Shinning light on the Rear Shock - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 38 (permalink) Old Oct 10th, 2007, 11:55 am Thread Starter
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Cool Shinning light on the Rear Shock

Hello All,

So recently I was at the track with this disaster of bike. Everything seems to be solved and I can move onto the handling characteristics of the 749.

One of the suspension experts at the track started talking to me about my rear shock being too soft for my wieght. That said, his immediate response was to either changet he spring or upgrade me to something that has a "top out" spring in it or do both change the spring and get a shock that has a "topping out spring" on it.

Now, I have some quetions... it is my understanding that having a shock with a top-out spring in it will HELP prevent the rear wheel from loosing some grip when the brakes are applied. However which shocks will provide such a feature? Presently, I have the so-called crappy Sach shock on my bike.

In terms of Sag this is what the bike is set up with:
-Front Forks (0.9kg springs Showa TIN) 35mm of rider sag and 30mm bike sag
-Rear shock with stock spring (don't know the wieght) was at 42mm sag in the rear which caused the bike to UNDERSTEER incredible and has been changed to 28mm sag. Note that the stock spring length is something like 164mm and mine is measuring 151 while the bike is sitting upright (on a rear stand) so i don't think that I Have OVER-PRELOAD the rear shock enough to warrent a new shock assembly in the rear.

Comments ?

My Scuderia : 2006 Ducati 749d - Showa TiN forks, Bitubo Steering Dampener, Ohlins rear shock (ARNOLD HASTINGS!!! AMA 2008 ), Dunlop 209/208 tires
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post #2 of 38 (permalink) Old Oct 10th, 2007, 2:45 pm
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I don't know of any shocks that have a top out spring...I though that was a fork thing, but could be wrong on that. IMO, if a shock is set up right, it wouldn't give you that feeling anyways. As a side note, when I took the Sachs shock off the wifes bike and played aroudn with it with no spring on it, the rebound adjustment made zero difference anywhere between full fast and full slow. POS!! Your current set up probably gives you that feeling because 28mm of sag on the shock is not enough. Go up to at least 30mm and maybe closer to 32mm.

'04 800SS...Strati Pipes, 42t sproket, DiD chain, Evoluzione fender eliminator, ABM Rotors, Carbon Lorane pads, Cogent-Dynamics Forks & Ohlins Shock.

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post #3 of 38 (permalink) Old Oct 11th, 2007, 10:15 am Thread Starter
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Another quetion,

Would the handling characteristic of the bike on the road shine light on what the bike will handle like on the track?

Or would anything on the road be amplified on the track.

My Scuderia : 2006 Ducati 749d - Showa TiN forks, Bitubo Steering Dampener, Ohlins rear shock (ARNOLD HASTINGS!!! AMA 2008 ), Dunlop 209/208 tires
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post #4 of 38 (permalink) Old Oct 11th, 2007, 10:21 am
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I'm with galaxy here, I've never heard of a shock with a top out spring.

As far as road testing...no. Nobody can ride hard enough on the road to simulate racetrack conditions.
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post #5 of 38 (permalink) Old Oct 11th, 2007, 12:56 pm
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Quote:
Originally Posted by rapter
Another quetion,

Would the handling characteristic of the bike on the road shine light on what the bike will handle like on the track?

Or would anything on the road be amplified on the track.
Hard to tell. Its such a different environment. At the track the bike feels like a very different animal.

At the track you are either hard on the gas or hard on the brakes. "Hidden" geometry or dampening characteristics/problems will become apparent at these much faster track speeds and when braking deep into corners. Also as you relax the bike will begin to feel looser, lighter and quicker to turn in. What might feel fine on the street or even beginner track group speeds, such as the compression damping you dialed out to soften the bumpy canyons or compansate for too stiff a spring will probably suck once you're going quicker. However until you get a track dialed in and can hit the apexes consistently it can be quite hard to separate what is you and what is the bike. That said, get the correct springs for your weight and spend $30 at the track to have your suspension set up and you will be a long way in the right direction. And yes there is a difference between shocks. The Race Tech technician at Buttonwillow drooled over my Penske 3 Way - not so much as to affect the handling mind you.

