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2002 919, Asphalt
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255 Posts
Discussion Starter · #1 · (Edited)
Here are the results for my comparative work on the factory shocks from '03 and '05.

I'm doing this because...
1. I would prefer a heavier spring in my '05 shock as my preferred for "one up" riding is 6. I'd like 3 or four "clicks" above that for riding "two up" with some gear.
2. I'm broke. Penske/Ohlins, while wonderful, are off the table. If I had that money, I'd look into a new bike, not spending $1k on a 19 year old bike with 50k+ miles.
3. Excellent opportunity to learn, especially for my daughter, about free sag, rider sag, etc.
4. I like data. Working through all of this is fun for me. Yes, I'm strange, lol...

Notes -
1. - This is a summary graph of a LOT of data. I have graphs for preload heights, rider sag as % of travel, free sag as % of rider sag, etc. etc. If you have a specific question, just let me know and I'll post it.
2. - Rider weight, geared up, is 172 pounds.
3. - The free length of the '03 spring (157 mm) is 6 mm longer than the '05 spring (151 mm). Also, the installed length of the '03 shock (151 mm) is 6 mm longer than the '05 shock (145 mm). Other than free length, there is no obvious difference between the '03 spring and '05 spring. The wire diameter (.505 in.) is identical as is the number of active coils, etc., which surprised me as my previous experience with the '03 combination was that the spring was way to heavy. Is it possible that the rebound damping (non-adjustable) on the '03 shock was stiff enough to keep the shock compressed, during operation, further down in its operating range, resulting in a stiffer ride?

Results -
Wheel Tire Land vehicle Fuel tank Vehicle


Sag was measured (*) at 1, 3, 5 and 7 for each combination as well as 6 (preferred) on the '05 combination.

Note that the rider sag is essentially identical for the '05 combination set on "6" and the '03 spring on the '05 shock set at "1" which is where the bike sits today. A 30 mile ride on a variety of roads confirm that the ride quality between the "6" on the '05 shock is essentially identical to the '03 spring on the '05 shock set at 1.

Next steps - While I accomplished my goal of having additional preload options above 6, the result is "preferred" is a 1. I'd like something below that for a random occasion of piling up miles on the interstate or if my daughter rides the bike.
I will double check when I next disassemble but I believe the difference in installed height is in the spring seat for each shock which are not interchangeable between the two shocks. If I can duplicate the 157 mm installed height on the '05 shock I will do so, but I doubt it is possible. Therefore, I am fabricating spring shims to install between the spring seat and the adjustment collar to use with the '05 spring/shock combination to reset the "6" to a "3" or so. Will report back when that work is done.

Here's a shot of my homemade spring compressor arrangement. It worked well but will do some refining if I keep doing this. I'd like to duplicate the arrangement on the right on the left. Just works better. (The white duct tape is there to attempt to prevent scratching the spring.)
Vehicle Automotive fuel system Car Automotive tire Motor vehicle


* - I'm confident in my sag measurements. Each data point was created using several measurements (bike being compressed and bike rebounding) and were repeatable.
 

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McTavish
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6,491 Posts
You've done lots of work.
Going by your info, the dusty stocker I have in the basement is an 04+ by virtue of its 147 mm installed spring height.
There has to be an error in your shock installed length measurements or reference points.
The eye centre to centre on the one I have is a nominal 280 mm, and my recollection is from years ago seeing tabled data of either 281 or 283.
My guess is that your reference points are different.
The eye to eye distance being different between 02/03 and 04+ shocks is news to me.
If the 02/03 unit is longer, I'd be using it for that reason alone, seeing how flat the swingarm angle is to begin with, noting a 6 mm difference makes a dramatic difference for a flat/flattish swingarm angle.
As for spring rates, I have to wonder if the spring on your 03 really is a stock unit.
The early springs have been checked (LDH perhaps?) as being the 1200#/inch they are said to be, as compared to the sub 900 (860 I recollect) springs of the 04+.
No amount of damping can replace inadequate spring rate, keeping in mind they are two entirely different things.
Having said that, a very heavy low speed compression circuit will slow the bump stroke of a too soft spring and depending on the input forcing curve, time included, reduce the total stroke displacement.
As for an 02/03 shock and spring, my guess was that position 1 or 2 would be best for a fair number of riders.
I think the harshness that many complained about was due to excessive preload along with horrid damping characteristics.
Anyway, it's great seeing how you're delving into it all.
 

