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Purpose of shimming the rear shock?

Gen 4: 2011-15 
19K views 73 replies 16 participants last post by  mpp12 
#1 ·
If you have correct dampening in the rear or enough "anti-squat" that your bike is holding a line, then what would be the purpose of shimming it? To change geometry was the way I always hear about it, to help speed up steering/flickability, but why would you try to adjust the geometry (other than minor fine tuning) with raising the rear instead of dropping the front? The change to rake/trail is way more effected by raising or lowering the front as opposed to raising/lowering the rear?


Back when I first got my bike, I ended up shimming the rear end 6.5 mm, but that was to help cure the under steer (which it did) until I got a rear shock that worked for my weight. Now that I have a shock that works for me, I have removed the shims and the bike completes a corner just fine, and to get the same rake and trail as I had before, I'd only need to lower the front end about 1.2 mm (or there about) I'm trying to understand what benefit there is to raising the rear if the bike is completing corners? The only possible thing that I can think of is maybe getting to run a bit less pre-load and compression?

Anyhow, I'd like to hear you guys thoughts and hopefully have a good suspension discussion.
 
#2 ·
I raised the rear on my 600s instead of lowering the front because I'm fat and drag the lower fairings a lot. I was hoping getting the bike up higher might help with that. I haven't run my new 10 on the track yet so don't know how my clearance will be on that. I might not have to raise it. Can't wait to find out though. :)
 
#3 ·
Raising the rear does not affect the swingarm angle relative to the ground, it adds ground clearance, raises the center of gravity, and keeps the fender-to-fairing clearance the same up front.

The biggest reason is to not change the swingarm angle while simultaneously increasing the rake and decreasing trail slightly. There's lots of ways to do this, but shimming the rear is easy and has lots of added benefits. It's not just about preload/compression/rebound adjustments. The entire geometry of the chassis is affected by this.
 
#5 ·
Actually raising the rear does affect swingarm angle slightly, the axle will be at the same height as before but the pivot point will be raised.
 
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#4 ·
The only reason to shim the shock is for the purpose to make the bike more flickable in corners, you can get the same results by bringing down the forks, whatever rocks your boat. You don't have to shim the shock, you can always work the spring in order to raise up the rear height, but after doing so you might have to do slight adjustment with the other clickers on the shock.
 
#7 ·
+10

Honestly it's not a good idea to fook with the fork position. Pretty much any conceivable handling concern can be corrected usually with just a spring preload adjustment.

If you have the right spring rate there is no reason I can see to shim the shock because you should be able to get the correct sag with the correct spring.

Also correct about having to make some adjustments to damping after changing preload or spring.

It's very easy to overdo it and get some serious oversteer and tendency to tuck and wash out the front. I mentioned in another thread, Troy Bayliss in his book "A Faster Way" talks about how too many guys are worried about getting the bike to turn "quick" and seriously overwork the shimming and raising of forks.

He likes to run the bike with just a bit lazy geometry and wider bars for leverage, makes it much more stable.
 
#11 ·
You guys need to do some more research. No mater what you do as far as shimming the rear shock if you exceed 12 to 12.5 degrees of swing arm angle relative to the swing arm pivot you are going to have other issues that you won't realize. If you don't understand the reaction this causes you won't have any clue on what is wrong with your handling and you will chase all the other settings and never have a proper handling machine.
 
#12 · (Edited)
No more research needed. You are correct, with the exception of the angle relative to the pivot point alone. It's measured relative to pivot-to-axle and from countershaft sprocket to pivot point. The angle is used to help with the anti squat properties of the suspension when the top chain run is tight. This keeps the front geometry in check mid Turin and the rear in good contract with the road with the rear suspension working properly.

The advantage of shimming the rear ride height though is to help get the and front better situated without affecting the angle too drastically.
 
#16 ·
Man... I'm such a noob when it comes to suspension and geometry. :badteeth: reading this thread and seeing how much ya'll know about this stuff makes me hate all ya'll. Are there books out there that teaches all this stuff?
 
#17 ·
Here's the Kawi race kit manual for this 6 showing the shims on page 40:

http://tinyurl.com/m8g2vxn

I also saw someone talking about the chain guard in another thread, and that's on page 37 in the above doc. I see there are a couple of race kit manuals for the earlier gen ZX10R in the manuals section on this site. Is there one out there for Gen 4? Here's one for an 06 showing the shims on page 41:

http://home.comcast.net/~wiggins7709/zx10r/06ZX10RRacingKitManual.pdf
 
#22 ·
#30 ·
One thing I like about this forum is people actually discuss this stuff in a reasonably intelligent manner. I was on one retrobike forum and man, these guys could not get their minds around ABS, let alone traction control, data acquistion, lean-angle sensors...the new R1 package is probably leaving them stupefied.

Also of course when I say "the ground" I mean "the horizontal plane" as a reference, assuming "the ground" is level.

When Computrack takes measurements they will use a level and something basically akin to a surveyor's transit, with laser measurements between all the key points which are extremely precise. This analysis will also find any chassis mis-alignment or frame/component twisting or damage.