Good Luck
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post #6 of 38 (permalink) Old Oct 11th, 2007, 4:20 pm Thread Starter
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Thumbs up

Feels like I am going to have to wait until next season to figure out what what the correct set up is going to be for the bike.

Thanks for all your help!

My Scuderia : 2006 Ducati 749d - Showa TiN forks, Bitubo Steering Dampener, Ohlins rear shock (ARNOLD HASTINGS!!! AMA 2008 ), Dunlop 209/208 tires
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post #7 of 38 (permalink) Old Oct 11th, 2007, 4:40 pm
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Yea, I agree... you need to ride it on the track to set it up. Even though I'm getting good lap times for a noob, I'm not pushing it hard enough to really feel the difference in the front end even on the track. Its depressing because its all set up properly and it is better, but my skills arn't there yet to feel a BIG difference. "sigh" like most of us noobs, its gonna take a while! heh. Hopefully you can contain yourself until the next track day!



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post #8 of 38 (permalink) Old Oct 11th, 2007, 6:12 pm
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Rapter, do you still have the non-adjustable ride-height arm. It definitely sounds like the shock is too soft. I belive stock rate is 7.65kg/mm. Combine that with too little rear ride height and the front will want to run wide on accel. You can cheat the soft spring a little by jacking up the rear. Either way the OE Sachs is junk for the track and will not handle much of a spring change.

I'm about 155-160 geared up, have an OEM 999BIP (Showa) shock and it can just handle my weight satisfactorily on the track. However, it is pretty well balanced to my forks, so no issues. Bottom line: my overall setup could be better, but it works reasonably well, especially for my cheap suspension upgrades ($100 .90 fork springs and $15 shock)

-MATT
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post #9 of 38 (permalink) Old Oct 11th, 2007, 6:23 pm
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What's really really cool is when you get to the point that one click on an adjustment makes a noticeable difference. I heard guys talking about this phenomenon for years and never believed it existed...until you get some good components. That's also only on the track! I can take my same bike where a click or two is night and day on the track but 5 clicks riding back and fourth to work don't mean diddly squat.

Don't bother with this rapter...20 clicks on your shock wont change a thing

'04 800SS...Strati Pipes, 42t sproket, DiD chain, Evoluzione fender eliminator, ABM Rotors, Carbon Lorane pads, Cogent-Dynamics Forks & Ohlins Shock.

'05 749s...Termi 54mm full system, 41t sproket, DiD chain, Evoluzione fender eliminator, PCIII/custom map, Pazzo Levers, Puig DB Windscreen, Penske Shock, CRS Forks, CF everything.

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post #10 of 38 (permalink) Old Oct 12th, 2007, 9:08 am
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shock spring and height adjuster

From what I know, Ducati still ships the superbikes with very stiff springs in the front and very soft spring in the rear. I have no idea why. It sounds like you've got the correct springs in the front already. I would get the correct rear spring for your weight and set the sag. A spring is about $100.
I would also buy a rear ride height adjuster. That's like another $100. The rear of the bikes are always set too low from the factory for agressive track riding and if yours is non-adjustable then your screwed until you can get the rear of the bike raised up. The soft rear spring is adding to the problem because the rear is going even lower (compresssing) under cornering load relative to the front which is being properly help up by the correct springs.

Put those two thing on the bike, then ride it and get the comp/rebound adjusters where you are happiest with them. Then start gradually raising the rear ride height to get the bike to turn. This has a huge effect.

I think you've got a spring rate/chassis geometry problem that you can cure for $200. Then you can still buy a fancy rear shock if you want to. I think you'll feel it is less necessary, though.
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