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2002 919, Asphalt
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Discussion Starter · #3 ·
Hey McTavis, None of my measurements relate to the eye to eye shock length. They are the same length, eye to eye. I know this because my baseline for full drop was the same from shock to shock. I was talking about the "installed height" of the spring within the shock. Here's a graph which also shows the free length of each spring.
Rectangle Slope Plot Line Font


I searched up the spring rates reported (on this site) so you can imagine how was very surprised at how similar the springs were. Nobody was talking about free length though. Given that F=kx, and the force multiplication through the swing arm, and the relatively short stroke of the shock as compared to the wheel, a little change in spring rate will have a big effect.

I made up some spring shims this afternoon out of some aluminum I had laying around. They're 2.5 mm thick. I plan to pull the spring off of that shock and verify that I can't alter the installed height with parts from the early shock to gain that 6mm. If I can't, I intend to add two spacers and sweep through the sag settings again. I've now recruited my wife to help as my daughter is growing weary of marking sag on pieces of paper at my direction, lol... Here's the shims.
Asphalt Road surface Automotive tire Font Material property

I painted them afterwards.

Wish me luck!
 

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2002 919, Asphalt
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Discussion Starter · #4 ·
Also, forgot to add. I bought the shock from Baldy (on this site) who said it came off of his '03. He, like me, swapped out the early shock for the later shock because it was so darn harsh. (I did the forks too.) It didn't appear that anybody had been into it before me but you can't be sure.
 

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Rob,
Glad that my old shock is giving you hours of entertainment. I weigh 180 and the 03 spring was just to harsh even set at 1. I like the ride of the later 919 rear shock better but I also added cbr600f4 forks up front. Highly recommend that setup. You can usually find 600fr4 forks cheap on ebay.
George (baldy)
 

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2002 919, Asphalt
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Discussion Starter · #7 · (Edited)
After going through the data (and looking at sheetmetal I have laying around) I fabricated a .080 (2mm) aluminum shim and an .040 (1mm) steel shim to be placed under the spring on the lower shock seat. (My original plan of putting it on top of the spring under the adjusting collar wouldn't work so new shims were made.)

So here's where we are. My preferred settings of 50 mm rider sag, and 22 mm of free sag can now be achieved between "3" and "4" on the '05 shock with the 3mm shim. I can also achieve the sag of the current "7" with a setting of "5" on the shimmed spring giving me "6" and "7" for a passenger.

Product Rectangle Slope Plot Font


And, to compare it to all of the other combinations...
Rectangle Slope Plot Font Parallel


Haven't taken it out yet (still watching F1 and it's about to rain) but have set it at 3 for the first ride.

(And the '03 spring vs. '05 spring comparison still baffles me. The springs are IDENTICAL except for the '05 spring being shorter. I like everybody else found the '03 spring to be way to stiff and the '05 spring to be a little soft.)

Edit: Took it out for a 25 mile backroads run. It acted exactly as expected, a little soft on "3", but good. Will play around with it during the coming rides. Now I'm measuring sag on the forks, lol...
 

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Wire diameter and active coils is the same but what about the spring diameter? That also effects stiffness.
 

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McTavish
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Wire diameter and active coils is the same but what about the spring diameter? That also effects stiffness.
It sure does, seeing as a coil spring is actually a torsion bar, the smaller the dia. of the coil, for any given wire/coil wind/free length, the smaller the smaller the OD of the coiled spring, the stiffer it is, because the total wire length is shorter.
 

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2002 919, Asphalt
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Discussion Starter · #10 ·
The springs are identical, in every way, save for the '05 spring being 6 mm shorter. I know... I know.. I'm as baffled about this as everybody else having experienced both and yes, the original spring on my '02, beat the crap out of me.

Really stretching here but can somebody confirm that the '03 swingarm is the same as the '05? Part numbers on Partzilla show a suffix change.
 
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