This is a list of the analysis points as of 1999...don't know if that info is even public any longer but at that time they were pretty friendly with the press, lol!

-Effective rake
-Trail
-Wheelbase
-Steering axis to front axle
-Steering axis to swing arm pivot
-Front ride height
-Swing arm pivot height
-Swing arm slope
-Swing arm pivot to front axle
-Swing arm pivot to rear axle
-Wheel diameter
-Rim width
-Center of countershaft sprocket forward of swing arm pivot
-Center of countershaft sprocket above swing arm pivot
 
#35 ·
Ive never tried shimming the shock...

On my 08 ZX10 I upgraded the rear spring and lowered the front a hair and it made a huge difference...

On the GEN IV I had the shock revalved, new spring and had the suspension adjusted.

It was like getting 15 extra HP! Lord keep blessing me; Ive never been this confident on a bike.

Even when I the bike moves around a little I still feel very confident and I know what the suspension is doing.

A friend of mine road my bike and compared to a stock suspension 2013 S1000RR and he said my bike was super smooth compared to the BMW.

Keep in mind most will not notice anything unless you were really pushing the stock suspension.

Oh, my bike draws the line and holds the line
 
#39 ·
Ive never tried shimming the shock...

Even when I the bike moves around a little I still feel very confident and I know what the suspension is doing.

Oh, my bike draws the line and holds the line
The Gen 4 is an extraordinary bike. It inspires HUGE confidence.

I don't say I've ridden every bike out there, but I also own a late model (L2) GSX-R 750 on which I've done several track days and have managed to get a little over 6500 miles on the clock as well. That bike is pretty much still known to be a gold standard of track handling and while I will say the GSX-R is definitely the better racebike, the Gen 4 is definitely the better street bike.

I think most decent riders can go quicker on the Gen 4, for sure, because the power makes it so easy to ride, but only because the suspension, brakes, and handling are first-class. I would also say that on a moderately tight racetrack the GSX-R could probably lap faster as it turns quicker and is about 20 lbs lighter, but it's a much rowdier bike, geared a lot lower and you want to spin it above 10K to really get a move on.

However, except for the weight and a little slower turn-in, the Kawi is right there, and more comfortable to boot.

Just saying again, I bought my first superbike in 1983, VF750F, have had a 2003 R1, a couple of R6s, several other Interceptors, so on and so forth.

This Gen 4 is the best sport bike I've owned or ridden and I think any manufacturer would be very hard pressed to claim they have done better in terms of a superbike that is so street-worthy but can still be raced very successfully.

My setup procedure was basically put on Q3's and crank up the rear preload 1/4 turn on the collar, about 1.5 mm.

Fookin brakes are awesome now they are broken in (have about 1,700 miles on it now).:mrgreen:
 
#40 ·
Ok here we go boys and gals......

First we start from the mega max. The machine is plugged into the swingarm pivot. At the top of the black thing you can see 2 black holes. These holes are infrared cameras. On the front of the frame you can see another little black box, this is the point the cameras measure off of. We take measurements of the frame only. This tell us if the frame is bent and what the rake of the frame (NOT THE WHOLE BIKE) is.



From there we take the height and the length of both the front and rear axle. These measurements are again based off the swingarm pivot. We also measure the circumference of the tires. One thing to note is we take these measurements with the suspension full extended, aka wheels off the ground. Also spring rate has zero affect on this because no matter what spring is installed the suspension is ALWAYS fully extended. We then punch these measurements into the software.



In the pic below youll have the simulator. This allows us to play with measurements without having to physically change things on the bike. First, everything in the left column is how the bike sits. Everything in the right column is what the bike would be IF we changed things.

So under "rear ref height" you can see I raised the rear 18mm. Now one thing to keep in mind this is raised at the tail, not the shock. So that means the shock would be shimmed 9mm if the leverage ratio is 1:2.

You can see that the bike started with with 11 degrees of swingarm angle. This is no bueno. By raising the rear by 18 mm it changes the rear to 12 degrees. The rear is now happy. BUT, look at the change of rake and trail. It decreased both by a full degree and almost 4 and half mm to trail. THATS HUGE!

 
#41 · (Edited)
Now lets take the same bike and leave the rear alone and drop the front 10mm. Two things to notice, first we made the rear WORSE! And second, even though we dropped the front 10mm, its still not as aggressive as when we raised the rear by 18 mm.



So a couple things we MUST discuss.....

It is NOT always better to raise the rear vs dropping the front. Every situation is different. Lots of times we have to raise the rear AND the front to get the numbers we want. So please dont think "just raise the rear and everything will be fine".

Like I mentioned every bike is different. So lets expand, the particular rider of this R1 is a friend of mine and I know A LOT about him and this bike. First the frame was bent pretty bad at the neck, so we were fortunate to get the numbers we wanted. If you know anything about geometry you know 103mm is a lot of trail. Well my buddy is a EXTREMELY hard braker, and if I gave him less trail he would have very little grip in entry of the turn because of the compression of the forks during braking. We always cater our numbers to not only the bike, but also the rider's style.

