Advice on Setting Up Suspension With Penske 8987 Shock

[FJRAlanF]

I know that there was a Group Buy in November 2006 for GP Suspension components, such as a Penske rear shock of some sort, and new fork components custom made by GP. Due to health and other issues, I've not ridden much for some time and I missed that Group Buy. However, nearly two years ago I bought a Penske 8987, along with linear front springs, both set up for my weight (about 210 loaded). I have a 2005 ABS FJR with low mileage.

At that time I installed the front springs along with a mixture of Redline fork oil recommended by the suspension tuner I bought the items from. Once I got the damping settings sorted out, this felt a good deal better than stock. I never got around to installing the 8987, but finally did a few days ago. With the 8987 at its out-of-the-box settings, the ride height increased by more than one inch, so I backed off on the preload until the ride height felt about where it was stock (I'm leg-length challenged and just my toes touch the ground).

Realizing I was at my limit of knowledge, I hooked up with a local racer who is also a dealer for GP Suspension (I later found out that many of the local riders I know, such as MSF instructors, use him for setting up their bikes). He set the damping, front and rear, so that it's hugely better than before. He didn't play with the preload.

Now for the problem: after reading about static sag and rider sag, I see that these are way off for the rear: too much static sag and too little rider sag. I haven't yet taken measurements, but the local tuner saw this immediately. He said that we can play with the rear spring rate and probably get things better dialed in.

Here's my question: I have two sets of dogbone links; a purchased one that lowers the stock suspension by one inch, and a custom made one that lowers it 1/2 inch. Is it reasonable to use these, in combination with the 8987 preload adjustment and selecting the right spring, to dial in the suspension? Or should the tuner and I try to dial it in using the stock dogbones?

AlanF

 

[deer slayer]

I think you need to get the spring rate correct. Changing the link will lower the ride height but it won't change the static and dynamic sag. Just my opinion, and I am no suspension tuner.

 

[Dangerous Dave]

I think you need to get the spring rate correct. Changing the link will lower the ride height but it won't change the static and dynamic sag. Just my opinion, and I am no suspension tuner.

Yeah...what he said. Anytime you're setting up suspension on a bike, sag comes first! Everything else revolves around that. Changing the links will change the overall geometry of the bike, some of which can be brought back by sliding the forks up in the clamps. Not the perfect answer, but it will help bring back rake where it oughta be. It won't change the charactersitics of the shock itself, you're only changing the positioning of the bike relative to the shock. Throw in your links, set sag at both ends, maybe slide the forks up 5 mm in the clamps, and work out from there.

 

[FJRAlanF]

Thanks for the advice! Now for some numbers.

My impression from reading several methods for setting sag for general bikes is to first get the "static sag" in the vicinity of 10-15mm, then to get the "rider sag" to 30-40mm. This gives a difference of 20-25mm. Are these numbers applicable to the FJR?

These methods imply to me that what you really want is to first ensure that the rear spring rate is correct by measuring the difference between static sag and rider sag, and getting it to 20-25mm. Then you fool with preload and dogbone links to set static sag. Correct?

I usually ride with the saddle bags and Yamaha rear trunk on, because I like to have a variety of clothing available due to the extremely variable mountain weather in Colorado and Wyoming. I figure that setting unloaded static sag (no bags on the bike) to 10mm and then ensuring that loaded static sag (with loaded bags on the bike) is close to 15mm would be good. Then I would check that rider sag is in the right ballpark. Does that sound reasonable?

Alan

 

[MCRIDER007]

My impression from reading several methods for setting sag for general bikes is to first get the "static sag" in the vicinity of 10-15mm, then to get the "rider sag" to 30-40mm. This gives a difference of 20-25mm. Are these numbers applicable to the FJR?
These methods imply to me that what you really want is to first ensure that the rear spring rate is correct by measuring the difference between static sag and rider sag, and getting it to 20-25mm. Then you fool with preload and dogbone links to set static sag. Correct?

I think you are really referring to free sag and static sag but to use your definitions:

You can use preload adjustments on many different springs to get 15 mm of static sag or 40 mm of rider sag but only one spring rate will give you (exactly) both at the same time. Since preload does not change the actual spring rate, all you can do is use preload to set either the static or the rider sag and then see if the other is close enough to what you want. If they are not, then you need to change the spring to get the desired result.

The dogbone links do not have anything to do with sag, they only effect ride height in the back end. If you lower the rear end, you need to raise your forks in the triple clamps by the same amount to keep the same steering geometry.

 

[S76]

No suspention guru here but I just installed an 8981, which is the same as you 8987 minus the low speed adjuster. What I read said to set the rear sag (with rider) at 7/8". That seemed kinda hard so I ended up setting it to 1.25". Much better. That is it for preload. You only have the one big preload adjusting nut so you can't really get two settings out of the one adjustment.

You can change the rear ride height by shortening the eyelet on the bottom of the shock. When my shock was delivered it was 1/2" (maybe 3/8", don't remember) longer than stock. I loosened the jam nut and turned the clevis in all the way. It was still 3/16" longer but much improved. That lowered the rear, but it was still a little higher than stock. At this point the bike rode like a haywagon. STIFF! So after many adjustments I ended up with the compression adjuster about 2 clicks in from all the way out. The rebound, I really don't know where it is. I had backed it way off to get the compression right, then kept turning it in until I got rid of the "pogo" effect from hittting multiple bumps, and then a couple more clicks for good measure.

The bike is awesome. Between this shock and the work GP did on the forks the bike feels like it is on rails. It is overall a significantly firmer ride than stock, but it is this firmness that tightens the bike up to hold a line in a corner, or easily pick a new one mid way if you so desire. You can't hold a line when the suspension is squishing and wallowing.

Try the inch and a quarter sag (with rider, gear, and a half eaten super) and back way out on compression. Unless your spring rate is way off, I think you will like it.

 

[FJRAlanF]

Well, having gathered a variety of information from fjrforum folks, some Traxxion Dynamics DVDs, my local tuner, and some good old

common sense, I've arrived at what appears to be a very workable solution to getting my rear suspension into good shape.

I had a couple of friends help measure free sag and rider sag. Based on these measurements, my local tuner and I agreed that changing

the present 950 lb/in. Hyperpro spring (which came with the original Penske 8987) to an 800 lb/in. Eibach spring he had on hand would

likely get the spring rate to where it ought to be, based on my measurement of (rider sag) - (free sag) being too low. Note that the

Traxxion Dynamics videos suggested setting free sag to 10mm and rider sag to 30mm for both track and street use on racing/sport

bikes. I got the impression from some comments here that free sag and rider sag should be about 12mm and 35mm. My results were as follows:

I ended up with 11mm and 30mm with no bags and just my bare, un-geared-up weight, and about 12mm and 33 mm with loaded bags and me fully geared-up, which I think is pretty good. I had to use the store-bought dogbone links, that lower a stock bike 1 inch, to get the ride height close to

stock (it ended up about 1mm higher than stock with the "hard" shock selection; the Penske's were already adjusted with zero ride-

height). Since I was comfortable with the "soft" shock selection ride height, I think I'll eventually go to my local machine shop and

have them make me custom dogbone links that lower the bike another 10-12mm. And then I'll adjust the front shocks accordingly.

I rode the bike about 120 miles in the Colorado mountains between Sat. and Sun., and it feels really good. It holds a line in a turn

much better (less effort keeping it on track), is easier to turn into the turn to begin with, and rides better over all road

surfaces. The next test will be this next Friday, when I do a semi-race track course with a racer named Ricky Orlando. Wish me luck.

AlanF