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6 mm Shim? NO!

20K views 142 replies 39 participants last post by  Mayfield07 
#1 ·
2003 'Bird with 20,400 miles. And I will always be thankful to the seller for admitting he had fitted the bike with a 6 mm shim placed above the rear shock. I knew nothing about this mod. He'd heard that it increased handling responsiveness.

If so, it would have been hard to tell during my initial, 3 mile test ride. But I bought the bike. Took it to a local, reputable shop for a full - and I mean FULL - service. New fluids, tires, brakes and a thorough shake-down ride. They blessed it as a solid, low-mileage machine.

Okay. Fast forward; 20 canyon rides and a few thousand freeway miles later.

I didn't like this bike.

It was twitchy, nervous at all speeds - always wanting to fall in to or out of a turn . . . refusing to maintain a steady line through fast sweepers . . . requiring constant correction at the bars. In my memory, the only bikes I owned that ever handled worse were an 82 Kaw LTD with that "spaghetti" frame, and an 84 gPZ that wanted to stand up if the brakes were touched while leaned over.

But this wasn't a Kawasaki. It was a Honda. 30 years of experience has taught me that shade-tree engineers and quick-buck aftermarket supply houses are no match for the engineering acumen and testing resources of a billion dollar manufacturer. There was something better there, waiting for me. I needed to get this bike back to stock. Yesterday.

So the shim came out. Chain, reload and damping re-adjusted. Tires set to spec. Couldn't wait for Sunday.

As the tires warmed and we re-acquainted ourselves with the Angeles Crest, a slight smile turned to a grin. The bike now held its line through the turns, tightening or expanding the radius ONLY in response to my input at the bars. No more nervous, twitchy behaviour. This CBR 1100 xx - this Blackbird is now the bike it always could have been. . . the bike it once was.

I'd offer you a free 6 mm shim for the cost of shipping. Unfortunately, I have no idea where it is at the moment. And I don't care.
 
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#3 ·
as has been said "odd" after all 9/10 cats prefer a shim :)


Also noted you've actualy made two changes (removed shim plus adjusted (p)reload & damping) that could affect the handling so how do you know it was the shim was the "culprit" ?

NB on that point what shock are you running? Is it the Honda OEM one? Only asking as some shocks may be a little longer than OEM so 6mm could potentially be more than 6mm
 
#4 ·
Doubt it was the shim as soooo many have fitted these with only improvement felt. Possibly as teef.au can attest, the shim was fitted incorrectly. If not pushed all the way in, it can catch on the frame lip and create another 3-4mm of lift.
 
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#7 ·
I absolutely 100% support what Epoc says here. I messed up using washers doing the install late at night on a work day and they fouled the lip on the frame. I didn't even ride it, I realized something was wrong when it almost fell over putting it on the side stand.

Both Epoc and I (along with others) have pushed these things pretty hard with the shim. We both have scrape marks on our fairings and neither of us would be without the shim or equivalent amount of lift.

I've also watched Epoc do a track day. He got to some pretty wild speeds on the main straight where I was watching, he didn't experience any instability and I couldn't see any.

If anything they are normally a little more towards the stable end of the spectrum than the twitchy end. It sounds like there is something wrong with your bike, but it's not just the fact that the shim was fitted.
 
#5 ·
I reckon it probably was your tyre pressure , low air pressure in the front does that.
The twitchiness could be a number of things , suspension, tyers ,wheel alignment etc.
You should try the Shim again,when you've gained more time on the bird and see any change
 
#6 ·
Raising the back (and/or) lowering the front both reduce the rake angle.

Are you sure the front is stock ?

I performed the 6 mm shim mod and I am very pleased with it. I assume too much of the rake angle was reduced and removing the shim brought it back in a "desireable" range.

Anyway, if you're happy with it, that's great. But it may be worth checking the front to at least know if it's stock or not and avoid future surprises.
 
#8 ·
Im going to replace the 6mm with a 3mm at some stage. Everything is within frame edges ok, but the bike does have a tendency towards a confused counter steer/turn vs lean feeling. Let you know the outcome.
 
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#10 ·
The ONLY reason I felt the shim useful was to increase ground clearance. Holes in the stator cover can turn a good day into a bad one quickly.

It makes the bike feel lighter, less stable, and turn-in was faster.

