring so Chiz should be good to go there...

Dunno about F4 shock having rebound adjustment. Sounds to me like he needs some.

[edit] I just checked the Race Tech web site and they show the stock spring on the Honda CBR600 F4 to the only 14.2 kg/mm which is ~793 lb/in...round up to 800 lb spring....too light for the FJ.
So my original comment remains...

[giantkiller]

Yes it has both rebound and compression adj. Limit on stock valving is about 900lbs(according to the Honda guys.)900 is a little light for my 285lbs.(according to sag measurements) but is great compared to the stock shock. I have $170 into mine including the spring tool.

[chiz]

nice discussion. I guess I should go in there and try and tighten things up a bit looks like a real bug--r to try and do so.. shock was cheap so if it is pouched a new one is in order.
Chiz

[chiz]

I did not bother to mess with the F4 shock just went for a bit of a ride and did not notice anything alarming. In fact the bike actually feels safe to ride with no weirdness going on with the handling. Ramp speeds can be exceeded now and not strictly adhered to as was the case before.
  Of course I will never know which was the single biggest contributor to fixing the issue it may have been new rubber for all I know. I cant decide if the pod filters are a plus as far as performance goes if there is supposed to be a performance gain then there must be some more work to be done like a jet change or something? I do notice that the bike starts very easily now and can only assume the filters have something to do with this?
Chiz

[FJ1100mjk]

Of course I will never know which was the single biggest contributor to fixing the issue it may have been new rubber for all I know.
Chiz

Suspension $ and tire $ ---- some of the wisest money that can be spent on an old bike.

[the fan]

Setting up a non standard shock can be a little tricky, especially if you have made other changes to the system. There is a lot of fuzzy math to do to calculate leverage ratios and wheel travel but in practice you can get pretty close with a few measurements.

On the FJ you should see 120-130mm of usable wheel travel with most of the common mods. Based on this I would use the following method:

Set rear wheel race* sag at 32mm using preload if using modern 17" tires and mostly riding solo. 30mm if you commonly carry a passenger. shoot for 30mm/28mm if running older 16" bias ply.

Once you have the race sag set you need to measure the free sag**. You should measure 10-12mm of free sag with the race sag set at the optimal number. If you are outside of the range on free sag you really need a different spring. A good guide to calculate what you need is that it will take appx. 50 in/lb (1.0 KG/mm) of spring rate on a straight rate spring to make up 2mm of free sag. What this means is that if you are set at 34mm race sag but only see 6mm of free sag you need to go up 100-150lbs on the spring (1.7-2.7 kg/mm) to get the number correct. If you see 14 mm you would need to go down on the rate by a similar amount.

The reason for this is that when you preload a soft spring to get the correct race sag then it will be initially too stiff to give a good ride and react to high speed motion (tar strip, gravel, expansion joint, washboard surface...) but it will not be stiff enough to handle low speed motion.(acceleration, braking, large impacts.)

On the other side of the coin if you have too stiff of a rate you will see less free sag as you are not using much preload to support the load. This will often give a good ride on high speed motions but kick your teeth out on the bigger stuff, decreasing traction on acceleration as well.

Once the springs are correct you can move on to the damping adjustments.

For most situations rebound is the more important of the two.

Rebound should be set loose enough to keep the wheel on the ground and tight enough that the bike does not pogo. What you are looking for is for the rear to move quickly to the free sag point without going past . I generally move the adjuster in 1 click (.25 turn) increments until it just rebounds over the 'top' and settles. Once I have found this point I turn the adjuster in 1 click (.25 turn). This ensures that you get full movement and keep the tire on the ground without a wallowy feel.  

Compression is generally set by feel. I usually adjust it to match the forks.

On the subject of forks...

Set them in a similar manner to above. You should be looking for a race sag number of 34mm using preload if using modern 17"  shoot for 32mm if running older 16" bias ply.

Free sag should be between 12-15mm up front. Finding the correct rate using the same method as you did for the shock, the correction factor is .25KG/mm for 1mm of free sag you need to make up.

Depending on your forks you may need to cut new shims or if using a more modern set up use the adjuster.

Rebound setting up front is similar to rear. You want to run it as loose as possible without overtopping for best results/performance. On cartridge forks this is usually pretty easy to do using the adjusters but on damping rod forks you will need to plat with the oil to get the right results. It can be time consuming, but well worth the effort.

Back to compression. I generally set this fairly soft as well. After a while you will develop a feel for it. Until then you should wrap a zip tie around one of the legs to see how much it actually moves. IIRC the FJ forks have around 125 mm of travel (YZF600 have 130) and you want to be using 80-85% of the travel during normal riding. The easiest way to measure this is to push the zip tie down to the dust seal and let it push the tie up the leg. After a normal ride measure the distance from the seal to the zip tie. Add the free sag number you got earlier and subtract it from the total travel. on the stock FJ you should see a result around 20-25mm of unused travel. Personally I like it closer to 20...

Once you are happy with the front, adjust the rear so that when you bounce the bike it move a similar amount. Again this is easier to do with a cartridge fork but you can adjust the compression damping via oil or in the case of emulators by adjusting the spring. I don't believe the RPM valves have this provision but they use a different method of controlling compression damping and should work well without the need for adjustment or set up.

One thing to keep in mind is that compression damping and heavy oils do NOT support the load or compensate for incorrect springs. No shock or fork valve can do so. I have worked extensively with damping rod style forks and shocks, and all manner of cartridge (shim stack) forks and valves. I have also worked with inertial style shocks (works performance , spring and check ball valve) but I have no experience with the RPM style shock and am not sure how they are doing the inertial damping.

Hope this helps, and I thank you for your time.


Pat,

I have been meaning to do a writeup like this for you for a while. Since 2011 work has kept me too busy to do much of anything. I think I did a similar thing like this on setting up a bike in the past, and if you like we can get together on here sometime and combine it all into a common thread.

Bill




* Race sag- many names used but in this case I am referring to the difference between completely unloaded suspension and suspension supporting weight of both rider and bike.
** Free sag- again different folks call it different things but I an referring to the difference between completely unloaded and suspension supporting the weight of the bike only.

[Country Joe]

Bill,
That is a great write-up, it distills the information down to easy to understand terms.
Thank  you very much.
Joe

[giantkiller]

Yes thank you. Is this going in the files

[the fan]

Yes thank you. Is this going in the files

Waiting on Pats reply.

Not sure if its appropriate for me to be the file guy these days as I don't visit the site often and have very little time to spare. Pat and I have discussed this in the past and there may already be something similar.

Hoping to get with him and get his input or a possible rewrite. Hopefully combining these types of posts into one thread. (I.E. I have no time but he may be able to fit it in between hair modeling and bike detailing gigs)

[FJscott]

Bill,
I just installed a FZ1 swing arm and fitted the FZ1 shock and relay arm. Not knowing how to set it up I just put all adjustments in the mid range adjustments. I'm happy with the results but not sure when setting the sag...
Where site sag measured?

Scott