Also this rider was having very bad rear tire grip. He would have to wait to stand the bike up before he could get on the throttle. If we had dropped the front we would make the rear worse. By raising the rear we gave him some massive grip, and made the front even better! So why is this? The the shallow swingarm angle meant he had too much squat, and not enough anti squat which was giving him the lack of grip.
 
#43 ·
Hey Eric, would it be of value to throw the brand new bike on the machine and record the stock measurements and get a baseline to start from? I've not even ridden this bike yet but just want to ride the stock suspension for a bit first just to see what I'm working with. Thinking I may upgrade at some point during the year though, depending on now things go...
 
#44 ·
You can shoot the bike at ANY point and here's why. Off the showroom floor almost NO bike will be properly set up. So whether it's brand new or fully decked out we can get the bike dialed in. The other advantage is if you change tires manufactures or size, we can figure out adjustments to geometry to make sure the bike has the exact same numbers as it did before the tire change. This also applies to changing sprockets and moving axles or extending forks.
 
#45 ·
So, if my suspension tuner doesnt do this process, I should assume that myou bike isn't dialed in for me to the best it could be ?
 
#46 ·
Oh man talk about a loaded question.... :badteeth:

Maybe and maybe not. If a tuner knows what he is doing and is good with working with you as a rider then there is the possibility that through trial and error, testing, and experience he has gotten pretty close to the numbers needed. The advantage I have as a tuner with this machine is I don't have to guess. I shoot the bike, make the proper adjustments and then give the bike back to you. From there we only need to make a few adjustments per your feedback to get the bike to 100%. In addition I just took what would be an entire trackday of trial and error to about 10 laps to make you happy on the bike.

Another thing to keep in mind guys, is at the top level (ama, wsbk, motogp, etc) teams do NOT use sag to get the bike set up. Guys like Shane Turpin, Kyle Wyman, Bobby Fong, Eric Bostrom have all had their bikes shot on a Scheibner machine. Hell Richard Stanboli LIVES on software like this and doesnt change a thing without going through the numbers first.
 
#47 · (Edited)
Thanks for enlightening me bro... wow I learned so much about this to have a good conversation with my tuner.

You guys are what this forum is about. !!! Unlike the epic discussion of paypal fees. We're beating a dead horse there... feel free to join us lol
 
#50 ·
Thanks for enlightening me bro... wow I learned so much about this to have a good conversation with my tuner.
Take your bike up to Gerry at GP Frame and Wheel in Woodside. He uses a different machine to measure the bike, but can give you the same output dimensions. Then you have a reference point to take to your suspension tuner. I think it's only $40 to measure a bike, maybe $80 depending on how much you're looking for.
 
#48 ·
One more... is the use of an adjustable dog bone with say the attack/kyle/MSS link more beneficial than the noneadjustable dog bone supplied with the link? Seems to me the answer would be yes as it facilitate raising/lowerin the rear without the need for shims/washers.
 
#49 ·
Now you're getting into leverage ratios and linkage curves. In general, but not always the case, manufactures will make linkage curves to be progressive, as in they get "stiffer" as you push further down on the tail. This is generally used as a safety measure to help resist bottoming due to a improper setup or riding two up.

You mention "adjustable" dogbones and then attack/kyle/mss links. These are kind of two different things. The later create a linkage/dogbone package that gives you a more linear (or whatever they find works best) type curve vs progressive. This provides you with more consistent tuning variables and in general better grip.

Adjustable dogbones are THE DEVIL!!!! Whomever came up with the idea should be shot. When you change to adjustable dogbones you NEVER know what kind of linkage curve and/or ratio you have created. Yes you have raised the rear, but you have changed a bunch of variables with it. The safest way to raise/lower the rear is at the shock. This includes aftermarket shocks with ride height adjusts, shims, and/or lowering the shock internally.

So to answer your question, adjustable dog bones BAAADDDDDDD. Attack/Kyle/MSS/Insert brand here race linkages GOOOOOODDDDDD. The big question is do you need it? This is just my personal opinion, if you are a front runner expert club racer or above, or an advance track day rider, race linkages can help quite a bit. If not, save your money for tires. :mrgreen:
 
#52 ·
Thanks for the info Evallarta! I think everyone can grasp the concept now that you've got the pictures and specific examples shown.

I wish you were closer to me so I could bring my bike by and get that machine rigged up on it. It would be very cool to see what it says. As of right now, my calibrated ass-o-meter says about 7mm of shim at the shock mount works pretty good. :badteeth:
 
#65 ·
He said 120 dollars for complete digitizing and provide a report.. he didnt say anything about giving recommendations... I'll have to call him again and ask. I was thinking the report would then be read by the suspension tuner, interpreted, and adjustments made. ??
 
#66 ·
He can give you recommendations, and will give you a thorough explanation of what the numbers mean that he measures. He's been in the business for a long time and worked with some of the top level AMA teams, so he knows how to set up a bike. You probably still want to take the info to whomever your suspension tuner is as they'll have a better idea how to make changes for your specific bike and riding style. If you tell Gerry who is tuning your suspension he can probably guide you in what questions to ask them to get the best out of your equipment.
 
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