I know what the bike weighs and it hasn't changed, I like stability, and if I need faster turn-in, I turn in faster.
 
#12 ·
+11mm on the supercharged Bird, stable at stupid speeds. Only feels unstable when you give it a decent handful ..... but what else would you expect?
(Oh how I wish I could take it out for a blast)

I've covered over 100,000 miles with a minimum of +7mm at the rear of Daily Bird and the only times I've had stability issues was when I had badly wearing/squared off front tyres or the front pressure was too low and then it was issues turning in and the bike wanting to 'fall over'.
 
#18 ·
I install a light upgrade shim close to 10mm today for a trip in prov. maritimes Canada and new Pirelli Angel GT spec A, new chain & sprockets (stock gearing) and new front brake pads Vesrah JL, plus new FPR (preventive).

PS: probably my last trip ( 5000km ) because I was Of Diagnosis cancer inoperable esophagus at 62, I refuse chemo treatment for as long as possible the bike !!!
 
#20 ·
:) That's interesting. Another reader stated that the stock set up was designed to make the bike stable at triple-digit speeds. You, on the other hand, decided otherwise . . . and you "fixed it" by steepening the steering angle and decreasing the rake? Wow.
 
#21 ·
I see. And why is that? Did the bike refuse to turn in its stock trim? Did it fall into, or out of, a turn without the shim?

Conspicuous by its absence in these threads is any mention of WHAT, exactly, the bike did WRONG before this ill-advised modification. After returning it to stock, my suspicion is that it did nothing at ALL wrong.

My 'bird, without the shim, holds the lean at which it is set and yet responds immediately to my input at the bars. Far, FAR better than a bike that is always hunting . . . demanding constant corrections to maintain a steady arc.

Seriously, you folks do what you want. I've already done that by removing that god-awful thing. And I applaud Honda for designing a bike that works across the greatest possible range of conditions . . . for a bike of its weight, size and wheelbase.

You can't turn an orca whale into a hammerhead shark by shoving a horseshoe up its ass.
 
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#23 ·
Hi Perzuki, I am sure all of us do respect your opinion, however some of us was reflecting only to facts. If you do more than one change at the same time, you cannot exactly tell what adjusment or change did the improvement. This is basic trouble shooting rule. Belive me, in this forum there are guys, they do all kind of racing, have done over 100.000 miles with the same bike, so lot of experience here. The lifting of the back is prooven as a good way to improve tight corner handling. Lifting the back you can do by changing the shock, adjusting the hight of original spring (setting shag for example), adding the shim or lowering the front. All these actions will have good and some negative effects.
The BB is stabile on straight roads at high speed, it is stabile and likes fast and wide turns, but is not that good in tight corners ( compared to my GSX750R) it tends to run wide - or better, not that easy to stear in.
If you feel that your bike is perfect than you are there, don't change anything enjoy it.
I will stay with the higher back, because I like it better when on track days and in the Alps.
As written above, the BB is a really, really great bike, but it can be improved.

Respect!
 
#24 ·
Hi Perzuki, I am sure all of us do respect your opinion, however some of us was reflecting only to facts. If you do more than one change at the same time, you cannot exactly tell what adjusment or change did the improvement. This is basic trouble shooting rule. Belive me, in this forum there are guys, they do all kind of racing, have done over 100.000 miles with the same bike, so lot of experience here. The lifting of the back is prooven as a good way to improve tight corner handling. Lifting the back you can do by changing the shock, adjusting the hight of original spring (setting shag for example), adding the shim or lowering the front. All these actions will have good and some negative effects. The BB is stabile on straight roads at high speed, it is stabile and likes fast and wide turns, but is not that good in tight corners ( compared to my GSX750R) it tends to run wide - or better, not that easy to stear in. If you feel that your bike is perfect than you are there, don't change anything enjoy it.
I will stay with the higher back, because I like it better when on track days and in the Alps. As written above, the BB is a really, really great bike, but it can be improved. Respect!
Thank you for your thoughtful response. Well done.

". . . adding the shim or lowering the front. . . all of these actions will have good and some negative effects." AGREED.

"The [stock] BB is stable on straight roads at high speed " AGREED. . . . but it is ALSO stable at moderate and low speed.

". . . not that good in tight corners." ". . . tends to run wide. . . not that easy to steer in." Well, of course - it's not as easy to turn in compared to a 600 or even a 750 GSX or any smaller sport bike. I believe it handles exactly as one would expect a well-designed, 590 lb., 59 inch wheelbase to handle.

"Boyo73," you've chosen to quicken the BB's handling in the tight stuff, for "track days and in the Alps." That works for you - good - and you've done the best job of explaining why.

We have a couple of favorite roads here in southern California; Mulholland and Angeles Crest. Mulholland includes an endless series of tight turns (posted 20mph stuff). Angeles Crest includes an endless series of posted 55mph curves ("posted" being the key word here). On Mulholland? Okay, your setup might have advantages.

But here in the U.S. - where the best day of traveling will include 600 miles of switchbacks mixed with sweepers mixed with freeway drones - I believe that Honda got it right with their stock setup . . . delivering me to my motel or campground at the end of the day feeling calm and relaxed, not frustrated by a day of tacit babysitting at the handlebars.
 
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#26 ·
I drived my BB for 16.000 Km before adding the 6mmm shim.

And now I can say that this should be the first thing to do on a Black Bird.

It's so much easier to drive on a twisty road!!

There should be something else on your bike causing these interferences.

And nothing was wrong with the original bike, but since I don't ride over 200 normally, this suits much better for me - better handling on thigh corners.

In the end, you must do what fits your riding style better! :thumb::thumb::thumb:
 
#32 ·
I would say that probably everyone understood that the shim is good...[snip]
Actually, I've spoken and corresponded with more than a few owners who agree that the nervous handling created by the shim is neither useful or necessary for daily use, that it in fact creates a rather unpleasant riding experience.

Nevertheless, I'll inform them that you've appointed yourself king of the free world, and that henceforth they shall offer opinions only via your keyboard, because only YOU know what "everyone" understands.

Nice to be surrounded by people so much smarter than me. <3.
 
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#34 ·
One thing that we all have in common are Blackbirds. Now the Blackbirds themselves are all not the same, even in stock form. What oil type and weight in front forks makes a big difference. A 5w Bell oil is not the same as a 5w Spectro oil, or just about any brand name, (I have a chart with mfg#'s) stickson of bushings and size, difference #1. Rear stock shock setting, oil degradation, piston wear etc. difference #2 Frame bolt torque, swing arm torque,engine to frame etc, differnce #34. The list could go on and on.

This coupled with the riders weight, height and abilities and riding style #4. Most of all tire choice and the pressure they run at makes a huge difference #5. Many other adjustments (head bearings) will play a part in the characteristics of motorcycles even if they are "identical". I've ridden "identical bikes back to back and have found differences in handling etc.

I think people forget that when comparing mods, bikes etc. You really can't get that specific unless you have all the CORRECT data of the bike or whatever. This really muddies the waters many times without realizing it. I do it myself at times when I even "know better". So if something really works for you stick with it. The only down side is if it's masking a real problem without the rider/mechanic knowledge. Which is, I feel, the correct knowledge of all the systems that incorporate a motorcycle. Not many have that knowledge. The last thing and I have experienced it many times is the riders psyche and what they believe is true.

My answer to all of this is "whatever floats your boat" if it works for you then great. Just like some people use car tires on the rear and don't really think the handling is bad.!? Whatever............

Welcome aboard Persukie, you'll love it here. They even have sheep..............................
 
#42 · (Edited)
Hello again!
With my stock bike, when flat out and GPS logged 292 km/h the bike was stabile. After adding the shim and adjusting rear shag, the bike was still as stabile as earlier.
Than I did upgrade front suspension with wilbers springs (fits to my weight) and oil. Still crazy stabile and better feeling in corners. than because my accident with my hand, I had to install the LSL superbike conv kit. The result was: slight wobbling above 220km/h and tend to tankslap when accelerating hard from tighter corners. Than I installed the MRA touring screen, still wobbling a bit but top end no more than 280 km/h. I think I killed the great aerodynamic of the bike.
To make a long story short, after long hours and miles spending with trouble shooting the resolution was. Adjusting the stearing head bearing made the bike stabile at high speed again, and the "tank slap sh.t" went away after I installed the really heavy bar end weights.

BUT as said earlier, bikes are different and there are too many parameters which can influence the handling, even a great tyre when the weight index is wrong can kill handling badly.
My intention is only to share experience and not to offend people.
Enjoy your bike guys.
I wish you wide roads!
Over and out...
 
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